Note: Descriptions are shown in the official language in which they were submitted.
CA 02096177 2002-03-20
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This appliGaCion relates to elactsroasgnatia radiatirig
structures euitabie !or use as aptene3.a or as
electromagnetic simulators. 14n elegy-.troaagnctfc s3aulatcr
is a type of test equlpment used for c~eecxirg the behaviour
of equipment in the presence of strong alactroaagnetic
fields.
Continuous Wave (cv) seasnratnmt o! electromagnetic
susceptibility and radiated interference can De carried out
using multiple antennas xhose alectromaqr~etic properties
must be veil known its the near field ar using Tt~i cells
Mhos,: volume and/or tre~uancy Baits aaice them unsuitable
for broadband testing at large (!ax mets~as in height)
electrotfiC sub-syste~as.
Pulse measurements of alectroma~gnetic susceptibility
are currently eondmcted using parallel line.simulators, G-
TE~1 cells or distributed load conical simulators_ the
parallel lilts simulators suffer from nigh frequency
Zo limitations. The uss of G-TE~i calls limits the vohtme of
the tested object and the conical sirmlator saffsss from
freguet~cy limitations.
B.S. Patent Ho. 4,546,358 issued CCtober 8, 1SB5 t0
Ediin et al. discloses a test cell formed in the spa~-a
betweels a parallel plate cottdurtvr and ground plane which
together fore a transmission lips. The parallel plate
conductor is fed by a tapored line 5actiori from a Coaxial
feed, in Order to maintain a Cons':ant impedance, sad the
parallel plate conductor terminates ire a llnted edge to
avoid reflections.
Canadian Pat~:nt too. 1,273,060, issued August Zl, 1996
to 88c Brown, 8overi l company, LimtP~3, (v.5. Patent ha.
4,837,5811 discloses a~1 ~ testing device usitlg a xave
guide of pyramidal shape but with added reatttrP.s. Tk~s . t,~t
device disclosed in this patent has tat intermediate plate
conductor suspended in the wave guide at a distance of
about one quarter of the
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total height of the wave guide from the 'top surface.
This defines a test volume between the intermediate
plate and the wave guide lower surface. Uniform field
strength in the test volume is achieved by a complex
termination arrangement consisting of a curved wall of
high frequency energy absorbing material coupled to
the intermediate plate by a number of terminal
resistors. The impedance of the line formed by the
a.mtermediate plate and the ground plane can be
l0 slightly varied, if required for fine 'tuning, by
altering the spacing of the intermediate plate from
the upper surface of the wave guide.
such equipment is unsuitable fog' the testing of
large pieces of electronic equipment. The apparatus
described in the present application can be expanded
to accommodate larger objects without degradation of
the bandwidth.
Generally, the simulator oescrmea ~n ~aa~s
application launches an electromagnetic wave from a
z0 high frequency coaxial feed line into an expanding
rectangular horn containing a plate conductor forming
an asymmetrical parallel line within the horn. The
parallel. line extends beyond the horn by means of a
forwardly extending conducting plate section which
functions as a radiating element and establishes a
test volume in the space between itself and a ground
plane extending forwardly from the lower surface of
the horn. The forwardly extending plate section is
connected to the parallel line either directly or
through a network of parallel inductance and
capacitance. Two modes of propagation occur in the
horn giving a complete coverage of the relevant
frequency spectrum.
Specifically, in one aspect the invention
relates to a broadband electromagnetic field simulator
comprising: an apen horn waveguide and a ground plane
conductor formed as a forward extension of the lower
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surface of the horn. A source of r.f. energy is
coupled to the apex of the horn and a relatively
narrow conducting plate positioned to form a septa
between the upper and lower surfaces of the horn. A
plate section of similar configuration to the septum
is coupled thereto and extends forwardly from the
mouth of the horn. The plate section extends
initially substantially parallel t~ the ground plane
and then curves downwardly to terminate adjacent to
it. The space between the forwardly e:rctending plate
section and the ground plane defines the reguired test
volume.
In an alternative embodiment the plate section
extends upwardly, initially with an exponential
configuration and then forwardly to terrtcinate at a
vertical, grounded wall faced with anechoic material.
tahen used as an antenna, the structure provides
an extremely wide band response due in part to greatly
reduced internal reflections. 7Cn its antenna aspect,
one form of the invention relates to an antenna
comprising: an open horn waveguide with a ground plane
conductor forming a forward extension of the lower
surface of the horn; the apex of the horn being
adapted to receive a detector or r.f. source; a
relatively narrow conducting plate positioned to form
a septum between the upper and lower surfaces of the
horn; and a conducting plate section of similar
configuration to the septum and coupled thereto and
extending forwardly from the mouth of the horn, said
plate section extending initially substantially
parallel to the ground plane and then curving
downwardly 'to terminate adjacent to it; whereby the
forwardly extending plate section functions as a
radiating element.
llnother form of antenna in accordance with the
invention consists of an open horn waveguide with a
ground plane conductor forming a forward extension of
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the lower surface of the horn; a pair of closely
spaced conducting plates positioned to form an upper
and lower septum, respectively, between the upper and
lower surfaces of the horn; a forwardly extending
conducting section spaced from and in front of the
horn; and a plurality of laterally spaced conductors
connecting the septums to the rear edge of the
conducting section; whereby the conducting section
functions as a radiating element. Probably the
conductors extending between the front edge of the
upper septum and the conducting section each contain a
resistive termination. This structure can also
function as an electromagnetic simulator.
BRIEF DESCRIPTION OF THE DRI~WINGS
Preferred embodiments will be described in
conjunction with the accompanying drawings, in which:
Fic.~ure 1 is a schematic view of one embodiment
of a simulator in accordance with the invention;
Figure 2 shows the coupling between the septum
within the hare and the forwardly extending plate
section;
Fagots 3 shows use of the simulator within an
anechoic chamber;
Figure 4 shows use of the simulator in free
space;
Figure 5 shows a further embodiment of a
simulator in accordance with the invention.
Figures 6 to 9 are embodiments of antennas in
accordance with the invention;
3p Figure 10 is a modification of the simulator
shown in Figure 3; and
Figure ~,1 is a further embodiment of a structure
in accordance with the invention, which can be used as
a simulator ar as an antenna.
DESCRTPTION OF PREFERRED EMBODINtENTS
Figure Z shows broadband electromagnetic field
s~.mulator in accordance with this invention having an
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r.f. signal, either pulse or continuous wave, supplied
from a generator 6 through a coaxial line 5 to a
transition coupling 7 connected to the input of a TENT
line formed by horn 10. The aperture of horn 10 is .
5 open and a ground plane 3 extends forwardly to form
the base of the test volume.
Within 'the horn a conducting plate or septum 9
is positioned spaced from the upper surface of the
horn and with a high voltage dielectric lining 8
l0 therebetween. At the output of the horn a forwardly
extending plate section 1 is provided to function as
the radiating element in the test apparatus. This
plate can be connected either directly to conducting
plate 9 or by means of the coupling network shown in
Figure 2. Plate 1 extends forwardly from the horn to
a support structure 19 and then curves downwardly
towards ground plane 3, being coupled to the ground
pJ.ane through a terminating resistor 2. Apparatus to
be tested, indicated schematically at 4, is located an
the ground plane under the forwardly extending
radiating element.
An alternative embodiment, shown in Figure 5 has
plate 1 extending upwardly, initially at an
exponential rate, towards a higher support structure
19" and then extending forwardly t~ terminate a~t a
vertical ground plane 3' via ter~ninata.ng resistor~2.
The side of the vertical ground plane is covered with
anechoic material. This peranits the testing of
objects 4 ~f larger dimensions.
3~ A preferred manner of coupling the fvrwardly
extending element to the septum in the horn is shown
in Figure 2. The septum shown a~t 16 farms a capacitor
with the radiating element 1 having a dielectric
formed by strip 12. An inductance is provided by line
17 extending from the radiating element back to the
conductive plate. The edges of the septum are
connected to the side walls of the radiating horn
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through terminating inductances 15 and high voltage
terminating resistors 1~.
The test apparatus can be used in an anechoic
chamber 32 as shown in Figure 3 provided with
absorbers 31 or in a shielded room having only side
walls lined with anechoic material. Other reference
numerals in Figure 3 correspond to 'those already shown
in Figure 1. Alternatively, the test apparatus can be
used in an unbounded electromagnetic f:Leld
to configuration as shown in Figure 4. Again the same
reference numerals are used in Figure :L.
A modification ~f the simulator uses two
building, each of the type shown in Figure 4, facing
one another with an open space between in which is
~.5 located the support 19. The terminating portion of
the forwardly extending plate as well as the
transmitting section are thus under cover. A further
modification of the simulator shown in Figures 1 and 5
uses shielded side walls to reduce any electroanagne~tic
20 leakage tc~ acceptable levels.
As is known, due to reciprocity any radiating
structure can also function as an antenna. The
structure of Figure 1 can also act as a sensitive wide
band antenna. Figure 6 is such a modification of the
25 simulator of Figure 5 adapted to function as an
antenna. The vertical ground plane and anechoic
material are removed for antenna operation and
terminating resist~rs 33 are c~nnected from about the
mid-line of plate 1 to the anetal upper edge of the
30 horn. The lt~wer surface of the horn is positioned on
a ground plane 39. Nigh voltage insulation 3~
separates the septum and plate 1 from the horn itself.
The function of resistors 33 is to reduce unwanted
reflections.
35 Figure 7 shows a similar, but more symmetrical
arrangement, ozaitting the ground plane thus avoiding
limiting the antenna to signals guided by ground. A
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pair of forwardly extending plates 1 and 1' define a
radiating arrangement with plate 1 connected in a
similar fashion as shown in Figure 6 but plate 1'
connected to the lower front edge of the horn. Figure
8 shows a similar but completely symmetrical
arrangement in which a pair of structures of the type
shown in Figure Z are provided with radiating horns
connected along one edge and for.~~:rdly extending
plates ~. and 1' are joined at their free ends by
terminating resistors 34. the horns require separate
feeds f and 6'. Figure 9 shows a still further
modified antenna which uses a reflector 35 fed by a
pair of symmetrically arranged horns having forwardly
extending conductive plates 35 conforming in shape to
the curvature of reflector 36 and connected to the
reflector by terminating resistors 3?.
Such double horn antennas can also be used in a
modification of the electromagnetic simulator of
Figure 3, shawn in Figure 10. 'the simulator shown in
Figure ZO has two plates or septums extending from the
antennas into the anechoic chamber and terminating at
the end of the side walls of the anechoic chambers.
The simulator projects into the anechoic chamber at an
angle in respect to the ground. Such design is
advantageous for an anechoic chamber with a ground
plane, since it can simulate the effects of ground
reflection. ~n the case of an anechoic chamber
without ground fall six walls covered with absorbing
material), or in the case of an open field simulator,
the simulator of Figure 10 can be arranged parallel to
the ground, simulating a perfectly horizontal
polarization. 3'he use of such double-horn simulators
permits the simulation of horizontal polarization,
providing broadband simulation for both vertical and
horizontal polarizations.
Figure 11 shows a further form of structure
useful both as an antenna or a simulator employing
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similar concepts as in the previously discussed
embodiments. A horn 40, located on a ground plate 48,
is provided with a pair of septums 41 and 42 separated
by an insulating member 43. As a result septums 41
and 42 are capacitively coupled. A forwardly located
conductive plate with sections 44 and 45 is connected
to the upper and lower septum edges by wires 47. The
wires from the upper septum have resistors 46 along
their length and the wires from the lower septum edge
are continuous. Plate sections 44 and 45 may be
formed from wire mesh and act as radiators when used
as an antenna. Resistors 46 provide appropriate
matching to avoid reflections. The antenna can be
used with a reflector as discussed in relation to
Figure 9.
then used as a simulator the area under the
wires defines a test volume. xt is necessary to
terminate the simulator with termination resistors and
an absorbing wall as shown for the embodiment of
Figure 5.
Thus, there has been disclosed broadband
antennas and broadband gigahert~ field simulators
capable of generating high power values of field
distributed uniformly across a test volume. The
simulator has the following advantages:
Reduced cost of testing by making possible
susceptibility and emission testing in one
simulator.
Provision of a wide~band simulator that can
be used in both open field and shielded
environments.
Provision for time (impulse), frequency
(cw) and current injection testing with one
simulator by suitably changing source 6.
Provision of both testing and calibration
facilities in one simulator.
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Provision of easily accessible large
(mufti°metre height) testing volume.
Extension of the maximum frequency of
operation into microwave (GFiz) frequencies for
testing of large height (mufti°metre) objects.
.As a result, the low cost, extremely accurate,
calibration simulator can be substituted for bulky ~'EM
cells presently used for calibration. The advantage
of this simulator, over others presently in use, is
o that it can be easily incorporated into existing
shielded or anechoic enclosures thereby eliminating
any environmental concerns by preventing the radiation
of high electromagnetic fields into the environment.
'his is done without reduction of the bandwidth or 'the
size of tested objects.
~'he structure has been shown to be useful as a
broadband high power radiator and a broadband
sensitive listening device f or electronic warfare
applications.
