A V-shaped slot antenna built on a dielectric substrate is presented. The antenna is a nonresonant, traveling-wave design, with a predicted impedance in the range from 50 Ω to 80 Ω. Calculations indicate that this antenna should have a gain of 15 dB with 3 dB beamwidths of 10° in the H plane and 64° in the E plane. Pattern measurements at 90 GHz support the theory. It should be possible to equalize the two beamwidths with a cylindrical lens. The broad bandwidth and high gain characteristics make the slot- V a good candidate for picosecond optoelectronic measurements. Fabrication is simple, and it should be possible to make this antenna at wavelengths as short as 10 μm with conventional photolithography

Moussessian, Alina

Rutledge, David B.

English

Caltech Authors - Main

A MILLIMETER-WAVE SLOT-V ANTENNA 
Alina Moussessian*, David B. Rutledge 
Division of Engineering and Applied Science 
California Institute of Technology 
Pasadena, CA 91125 
Abstract-A new V-shaped slot antenna built on a dielectric substrate is pre- 
sented. The antenna is a non-resonant, travelling-wave design, with a predicted 
impedance in the range from 50R t o  €400. Calculations indicate that this antenna 
should have a gain of 15 dB with 3-dB beamwidths of loo in the H plane and 134' 
in the E plane. Pattern measurements at QOGHz support the theory. It should 
be possible t o  equalize the  two beamwidths with a cylindrical lens. The broad 
bandwidth and high gain characteristics make the slot-V a good candidate for 
picosecond optoelectronic measurements. Fabrication is simple, and it should be 
possible to  make this antenna a t  wavelengths as short as 10pm with conventional 
photolithography. 
INTRODUCTION 
Antennas on dielectric substrates suffer from losses t o  substrate modes, and tend to  have 
low gain and poor patterns. An example of this is the bow-tie antenna[l]. An elegant way 
to solve the substrate problem is t o  fabricate the antennas on silicon-oxynitride membranes 
inside horns (21, but this requires sophisticated fabrication techniques. An alternative is to  
add a superstrate so that the antenna is entirely inside the dielectric, to  make a sandwich. 
This has been demonstrated with a V antenna [3]. Here we propose a simpler approach, a 
slot antenna in the shape of a V (Figure 1). One can get a feeling for how the slot-V works 
Figure 1. Diagram of the slot-V antenna on fused quartz. The arm length L is 5Xd. The  
slot angles are 41 = 57.5' and 4 2  = 10'. The substrate is 25 mm square and 14 mm thick. 
1~7803Q730~5FJ2 53 W O  1992 IEEE. 1894 
by considering how waves propagate along conductors a t  a dielectric interface. A wave in a 
slot tends to  propagate a t  a velocity that  is intermediate between the velocity of waves in air 
and the velocity of waves in the dielectric. The wave is slow compared to the air velocity, and 
excites primarily evanescent waves in the air. This means that  little power radiates directly 
into the air. On the other hand, the wave velocity is fast compared to  the dielectric velocity, 
and the antenna radiates strongly into the dielectric a t  an angle 11, = arccos(wd/ws), where 
wQ is the slot phase velocity and wd is the dielectric velocity[4]. When the angle between 
the slot arms is twice this radiation angle, the radiation from the two arms adds in phase, 
producing a strong beam on the V axis. 
THEORY 
This is a non-resonant travelling-wave antenna, and we can estimate the impedance its a 
special case of a conformal-mapping formula developed for V-couplers [5J. 
where 70 is the free-space wave impedance, and n e ,  the effective refractive index, is given 
by 6. -c tL  The assumption is that propagation is similar to  that in a material that hits 
a dielectric constant that is the mean of the dielectric constant of the substrate and the 
dielectric constant of air. The dielectric constant of fused quartz is 3.78 [GI. The functions 
I< and I<' are elliptic integrals, and the parameter m is given by 
Incident angle, degrees 
(b)  
Figure 2 .  (a) Impedance of the slot-V, calculated from Equation 1. (b) Calculated slot-\' 
patterns in the dielectric. 
1895 
Figure 2a shows a plot of the impedance as a function of 41, with $2 as a parameter. For 
convenient angles the impedance ranges between 50R and 8 0 0 .  To estimate the radiation 
pattern of the slot-V, we assume a radial magnetic current in the left slot of the form I ,  = 
exp(-jn,kor), where IC0 is the propagation constant of free space. The magnetic current for 
the right slot changes sign. We can then integrate these currents to  calculate the magnetic 
radiation vectors and the pattern in the dielectric [7]. The patterns are shown in Figure 2b. 
The gain on axis is 15dB and the 3-dB beamwidths are 10" in the H-plane and 64' in the 
Eplane. There is a 5 d B  sidelobe a t  75" in the Eplane. 
FABRICATION A D MEASUREMENTS 
The antenna is fabricated by evaporation and lift-off. The metal film is a 1600-A layer of gold 
on top of l20.k of chrome. A M/A-Corn GaAs Schottky diode (MA 40417), mounted across 
the slot a t  the apex of the V, acts as a detector. The diode is biased a t  100pA. The substrate 
is covered with absorber on the bottom face and three side faces, so that the antenna receives 
power only from the front and top faces. The source is an HP 83558A mm-wave multiplier, 
driven by an HP83620 synthesized sweeper with an HP8349B amplifier. 
The measured patterns are shown in Figure 3. In the Ep lane  (Figure 3a), the antenna is 
much more sensitive to  radiation from the dielectric side. The peak in the pattern is not 
along the antenna axis but is 20" off. We suspect that this effect comes from the fact that 
the edge of the groundplane is only 12mm from the apex of the V. The measured pattern 
decays faster than theory predicts, and this may be due t o  the fact that the substrate is only 
14 mm thick. In the H-plane (Figure 3b), theory and experiment agree. The patterns are 
broader than in Figure 2b, primarily because of refraction a t  the front face of the substrate. 
-30-00 -EO -30 0 30 BO 90 
Incident angle, degrees 
( 4  
-90 -BO -30 0 30 BO 80 
Incident angle, degrees 
(b) 
Figure 3. (a) Measured 90-GHz Ep lane  pattern. For positive angles, radiation is incident 
from the dielectric, and for negative angles, radiation is incident in the air. The theoretical 
pattern is for dielectric incidence only, and takes reflection and refraction through the front 
face into account. (b) Measured 90-GHz H-plane pattern. This pattern is actually measured 
at 20" in the E-plane, where the gain is maximum. The theory is for an E-plane angle of Oo,  
and takes reflection and refraction through the front face into account. 
1896 
CONCLUSIONS 
We have developed a new slot-V antenna on a dielectric substrate and tested it a t  90 GHz. 
The predicted impedance is in the range from 50Q to 60Q. The calculated gain is 15dB 
with 3-dB beamwidths of 10” in the H plane and 64” in the E plane. Pattern measurements 
a t  90 GHz support the theory. In many applications it is desirable that E-plane and 11-plane 
beamwidths be the same so that the antenna can couple efficiently to an optical system. It 
should be possible to  equalize the two beamwidths with a cylindrical lens that would reduce 
the E-plane beamwidth without changing the H-plane beamwidth. The broad bandwidth 
and high gain characteristics make the slot-V a good candidate for picosecond optoelectonic 
measurements [6,9]. Fabrication is simple, and it should be possible to  make this antenna a t  
wavelengths as short as 10 pm with conventional photolithography. 
ACKNOWLEDGMENTS 
We appreciate the support of Aerojet Electrosystems and the Army Research Office through 
the Jet Propulsion Laboratory. The design was conceived with funding by SDI/IST and 
managed by ONR (contract number N00014-87-C-0806, contractor: TRW). 
REFERENCES 
(11 R. C. Conipton, R. C. McPhedran, 2. Popovit, G .  M. Rebeiz, P. P. Tong, and D. B. 
Rutledge, “Bow-Tie Antenna on a Dielectric Half-space: Theory and Experiment,” IEEE 
Trans. on Antennas and Propagation, AP-35, pp. 622-631, June 1987. 
[2] G. V. Eleftheriades, W. Y. Ali-Ahmad, L. P. Ketehi, G. M. Rebeiz, “Millimeter-W-ave 
Integrated-Circuit Horn Antennas, Par t  I-Theory, Part 11-Experiment,” IEEE Trans. 011 
Antennas and Propagation, AP-39, pp. 1575-1566, November 1991. 
[3] D. B. Rutledge, S. E. Schwartz, and A. T. Adams, “Infrared and Submillimeter Antennas,“ 
Infrared Physics, 18, pp. 713-729, 1976. 
[4] D. B. Rutledge, D. P. Neikirk, D. P. I<asilingam, “Integrated Circuit Antennas,” in Infrared 
and Millimeter Waves, 10, I<. J .  Button, ed., Academic Press, Inc., 1983, pp. 1-90, 
[5] D. B. Rutledge, S. E. Schwarz, T.  L. Hwang, D. J. Angelakos, I<. I<. Mei, and S. Yokota, 
IEEE J.  Quantum Electronics, QE-16, pp. 508-516, May 1980. 
[GI Reference Data for Radio Engineering, sixth ed., Howard W. Sams & Co., Inc., pp. 4-26. 
The dielectric constant for fused quartz is quoted a t  25 GHz. 
[7] S. Ramo, J. R. Whinnery, and T. Van Duzer, Fields and Waves in Communication Elec- 
tronics. John Wiley & Sons, Inc., 1965, sec. 12.10 and 12.16. 
[SI G. Arjavalingam, Y. Pastol, J .  M. Halbout, and G. V. Kopcsay, “Broad-Band Microwave 
Measurements with Transient Radiation from Optoelectronic Pulsed Antennas,” IEEE Trans. 
on Microwave Theory and Techniques, 38, pp. 615-621, May 1990. 
[9] W. M. Robertson, G. 1’. Kopcsay, and G. Arjavalingam, “Picosecond Time- Domain 
Electromagnetic Scattering from Conducting Cylinders,” IEEE Microwave and Guided Wave 
Letters, MGWLI, pp. 371-373, December, 1991. 
1897 


A millimeter-wave slot-V antenna

Crossref

Bow-Tie Antenna on a Dielectric Half-space: Theory and Experiment,”

Fields and Waves in Communication Electronics.

Integrated Circuit Antennas,”

Millimeter-W-ave Integrated-Circuit Horn Antennas, Par t I-Theory,

Millimeter-W-ave Integrated-Circuit Horn Antennas, Part I-Theory,

Picosecond Time- Domain Electromagnetic Scattering from Conducting Cylinders,”

The dielectric constant for fused quartz is quoted a t 25 GHz.

The dielectric constant for fused quartz is quoted at 25 GHz.

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A millimeter-wave slot-V antenna

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