MAGNETICALLY SCANNABLE MICROSTRIP ANTENNA EMPLOYING A LEAKY GYROMAGNETIC MICROSTRIP LINE

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Conclusions: We have demonstrated the feasibility of using a silicon micromachined waveguide with a simple diagonal horn structure. The radiation patterns were very similar to those obtained with a conventional diagonal horn. However, to obtain good patterns, the micromachined waveguide was modified by eliminating the outer wafers near the horn. The copolarised radiation patterns were not sensitive to the amount of undercut modelled for the iso- tropically etched surfaces. We also saw a significant reduction in the on-axis cross-polarisation response when the flared section had flat walls. This result could be used to design an improved waveguide-to-horn transition for conventionally manufactured diagonal horns. Furthermore, at IlOGHz a large die area will be required for silicon inserts. Hence this technique will he better suited for higher frequencies where less area is needed.

Acknowledgments: We wish to thank the Alberta Microelectronic Centre, the Natural Sciences and Engineering Research Council of Canada, and the Central Research Fund of the University of Alberta for support.

0 IEE 1995

Electronics Letters Online No: 19950903

B. Veidt, J.F. Vaneldik, D. Routledge and M.J. Brett (Department of Electrical Engineering, University of Alberta, Edmonton. Alberta T6G ZG7, Canada)

K. Kornelsen (Alberta Microelectronics Centre, 1135-87 Avenue, Edmonton, Alberta T6G 2T9, Canada)

13 June 1995

0 0 3 I ? I I , I : / I

References

I PETERSEN, K.E.: ‘Silicon as a mechanical material’. Proc. IEEE, 1982, 70, pp. 420457

2 YAP, M., TAI,Y.-c., MCGRATH, w.R., and WALKER, c.: ‘Silicon micromachined waveguides for millimeter and submillimeter wavelengths’. Proc. 3rd Int. Symp. Space Terahertz Technology, Ann Arbor, MI, USA, 1992, pp. 316-323

3 KATEHI, L.P.B.: ‘Novel transmission lines for the submillimeter-wave region’, Proc. IEEE, 1992, 80, pp. 1771-1787

4 LOVE, A.w.: ‘The diagonal horn antenna’, Microw. J., 1962, 5, pp. 117-122

5 JOHANSSON, J.F., and WHYBORN, N.D.: ’The diagonal horn as a submillimeter wave antenna’, IEEE Trans., 1992, MTT40, pp. 795- 800

6 WITHINGTON, s., and MURPHY. J.A.: ‘Analysis of diagonal horns through Gaussian-Hermite modes’, IEEE Trans., 1992, AP-40, pp. 198-206

0 0

Magnetically scannable microstrip antenna

employing a leaky gyromagnetic microstrip

line

Kuen-Fwu Fuh and Ching-Kuang

C. Tzuang

Indexing terms: Microstrip antennas, C h i d materials, Strip lines

l o 0 8

1

dominantsurface wave Bs I 1 5 , , I 0 0 -1 m -0-5 - 0 . 0 I-

-

I I I 0.0 2.7 2 .B 2 - 9 3 .O 3-1

Fig. 2 Bias-dependent leaky characteristics offirst higher-order mode at 14.9GHz

H O ’ M S 159112

Rigorous full-wave spectral-domain analyses of a magnetically scannable gyromagnetic microstrip leaky-wave antenna are presented. Varying the DC magnetic bias field by -6.5%. the maximum radiation angle of the leaky-wave antenna, measured from the horizon, shifts from zero to almost 90”.

Introduction: Ferrite-loaded microstrip patch antennas have beenm widely investigated [I - 41, owing to their abilities for DC magnetic bias control of beam scanning, antenna pattern, radar cross- section, etc. In contrast to these patch antennas which radiate at the resonance modes, a new travelling-wave antenna is presented. The new antenna, as shown in the inset of Fig. I , employs the concept of leaky-wave propagation of the first higher-order mode on gyromagnetic microstrip line. Recently, many such leaky-wave antennas integrated on isotropic dielectric substrates have been reported 5 - 71. The aim of this Letter is to study the feasibility of the new scannable gyromagnetic leaky-wave antenna by employing the rigorous full-wave spectral domain approach (SDA) based on the dyadic Green impedance formulation.

ELECTRONICS LETTERS 3rdAugust 1995

Vol. 31

Fig. 2 shows the hias-dependent leaky-mode properties of the first higher-order mode at 14.9GHz. Notice that the normalised propagation constant

p

decreases from 1 to almost 0 by only varying the normalised DC magnetic bias field H J M , from 2.9 to 3.1.

This indicates that the maximum beam angle, measured from the z-axis and approximated by

On,

= cos-’(p/k,), can be tuned from 0 to almost 90” by adding a smaller tunable magnetic field to a fixed magnetic bias field H, = 3M,. For millimetre-wave application, the fixed bias field may be replaced by the internal field of anisotropy of hexagonal ferrite. By extending the results given in Fig. 2, Fig. 3 shows that the beam angle 0, on the z-x plane scans almost lin- early up to 80” when H, is changed by 6.5%. Under different D C

magnetic bias conditions, the normalised radiation patterns are plotted in Fig. 4 by employing the Huygen magnetic current source. Since the magnetic currents on the two apertures under- neath the edges of microstrip differ by a small amount, the direc- tion of the main beam will slightly depart from the z-x plane. The gyromagnetic leaky-wave antenna is assumed to he five free-space wavelengths long and properly terminated. The maximum beam

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References 90 80 7 0

-

Q x 6 0 N

k

50 E a

-

a 4 0

8

m E 30 n 2 0 IO 0 I , l , l , , , 2 - 9 0 2 - 9 4 2 . 9 8 3 02 3 06 3.10 Ho / M s Fig. 3 Bias-dependent beam angle 8, on z-x plane

angles on the z-x plane for various DC magnetic bias conditions are mapped to Fig. 3. The results show that the angle of maximum radiation agrees well with the approximate 0, = COS^^(!^/^,) and the discrepancy at lower bias field is caused by the insufficient length of microstrip. Referring to Fig. 2, the attenuation constant

(x increases as the D C magnetic bias field increases, resulting in

the observed widened beam width in Fig. 4.

\

/

Fig. 4 Theoretic bias-dependent radiation patterns on i-x plane The length of the microstrip line is assumed to be five free-space wavelengths at 14.9GHz and the terminal is matched.

~ H J M , = 2.92

-. .- H J M , = 2.96 . . . H J M , = 3.00 _. ._ H J M , = 3.05 H J M , = 3.10

Conclusion: A new gyromagnetic microstrip leaky-wave antenna capable of D C magnetic bias control of beam scanning is presented and validated by a rigorous spectral domain approach. The results show that the proposed antenna is a viable approach for beam scanning applications.

Acknowledgment; This work was supported by National Science Council under Grants: NSC 84-2221-E009-010 and NSC 84-2623- D-009-008

0 IEE 1995

Electronics Letters Online No: 19950951

Kuen-Fwu Fuh and Ching-Kuang Tzuang (Institute of Electrical Communication Engineering, National Chiao-Tung University, No.

1001, Ta Hsueh Road, Hsinchu. Taiwan, Republic of China) 5 June 1995

1310

YANG, H.Y., CASTANEDA, J.A., and ALEXOPOULOS, N.G.: 'The RCS of a microstrip patch on an arbitrarily biased ferrite substrate', IEEE Trans., 1993, AP41, pp. 1610-1614

POZAR, D.M.: 'Radiation and scattering characteristics of microstrip antennas on normally biased ferrite substrates', IEEE Trans., 1992, AP-40, pp. 108&1092

ROY, J.S., VAUDON, P., REINEIX, A., JECKO, F., and JECKO, B.:

'Circularly polarized far fields of an axially magnetized circular ferrite microstrip antenna', Microw. Opt. Technol. L e f t . , 1992, 5, pp. 228-230

HENDERSON, A., JAMES, J.R., and FRAY, A.: 'Magnetised microstrip antenna with pattern control', Electron. Lett., 1988, 24, pp. 4547

TZUANG. c.K.c., CHOU, G.J., and LO, w.T.: 'A new quasi-planar leaky- wave antenna structure'. 19th Int. Infrared and Millimeter Waves Conf. Dig., Sendai, Japan, 1994, pp. 518-519

LIN, Y.D., SHEEN, J.w., and TZUANG, c.K.c.: 'Analysis and design of feeding structures for microstrip leaky wave antenna'. IEEE MTT- S Intl. Microwave Symp. Dig., Orlando, USA, 1995, pp. 149-152, Section TU3B

TZUANG, c.K.c., and CHOU, G.J : 'An active microstrip leaky-wave antenna employing uniplanar oscillators'. 1995 European Microwave Conf., Bologna, Italy, 1995, Section B3.1

BORBURGH, I.: 'The behaviour of guided modes on the ferrite-filled microstrip line with the magnetization perpendicular to the ground plane', Arch. Elek. Ubert., 1977, 31, (2), pp. 73-77

OLINER, A.A., and LEE, K.s.: 'The nature of the leakage from higher modes on microstrip line'. IEEE MTT-S Int. Microwave Symp. Dig., 1986, pp. 57-60

Single-layer single-patch wideband

microstrip antenna

T. Huynh

and K.-F. Lee

Indexing terms: Microstrip antennas, Antennas

A coaxially-fed single-layer single-patch wideband microstrip antenna in the form of a rectangular patch with a U-shaped slot is discussed. Measurements showed that this antenna can attain 10-40"h impedance bandwidth without the need of adding parasitic patches in another layer or in the same layer. Introduction: Microstrip antennas offer the advantages of thin profile, light weight, low cost, and conformability to a shaped surface and compatibility with integrated circuitry. In addition to military applications, they have become attractive candidates in a variety of commercial applications such as mobile satellite communica- tions, the direct broadcast (DBS) system, global positioning sys- tem (GPS), remote sensing and hyperthermia. This is due in large measure to the extensive research aimed at improving the impedance bandwidth of microstrip antennas in the last several years.

The basic form of the microstrip antenna, consisting of a con- ducting patch printed on a grounded substrate, has an impedance bandwidth of 1-2%. One way of improving the bandwidth to IO-20% is to use parasitic patches, either in another layer [I] (stacked geometry) or in the same layer [2, 31 (coplanar geometry). However, the stacked geometry has the disadvantage of increasing the thickness of the antenna while the coplanar geometry has the disadvantage of increasing the lateral size of the antenna. It would therefore be of considerable interest if a single-layer single-patch wideband microstrip antenna could be developed. Such an antenna would better preserve the thin profile characteristics and would not introduce grating lobe problems when used in an array environment. In this article, we report the experimental results of a rectangular patch with a U-shaped slot which appears to have wide bandwidth characteristics.

Experimental results: The rectangular patch antenna with a U- shaped slot used in our experiment is shown in Fig. 1. The patch has dimensions 8.65" x 4.90". The dielectric medium between the patch and the ground plane is air. The patch is fed at the centre by a 50Q coaxial probe, the outer and inner diameters of which are