Note: Descriptions are shown in the official language in which they were submitted.
CA 02324383 2002-11-29
1 ~ PATENT
DUAL-MUDE SATELLITE AND
TERRESTRJAL ANTENNA
DESCRIPTION
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates generally to a multimode antenna
assembly and, more particularly, to a multimode antenna assembly that
incorporates a satellite communications radiating element positioned
concentrically around and external to a terrestrial communications radiating
element.
Background Description
Mobile communications systems are known in the art for providing a
communications link between a mobile vehicle such r:~ an automobile, truck,
trailer, airplane or the like, and a stationary base or another mobile
vehicle. A
communications link, as used in the present application, is defined, but not
limited to voice, data, facsimile, or video transmission or the like. Some
such
known systems utilize local radio dispatched vehicles (e.g., taxis, police,
deliveries, repair services, or the like), ham or amateur radio, Citizens Band
110275-4201 ORD
CA 02324383 2000-10-26
2 PATENT
(CB} Radio, commercial transmitters, cellular receivers and the like. Such
systems are known as terrestrial systems.
Terrestrial systems can be linked via a network to provide greater
range and/or service. Terrestrial transmission generally involves strong
received signals at the mobile terminal and at the base stations, and short
delays owing to relatively short propagation distances. These factors simplify
receiver design and reduce mobile transmit power required. In addition, the
cost of terrestrial transmission, on a per mobile terminal basis, is typically
lower than that of satellite transmission. One such terrestrial transmission
network, shown in Figure 1, is the MotientsM network 100. Networks of this
nature provide secure, portable, two-way communication between handheld
wireless data terminals, mobile data terminals, and their respective host
computers.
The network 100 is a terrestrial wireless two-way data network that
allows subscriber units such as an intelligent terminal or computing device
102, handheld device 104, or other communications device 106 to
communicate with their respective host computer 108 and each other without
a phone line connection. Subscriber units 102, 104, 106, therefore, typically
have a radio frequency (RF) modem for sending and receiving signals.
The network 100 has over 1750 base stations (110) providing service
to cities and towns throughout the United States, Puerto Rico, and U.S. Virgin
Islands. Each base station 110 covers a radius of approximately 15-20 miles.
The base stations 110 are radio frequency towers that transmit or receive
radio
signals between subscriber units 102, 104, 106 and the Radio
Frequency/Network Control Processors (RF/NCPs) 112. Base stations 110
transmit and receive radio signals, preferably using a narrow band FM
transmitter and receiver operating in the 800 MHz frequency band. There are
separate frequencies for the transmit path and the receive path; together
these
two frequencies represent a full duplex channel that normally transmits data
at
4800 bps in both directions. In operation, for a message "inbound" to the
110275-4201 ORD
CA 02324383 2000-10-26
3 PATENT
network 100 from a subscriber unit 102, 104, 106, the signal is "heard" by the
base stations 110 and sent over a phone line 116 to a RF/NCP 112. The
network 100 employs an automated roaming capability that allows the free
movement of subscriber units 102, 104, 106 between cities and between
multiple channels within a given city. This capability allows the subscriber
units 102, 104, 106 to freely move (roam) across the country and take
advantage of all the network 100 services that are available in every locale.
The RF/NCPs 112 are high-speed computers that interconnect multiple
base stations 110 with the ARDIS~ Connect Engines) (ACEs) 114. A number
of RF/NCPs 112 are located together serving a particular geographical area,
each being connected by high speed digital phone service to one of the ACES
114, which route messages to a destination such as a customer host computer
108 that is directly connected to the network 100 by, for example, a leased
telephone line or a value added network. RF/NCPs 112 pass information
relating to source, destination and length of each message to an ACE 114 that
enables the network 100 to do network analysis of traffic density in, for
example, each city. An ACE 114, in turn, passes information back to a
RF/NCP 112 concerning whether the subscriber unit 102, 104, 106 is properly
registered to the network 100 and, if so, what level of service of provided to
the respective subscriber 102, 104, 106. The RF/NCPs also help manage the
roaming capability of the network 100. Subscriber units 102, 104, 106 can
automatically move (roam) between any of the network 100 frequencies on
either of the two protocols (MDC 4800 and RD-LAP 19.2), or between any of
the configured network 100 layers that have been configured for in-building or
on-street usage.
The ACEs 114 are general purpose computers that act as the heart of
the network 100. The ACES 114 route messages to the proper destination,
store subscribe registration information including entitlement, and perform
accounting and billing functions. The ACEs 114 also serve as a point of
connectivity to customer host computers 108, perform protocol conversion,
110275-4201 ORD
CA 02324383 2002-11-29
4 PATENT
and perform network 100 troubleshooting and test functions. A plurality of
ACEs 114 are interconnected throL~gh dedicated leased lines, with alternate
paths available from each switch as a contingency measure against line
interruptions.
The wireline network 116 provides communication between the
customer host computers 1.08, the .ACES 114, the h.F/NCPs 11.2, and the base
stations 110. The wireline network 116 is equipped with sophisticated
communications equipment that relays customer messages. This equipment
includes intelligent multiplexers, leased telephone circuits, high-speed
modems or digital service units, and modems for both RF/NCP 112 and
customer host computer 108 connectivity.
Satellite relay mobile communications systems are also known, such as
that disclosed in U.S. Patent No. 5,594,461 to O'Neill Jr., and that disclosed
in
U.S. Patent No. 5,485,170 to McCarrick. Satellite transmission affers the
advantage
of wide coverage area owing to the large footprints of its beams. However,
some of its major disadvantages are weak received signals, both on the ground
and at the satellite, and long transmission delays because of great
propagation
distances. In addition, satellite network infrastructure costs tend to be
higher
than their terrestrial counterparts.
The O'Neill Jr. assembly relates particularly to a satellite relay mobile
communications system in which a great number of mobile earth stations are
expected to communicate via a single satellite relay station to an earth base
station. This assembly provides a quadrature matching network for a
quadrifilar helix antenna, wherein the network is compact and conveniently
located adjacent an antenna element. The O'Neill Jr. invention is embodied in
a quadrature matching network of transmission line transformer elements
which couples a quadrifilar helix antenna to transmit or receive signal
shaping
circuits of a radio (the term radio, pertains generally to either a receiver
or a
transmitter, or to a transceiver'.) 'fhe quadrifilar helix has first, second,
third
110275-4201 ORD
CA 02324383 2000-10-26
PATENT
and fourth antenna elements disposed in a 90 degree phase relationship with ,
respect to a nominal wavelength of an RF signal in the microwave range. The
network comprises first and second transmission line transformer elements
coupling the second antenna element to the first antenna element and the
fourth antenna element to the third antenna element, respectively. The first
and second transmission line transformer elements have respective
impedances which are matched to the antenna impedance of their respective
antenna element. The first and second transmission line transformer elements
each have a length of quarterwave of the receive signal. A third transmission
line transformer element couples the third and fourth transformer element, has
a length of a halfwave of the receive signal, and has an impedance which is
matched to a combined effective impedance of the third and fourth antenna
elements. The combined and phase corrected signal is coupled through an
output quarterwave transmission line transformer to a signal terminal of a
microwave transceiver.
In reference to the O'Neill Jr. patent, Figure 2 shows a quadrifilar
microwave antenna assembly 210. The antenna assembly 210 extends from a
circular pan-like sturdy mounting base 211, preferably an aluminum casting,
and which also serves as a bottom housing or cover and RF shield. A
quadrifilar helical antenna ("antenna") 212 extends centrally above a
circular,
rigid RF shield 214, which is preferably a 1/4-inch thick aluminum disc. The
shield 214 also serves as a convenient heat sink and dissipator for RF power
transistors while the antenna 212 is operating in a transmit mode. The shield
214 may be mounted to, and rigidly supported by, the mounting base 211. A
parabolic or hemispherical cover 215 (i.e., a radome cover) of preferably a
microwave transparent material, such as plastic or fiberglass material,
encases
and protects the antenna 212. The mounting base 21 I may be mounted to a
cab of a truck, train or other transportation instrumentality, where the
numeral
216 designates a portion of a roof line of a vehicle, in accordance with a
110275-4201 ORD
CA 02324383 2000-10-26
6 PATENT
preferred use of the antenna assembly 210 as part of a mobile, earth orbiting
satellite communications system.
Further in reference to Figure 2, a dielectric substrate 217 is preferably
firmly mounted or adhesively attached to the shield 214 opposite the side from
which the antenna 212 extends. The shield 214 has insulated apertures 218
with respective axially disposed lead through terminations 219 of four
quadrifilar antenna elements 221, 222, 223 and 224. The terminations 219 are
electrically short coaxial extensions of the respective antenna elements 221,
222, 223 and 224 to preserve the preferred characteristic 50 ohm (SZ) antenna
impedance. In a preferred implementation of the antenna 212, the apertures
218 are arranged in a square pattern in the shield 214. From the terminations
219, the antenna elements 221, 222, 223 and 224 wind spirally about a
cylindrical dielectric core 225.
As shown in Figure 3, the McCarrick assembly provides a mufti-turn
quadrifilar helix antenna fed in phase rotation at its base. The antenna of
the
McCarrick disclosure provides for an adjustment of the helix elements,
causing beam scanning in the elevation plane. This quadrifilar helical antenna
is omni-directional in azimuth, making the antenna suitable for mobile
vehicular antenna accessing stationary satellites.
More specifically, the McCarrick assembly comprises a mufti-turn
bifilar helix antenna ("antenna") using a mechanical design which permits the
pitch and diameter of helix elements 305 and 306 to be adjustable. This
mechanical adjustment elicits an electrical response in the radiation
characteristics of the antenna which permits beam steering of the radiation
pattern in the elevation plane. The antenna is capable of scanning its main
radiation beam from 20 degrees to 60 degrees in elevation while maintaining
relatively omni-directional coverage in azimuth.
The antenna is designed to mount to a detachable base located on the
vehicle skin (e.g., trunk, fender, roof, or the like). Its scanned radiation
angle
110275-4201 ORD
CA 02324383 2000-10-26
7 PATENT
is set manually by the vehicle operator with the relatively simple adjustment
of
knurled sleeve 322 at base 317 of the antenna.
Bifilar helix 304 comprises two helix elements 305 and 306 separated
180 degrees apart, but sharing a common axis. In the preferred embodiment,
helix elements 305 and 306 have conductors made of a highly conductive
material, such as copper. Helix elements 305 and 306 serve as the radiating
portion of the antenna. Helix 304 has distal end 309 and proximal end 310.
In general, distal end 309 of the vertically mounted antenna is the end which
is
furthest from the ground plane formed by the vehicle skin. The antenna is fed
at distal end 309 with a balanced assembly comprising coaxial cable section
311 terminating in balun 314. This distal feed technique is sometimes referred
to as the backfire mode. Helix elements 305 and 306 are formed by being
wound around a constant diameter tube to form a uniform helix. The angle of
pitch of helix 304 is determined by the number of helix turns for a given
axial
length. Pitch in unit length is defined as the axial length required for the
helix
to make one complete turn about its axis. When helix elements 305 and 306
are wound 180 degrees apart as suggested above, a criss-cross effect of the
elements is observed when the structure is viewed from the side.
The spacing (helix diameter) and angle of pitch of helix 304
determines the polarization and radiation characteristics of the antenna. A
bifilar helix with left-handed helices (ascending counter-clockwise as viewed
from the bottom) radiates a right-hand circularly-polarized (RHCP) wave
which is relatively omni-directional in azimuth. If the pitch angle and or the
diameter of helix 304 is increased from an initial reference point, the
radiation
in elevation is scanned towards the horizon. In the present invention, the
element pitch angle and helix diameter are adjusted by varying the number of
helix turns for a fixed axial length.
In one embodiment, helix elements 305 and 306 are made from 300
ohm twin lead line commonly used in FM receivers and some television leads.
One of the conducting leads is removed from the polypropylene sheathing of
110275-4201 ORD
CA 02324383 2000-10-26
8 PATENT
each of helix elements 305 and 306, while the remaining lead serves as the
radiating element. Thus, helix elements 305 and 306 each contain only one
wire. Polypropylene is preferred because it readily takes a helix shape when
wrapped around a metal tube (not shown) and heated with a hot air gun. Other
heating techniques can also be used including heating the metal tube itself.
Helical elements 305 and 306 may be formed from two 37 inch lengths of 300
Ohm twin lead line suitably modified as discussed above by stripping one of
the leads from the sheathing. When wound six and one-half times around a
5/8 inch diameter tube, helical elements 305 and 306 are formed at an axial
length of about 31 inches.
Formed helix elements 305 and 306 are placed over a 31 inch long 3/8
inch diameter hollow supporting tube 312 which may be made of any fairly
robust insulating material such as phenolic resin. Supporting tube 312 is
centrally located within a 32 inch long outer sheath 313 which is one inch in
diameter. Outer sheath 313 also may be formed of any robust insulating
material such as polycarbonate and serves to provide environmental sealing of
the antenna assembly. Coaxial cable 311 is fed through the center of
supporting tube 312 and is terminated at the distal end 309 at balun 314.
Coaxial cable 311 may be formed from a UT141 semi rigid coaxial line.
Balun 314 comprises a hollow 3/16 inch diameter brass tube with two
feed screws 323 and 324 located 180 degrees apart. The wire portions of helix
elements 305 and 306 are secured to the termination of balun 314, one on each
side, by feed screws 323 and 324. Proximal end 310 of coaxial line 311 is
terminated by connector 316 which may be press fitted into base 317 of the
antenna. Balun 314 serves to maintain a relative phase difference of 180
degrees between the radiating elements for the required frequency bands.
In an alternative embodiment, balun 314 comprises a hollow 3/16 inch
diameter slotted brass tube with two slots in the tube located 180 degrees
apart. The slots are 0.124 inches wide by 1.85 inches long. The wire portions
110275-4201 ORD
CA 02324383 2000-10-26
9 PATENT
of helix elements 305 and 306 are soldered to the termination of balun 314,
one on each side, separated by the slots.
Support tube 312 is captured at distal end 309 by end cap 318 set into
distal end 309 of outer sheath 313 so as to prevent support tube 312 from
rotating. End cap 318 is secured to distal end 309 of outer sheath 313 by
glue,
screws, threading, press fit, or the like.
Proximal end 310 of support tube 312 is movably attached to inner
rotatable sleeve 319 by threaded member 326. Threaded member 326 may be,
for example, a 1/4-20 threaded stainless steel sleeve. Spring 325 is installed
at
the point of rotation between support tube 312 and inner rotatable sleeve 319
to prevent undesired relative movement between inner rotatable sleeve 319
and support tube 312. Spring 325 may be made of, for example, stainless
steel. Inner rotatable sleeve 319 is held in place by two set screws 321
within
knurled adjustment outer sleeve 322. Inner sleeve 319 and outer sleeve 322
are located within base 317 which supports outer sleeve 313 and connector
316. The two grounded ends of helix elements 305 and 306 are attached to
rotating set screws 321, creating a mechanism for changing helix pitch.
Access to knurled outer sleeve 322 is made by machining two window slots
(not shown) in the base 317. Base 317, inner sleeve 319 and outer sleeve 321
may be made from any suitable insulating plastic material with requisite
strength requirements, such as DELRIN° plastic.
Helix 304, preferably made of polypropylene, has the desirous property
of maintaining a uniform pitch along its axial length, even when one end is
rotated with respect to the other. By fixing proximal end 309 of helix
elements 305 and 306 from rotation to balun 314 and attaching proximal ends
310 of helix elements 305 and 306 to rotatable outer sleeve 322, an elevation
steerable antenna with fixed height and adjustable pitch is achieved.
In operation, the operator loosens knurled locking bolt 303 (held firm
by spring 320) and twists knurled outer sleeve 321 through the two window
slots (not shown) to adjust the axial pitch of antenna 300. In its initial
110275-4201 ORD
CA 02324383 2000-10-26
PATENT
position, helix elements 305 and 306 make approximately six and one-half
turns within the axial length of the antenna. This allows for coverage within
degrees above the horizon. In the other extreme, helix elements 305 and
306 make just under ten complete turns, allowing for coverage up to 60
5 degrees above the horizon. A mechanical limiter (not shown) and elevation
angle indicator (not shown) are used to prevent the user from forcing the
helix
elements beyond their six and one-half and ten turn limits and to simplify the
process for optimizing the antenna for elevation coverage. The operator's
choice of elevation angle can be determined from the latitude where the
10 vehicle is located, or can be positioned with the aid of a standard
electronic
antenna peaking device.
Functional Considerations
15 Functional considerations which seek to minimize size and shape of
mobile earth antennas (both terrestrial and satellite systems) are also
inherently related to system cost reduction. The size of antenna assemblies
for
mobile transceiver units is considered a source of possible problems because
of limited mounting space for such antenna assemblies on mobile equipment,
20 such as trucks or automobiles. The operation of the mobile transceiver
units
presupposes an exposure of the respective antenna assemblies to the position
of the satellite relay, desirably omnidirectional quality, and further, from a
practical standpoint, a practical shape and size realization to permit an
antenna
assembly to be mounted on the roof of a truck, cab, or a similar sky
accessible
location of a vehicle. In addition, a compact size of a desirable antenna
assembly will further reduce a wind resistance profile at the top of a moving
vehicle. Antennas and corresponding antenna coupling circuits of the mobile
earth stations are consequently under constraint to be efficient from both
functional and cost standpoints.
110275-4201 ORD
CA 02324383 2000-10-26
11 PATENT
A need exists for an integrated antenna that can provide parallel use of
the terrestrial and satellite network while conforming with the aforementioned
constraints. The present invention fulfills this need by providing a multimode
antenna assembly having both satellite and terrestrial communications
elements, where the satellite communications element is positioned
concentrically around and external to the satellite communications element.
SUMMARY OF THE INVENTION
It is a feature and advantage of the present invention to provide an
antenna assembly that incorporates both a satellite communication radiating
element and a terrestrial communication radiating element, forming a dual
mode antenna assembly of compact size.
It is a further feature and advantage of the present invention to provide
a dual mode antenna assembly that is efficient from both functional and cost
standpoints.
It is another feature and advantage of the present invention to provide a
dual mode antenna assembly that is compatible with existing antenna devices.
It is another feature and advantage of the present invention to provide a
dual mode antenna assembly that is manageable and practical in its
implementation.
It is another feature and advantage of the present invention to provide a
dual mode antenna assembly that does not require significant additional
hardware in its implementation.
It is another feature and advantage of the present invention to provide
an dual mode antenna assembly that uses and/or adapts existing hardware to
achieve desired effects, such as being detachable.
To achieve these features and advantages, a dual mode antenna
assembly is provided that, in a preferred embodiment, comprises both a
satellite and a terrestrial communications element, where the satellite
110275-4201 ORD
CA 02324383 2000-10-26
12 PATENT
communications element is positioned concentrically and external to the
terrestrial element. The satellite element is preferably a quadrifilar helical
antenna, and the terrestrial antenna is preferably a monopole. The dual mode
antenna assembly also comprises an impedance matching network that
compensates for the impedance loading effect of the quadrifilar helical
antenna on the monopole antenna. The impedance matching network makes
the impedance of the terrestrial monopole located inside the quadrifilar helix
have essentially the same impedance as that of an isolated (i.e., single)
monopole not surrounded by a quadrifilar helical antenna.
There has thus been outlined, rather broadly, the more important
features of the invention in order that the detailed description thereof that
follows may be better understood, and in order that the present contribution
to
the art may be better appreciated. There are, of course, additional features
of
the invention that will be described hereinafter and which will form the
subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the
invention in detail, it is to be understood that the invention is not limited
in its
application to the details of construction and to the arrangements of the
components set forth in the following description or illustrated in the
drawings. The invention is capable of other embodiments and of being
practiced and carried out in various ways. Also, it is to be understood that
the
phraseology and terminology employed herein are for the purpose of
description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception,
upon which this disclosure is based, may readily be utilized as a basis for
the
designing of other structures, methods and systems for carrying out the
several
purposes of the present invention. It is important, therefore, that the claims
be
regarded as including such equivalent constructions insofar as they do not
depart from the spirit and scope of the present invention.
110275-4201 ORD
CA 02324383 2000-10-26
13 PATENT
Further, the purpose of the foregoing abstract is to enable the U.S.
Patent and Trademark Office and the public generally, and especially the
scientists, engineers and practitioners in the art who are not familiar with
patent or legal terms or phraseology, to determine quickly from a cursory
inspection the nature and essence of the technical disclosure of the
application.
The abstract is neither intended to define the invention of the application,
which is measured by the claims, nor is it intended to be limiting as to the
scope of the invention in any way.
These together with other objects of the invention, along with the
various features of novelty which characterize the invention, are pointed out
with particularity in the claims annexed to and forming a part of this
disclosure. For a better understanding of the invention, its operating
advantages and the specific objects attained by its uses, reference should be
made to the accompanying drawings and descriptive matter in which there is
illustrated preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The Detailed Description including the description of a preferred
structure as embodying features of the invention will be best understood when
read in reference to the accompanying figures wherein:
Figure 1 is a schematically simplified representation of the MotientsM
terrestrial communications network;
Figure 2 is a schematically simplified pictorial representation of a
known microwave transmit and receive antenna assembly;
Figure 3 is a schematically simplified, alternative, known satellite
antenna embodiment;
Figure 4A is a schematically simplified representation of the dual
mode antenna assembly;
110275-4201 ORD
CA 02324383 2000-10-26
14 PATENT
Figure 4B-4D are a schematically simplified representation of a side
and front view of the dual mode antenna assembly, showing cable connectors;
Figure 5 is a front view having a partial cross section of the dual mode
antenna assembly;
Figure 6A is a schematically simplified, exploded view of the dual
mode antenna assembly;
Figure 6B is a schematically simplified, exploded view of an
alternative embodiment of the dual mode antenna assembly;
Figure 6C is a schematically simplified, exploded view of an
alternative embodiment of the dual mode antenna assembly;
Figure 6D is a schematically simplified, exploded view of an
alternative embodiment of the dual mode antenna assembly;
Figure 6E is a schematically simplified, exploded view of an
alternative embodiment of the dual mode antenna assembly;
Figure 7 shows a plot of the electrical radio frequency isolation
between the terrestrial antenna and the satellite antenna, across a frequency
band that covers both the terrestrial and satellite system operational
bandwidths;
Figure 8A is an operationally representative impedance plot for the
monopole terrestrial antenna;
Figure 8B is the impedance of the monopole terrestrial antenna with
the effect of loading by the satellite quadrifilar helix antenna;
Figure 9A shows a preferred method of a simplified method of
assembly of the dual mode antenna assembly;
Figure 9B shows a more detailed method of assembly of the dual mode
antenna assembly; and
Figure 10 is a block diagram illustrating a wireless packet data
transmission network that can utilize the dual mode antenna assembly of the
present invention to communicate with mobile terrestrial vehicles.
110275-4201 ORD
CA 02324383 2000-10-26
15 PATENT
DETAILED DESCRIPTION OF A PREFERRED
EMBODIMENT OF THE INVENTION
An integrated dual mode antenna assembly is therefore disclosed that
can provide parallel use of the terrestrial and satellite networks while
conforming with function and cost constraints. The present invention fulfills
this need by providing a dual mode antenna assembly that comprises an
impedance matching network that compensates for the impedance loading
effect of the quadrifilar helical antenna on the monopole antenna. The
impedance matching network makes the impedance of the terrestrial
monopole located inside the quadrifilar helix have essentially the same
impedance as that of an isolated (i.e., single) monopole not surrounded by a
quadrifilar helical antenna. In a preferred embodiment, the satellite element
comprises a quadrifilar helical antenna, and the terrestrial element comprises
a
monopole antenna.
Figure 4A illustrates a quadrifilar helical antenna 410 (comprising
antenna elements 422, 424, 426 and 428) with concentrically located
terrestrial antenna 430. In a preferred embodiment, terrestrial antenna 430 is
a
component of a network such as an MotientsM network 100. It should be
understood that antennas other than a quadrifilar helical antenna 410 (e.g., a
bifilar helix antenna) that preferably have a virtual electronic null in their
center (to avoid being perturbed by the terrestrial antenna 430) may be
utilized. Antenna assembly 400 comprises helical antenna 410 and terrestrial
antenna 430, and extends from mounting base 402, and antenna mounting
base 404, which also preferably serves as a RF shield. Helical antenna 410
extends centrally above antenna mounting base 404.
Mounting base 402 is preferably of aluminum casting, and also serves
as a bottom housing or cover. As shown, mounting base 402 is circular or
pan-like, and further comprises coaxial cable connector 406 and a SMA cable
connector 408 (preferably 800 MHz). Alternatively, any other type of
110275-4201 ORD
CA 02324383 2000-10-26
16 PATENT
connections) may be used that connects) the dual-mode antenna of the
present invention with the transceiver of the communication device.
Mounting base 402 can be mounted to a cab of a truck, train or other
transportation instrumentality as illustrated by portion of roof line 414 of
such
a vehicle.
Antenna mounting base 404 is preferably a circular, substantially rigid,
1/4 inch thick aluminum disc, serving as a convenient heat sink and dissipator
for RF power transistors when helical antenna 410 is operating in a transmit
mode. In alternative embodiments, antenna mounting base 404 may be of
other suitable shapes and/or materials that principally function as an antenna
base of the dual-mode antenna assembly 400 of the present invention.
Antenna mounting base 404 can be mounted to, and rigidly supported by,
mounting base 402. Antenna mounting base 404 has optional insulated
apertures 418 which receive respective axially disposed lead through
terminations 420 of antenna elements (i.e., sections) 422, 424, 426 and 428 of
the integrated or composite helical antenna 410. Ternunations 420 are
electrically short coaxial or other extensions of respective antenna elements
422, 424, 426 and 428 that preserve the preferred characteristic 50 ohm
antenna impedance or other predetermined impedance characteristics, and also
serve to mechanically secure the helical antenna 410 to the antenna mounting
base 404. In a preferred implementation of helical antenna 410, apertures 418
are arranged in a square pattern in antenna mounting base 404. Apertures 418
may alternatively be arranged in other patterns such as triangular,
rectangular,
parallelogram, and the like, depending on the number of antenna elements.
From terminations 420, antenna elements 422, 424, 426 and 428 wind spirally
about cylindrical core 436. Preferably, the cylindrical core is comprised of a
low-loss dielectric material with a dielectric constant as close to air as
possible. A stabilizing element is preferably disposed between the helical
antenna 410 and core 436. Preferably the stabilizing element is a foam-like
material widely used in industry practice. It is further preferred that the
foam-
110275-4201 ORD
CA 02324383 2000-10-26
17 PATENT
like material be a dielectric or substantially dielectric material. Each of
the
antenna elements 422, 424, 426 and 428 optionally and advantageously works
against the other three, effectively setting up a field in the free air
dielectric
(e.g., the conical tube supporting the radiating elements). In a preferred
embodiment, antenna elements 422, 424, 426 and 428 have conductors made
of a highly conductive material such as copper.
Components of the amplifier and preselector assembly 432 are
advantageously disposed on underside 434 of substrate 416, and are thus
accessibly located to be directly coupled via a quadrature matching network
(not shown) to antenna assembly 400. Of course, the components of the
amplifier and preselector assembly 432 may be disposed on other areas of the
mufti-mode antenna. The components of the amplifier and preselector
assembly 432 are coupled to terrestrial antenna 430, and the components of
the amplifier and preselector assembly 433 are coupled to helical antenna 410.
Other shapes of the core 436 may alternatively be used such as square,
pyramidal, rectangular, triangular, and the like. However, the shape of core
436 must be cylindrical to meet INMARSAT C certification requirements.
Azimuthal gain symmetry and axial ration will generally deteriorate with non-
cylindrical shape.
Parabolic or hemispherical cover 412 encases and protects antenna
assembly 400, and is preferably a microwave transparent material, such as
plastic or fiberglass material. Parabolic or hemispherical cover 412 is also
known by those skilled in the art as a radome cover or enclosure. Other
suitable shapes and materials may be used for hemispherical cover 412.
In further reference to Figure 4A, optional dielectric substrate 416 is
preferably firmly mounted or adhesively attached to antenna mounting base
404 opposite the side from which antenna assembly 400 extends. Other
configurations of the mounting of substrate 416 may alternatively be used.
Though the antenna mounting base 404 and the dielectric substrate 416 are
illustrated as being circular in configuration, it should be realized that the
110275-4201 ORD
CA 02324383 2000-10-26
18 PATENT
circular shapes were chosen in support of a non-directional symmetry with
respect to the terrestrial antenna 430. The circular footprint particularly
facilitates mounting the parabolic or hemispherical cover 412 to the antenna
assembly 400. However, the invention is not dependent upon this circular
configuration and is equally applicable to antenna assemblies of various other
shapes.
In reference to Figure 4B - 4D, there is shown a 'side view (Figure 4C)
and two front views (Figures 4B and 4D) of the mounting base 402 with
optional coaxial cable connector 406 and a SMA cable connector 408
(preferably 800 megahertz). Coaxial cable 406 and SMA cable connector 408
are optional in that they are chosen for identification purposes so that one
cable of each type is connected to each of the helica antenna 410 and the
terrestrial antenna 430. Accordingly, two SMA cable connectors 408, or two
coaxial cable connectors 406 could equally be used in lieu of the coaxial
cable
connector 406 and a SMA cable connector 408.
Referring again to Figure 4A, coaxial cable connector 406 provides for
the receive or transmit signals to be transferred via a communication line,
such
as a coaxial conductor between, for example, a transceiver and preselector
assembly 432. SMA cable connector 408 provides for the receive or transmit
signals to be transferred via a second coaxial conductor between a second
transceiver and preselector assembly 433. The components of the amplifier
and preselector assembly 432 are coupled to terrestrial antenna 430, and the
components of the amplifier and preselector assembly 433 are coupled to
helical antenna 410, as will be discussed in further detail in the discussion
pertaining to Figures 6A-6E.
In reference to Figure 5, there is shown partial front and partial front
cross sectional views of the antenna assembly 400. Mounting base 504
preferably serves as a convenient heat sink and dissipator for RF power
transistors while antenna assembly 400 is operating in a transmit mode. A
printed circuit board 502 underlying antenna mounting base 404 provides
110275-4201 ORD
CA 02324383 2000-10-26
19 PATENT
signal mix/demix of radio frequency. Circuit board 504 is preferably
populated by receiver/transmitter circuitry (Rx/Tx). An O-Ring 506 is
preferably placed within a groove within the mounting base 402, and a ring
clamp 508 is preferably secured to the mounting base 402 and radome cover
412 to provide a substantially moisture resistant seal which protects the
antennas 410, 430 from adverse weather, corrosion, etc. Other means to
provide a substantially airtight seal could be used other than the O-Ring 506
and the ring clamp 508.
Electronic impedance matching preferably occurs on antenna mounting
base 404 and on antenna board 504, as necessary. In a preferred embodiment,
an impedance matching network compensates for the impedance loading
effect of the helical antenna 410 on the terrestrial antenna 430.
Specifically,
the impedance matching network makes the impedance of the terrestrial
antenna 410 substantially the same as essentially the same as the impedance of
the same monopole antenna when it is not surrounded by a helical antenna
430. Note that the helical antenna 430 does not need to be radiating in order
to affect the impedance of the terrestrial antenna 410; the physical proximity
of the helical antenna 430 to the terrestrial antenna 410 will affect the
impedance of the terrestrial antenna 410.
In reference to Figure 6A, there is shown an exploded view of helical
antenna 410 with concentrically located terrestrial antenna 430. In a
preferred
embodiment, terrestrial antenna 430 operates at approximately 800 MHz, and
the satellite antenna 410 operates at a frequency designated for satellite
communications. The printed circuit board 502 underlying antenna mounting
base 404 provides signal mix/demix of radio frequency to isolate only the
desired signal to the proper antenna 410, 430. Further, first cable, in its
respective portions 604 and 624, is a signal feeding cable for helical antenna
410. Cable 604 connects to mounting base 402 via SMA cable connector 408.
Similarly, second cable, in its respective portions 606 and 622, is a signal
feeding cable for terrestrial antenna 430. Cable 606 connects to mounting
110275-4201 ORD
CA 02324383 2000-10-26
20 PATENT
base 402 via coaxial cable connector 406. Cables 622 and 624 may be
pendant cables, integral with circuit board 502, or may form an electrical
connection with terrestrial antenna 430 and satellite antenna 410,
respectively,
via any other suitable cable connection means known and practiced in the art.
First connection 608 is a connection to the helical antenna 410, and
second connection 610 is a connection to the terrestrial antenna 430. First
connection 608 and second connection 610 are proximate circuit board 504,
and may be electrically connected thereto via any suitable cable connection
means widely known in the art. In a preferred embodiment, circuit board 504
is populated by receiver/transmitter circuitry (Rx/Tx), and provides isolated
internal trace from input cables 604 and 606 to third and fourth connectors
614 and 616, respectively, as well as the potential filtering required to
isolate
the preferred 800 megahertz Rx signal. Third connection 614 and fourth
connection 616 are each proximate to circuit board 504 and provide passage
for cables 604 and 606, respectively. Circuit board 504 is proximate O-Ring
618, which is proximate ring clamp 620, which is proximate mounting base
402. In a preferred embodiment, circuit board 504 also contains at least the
majority of the RF circuitry, as well as power amplifiers and filters. DC
voltage preferably controls the state of the receiver/transmitter circuitry.
The
most common state of helical antenna 410 is in receive mode, which is
preferably at approximately 10 volts. Transmit mode preferably occurs at
approximately 24 volts, and idle mode preferably occurs at approximately 15
volts. DC voltage is provided via cables 604 and 624 to the helical antenna
410, and radio frequency signals are superimposed on the DC voltage. DC
voltage also controls the receiver/transmitter switch (not shown).
Figure 6B depicts an alternative embodiment, wherein cables 622 and
624 shown in Figure 6A are combined into a single cable 626 that feeds both
the helical antenna 410 and the terrestrial antenna 430. In this embodiment,
as
will be recognized to those skilled in the art, a diplexer, for example, can
be
utilized to combine cables 622 and 624 into cable 626. Similarly, a second
110275-4201 ORD
CA 02324383 2000-10-26
21 PATENT
diplexer can be used to split cable 626 into respective portions that connect
to
the helical antenna 410 and the terrestrial antenna 430, respectively. The
receiver or transmitter signal is frequency matched to isolate the desired
signal
which is then sent to the proper antenna. In this embodiment, the signal is
split in circuit board 504, with each of the two resulting signals then
directed
to the respective first cable 604 and second cable 606 (i.e., signals
corresponding to the helical antenna 410 and the terrestrial antenna 430,
respectively), which are housed by the third connection 614 and fourth
connection 616, respectively.
Figure 6C depicts an alternate embodiment, wherein first cable 624
and second cable 622 are combined to form cable 636, which exits through
single connection 628. First cable 624 and second cable 622 are again
preferably combined via a diplexer. In this embodiment, cable 636 is
preferably either a coaxial cable or a SMA-type cable, which connects to
either the coaxial cable connector 406 or the SMA cable connector 408.
Accordingly, only one of either the coaxial cable connector 406 or the SMA
cable connector 408 is required in mounting base 402.
Figure 6D depicts an alternate embodiment, wherein circuit board 504
and O-Ring 618, each shown in Figures 6A, 6B and 6C, are combined to form
combined circuit board and O-Ring 632. As shown in Figure 6A, a printed
circuit board 502 underlying antenna mounting base 404 provides signal
mix/demix of radio frequency. First cable, in its respective portions 604 and
624, is a signal feeding cable for helical antenna 410. Similarly, second
cable,
in its respective portions 606 and 622, is a signal feeding cable for
terrestrial
antenna 430. First connection 608 is a connection to the helical antenna 410,
and second connection 610 is a connection to the terrestrial antenna 430.
First
connection 608 and second connection 610 are proximate combined circuit
board and O-Ring 632. In a preferred embodiment, combined circuit board
and O-Ring 632 is populated by receiver/transmitter circuitry (Rx/Tx), and
provides isolated internal trace from input cables 604 and 606 to third and
110275-4201 ORD
CA 02324383 2000-10-26
22 PATENT
fourth connectors 614 and 616, respectively, as well as the potential
filtering
required to isolate the preferred 800 megahertz Rx signal. Third connection
614 and fourth connection 616 are each proximate to combined circuit board
and O-Ring 632, and provide passage for cables 604 and 606, respectively.
Combined circuit board and O-Ring 632 is proximate ring clamp 620, which
is proximate mounting base 402. In a preferred embodiment, combined circuit
board and O-Ring 632 contains the majority of the RF circuitry, as well as
power amplifiers and filters. DC voltage preferably controls the
receiver/transmitter circuitry. The most common state of helical antenna 410
is in receive mode, which is preferably at approximately 10 volts. Transmit
mode preferably occurs at approximately 24 volts, and idle mode preferably
occurs at approximately 15 volts. DC voltage is provided via cables 604 and
624 to the helical antenna 410, and radio frequency signals are superimposed
on the DC voltage. DC voltage also controls the receiver/transmitter switch
(not shown).
Figure 6E depicts an alternate embodiment, wherein O-Ring 618 and
ring clamp 620 shown in Figures 6A, 6B and 6C are combined to form
combined O-Ring and ring clamp 634. Circuit board 502 underlying antenna
mounting base 404 provides signal mix/demix of radio frequency. First cable,
in its respective portions 604 and 624, is a signal feeding cable for helical
antenna 410. Similarly, second cable, in its respective portions 606 and 622,
is a signal feeding cable for terrestrial antenna 430. First connection 608 is
a
connection to the helical antenna 410, and second connection 610 is a
connection to the terrestrial antenna 430. First connection 608 and second
connection 610 are proximate circuit board 504. In a preferred embodiment,
circuit board 504 is populated by receiver/transmitter circuitry (Rx/Tx), and
provides isolated internal trace from input cables 604 and 606 to third and
fourth connectors 614 and 616, respectively, as well as the potential
filtering
required to isolate the preferred 800 megahertz Rx signal for the terestrial
antenna 430. Third connection 614 and fourth connection 616 are each
110275-4201 ORD
CA 02324383 2000-10-26
23 PATENT
proximate to circuit board 504 and provide passage for cables 604 and 606,
respectively. Circuit board 504 is proximate combined O-Ring and ring clamp
634, which is proximate mounting base 402. In a preferred embodiment,
circuit board 504 contains the majority of the RF circuitry, as well as power
amplifiers and filters. DC voltage preferably controls the state of the
helical
antenna 410. The most common state of helical antenna 410 is in receive
mode, which is preferably at approximately 10 volts. Transmit mode
preferably occurs at approximately 24 volts, and idle mode preferably occurs
at approximately 15 volts. DC voltage is provided via cables 604 and 624 to
the helical antenna 410, and radio frequency signals are superimposed on the
DC voltage. DC voltage also controls the receiver/transmitter switch (not
shown).
Figure 7 shows a plot of the electrical radio frequency isolation
between the terrestrial antenna 410 and the helical antenna 430, across a
frequency band that covers both the terrestrial and satellite system
operational
bandwidths. As shown, the band edges for the terrestrial antenna 430 occur at
approximately 806 MHz and 871 MHz, and the band edges for the helical
antenna 410 occur at approximately at 1530 MHz and 1660 MHz. As will be
recognized by those skilled in the ast, the data indicate that the terrestrial
antenna 430 does not load the helical antenna 410 (which is generally more
sensitive than the terrestrial antenna 410).
Figure 8A shows a representative operational impedance plot for the
terrestrial antenna 430. Figure 8B shows a representative operational
combined impedance plot for the terrestrial antenna 430 and the helical
antenna 410. As will be recognized by those skilled in the art, the second
plot
indicates that an impedance matching circuit, preferably obtained using either
commercially available printed circuits or known circuit matching techniques,
can be obtained without undue experimentation such that the impedance of the
terrestrial monopole located inside the quadrifilar helix has essentially the
same impedance as that of an isolated (i.e., single) monopole not surrounded
110275-4201 ORD
CA 02324383 2000-10-26
24 PATENT
by a quadrifilar helical antenna. When this is accomplished, Figure 8B will
then have a plot very similar to that of Figure 8A. If desired, the impedance
matching circuit can be integrated with circuit board 502.
Figure 9A shows a preferred method of assembly of the antenna
assembly 400. In step 900, a mounting structure is provided. Preferably the
mounting structure will be the same as or similar to that of mounting base 402
and/or antenna mounting base 404. In step 902, the helical antenna 410 and
the terrestrial antenna 430 are mounted. In step 904, an impedance matching
circuit is electrically connected to the helical antenna 410 and the
terrestrial
antenna 430 so that when they are radiating simultaneously their combined
impedance is substantially equal to that of the terrestrial antenna 430 when
radiating alone. In step 906, a cover is provided, preferably the same as or
similar to the parabolic or hemispherical cover 412 described herein that
encases and protects the antenna assembly 400.
Figure 9B shows a more detailed method of assembly of the antenna
assembly 400. In step 950, an antenna mounting base is provided. Preferably
the antenna mounting base will be the same as or similar to that of antenna
mounting base 404. In step 952, a dielectric substrate 416 is secured to the
underside of the antenna mounting base 404. The antenna mounting base
preferably serves as a RF shield, as well as a ground for this particular type
of
helical antenna 430 (e.g., a helical antenna 430 with open circuited, 3/4 wave
length radiating elements).
In step 954 the helical antenna 410 and the terrestrial antenna 430 are
mounted on antenna mounting base 404. Preferably, the combination of the
apertures 418 and lead through terminations 420 of antenna elements 422,
424, 426 and 428 serve to secure the helical antenna 410 and the terrestrial
antenna 430 in place. If desired, an adhesive such as a silicon adhesive, may
be placed on the bottom portion of the terrestrial antenna 430 and/or the
satellite antenna 410 to further secure them to the antenna mounting base 404.
A foam material, preferably being dielectric or substantially dielectric, of a
110275-4201 ORD
CA 02324383 2000-10-26
25 PATENT
type widely used in industry practice is optionally disposed between the
helical antenna 410 and the core 436. Preferably, the terrestrial antenna 430,
when embedded within the foam material, should be substantially rigid and
have minimal play.
In step 956, the circuit board 502 for RF mix/demix is attached,
preferably to the antenna mounting base 404. The circuit board 502 is
preferably attached on the side opposite to which the helical antenna 410 and
the terrestrial antenna 430 are mounted. In step 958 cables are attached
between circuit board 502 and circuit board 504, as previously discussed.
In step 960, a mounting base 402 is provided, preferably having cable
connectors 406, 408, and an O-Ring slot as shown in Figure 5. In step 962,
cables are attached between circuit board 504 and cable connectors 406, 408,
as previously discussed. In step 964, an impedance matching circuit is
electrically connected to the terrestrial antenna 430. The impedance matching
circuit is preferably integrated with, or embedded into, circuit board 502.
However, the impedance matching circuit may also be physically separated
from circuit board 502.
In step 966, an O-Ring 506 in inserted into the O-Ring slot within
mounting base 402. In step 968, the radome cover 412 is placed over the
antennas 410, 430 and O-Ring 506. In step 970, the ring clamp 508 is secured
to the radome enclosure 412 and mounting base 402 to protect against adverse
weather, corrosion, etc.
It should be understood that the individual steps in Figures 9A and/or
9B may be performed in an order other than described. It should also be
understood that, depending on a particular assembly technique, that one or
more individual steps shown in Figures 9A and/or 9B may be combined into a
single step.
Figure 10 is a block diagram illustrating a wireless packet data
transmission network that can utilize the dual mode antenna of the present
invention to communicate with, for example, mobile terrestrial vehicles. The
110275-4201 ORD
CA 02324383 2000-10-26
26 PATENT
network shown in Figure 10 is disclosed in U.S. Patent No. 5,953,319 to Dutta
et al., and is incorporated herein by reference. Network 1000 is a mufti-mode
packet data network which includes mobile vehicle equipment 1010, base
station packet switch 1020 and multiple radio frequency transmission paths
(only first transmission path 1030, second transmission path 1040 and Nth
transmission path 1050 are shown). Mobile vehicle data terminal equipment
1060 and fixed user data terminal equipment 1070 are the end user equipment
of this mufti-mode network. The multiple radio frequency transmission paths
may be proprietary, or may be leased sub-networks for use with or in the
present invention to facilitate mobile communications in the manner
described.
Mobile vehicle equipment 1010 is a terrestrial vehicle based device or
system which facilitates communication between mobile vehicle data terminal
equipment 1060, located on board the mobile vehicle, and fixed user data
terminal equipment 1070, through base station packet switch 1020. Mobile
vehicle equipment 1010 can be selectively coupled to any of the multiple radio
frequency transmission paths for establishing a "logical" communication link
with base station packet switch 1020.
Mobile vehicle equipment 1010 incorporates "intelligent" routing and
control mechanisms to determine which of the radio frequency transmission
paths a particular message data packet will be delivered through. Mobile
vehicle data terminal equipment 1060 is coupled to mobile vehicle equipment
1010 and can be any of a variety of devices which exchange information with
equipment 1010 for transmission/reception to/from fixed user data terminal
equipment 1070. For example, mobile vehicle data terminal equipment 1060
can be other computer based systems, sensors and/or human interface devices.
Base station packet switch 1020 performs a routing function similar to
mobile vehicle equipment 1010, but is positioned at a fixed location. Base
station packet switch 1020 can be selectively coupled to any of the multiple
radio frequency transmission paths for sending packet data messages to, and
110275-4201 ORD
CA 02324383 2000-10-26
27 PATENT
receiving packet data messages from, mobile vehicle equipment 1010. Base
station packet switch 1020 incorporates intelligent routing and control
mechanisms to control which of the multiple radio frequency transmission
paths a particular packet data message will be transmitted through.
Fixed user data terminal equipment 1070 is coupled to base station
packet switch 1020 and can be any of a variety of devices which exchange
information with base station packet switch 1020 for transmission/reception
to/from mobile vehicle data terminal equipment 1060. For example, data
terminal equipment 1070 can be other computer based systems such as a
IO management information system (MIS) and/or data terminal equipment 1070
can be human interface devices.
Radio frequency transmission paths 1030, 1040 and 1050 are typically
different wide area communication sub-networks available from any of a
number of service providers. The radio frequency transmission paths are
therefore typically independent and self-sufficient sub-networks having no
inter-network communication links between one another. There are at least
two transmission paths, typically with at least one being a satellite-based
sub-
network and at least one being a terrestrial-based sub-network. For example,
first radio frequency transmission path 1030 is provided by Motient
Corporation's Inmarsat-C satellite sub-network. Here, the mobile-satellite
communication sub-network utilizes geostationary satellites operating in the
L-band of the radio spectrum. Second radio frequency transmission path 1040
is preferably a terrestrial based sub-network such as the one provided by the
ARDIS~ Special Mobile Radio (SMR) sub-network. Other transmission paths
can be used in addition to the Motient Corporation (or Inmarsat-C) sub-
networks. For example, cellular phone and low earth orbit (LEO) sub-
networks can be used as transmission paths in the present invention as well.
Further, the sub-networks need not be wide-area in coverage. They can be
specialized local area coverage networks.
110275-4201 ORD
CA 02324383 2000-10-26
28 PATENT
As discussed above, a number of wide area mobile communication
sub-networks are in operation in the United States and in other countries. As
a
transmission path, each sub-network has characteristics which provide certain
advantages over other sub-networks. Satellite-based sub-networks have the
highly desirable characteristic of ubiquitous coverage for many areas,
particularly for rural areas of the North American continent. However,
satellite-based sub-networks frequently experience blockages in urban
coverage areas. Further, the signal strength of satellite-based sub-networks
is
low. Also, satellite equipment costs and data transmission costs are higher
than those of their terrestrial counterparts.
As transmission paths, terrestrial-based sub-networks frequently offer
practically full coverage in urban areas, the coverage area in which satellite
sub-networks frequently experience blockages. Terrestrial-based sub-
networks such as the MotientsM network 100 can even provide in-building
reception by mobile vehicle equipment 1010. Further, terrestrial-based sub-
networks provide advantages over satellite-based sub-networks in that signal
strength is higher, data transmission rates are typically higher, the costs of
sending data messages are lower, and the costs of equipment are lower.
However, while terrestrial-based sub-networks continue to grow in coverage,
the coverage remains concentrated in metropolitan areas with major gaps
existing in rural areas.
In network 1000, one or more of the differentiating characteristic
features of coverage, signal strength, data rates, message delivery times and
data costs are used as factors which allow mobile vehicle equipment 1010 and
base station packet switch 1020 to select the most appropriate one of radio
frequency transmission paths 1030,1040 and 1050. Realizing the
complimentary nature of satellite and terrestrial-based sub-networks, the
mufti
mode antenna assembly 400 of the present invention offers users the benefits
of ubiquitous satellite coverage and the high data rates and in-building
penetration capabilities of a terrestrial system. The antenna assembly 400
110275-4201 ORD
CA 02324383 2000-10-26
29 PATENT
according to the present invention can thus be utilized in conjunction with a
network 1000 such as shown in Figure 10 to achieve the respective advantages
associated with each of terrestrial and satellite transmissions.
The many features and advantages of the invention are apparent from
the detailed specification, and thus, it is intended by the appended claims to
cover all such features and advantages of the invention which fall within the
true spirit and scope of the invention. Further, since numerous modifications
and variations will readily occur to those skilled in the art, it is not
desired to
limit the invention to the exact construction and operation illustrated and
described; and accordingly, all suitable modifications and equivalents may be
resorted to, falling within the scope of the invention. While the foregoing
invention has been described in detail by way of illustration and example of
preferred embodiments, numerous modifications, substitutions, and alterations
are possible without departing from the scope of the invention defined in the
following claims.
110275-4201 ORD
