The measurement of cryogenic antennas poses unique logistical problems since the antenna under test must be embedded in a cooling chamber. A method of measuring the performance of cryogenic microstrip antennas using a closed cycle gas cooled refrigerator in a far field range is described. Antenna patterns showing the performance of gold and superconducting Ka-band microstrip antennas at various temperatures are presented

Bhasin, K. B.

Claspy, P. C.

Gilbert, C.

Metzler, S.

Richard, M. A.

English

NASA Technical Reports Server

NASA Technical Memorandum 105183 
Measurement Techniques for Cryogenic 
Ka-Band Microstrip Antennas 
M.A. Richard 
Case Western Reserve University 
Cleveland, Ohio 
K.B. Bhasin 
Lewis Research Center 
Cleveland, Ohio 
C. Gilbert and S. Metzler 
Ball Communications Systems Division 
Broomsfield, Colorado 
and 
P.C. Claspy 
Case Western Reserve University 
Cleveland, Ohio 
Prepared for the 
13th Annual Meeting and Symposium of the Antenna 
Measurement Techniques Association 
sponsored by the National Institute of Standards and Technology 
Boulder, Colorado, October 7 - 11, 1991 
NI\S/\ 
https://ntrs.nasa.gov/search.jsp?R=19910021112 2020-03-19T16:59:41+00:00Z
MEASUREMENT TECHNIQUES FOR CRYOGENIC KA-BAND MICROSTRIP ANTENNAS 
M.A. Richard 
Case Western Reserve University 
Department of Electrical Engineering 
Cleveland, Ohio 44106 
K.B. Bhasin 
National Aeronautics and Space Administration 
Lewis Research Center 
Cleveland, Ohio 44135 
C. Gilbert and S. Metzler 
Ball Communications Systems Division 
Broomsfield, Colorado 80020 
P.C. Claspy 
Case Western Reserve University 
Depatment of Electrical Engineering 
Cleveland, Ohio 44106 
ABSTRACT 
The measurement of cryogenic antennas poses unique logistical 
problems since the antenna under test must be embedding in the 
cooling chamber. In this paper, a method of measuring the per-
formance of cryogenic m;crostr;p antennas using a closed cycle 
gas-cooled refrigerator in a far field range is described . 
Antenna patterns showing the performance of gold and super-
conducting Ka-band microstrip antennas at various temperatures 
are presented. 
1. INTRODUCTION 
Printed circuit antennas have been the focus of much research 
in recent years as candidates for applications such as satellites 
where weight and volume are a premium [1]. In theory, many-
element microstrip arrays could rival the gain of traditional 
parabolic dishes. However, microstrip antennas have high ohmic 
losses which act to limit the maximum obta i nable gain. This 
problem i s compounded at millimeter wave frequencies since the 
surface resistance of metals increases with f1/2, causing micro-
strip transmission lines to be much more lossy. 
It is well known that ohmic losses may be reduced sig-
nificantly by cooling the circuit to cryogenic temperatures. 
Gold has a resistance temperature coefficient of approximate ly 
10 nQ cm/K. Computer simulations show that a reduction in 
temperature from 300 K to 77 K translates to 10 dB/m less loss at 
30 GHz for a microstrip line on 0.25 mm alumina. The use of 
cryogenics has the additional benefit of reducing the noise fig-
ure of the system, which is critical for radiometric antennas. 
Recently, much attention has been given to the use of high 
temperature superconductors (HTS) as a solution to the problem of 
gain limitation in many-element microstrip array antennas [2 ,3 J. 
According to [3] , an HTS 100 element linear array at 35 GHz could 
e xperience a gain increase of 8 to 10 dB over an identical copper 
array. Measurements of 35 GHz HTS ring resonators have shown an 
improvement in microstrip line attenuation of 10 dB over identi-
ca l gold circuits when both are at 77 K. [4] 
In a practical sense, measuring the performance of antennas 
at cryogenic temperatures is quite difficult. If the antenna is 
to be cooled in a cryogen such as liquid nitrogen or liquid 
helium, a radio-transparent dewar must be used. In general such 
an arrangement allows performance measurements only at two 
temperatures: room temperature and the boiling point of the 
cryogen. Th is type ,of cryostat has been used by [5] to measu re 
electrically small superconducting arrays at 650 MHz and by [6J 
to measure a 500 MHz HTS dipole. A gas refrigerator, on the 
other hand, has the advantage that the temperature can be set to 
any value within its range. However, a vacuum must be main-
tained, which necessitates the use of some type of radio-
transparent vacuum jacket. 
In this paper, we discuss the design of a temperature-
controlled cryostat which has been used to successfully test 
planar superconducting microstrip arrays at 30 GHz. To our 
knowledge this is the first reported use of a gas refrigerator 
f or cryogenic antenna measurements. 
2 
I 
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2. DESIGN 
The cryostat used is based upon a CTI-Cryogen ics compressor 
and cold head. The unit is a closed-cycle helium refrigerator. 
·A Lakeshore Cryogenics temperature controller controls the cur-
rent through a heater element to provide temperature control over 
the system. The two-stage cold finger is enclosed by a stainless 
steel tube, capped with a lid machined from high-density 
polyethylene (HO PE) as shown in Fig. 1. HOPE was chosen because 
of its low relative permittivity (2.34) [7] and loss tangent and 
because it is inexpensive in comparison to other polymers such as 
teflon. The lid is spherical with an inner radius of 12.7 cm and 
thickness of .508 cm. A hermetically sealed coaxial feedthru 
(two back-to-back uK" sparkplug launchers) passes the RF into the 
vacuum chamber. Semirigid coaxial cable connects the feed thru to 
the antenna test fixture. 
The antennas used are 4 element microstrip arrays with a 
resonance at 31.7 GHz. The antennas were patterned onto their 
respective substrates, magnesium oxide (MgO) and lanthanum 
aluminate (LaA1203), and assembled into a brass test fixture 
(Fig. 2). A 50 Q gold microstrip feed line patterned on an 
alumina substrate separates the coax-to-microstrip transition 
(Wiltron V-connector) from the antenna. The test fi xture was 
made as thin as practically possible to reduce the thermal load-
ing of the cryostat, thereby hastening the cool-down and warmup 
times involved. Wire bonds connect the feed line to the antenna. 
To test the antennas, each test fixture was in turn mounted at 
the second stage of a 2-stage closed-cycle helium refrigerator. 
A high-density polyethylene (HOPE) cap serves as both a vacuum 
jacket and a radome. S-parameter (S1 1 ) measurements us i ng an HP 
8510B were done by calibrating to the coax i al connector inside 
the cryostat while at room temperature. The entire cryostat was 
mounted on a plexiglass stand, which in turn was fastened to the 
rotating pedestal of a far-field antenna range for pattern 
measurements in th~ receive mode (Fig. 3), 
3 
---- --
3. ANTENNA MEASUREMENTS 
This setup was used to measure H-plane patterns of the 
aforementioned Ka-band microstrip arrays. The arrays were fab-
ricated with high-temperature superconductors (HTS) and, for com-
parison purposes, with evaporated gold. The antennas were 
measured at 30 K, 70 K and room temperature (295 K). In addi-
tion, the array patterns of the gold antennas were measured with 
and without the HOPE lid to judge the effect of the radome. The 
measured patterns are shown in Fig. 2. Comparison of the pat-
terns with and without the lid show the H-plane patterns to be 
essentially unchanged, except for a 3-dB amplitude decrease when 
the lid is removed. This is most likely a result of the l i d 
acting as a dielectric lens, thereby weakly focusing the radia-
tion. The thickness of the HOPE lid was chosen arbitrarily, and 
at the resonant frequency of the antennas is 1.22 dielectric 
wavelengths. The gold antenna patterns show a 3 dB increase in 
received power as the temperature is lowered from 295 K to 30 K. 
The HTS arrays show a distinct difference in pattern below and 
above the critical temperature (Tc), with the received power 
increasing by more than 10 dB below Tc. 
4. CONCLUSIONS 
A specially designed cryogenic unit has been developed for 
the measurement of microstrip antennas at temperature down to 
25 K. The use of the unit was demonstrated by measuring far-
field patterns and the reflection coefficients of superconducting 
and gold Ka-band microstrip arrays. H-plane measurements show no 
substantial effects resulting from the presence of the HDPE 
radome. 
ACKNOWLEDGMENT 
The authors would like to thank Mr. Ed Smith for his help in 
the measurement of these antennas, and Dr. R.Q. Lee for his con-
structive suggestions. One of the authors (M.A. Richard) 
4 
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acknowledges support through a NASA Space Grant / Ohio Aerospace 
Institute Doctoral Fellowship. 
5. REFERENCES 
1. Ely Levine, Gabi Malamud, Shmuel Shtrikman , and Dav i d T r eves , 
" A Study of Microstrip Array Antennas with the Feed Networ k," 
IEEE Trans . Antennas and Propagat., vol. AP-37, no. 4, pp. 4 26-
434 , Apr. 1989. 
2 . R.C. Hansen , "Superconducting Antennas, " IEEE Trans . o n 
Aero space and E7ectronic Systems, vol. 26, no. 2, pp. 345- 354 , 
March 1990. 
3 . Robert J. Dinger, "Some Potential Antenna Appl i cations of 
High Temperature Superconductors," Journa7 of Superconductiv i t y. 
vol. 3 , no. 3 , pp. 287-296, 1990. 
4. C.M. Chorey, K.B. Bhasin, J.D. Warner , J. Y . Joesfowicz, D.B. 
Rensch, and C.W. Nieh, "An Experimental Study of High Tc Su per-
conducting Microstrip Transmission Lines at 35 GHz and the Effect 
of Film Morphology, IEEE Trans. on Magnetics, pp. Ma r ch 1991. 
5 . G.B. Wal ker, Clovis R. Haden, and O.G. Ramer , " IEEE Trans. 
Antennas and Propagat., vol. AP-25, no. 6 , pp. 885- 8 87 , Nov. 
1977. 
6. S. I<. . Khamas, M.J. Mehler, T.S. Maclean, C.E. Gough, " Hi gh Tc 
Superconducting Short Dipole Antenna," E7ectronics Letters, 
vol.24, no. 8, pp. 460-461, April 1988. 
7. Karlheinz Seeger, "Microwave Measurement of the Dielec tric 
Constant of High-Density Polyethylene," IEEE Trans. Mic r owa ve 
Theory and Tech., vol. 39, no. 2, pp. 352-354, Feb. 1991. 
5 
HIGH-IINSITY 
PQ YETHYLEt£ RAOO~E ~ 
COAX I AL CABLE 
K -COI't£CTOR 
FEEOTI-RU~ 
Fig. 1 . 
ANTEt-lIlA 
TEST FIXTURE 
COLD FINGER 
~ STAINLESS STEEL 
/ VI\CUUII JACKET 
~ VACW~POOT 
Cryogeni c antenna test unit. 
V-CONNECTOR 
FEED SUBSTRATE 
~r-,.~--~----~~ ANTENNA 
BRASS 
FIXTURE 
Fig. 2 . Four element microstrip antenna in brass test fi x ture. 
6 
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...., 
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...... 
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Fi g . 4. 
Cryogen ic unit mounted on rotating pedestal of the far 
field antenna range . 
:. :", -20 
- 40 
-50 
-60 -30 0 30 
Angle (Degrees) 
I 
I' 
60 
30 K 
70K 
290 K 
90 
H-plane patterns o f 4--eiemen t HTS array 0 11 MgO substrate 
taken at 290, 70, and 30 Kel v in. 
7 
1 
I 
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4. TITLE AND SUBTITLE >. 5. FUNDING NUMBERS 
Measurement Techniques for Cryogenic Ka-Band Microstrip Antennas .', 
II. AUTHOR(S) WU 506-59-4C 
M.A. Richard, K.B. Bhasin, C. Gilbert, S. Metzler, and P.e. Claspy 
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION 
REPORT NUMBER 
National Aeronautics and Space Administration 
Lewis Research Center E-6479 
Cleveland, Ohio 44135 - 3191 
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AGENCY REPORT NUMBER 
National Aeronautics and Space Administration 
Washington, D.C. 20546-0001 NASA TM-I05183 
11. SUPPLEMENTARY NOTES 
Prepared for the 13th Annual Meeting and Symposium of the Antenna Measurement Techniques Association sponsored 
by the National Institute of Standards and Technology, Boulder, Colorado, October 7-11, 1991. M.A. Richard, Case 
Western Reserve University, Department of Electrical Engineering, Cleveland, Ohio 44106 (work partially funded by the 
12 •• DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE 
Unclassified -Unlimited 
Subject Category 33 
13. ABSTRACT (Maximum 200 words) 
The measurement of cryogenic ante1Ulas pOses unique logistical problems since the antenna under test must be embedding 
in the cooling chamber. In this paper, a method of measuring the performance of cryogenic microstrip antennas using a 
closed cycle gas-cooled refrigerator in a far field range is described. Antenna patterns showing the performance of gold 
and super-conducting Ka-band microstrip antennas at various temperatures are presented. 
14. SUBJECT TERMS 
Microwave antenna; High temperature superconductivity; Low temperature tests 
17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 
OF REPORT OF THIS PAGE OF ABSTRACT 
Unclassified Unclassified Unclassified 
NSN 7540-01-280-5500 
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Standard Form 298 (Rev. 2-89) 
Prescribed by ANSI Std. Z39-18 
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11. Supplementary Notes (continued) 
NASA Space Grant College Fellowship's Program, Grant Number NGT - 40016, and a NASA Space Grant Fellowship from the 
Ohio Aerospace Institute). K.B. Bhasin, NASA Lewis Research Center. C. Gilbert and S. Metzler, Ball Communications Systems 
Division, Broomsfield, Colorado 80020. P.C. Claspy, Case Westem Reserve University, Department of Electrical Engineering. 
Responsible person, K.B. Bhasin, (216) 433-3676. 
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Measurement techniques for cryogenic Ka-band microstrip antennas

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