NATIONAL RADIO ASTRONOMY OBSERVATORY
CHARLOTTESVILLE, VIRGINIA
ELECTRONICS DIVISION INTERNAL REPORT No. 278
DESIGN AND PERFORMANCE OF CRYOGENICALLY-COOLED,
14.4-15.4 GHz HEMT AMPLIFIER
M. W. POSPIESZALSKI AND W. LAKATOSH
AUGUST 1988
NUMBER OF COPIES: 250
DESIGN AND PERFORMANCE OF CRYOGENICALLY-COOLED,14.4-15.4 GHZ HEMT AMPLIFIER
M. W. Pospieszalski and W. Lakatosh
I. Introduction
This report covers the design and performance of cryogenically-cooled,14.4-15.4 GHz amplifiers built with commercially-available FHRO1FH (Fujitsu)HEMT's. The design was computer optimized for gain and noise performancein a manner similar to previously described X-band designs [1], [2],although a different topology of an input matching network was assumed. Acommercially-available Fujitsu HEMT, FHRO1FH, was used. The signal andnoise model of this transistor was extensively discussed in [3]. Thetypical parameters measured at the cold input of the amplifier were:minimum noise temperature at midband Tmin — 17 K, average noise temperatureover 1 GHz bandwidth
Tnav 19 K and gain GT — 30 dB ± 2 dB over the same
bandwidth. The noise temperature is by a factor of two better in the bandcenter and by a factor of three better at the band edges than for theprevious NRAO design [4]. This can be mostly attributed to the use of amuch better device (HEMT instead of a FET), but also to a different designapproach.
II. Amplifier Design and Realization
Photographs of a finished amplifier are shown in Figure 1. Manydesign features are similar to the previously described designs [1], [2].A most notable difference is a topology of an input matching network whichconsists of (starting at the generator side): a parallel high impedanceopen-circuited stub, a length of 50 0 air slab line and length of lowimpedance slab line (partially filled with teflon). The input and firstinterstage matching networks were computer optimized to yield minimumaverage noise in 14.4-15.4 GHz band at 12.5 K ambient temperature, whilethe interstage coupling network and output network were optimized for gainflatness.
The details of the d.c. separation circuit and bias circuit and theirmicrowave and low frequency equivalent circuits are shown in Figure 2.The comparison between computer predicted and measured performance of thethree-stage amplifier (U-5) at room and cryogenic temperature is shown inFigure 3. The experimental data of Figure 3 are taken for all transistorsbiased at Vds — 2 V, Ids — 10 mA and Vds — 2 V, Ids — 5 mA for room andcryogenic temperatures, respectively. The cryogenic measurement was donewith all HEMT's illuminated. The computed data are for the circuitdescription as given in Figures 1 and 2, using the signal and noise modelof the FHRO1FH HEMT developed in [3]. The input and output return lossmeasured at room temperature is compared with the model prediction inFigure 4.
The amplifier characteristics were found to be very sensitive to theelectrical length of the open-circuited stub. This is because the lengthof this stub becomes quarter-wave at the frequency of 17.5 GHz. The stubis realized by placing a tinned copper wire of 10 mills in diameter in achannel milled in the amplifier housing (compare Figure 1). The end ofthe stub rests in a movable rexolite support, which provides at the sametime the mechanical stability and required fine tuning.
III. Summary of Performance of Ku-Band Amplifiers
The summary of cryogenic performance of eight K u-band amplifiers isgiven in Table I. Full noise and gain characteristics of six of thoseamplifiers are shown in Figure 5. For most of the amplifiers, the onlyrequired tuning procedure was an adjustment of electrical length of theparallel stub by movement of its rexolite support. Indeed, the repeatabilityof amplifier characteristics was quite good. All the amplifiers werebuilt with FHRO1FH HEMT's from lot #C923. The spread in minimum noisetemperature at midband was less than 3.5 K for seven amplifiers. This isconsistent with the repeatability of noise performance of Fujitsu HEMT's withgood pinch-off characteristics, as observed in X-band amplifiers (± 1.5 K)[31, [5], and also with estimated accuracy of measurement (± 2 K in Ku-band).
IV. Conclusions
The design, construction and performance of cryogenically-cooled,14.4-15.4 GHz HEMT amplifiers were described. The cryogenic noiseperformance of these amplifiers is believed to be the best yet reported atthis frequency.
V. References
[1] M. W. Pospieszalski, "Low-Noise, 8.0-8.8 GHz, Cooled GASFET Amplifier,"NRAO Electronics Division Internal Report No. 254, December 1984.
[2] M. W. Pospieszalski, "Design and Performance of Cryogenically-Cooled,10.7 GHz Amplifier," NRAO Electronics Division Internal ReportNo. 262, June 1986.
[3] M. W. Pospieszalski, "A New Approach to Modeling of Noise Parametersof FET's and MODFET's and Their Frequency and TemperatureDependence," NRAO Electronics Division Internal Report No. 279,July 1988.
[4] S. Weinreb and R. Harris, "Low-Noise, 15 GHz, Cooled, GaAsFETAmplifier," NRAO Electronics Division Internal Report No. 235,September 1983.
[5] M. W. Pospieszalski, S. Weinreb, R. Norrod and R. Harris, "FET's andHEMT's at Cryogenic Temperatures - Their Properties and Use inLow-Noise Amplifiers," IEEE Trans. Microwave Theory Tech., vol.MTT-36, pp. 552-559, March 1988.
2
TABLE I. The Summary of Cryogenic Performanceof the 14.4-15.4 GHz Amplifiers
Noise Temp.' [K] Gain2 [K]
Amplifier Minimum Average Minimum Maximum
U-13
20.5 22.8 25.3 29.1
U-2 3 18.3 22.5 27.2 29.3
U-3 18.2 21.1 28.2 32.1
U-4 18.3 20.0 28.3 31.0
U-5 16.2 18.1 28.7 32.1
U-6 17.4 20.2 27.8 30.6
U-7 15.0 16.0 28.6 30.4
U-8 15.6 19.1 28.1 31.6
'Referred to the cold input of an amplifier.
2Includes a cold isolator and dewar transition at theoutput side.
3Prototypes.
40404.;4441.0411111.1.10,
,
evo,;I:K4W,,St%/
Fig. 1. Three-stage 14.4-15.4 GHz amplifier with cover plate removed.
4
L. F. SIAS Set E50 l k
GATE StASSvPpi.y
I6 t4v55/ —,--- 680
leLSO4--
I At16 4099 — 10
DRAIN MIASSUPPLV
# 01.111..."
Fig. 2. (A) Schematic view of the realization of the d.c. separationcircuit. (B) Cross-section of the reentrant line after assembly.(C) High frequency equivalent circuit of the bias and d.c.separation circuits. (D) Schematic of the bias circuit.Element values are given in ohms, picofarads, nanohenries, andinches.
1 6.1i
LGRa]
Fig. 3. Comparison between model prediction and measured performanceof three-stage, Ku-band, FHRO1FH amplifier (U-5) at 297 K and12.5 K. At room temperature all transistors are biased atVds = 2 V, Ids — 10 mA. At cryogenic temperature all transistorsare biased at Vds — 2 V, I ds = 5 mA.
30
13.1i /4,9 FEGi4.1 16.4
Fig. Comparison between model prediction and measured return loss ofthe three-stage, Ku-band, FHRO1FH amplifier (U-5) at 297 K. Alltransistors are biased at Vds — 2 V, Ids — 10 mA.
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Fig. 5. Cryogenic performance of six Ku-band amplifiers under optimalbias conditions. The noise temperature is referred to coldinput of an amplifier. The measured gain characteristics includethe contribution of the cold isolator at the output and thedewar transition (about 1 dB of loss).
8
APPENDICES
Appendix I. Parts List for Ku-Band HEMT Amp (14.4-15.4 GHz)
Appendix II. Drawings
A. Amplifier Alignment Procedure
B. Stub Dielectric Support
C. Chassis
D. Amplifier Cover
E. Transistor Strap
F. Output End Plate
. Input End Plate
. Coaxial Transformer
. Support Inner Conductor
J. Interstage Inner Conductor
K. Output SMA Modified
L. Input SMA Modified
PARTS LIST Ku-Band HEMT AmD
(14
.4-1
5.4
GHz)
DATE August 1988
REVISION
ITEM
QUANTITY
REF.
DESI
G.DESCRIPTION
MFG.
PART NUMBER
11
Amplifier alignment procedure
NRAO
C53208M017
21
Stub dielectric support
NRAO
A53208MO20
1Chassis
NRAO
C53208M009, Rev. C
41
Amplifier cover
NRAO
B53208M010
56
Transistor strap
NRAO
A53208M011, Rev. A
61
Output end plate
NRAO
A53206M072, Rev. D
71
Input end plate
NRAO
A53206M071, Rev. D
81
ea.
Coaxial transformer
NRAO
A53208M016
92
Support inner conductor
NRAO
A53208M012, Rev.
A
102
Innerstage inner
con
du
cto
rNR
AOA53208M013, Rev. B
111
Out
put
SM
A modified
NRAO
A53208M015, R
ev.
A
121
Input
SM
A m
odif
ied
NRAO
A53
208M
014,
Rev
. A
131
Power co
nnec
tor
Omni-Spectra
ER-7
S-6
143
HEMT
Fuji
tsu
FHR
O1F
H
156
HE
MT
bia
s le
ads,
#3
6 A
WG
Bel
dso
lB
elden
8058
166
Bias w
ires
, #30 A
WG
Bel
dso
lB
elden
8055
171
LE
D, bia
s w
ire,
#30 A
WG
Alp
ha18
51
Appendix I
PARTS LIST Ku-Band HEMT Amt (1
4.4-
15.4
GHz
)
DATE
August 1988
REVISION
ITEMQUANTITY
REF.
DESI
G.DESCRIPTION
MFG.
PART NUMBER
186
0.08x3/16 filister hd
screws, gold-plated
192
2-56 x 1/2" socket head SS screws
All-Metal
202
2-56 x 3/8" socket head SS screws
All-Metal
214
2-56 x 3/16" socket head SS screws
All-Metal
224
2-56 x 1/4" socket head SS screws
2312
4-40 x 1/4" socket head SS screws
All-Metal
241
4-40 x 3/8" socket head SS screw
All Metal
251
4-40 x 1/2" socket head SS screws
All-Metal
266
.3 pF chip
cap
acit
ors
ATC
100-A-0R3-B-P-150
276
16
pF
chip
capacit
ors
ATC
100-A-160-K-P-50
286
680 pF chip capacitors
ATC
100-B-681-M-P-50
299
50 ohm chip resistors
Mini-Systems
WA13PG-500-J-S
303
10 ohm 1/8 W metal film resistor
Corning
RLRO5C-10RO-FS
313
1000 ohm 1/8 W metal film resistor
Corning
RLRO5C-1001-FS
323
Diode Zener
Moto
rola
IN40
99
336
LED
Lit
ron
ixR
L-5
0
34Solder, 2% silver
Ersin
SN-62-.028
PARTS LIST Ku-Band HEMT Amp (14.4-15.4 GHz)
DATE August 1988
REVISION
ITEMQUANTITY
REF.
DESI
G.DESCRIPTION
MFG.
.PART NUMBER
35,
Flux, rosin liquid
Lester
#1544
36Mylar tape
Scotch
RT-56
37Input stub, #30 AWG
Belden
8025
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