A 36-element monolithic grid amplifier has been fabricated. The active elements are pairs of heterojunction-bipolar-transistors. Measurements show a peak gain of 5 dB at 40 GHz with a 3-dB bandwidth of 1.8 GHz (4.5%). Here we also report comparisons of patterns and tuning curves between the measurements and theory. The grid includes base stabilizing capacitors which result in a highly stable grid. The maximum saturated output power is 670 mW at 40 GHz with a peak power-added efficiency of 4%. This is the first report of power measurements on the monolithic quasi-optical amplifier

De Lisio, Michael P.

Higgins, J. A.

Ho, Wu Jing

Liu, Cheh-Ming

Rutledge, David B.

Sovero, Emilio A.

Caltech Authors - Main

Monolithic 40-GHz 670-m W HBT Grid Amplifier

WE4B-4 
Monolithic 40-GHz 67O-rn’w HB‘T Grid Amplifier 
Cheh-Ming Liu, Emilio A .  Sovero, Wu Jing Ho, J .  A. Higgins, Michael 1’. DeLisio, and David B. Rutledge 
Abstract-A 36-element monolithic grid ampli- 
fier has been fabricated. The active elements are 
pairs of heterojunction-bipolar-transistors. Mea- 
surements show a peak gain of 5dB at 40GHz 
with a 3-dB bandwidth of 1.8 GHz(4.5%). Here 
we also report comparisons of p a t t e r n s  and tun- 
ing curves between the measurements and the- 
ory. The grid includes base stabilizing capaci- 
tors which result in a highly stable grid. The 
maximum saturated output power is 670 xnW at 
40 GHz with a peak power-added efficiency of 4%. 
This is the first report of power measurements on 
the monolithic quasi-optical amplifier. 
I .  INTRODUCTION 
A grid amplifier is a spatial power-combining device 
that amplifies a microwave beam and combines the out- 
puts of many transistors, making it possible ‘to greatly 
increase power [l-31. Combining the power in free space, 
grid amplifiers eliminate losses associated with waveg- 
uides and transmission-line networks. Grid amplifiers 
have demonstrated gains of 10 and l l d B  att 10GHz 
with HBT’s [1,2], and 12 dB at  9 GHz with pNEMT’s [3]. 
Other spatial-power combining approaches are actively 
being pursued [4-91. Recently, Higgins, Sovero and Ho 
demonstrated a monolithic Q-band plane-wave amplifier 
using slot and patch antennas [lo]. Based on the gain 
and stability models of the hybrid grid amplifiers [2,3], 
we reported monolithic HBT and pHEMT grid ampli- 
fiers [11,12]. In this paper, we report additional measure- 
ments on the monolithic HBT grid amplifier, including 
gain, tuning curves, patterns, and power measurements. 
The grid has a 5-dB gain and 670-mW saturated output 
power at  40 GHz. 
The monolithic grid amplifier, shown in Fig. 1, is com- 
posed of 36 unit cells on a 565- pm thick GaAs substrate. 
There are 6 elements on each side. The length is 12 m m  
on one side. The grid was fabricated wil,h the BBT pro- 
cess established a t  Rockwell International [13]. The max- 
imum available gain of an individual transistor at  40 GHz 
is 9 dB. 
Manuscript submitted February 2 2 ,  1996. This research 
was supported by the Air Force Material Command/Rome 
Laboratory, ARPA Contract #F30602-93--C-0188, and the 
Army Research Office. 
C.-M. Liu, M.P. De Lisio and D.B. Rutledge are with the 
Division of Engineering and Applied Science, California Insti- 
tute of Technology, Pasadena, CA, 91125. 
E.A. Sovero, W.J. Ho, and J.A. Higgins are with the Science 
Center, Rockwell International Corporation, 1049 Camino 
Dos Rios, Thousand Oaks, CA 91385. 
.Fig. 1. Photograph of the 36-element monolithic grid ampli- 
iker compared with a dime. The chip is 12 mm on each side. 
11. DESIGN 
The unit cell1 is shown in Fig. 2. The period of the 
unit cell is 1.9 mm. In the unit cell, the input leads re- 
‘ceive the horizontally-polarized input beam. The input 
matching capacitor cancels the inductive reactance of the 
input lead. The stabilizing capacitor prevents common- 
mode oscillations. The  output leads radiate the output 
beam with vertical polarization. 
The grid-amqlifier system(Fig. 3a), can be represented 
by an equivalent-circuit model(Fig. 3b) [2]. The input 
beam is on the left-hand side with horizontal polariza- 
tion. The input beam is received by the amplifier grid, 
amplified, and then reradiated with vertical polarization, 
as the output beam to the right. The unit cell links the 
input and out.put. The polarizers confine the signal path 
from the left, input with horizontal polarization, to the 
right, output with vertical polarization. The matching 
conditions are determined by the polarizers and tuning 
slabs. 
At 40GHz, the HBT input impedance for the m a -  
imum availabk gain is 8 + j5.5 R. It is important to 
match the input because the resistive part of the cor- 
responding input impedance is much lower than the free- 
space impedance. To match the input, the GaAs sub- 
strate acts as a quarter-wavelength transformer. 
In previous grid amplifiers, common-mode oscillations 
were observed 1:2,3]. Hence stability is an important issue 
in the design. Based on the stability analysis in [2], if 
stabilizing capacitors are not included, we predict the grid 
, 
0-7803-324h-h/c)6/rgS.O~ 0 IEEE 
1123 
1996 IEEE MTT-S Digest 
Input Matchmg 
Gap Capaator I; 
- 1.9 Inm P 
Fig. 2 The unit cell. The input leads are 120 pm wide and 
the output leads are 300pm wide. The width of the input 
matching gap is 30pm. The stabilizing capacitor is 27 f f .  
The bias resistors are 4 kR and the emitter resistors are 150 R.  
The width of the meandering bim line is 20 pm, 
Unit Cel l  
Input Input Monolithic Ootput Output 
Tunlng Slab P d a r i x s r  Grid P d a r i z s r  fining Slab 
fa) 
Lb : Bias-Line Reactance 
Cn : Input  Matching Capacitor 
LZ : Input  Lead 
cs : Stabilizine CaDacitor 
I .  
Le : Output Lead 
output  
_I U n i t  Cell  
Polarizer 
(b) 
Fig. 3 (a) Cross-section of the grid amplifier. The input beam, 
with horizontal polarization, is fed from the left. The output 
beam, with vertical polarization, is measured on the right. (b) 
Equivalent-circuit model. 
will oscillate at 22 GHz. With the stabilizing capacitors, 
the grid is stable with a phase margin of 58 degrees and 
a gain margin of 6.6 dB [ll]. 
1 -  
37 38 39 40 41 42 43 
Frequency, GHz 
Fig. 4 Gain measurements. The peak gain is 5 dB at 40 GHz. 
The 3-dB bandwidth is 1.8 GHz(4.5%). The theory is calcu- 
lated from the transmission-line equivalent-circuit model [a].  
-M 
-25 L- 
10 15 20 
Bias Current, mA / transistor 
Fig. 5 Gain versus bias current at 40 GHz. The peak gain is 
5 dB at 16 mA per transistor. The on-off ratio is 27 dB. 
111. GAIN 
The gain is measured in the far-field[l]. Due t o  the 
high DC dissipation, the grid was biased for only 0.6 
seconds a t  a time to avoid thermal damage. The  gain 
response, from 37 to 43 GHz as shown in Fig. 4, has 
a peak gain of 5 dB a t  40 GHz and 3-dB bandwidth 
of 1.8 GHz(4.5 %). Fig. 5 shows the gain versus the 
bias current a t  40 GHz. The  gain inceases monotonically 
from -22  dB to 5 dB as the bias current increases from 
0 t o  16 m A  per transistor. The  difference between biased 
and zero-biased gains is 27 d B  at 40 GHz. No oscillation 
was observed-the grid is highly stable. 
1124 
L A  
0 90 180 270 360 450 540 
Offset Angle, deg 
Fig. 6 Relative gain at 40 GHz as a function of output polar- 
izer position. 
0 90 180 270 350 450 540 
Offset Angle, deg 
Fig. 7 Relative gain at 40 GHz as a function of input polarizer 
position. 
80 30 0 30 60 90 
Angle, deg 
Fig. 8 Output H-plaie radiation pattern at 40 GHz. 
Input Power, mW 
1w 
- = I----- 
E25 - 
v .  m 
z 
6 
g20 - 
6 
a 
L--.L-- i 
15 20 :25 30 
Input Power, dBrn 
Fig. 9 Output jpower versus input power at 40 GHz. The 
peak output power is 670 mW at 7 V. 
Iv. TUNING AND PATTERN 
Fig. 6 and F.ig. 7 show input and output tuning curves 
a t  40 GHz. The tuning curves are plots of the gains versus 
the polarizer positions. The measured input-tuning curve 
is different from the theoretical one. This may be due to 
the critical matching condition a t  the input. However, 
the measured output-timing curve matches to the theory 
well. 
The output H-plane radiation pattern is shown in 
Pig. 8. This pattern is measured by fixing the grid ampli- 
ffier and the input antenna, and rotating the output an- 
tenna. The theoretical pattern of six elementary dipoles 
.with a mirror 8.5-mm behind is also shown in Fig. 8. The 
:measurement shows reasonable match to the theory in the 
main lobe 
V. POWER 
In the ]power measurement, we used a 10-W Ka-band 
Traveling-Wave Tube(TWT) amplifier as the source. The 
power war; measured in the far field a t  40 GHz. Fig. 9 
shows the output power versus the input power of the grid 
amplifier at  three bias levels. The peak output power is 
670 mW a.t 7 V with the bias current of 16 mA per tran- 
sistor. Fig. 10 shows the gain and power-added efficiency 
versus the input power. The gain drops to 2.5 dB at the 
maximum output power. The peak efficiency is 4% with 
500-mW output power. At 7 V, 70% of the DC power is 
actually dissipated in the bias lines and emitter resistors. 
KV. CONCLUSION 
We have deinonstrsted a 36-element monolithic HBT 
grid amplifier. Based on the gain and stability models, 
the result is a highly stable grid amplifier. The grid has 
a 5-dB gain a t  40 GHa with 4.5% 3-dB bandwidth. The 
Input Power, mW 
rm 
5 , , , , , . . /  
i 5  
’ t  
i 
a - ’ ” ’  0 
Input Power, dBm 
15 20 25 
Fig. 1 0  Gain and power-added efficiencies versus input power 
at 40 GHz. The gain at maximum output power is 2 . 5  dB. 
The peak grid efficiency is 4%. 
maximum measured output power is 670 mW with 4% 
power-added efficiency at  40 GHz. 
V. REFERENCES 
[l] M. Kim, E. Sovero, J .  Hacker, M. De Lisio, J.-C. Chiao, 
S. Li, D. Gagnon, J .  Rosenberg, and B. Rutledge, 
“A 100-Element Grid Amplifier,” IEEE Trans. Mz- 
crowave Theory Tech., RITT-41, pp. 1762-1771, Oc- 
tober 1993. 
[2] C.-M. Liu, E. Sovero, M. DeLisio, A. hfoussessian, 
J .  Rosenberg, and D.  Rutledge, “Gain and Stability 
Models for HBT Grid Amplifiers,” 1995 IEEE AP-S  
Int. Symp. Dzg., pp.1292-1295, 1995. 
[3] M. DeLisio, S.W. Duncan, D.-\V. Tu. C.-hI. Liu: A 
Moussessian, J .  Rosenberg, and D. Rutledge, “hfod- 
elling and Performance of a 100-Element pHEXlT 
Grid Amplifier,” submitted to IEEE Trans. M Z C T O W U Z ~ ~  
Theory Tech, 1995. 
[4] H . S .  Tsai, M.J.W. Rodrvell, and R.A. York “Pla- 
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Let ters ,  MGWL-4, pp. 899-901, May 1994. 
[5] J .  Benet, A. Perkons, S. Wong. and A. Zaman, “Spa- 
tial Power Combining for Millimeter-wave Solid State 
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[6] T. Mader, J .  Schoenberg, L. Harmon, and 2.  PopoviC. 
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“Planar MESFET Transmission Wave Amplifier,” Blec- 
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[7] N .  Sheth, T. Ivanov, A. Balasubramaniyan, and A. 
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[8] “Quasi-Optical Power Combining Techniques,” Robert 
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[9] J .  Hubert, J .  Schoenberg, and Z. Popovit, “High- 
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[lo] J.A. Higgins, E.A. Sovero, and W.J. Ho, “44-GHz 
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Guzded Wave Let t . ,  MGWL-5, pp. 347-348, October 
1995. 
[ll] C.-M. Liu, E. Sovero, W.-J. Ho, J.A. Higgins, and D. 
Rutledge. “A Millimeter-Wave Monolithic Grid Am- 
plifier,” Int. JOUTnd of Infrared and Millzmeter Waves 
, pp. 1901-1910, Vol. 16, November 1995. 
[I21 hl. DeLisio, S.W. Duncan, D.-W. Tu, S. Weinreb, C.- 
RI. Liu, and D. Rutledge, “A 44-60 GHz Monolithic 
pHEMT Grid Amplifier,” to be presented in the 1996 
IEEE MTT-S Int. Mzcrowave Symposium. 
[13] P. Asbeck, F. Chang, K.-C. Wang, G.  Sullivan, D. 
Cheung, “GaAs-Based Heterojunction Bipolar Tran- 
sistors for Very High Performance Electronic Cir- 
cuits,” Proceedings of the IEEE, vol. 18, pp. 1709- 
1726. December 1993. 
1126 


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Monolithic 40-GHz 670-m W HBT Grid Amplifier

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