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References
1
30
21 7
22.0
22 3
frequency, GH z
22.6
22.9
1822111
Fig. 3 Gain and antenna efficiency
experiment
calculation including measured phase taper along feed
waveguide
n
“I
-1 0
H-plane
-20
m
U
-
-30
U
3
c
z
e
-40
01
E-plane
Ill
.g
-0
-10
2
-2 0
-30
-40
-90
-60
-30
0
30
angle,deg
60
‘Microstrip antenna for millimeter waves’, IEEE
Trans., 1981, AP-29, (l), pp. 171-174
2 HUANG, J.: ‘A Ka-band circularly polarized high-gain microstrip
array antenna’, IEEE Trans. Antennas Propag., 1995, pp. 113-116
3 OHTA, M., ISHIZAKA.H.,KOSE,R., SAITO,T., OKUBO, N , and
HANEISHI, M.: ‘Radiation properties of circularly polarized triplatefeed-type patch antennas at 60GHz band’. IEICE Natl. Conv.
Rec., B-115, September 1994
4 KITAO, s., YAMOTO, M., OHMINE, H., AOKI, H., and HARUYAMA, T :
‘Radiation properties of triplate line fed microstrip array antenna
with polarization grid in the 60 GHz band’. IEICE Natl. Conv.
Rec., B-60, September 1994
5 SAKAKIBARA, K., HIROKAWA, J., ANDO, M., and GOTO, N.: ‘A slotted
waveguide planar array antenna for entrance radio systems in
mobile communication’. 4th IEEE Int. Conf. on Universal
Personal Commun., November 1995, (Tokyo), pp. 373-376
6 R.C.R. news, No. 403, Research & Development Center for Radio
Systems, 4 May 1993
7 HIROKAWA, J., ANDO, M., and GOTO, N.: ‘A single-layer multiple-way
power divider for a planar slotted waveguide array antennas’,
IEICE Trans. Commun., 1992, E75-B, (8), pp. 781-787
8 TAKAHASHI, T., HIROKAWA, J., ANDO, M., and GOTO, N: ‘The
suppression of the reflection by an inductive wall of a power
divider for a slotted waveguide array’. Tech. Rep. of IEICE, AP94-7, April 1994
9 JOHNSON, R . C , and JASIK, H.: ‘Antenna engineering handbook’
(McGraw-Hill, New York, 1984), Chap. 9
10 HIROKAWA, J., SAKURAI, K., ANDO, M., and GOTO, N.: ‘Matching slot
pair for a circularly-polarized slotted waveguide array’, IEE Proc.
H, 1990, 137, (6), pp. 367-371
11 SEKI, H.: ‘An alternative representation of electromagnetic fields in
a rectangular waveguide with an aperture in its wall’. IEICE Natl.
Conf. Rec., 1, (16), September 1984
12 EDELBERG, S., and OLINER, A.A.: ‘Mutual coupling effects in large
antenna arrays: part I - slot arrays’, IRE Trans. Antennas Propag.,
1960, pp. 286297
13 SAKAKIBARA. K.; HIROKAWA, J., ANDO, M., and GOTO, N.: ‘Simple
evaluation of mutual slot couplings in a slotted waveguide planar
array antenna’. IEEE AP-S, June 1995, (Newport Beach), pp.
1838-1841
14 GOTO, N.: ‘A waveguide-fed printed antenna’. Technical Report of
IEICE, AP 89-3, April 1989, pp. 17-21
WEISS, M.A.:
90
1822141
Fig. 4 Radiation pattern
big. 4 shows the radiation patterns at LL.LbJ=lz. lhe H-plane
pattern reflects the illumination along the radiating waveguide.
The measured radiation pattern reasonably agrees with the predicted one. Furthermore, the symmetrical radiation pattern is
obtained in the E-plane, and reflects the uniform power division
provided by the feed circuit.
Conclusions: A high-efficiency and high-gain planar slotted
waveguide array is fabricated in the 22GHz band. The single-layer
feed circuit composed of a cascade of -n-junctions is adopted which
is suitable for mass-production. The peak antenna efficiency of
75.6% and the gain of 35.9dBi are obtained at 22.15GHz, which is
quite high in comparison with any other planar antennas in this
frequency and gain range. Realisation of perfect contact between
the two components without degrading the mass produceability is
the aim of future study, to fully demonstrate the superiority of a
single-layer waveguide slot antenna [141.
Acknowledgments: The authors are indebted to H. Ishiwata of
NHK Spring Co., Ltd. for fabricating test antennas. This work is
partly supported by The Murata Science Foundation.
0 IEE, 1996
Electronics Letters Online No: 19960268
I8 December 1995
K. Sakaltibara, J. Hirokawa, M. Ando and N. Goto (Tokyo Institute
of Technology, Faculty of Engineering, Department of Electrical and
Electronic Engineering, 2-12-1, 0-okayama, Meguro-ku, Tokyo 152,
Japan)
284
Independent control ofresonant frequency
and input impedance of a microstrip patch
by individually biased varactor diodes
P.M. Haskins and J.S. Dahele
Indexing terms: Patch antennas, Microstrip antennas, Tuning
Individually biased varactor diodes fitted to the radiating edges of
microstrip patch antennas enable independent control of the
resonant frequency and input impedance. The technique has been
successfully applied to polarisation-agile patch antennas and it
affords a solution to the problem of the change in input
impedance when switching between polarisations.
Introduction: Du Plessis and Cloete [l] showed that the effective
length and feed position of a rectangular microstrip patch antenna
can be adjusted by trimming the lengths of stubs located on the
two opposite radiating edges, thereby permitting optimisation of
both resonant frequency and input impedance. This method, however, only allows one way, non-repeatable adjustment, in that it
involves the physical shortening of the stubs by trimming metal
away.
Varactor diodes are extensively employed in microstrip antennas for varying the resonant frequency, [2,31, but here we describe
a technique in which independently biased varactor diodes perform functions similar to the stubs in [l], thereby enabling continuous repeatable independent variation of the resonant frequency
and input impedance.
A practical application for this technique is in polarisation-agile
antennas as described in [4].We observed that while the input
ELECTRONICS LETTERS
15th February 1996
Vol. 32
No. 4
match is good with linear polarisation, it degraded when circularly
polarized. The method we describe here, however, enables the
optimisation of the input match for both polarisations.
patch
I
--
polarised, the input return loss at the same frequency was
17dB, (Fig. 3) with a boresight axial ratio better than 0SdB
(Fig. 4).
R.F. feed point
1
1
-10
m
D
-20
Fig. 1 Patch schematic diagram showing connections to individually
biased diodes
-30
Initial tests: To test the principle, a rectangular patch antenna
with a BAR28 diode fitted to each radiating edge as in Fig. 1, and
separate bias return paths decoupled to the ground plane at radio
frequency via capacitors C, and C,, was measured on a vector network analyser. It was observed, inter alia, (i) The resonant frequency can be vaned from 2.05 to 2.15GHz (4.4?4 bandwidth)
with the input impedance maintained by adjustment of the bias at
50R f l a , throughout the band, or, (ii) The resonant frequency
can be maintained at a predetermined fiied value in the range 2.05
to 2.1SGHz with the resistive part of the patch input impedance
adjusted to any value from 34 to 63R. (See Fig. 2).
2.25
2.50
frequency, GHz
2.75
18)8/3(
Fig. 3 Measured return loss of new polarisation-agile antenna in circular polarisation at 2.45GHz
angle,deg
90
0
60
30
0
30
60
90
-10
m
D
I
rn
Fig. 4 Measured circularly polarised radiation pattern at 2.45GHz with
axial ratio deviations
For comparison, Sharma and Gupta [6] reported an optimised
diagonally fed nearly-square patch antenna which had a input
return loss of --13dB (1.55 VSWR) and an axial ratio of 0.25dB.
Fig. 2 Measured input impedance loci at bias voltages iving real part
values at 2.1 GHz resonant frequency of34, 50, and 6 3 h
(i) 34Q, (ii) 50R, (iii) 63Q
Start: 2.0GHz, stop: 2.2GHz
Marker 1: 2.1 GHz
Application to polarisation-agile antennas: When a polarisation-
agile antenna of the type in [4], with the feed point optimised for
linear polarisation is switched from linear to circular polarisation,
two detuned orthogonal modes are established resulting in the
reduction of the real part of the input impedance. (This effect is
predicted from the model of a circularly polarised patch as two
parallel resonant circuits in series presented by Long and McAllister [SI). Whereas in [4], there was no way to compensate for this,
and the input match degraded consequently, in our new antenna,
the additional flexibility to control the real part of the input
impedance independently of the resonant frequency affords optimum matching with all polarisations.
Experimental results: A new polarisation-agile square patch
antenna was constructed with an independently biased diode on
each side to control the resonant frequency and impedance of the
orthogonal modes. With appropriate bias, the input return loss in
linear polarisation was better than -30dB with boresight cross
polar levels better than -25dB at 2.45GHz. When circularly
ELECTRONICS LETTERS
15th February 1996
Vol. 32
Conclusions: Fitting individually biased varactor diodes to radiating edges of a patch antenna allows the independent adjustment of
both the resonant frequency and the input impedance, thereby
allowing the optimisation of the input match at the selected frequency. This technique has been successfully applied to polarisation-agile antennas and offers a solution to the problem of the
degraded input match when they are circularly polarised. The
input match and axial-ratio performance of polarisation-agde
antennas with this facility compare favourably with that of optimised diagonally fed nearly-square conventional non-agile circularly polarised patch antennas.
0 IEE 1996
Electronics Letters Online No: 19960272
19 December I995
P.M. Haskins and J.S. Dahele (School of Engineering and Applied
Science, CranJield University, Royal Military College of Science,
Shrivenham, Swindon, Wilts, SN6 8LA, United Kingdom)
References
and CLOETE, J : ‘Tuning stubs for microstrip patch
antennas’, ZEEE Antennas Propag. Mag., 1994, 30, (6), pp. 52-56
2 BHARTIA, P., and BAHL, I.J.: ‘Frequency-agile microstrip antennas’,
Microw. J., 1982, pp. 67-70
3 WATERHOUSE, R.: ‘Modelling of Schottky-barrier diode loaded
microstrip array elements’, Electron. Lett., 1992, 28, (19), pp. 17991801
1
DU PLESSIS, M.,
No. 4
285
4
HASKINS, P.M.,
and
DAHELE, J.S :
'Varactor-diode loaded passive
polarization agile patch antenna', Electron. Lett., 1994, 30, (13),
5
pp. 1074-1075
LONG, S.A., and
6
SHARMA, P.c ,
MCALLISTER, M.W.: 'The impedance Of an elliptical
printed circuit antenna', ZEEE Trans., 1982, AP-30, (6), pp. 1197-
1200
and CUPTA, K.C.: 'Analysis and optimised design of
single feed circularly polarized microstrip antennas', ZEEE Trans.,
1983, AP-31, (6), pp. 949-955
taken from opposite edges of the two patches and the phases of
the direct feedthrough signals from transmit to receive are
adjusted so that they are 180" out of phase, which on combining
will cancel. The received signals are forced to be 180" out of phase
by the positions of the receiver outputs, thus when combined they
will add in phase. This method can increase the isolation by 20 to
30dB.
Results: The basis for the transmit-receive isolation is the orthogo-
lntegrate~active antenna with simultaneous
transmit-receive operation
M.J. Cryan and P.S. Hall
Indexing terms: Active antennas, Antennas
nal positioning of the oscillator and amplifier. Measurements were
canid out to assess the levels of isolation obtainable. These
results are shown in Fig. 1. Two sets of results are shown, 50R
transmission lines connected directly to the edge and wire bonds
connected across a gap from the transmission line to the edge of
the patch. It is seen that the isolation can be dramatically
improved with the use of wire bonds. The improved isolation is
caused by the wire contact exciting fewer higher order modes than
the 50Q line; such modes have been shown to be primarily responsible for cross polarisation and hence breakthrough into the
orthogonal mode.
substrate
patch1
The authors present results for a novel two element active
transmit-receive array using dual linear polarisation and
sequential rotation. Each element includes an integrated oscillator
and amplifer mounted on orthogonal edges of a square patch,
such that transmit and receive paths are isolated and polarisation
duplexed. The array gives in excess of 55dB transmit-receive
isolation at 3.77GHz.
substrate
patch 2
Introduction: An active antenna integrates an active device into a
printed antenna to improve its per formance or combine functions
within the antenna itself. Such antennas are of increasing interest
[l] as system designers require more complex functions to be
implemented in reduced space. New, high volume millimetric
applications such as vehicle collision avoidance radar, wireless
LAN and electronic tagging are driving costs down and putting
further constraints on size and weight. This Letter aims to address
these demands by taking further steps in the integration of active
antennas, using polarisation duplexing to combine transmit and
receive functions in a single antenna.
Sequentially rotated active antennas: This work uses a square
microstrip Patch antenna, resonant at 4 . 0 G E j with a MESFET
mounted centrally on the edge Of the patch to form an OSCillatOr
[21 and another MESFET, configured as an amPmer on the
orthogonal edge, to act as the first stage in a receiver. The inherent isolation of the centre points of orthogonal edges Of a square
patch is used as the basis for the transmit-receive isolation. This
transceiver is linearly polarised with transmit and receive channels
on orthogonal Polafisations. The Channels can be Same frequency
or offset depending on the application.
pi
0
-1 0
-2 0
m
U
z-3 0
rT)
-40
-50
3-9
4.1
4.3
A.5
frequency,GHz
593111
Fig. I Transmission between orthogonal sides of a 24mm square patch
3-5
37
E, = 2.32, H = 0.508mm
1.6 mm microstrip line
_ _ _ - wire bonds
One method for improving the isolation of the single patch is
that of sequential rotation [3, 41. Here the receiver outputs are
286
I
I
1693ipJ
variable phase
shifter
Fig. 2 Sequentially rotated two element active array
Having established good isolation for a passive patch, the active
components are added. A schematic diagram of the array is shown
in Fig, 2.
FETs are type ATF-26884. The drain of the oscillator FET is connected to the centre of the patch and a short circuit
transmission b e is connected to the source, Fhe gate is also connected to a short circuit transmission line. A DC blocking cap&tor allows the gate bias to be applied, giving greater flexibility of
operating point, The drain bias is applied via a high impedance
bias circuit connected to the isolated edge of the patch. The source
and gate terminations provide the negative resistance at the drain
port required for oscillation conditions [5]. The amplifier FET is
mounted in a 50R transmission line with DC blocks and choke
coils for biasing. At this stage no matching circuits have been
implemented.
To form the array two elements are spaced by -3&/4. Each
stubstrate was 90mm square. The outputs from the two amplifiers
were connected to a power combiner through lines with 180"
phase difference. A variable phase shifter was used to offset the
small phase dfferences in the amplifiers.
The oscillators lock together by mutual coupling, and power
combining occurs in the far field. Frequency tuning is performed
by adjusting the oscillator drain and gate bias voltages and the
tuning bandwidth was found to be 47MHz, centred on 3.77GHz.
Cancellation of the transmit signals breaking through into the
raeiver was achieved by control of both the phase shifter and the
amplifier gains. We found that small differences in the wire bond
positions and oscillator output powers produced differences in the
two signals of as much as 5dB and this was offset by reducing the
gain of one of the amplifiers. Because of this the receive performance was not optimised. Despite the problems, isolation better
than 50 dB was achieved from the array as Fig. 3 shows.
The output power of the oscillator was calculated from the
effective isotropic radiated power (EIRP) and measurements of the
gain of an identical passive array. Fig. 3 shows the oscillator output power together with the isolation signal after cancellation. The
ELECTRONICS LETTERS
15th February 1996
Vol. 32
No. 4
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