Note: Descriptions are shown in the official language in which they were submitted.
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ULTRAWIDE BANDWIDTH ELECTROMECHANICAL PHASE SHIFTER
FIELD OF TIC INVENTION
The present invention relates generally to antenna technology, and more
particularly to electromechanical phase shifter antenna technology.
BACKGROUND OF THE RELATED ART
It is widely known in the wireless communication community that a base station
antenna needs to be downtilted from the horizon to reduce intercell
interference among antenna
beams. Current practice to configure antenna beams involves adjusting downtilt
angles of the
antennas via their mechanical mountings. The configuration of the antennas is
dependent upon a
cell installer's experience. Such antenna adjustment is costly, time-consuming
and inaccurate.
Typically, once the downtilt angles of the antennas are adjusted by the cell
installer, the downtilt angles will not be re-adjusted. Thus, the downtilt
angles and the antenna
beams are typically fixed. Fixed antenna beams makes it near impossible to
optimize system
performance when there are variations in environmental conditions, such as
seasonal traffc
changes and network growth. One manner for resolving this dilemma involves
employing
steerable phased-array antennas. Such antennas allows for remote manipulation
of the antenna
beams.
Steerable phased-array antennas are directive antenna comprising a group of
individual, properly distributed and oriented radiators in a one or two-
dimensional spatial
configuration. The phase associated with each radiator can be individually
excited using phase
shifters to form a desired radiation pattern in space. This allows for the
positioning of antenna
beams by varying the relative phase associated with the excitations being
applied to the individual
radiators. Hence, beam steering in the azimuth or beam tilting in the
elevation can be
accomplished without re-adjusting the downtilt angle of the antennas via
manipulating the
mechanical mountings.
There exist several categories of phase shifters for generating differential
phases
among the radiators. The first category employs switchable delay lines having
different lengths,
wherein phases are linearly adjusted by varying the distance signals travel.
This category of
phase shifters are usually big and expensive. The second category utilizes
solid state hybrid
coupled diodes that initiate phase shifting based on different bias voltages.
This category of
phase shifters suffer from non-linearity (between current and voltage in high
power
circuitry/devices) and high insertion loss.
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The third category of phase shifters uses ferromagnetic material, such as
ferrite.
These phase shifters shift phases by varying the permeability of the
ferromagnetic material using
an applied DC magnetic field. Due to the permeability change, the phase
associated with an
electromagnetic wave traveling through the ferromagnetic material is changed.
Ferromagnetic
material, however, are large, heavy and expensive. The fourth category of
phase shifters involves
the introduction of dielectric material in the signal path to cause phase
delay. This category,
however, has associated impedance mismatch causing high return loss, therefore
degrading
performance.
The fifth category of phase shifters are referred to in the art as
"trombones."
FIG. 1 depicts a trombone phase shifter 10 comprising an input coaxial cable
12, an output
coaxial cable 14 and an trombone arm 16. Coaxial cables 12, 14 comprise cables
18, 20 and
shielding 22, 24. Trombone arm 16 is preferable constructed using a solid
metal piece and
configured to slidably fit between cables 18, 20 and shielding 22, 24 in order
to complete a signal
trace between input and output coaxial cables 18, 20. The phase of a signal
traveling though
trombone phase shifter 10 is linearly adjusted by sliding trombone arm 16.
Trombone phase
shifter 10, however, suffers from some drawbacks. Specifically, since the
trombone phase shifter
is manufactured to make sure to have a good metallic contact to minimize the
insertion and return
loss, the trombone arm 16 must be precisely constructed to fit provide
sufficient electrical
coupling with cables 18, 20 while minimizing friction with cables 18, 20.
However, such precise
construction increase the cost significantly and make this approach become
uneconomical for the
commercial applications. Besides, because of this type of configuration is
meant to be metallic
contact, it suffers from corrosion and metallic contact problems over time.
Accordingly, there exists a need for a phase shifter that does not have the
drawbacks associated with the above prior art phase shifters. Specifically,
there is a need for a
phase shifter that can provide extremely linear performance (in high power
circuitry/devices) over
a very broad bandwidth, while still maintaining lightweight and inexpensive
with minimal
insertion and return losses. There also exists a need for a phase shifter with
little or no metal
contact and not subject to corrosion.
SUMMARY OF THE INVENTION
The present invention is a phase shifter that does not suffer from metallic
contact
and corrosion problems and that is linear (in high power circuitry/devices),
light weight and
inexpensive with minimal insertion and return losses over a very broad
bandwidth. The present
invention phase shifter is constructed using a stripline structure. The
present invention comprises
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a first signal board having an input signal line and an output signal line and
a second signal board
having a U-shaped signal line. The U-shaped signal line being configured to
complete a signal
trace between the input signal line and the output signal line when the second
signal board is
positioned a distance D over the first signal board with an overlap OD. The
distance D and
overlap OD being a distance sufficient to enable electrical coupling between
the U-shaped signal
line and the input and output signal lines. The first and/or second signal
boards are mounted
using a slidable mounting system such that the length of signal trace may be
varied by moving the
first and/or second signal board - that is, the phase of a signal is varied by
varying the distance
the signal travels from the input signal line to the U-shaped signal line to
the output signal line.
Advantageously, the present invention does not require a metallic contact. The
two signal boards
are separated by the distance D in order to make sure no friction exist during
the moving process.
Since there is no metallic contact between the signal boards, consequently,
there is no friction or
corrosion problem.
BRIEF DESCRIIrTION OF THE DRAWINGS
The features, aspects, and advantages of the present invention will become
better
understood with regard to the following description, appended claims, and
accompanying
drawings where:
FIG. 1 depicts a trombone phase shifter used in the prior art;
FIG. 2 depicts a side view of a phase shifter in accordance with the present
invention;
FIG. 2a depicts a cross sectional view of the phase shifter of FIG. 2 having a
slidable
mounting with a moving slide;
FIGS. 3 and 4 depict top views of input/output signal boards and U-shaped
signal board;
FIG. 5 depicts inputJoutput signal board overlapping with U-shaped signal
board; and
FIGS. 6 and 7 depict and input/output signal board and a double U-shaped
signal board.
DETAILED DESCRIPTION
FIG. 2 depicts a side view of a phase shifter 26 in accordance with the
present
invention. Phase shifter 26 is a stripline structure comprising top plate 28,
bottom plate 30, a
slidable mounting system 31, input/output signal board 34 and U-shaped signal
board 36. Top
and bottom plates 28, 30 are ground plates and are preferably constructed
using metal. Signal
boards 34 and 36 are mounted to bottom and top plates 28, 30, respectively,
using slidable
mounting system 31. In one embodiment, slidable mounting system 31 comprises a
plurality of
spacers 32 and a moving slide 29. Spacers 32 are used to mount input/output
signal board 34 to
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bottom plate 30, and to mount U-shaped signal board 36 to moving slide 29, as
shown in FIG. 2a
which depicts a cross-sectional view of phase shifter 26 having this
embodiment of slidable
mounting system 31. Moving slide 29 is slidably mounted within a channel in
top plate 28, thus
allowing for U-shaped signal board 36 to slide over input/output signal board
34. Note that
input/output signal board 34 is mounted in a fixed position. Alternately,
input/output signal
board 34 is mounted to moving slide 29 and U-shaped signal board 36 is mounted
in a fixed
position, or both signal boards 34, 36 are mounted to different moving slides.
Spacers 32 are
constructed using conductive or non-conductive material, such as metal and
nylon.
FIGS. 3 and 4 depict top views of input/output signal boards 34 and U-shaped
signal board 36, respectively. In one embodiment, inputloutput signal board 34
is a planar circuit
board 44 having an input signal line 40 and an output signal line 42, and U-
shaped signal board
36 is a planar circuit board 46 having a U-shaped signal line 48, wherein the
U-shaped signal line
has legs 50, 52 and an arc 54. The signal lines 40, 42, 48 are preferably
etched onto circuit
boards 44, 46 and configured into a transmission line structure. Possible
transmission line
structures include, but are not limited to, microstrip line, stripline and
finline. If thin film
technology is applied to signal boards 34, 36, circuit boards 44, 46 can be
structured to comply
with specified geometry or curved surfaces (and may not be planar).
Input and output signal lines 40, 42 are etched parallel to each other onto
circuit
board 44, wherein the space between input and output signal lines 40, 42 is
equal to the space
between legs 50, 52 of U-shaped signal line 48. Input, output and U-shaped
signal lines 40, 42,
48 preferably having a same thickness. When U-shaped signal board 36 is
positioned over
input/output signal board 34 such that U-shape signal line 48 overlaps a
minimum amount OD
with input and output signal lines 40, 42, a complete signal trace is formed
from input signal line
40 to U-shaped signal line 48 to output signal line 42, or vice versa, where
OD is a minimum
overlap/overlay amount between the input/output signal board and U-shaped
signal board that
allows for su~cient electrical coupling between the input/output signal lines
and the U-shaped
signal line. The value of OD being dependent upon the circuit board material,
the stripline
structure dimensions (i.e., distance between the top and bottom plates), and
the signal line widths.
See FIG. S. Note that the term "U-shaped" is used to describe the shape of the
signal line etched
onto circuit board 46 (and not for describing the shape of circuit board 46).
Further note that the
present invention should not be construed as limited to a U-shaped signal line
etched on circuit
board 46. For purposes of this application, the term "U-shaped" should be
construed to describe
any shape for a signal line etched on circuit board 46 that will allow for a
complete signal trace to
be formed when circuit board 46 is positioned over circuit board 44.
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As mentioned earlier, U-shaped signal board 36 is configured using spacers 32
such that U-shape signal board 36 can slide over input/output signal board 34.
When U-shaped
signal board 36 slides along its slidably mount (via spacers 32) over
input/output signal board 34,
the distance a signal traveling from input signal line 40 to output signal
line 42 (via U-shaped
signal board 46) varies, thus causing the phase of the signal to shift at the
output signal line.
Signal boards 34, 36 are spaced a maximum distance D apart from each other,
wherein D represents a ma~cimum distance that enables suflzcient electrical
coupling between
input and output signal lines 40, 42 with U-shaped signal line 48 while
avoiding friction between
signal boards 44, 46. The distance D being dependent upon the circuit board
material, the
stripline structure dimensions (i.e., distance between the top and bottom
plates), and the signal
line widths.
Provided here is an example of a phase shifter in accordance with the present
invention. The phase shifter is a stripline structure with the two metallic
plates (top and bottom
plates) being spaced 332 mil apart. The circuit boards used for etching the
input/output signal
lines and the U-shape signal line are Rogers 4003 32 mil laminated with a
dielectric constant of
3.38 and loss tangent of 0.002. Under such stripline dimension and material
used, the signal line
width would be 425 mil. A return loss of less than -20 dB and an insertion
loss of less than 0.2
dB over a 50% frequency bandwidth can be obtained if the circuit board spacing
and signal line
overlap dimension are less than 10 mil and more than 2",respectively.
Phase shifters of the present invention may be incorporated into steerable
phased
array antennas. This will allow transmitting entities, such as base stations,
to form desired
radiation patterns without re-adjusting the downtilt of their antennas.
Although the present invention has been described in considerable detail with
reference to certain embodiments, other versions are possible. For example,
the phase shifter
may have a double U-shaped signal line, as shown in FIGS. 6 and 7. Therefore,
the spirit and
scope of the present invention should not be limited to the description of the
embodiments
contained herein.
