A 36-element hybrid grid oscillator has been fabricated. The active devices are InP-based High Electron Mobility Transistors (HEMT's). The grid oscillates at 43 GHz with an effective radiated power of 200 mW. Measurements show the E and H-plane radiation patterns have side lobes 10 dB below the main beam. These results are a significant improvement over a previous millimeter-wave grid oscillator, which had a divided beam because of substrate mode

Matloubian, Mehran

Preventza, Polly

Rutledge, David B.

English

Caltech Authors - Main

WE4C-2 
A 43-GHz AlInAs/GaInAs/InP HEMT Grid Oscillator 
Polly Preventza,' Mehran Matloubian,' and David B. Rutledge,' 
'Department of Electrical Engineering, California Institute of Technology , Pasadena CA 91 125 
'Hughes Research Laboratories, Malibu CA 90265 
Abstract-A 36-element hybrid grid oscillator 
has been fabricated. The active devices are 
InP-based High Electron Mobility Transistors 
(HEMT's). The grid oscillates at 43GHz with 
an effective radiated power of 200mW. Mea- 
surements show the E and H-plane radiation 
patterns have side lobes 10dB below the main 
beam. These results are a significant improve- 
ment over a previous millimeter-wave grid os- 
cillator, which had a divided beam because of 
substrate modes. 
I. INTRODUCTION 
In order to produce high power at microwave and 
millimeter-wave frequencies the output powers of many 
solid-state devices are combined. Quasi-optical free- 
space power combiners eliminate losses associated with 
waveguides and transmission lines. Quasi-optical grid 
oscillators are periodic, strongly coupled, oscillating 
structures based on integrating active devices directly 
into a planar array. Fig. 1 shows the approach. The 
first grid oscillator was a 5-GHz 100-MESFET grid 
demonstrated by Popovic e2 al. [l]. A 100-MESFET os- 
cillator grid produced 10 W at  10 GHz [2]. A monolithic 
grid was demonstrated that oscillated at  35GHz [3]. 
The Eplane radiation pattern of this grid is shown in 
mirror active grid tuning slab 
1" 
output 
Beam 
Eplane angle, degrees 
Fig. 2. E-plane radiation pattern of a 36-element mono- 
lithic grid oscillator operating at 35 GHz [3,4]. 
Fig. 2. The side-lobes have a peak value only 2dB 
less than the main-lobe peak. D.W. Griffin [5] pointed 
out that the unsatisfactory Eplane pattern is due to 
substrate-mode excitation that contributes to the radi- 
ation pattern through the edges of the grid. 
In this paper the design and performance of a 36- 
element InP HEMT grid oscillator is described. A pho- 
tograph of the grid is shown in Fig. 3. The period of the 
grid and the electrical thickness of the substrate, con- 
trol the substrate-mode excitation. To minimize the 
power in the substrate modes we use a thin (254pm) 
Duroid substrate with a dielectric constant of 2.2. This 
gives an electrical thickness a t  the oscillation frequency 
of only 19'. We also chose the vertical and horizontal 
period of the grid to minimize substrate-mode excita- 
tion. 
Fig. 1. A grid oscillator. The mirror and the dielectric slab 
provide tuning and help the devices to lock together. 
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0-7803-3814-6/97/$5.00 0 IEEE 1997 IEEE M'IT-S Digest 
Fig. 3. Photograph of the 36-element hybrid HEMT grid 
oscillator. The horizontal lines are bias lines. Ferrite slabs 
are placed on each side of the grid underneath the bond 
wires to suppress oscillations at low frequencies. Ferrite 
beads are also added along the leads to suppress bias line 
oscillations. 
2.25 m m  1 
Fig. 4. The equivalent waveguide unit cell. Electric walls 
(solid lines) and magnetic walls (dashed lines) are imposed 
by symmetry on the boundaries of the unit cell. The drain 
and source of the devices are wire-bonded to the vertical 
leads. The gate is wire-bonded to the horizontal leads. 
11. DESIGN 
The devices are AlInAs/GaInAs on InP HEMT's 
fabricated at Hughes Research Laboratories. The 
HEMT's have a total gate width of 75pm [6,7]. The 
devices have a peak transconductance of 848 mS/mm 
and a full channel current of 750 mA/mm measured at  
a gate bias of 0.2V and a drain bias of 1.5V. 
In order to analyze the grid we assume that all de- 
vices are identical. Each device lies in an equivalent 
waveguide unit cell which is defined by the symmetry 
of the grid. This equivalent unit cell has magnetic walls 
on the sides and electric walls on the top and the bot- 
tom as shown in Fig. 4. The vertical spacing deter- 
mines the excitation of TM modes and the horizontal 
spacing determines the T E  mode power. We calcu- 
lated the substrate-mode power for a 6x6  array of uni- 
formly excited dipoles and another array with alternat- 
ing 180" phase shifts. We selected spacings that gave 
low substrate-mode power levels. The transmission-line 
equivalent circuit is shown in Fig. 5. The inductances 
and capacitances shown are calculated using the EMF 
method [8]. Free space is represented by 3 7 7 4  scaled 
by the aspect ratio b /a  of the unit cell. The circula- 
tor is inserted a t  the drain terminal to calculate the 
saturated circular function. This approach is described 
in [9]. The locus of the function crosses the zero-phase, 
unity-magnitude point at 44.3 GHz, indicating an oscil- 
lation at this frequency. 
111. PERFORMANCE 
An HP8563A spectrum analyzer with an HP11974- 
series preselected mixer was used to measure the oscil- 
lation spectrum of the grid (Fig.7). An output tuner 
was placed in front of the grid that stabilized the signal 
and maximized the output power. The tuner used is a 
X,/4-thick dielectric slab with a dielectric constant of 
10.5 placed 6.5 mm in front of the grid. All devices in a 
single row are biased in parallel. Four separabe dc sup- 
plies are used (one for each of the top and bottom rows, 
one for rows 2 and 3, and another for rows 4 and 5). The 
separate supplies allowed us to control the angle of the 
Fig. 5. Transmission-line equivalent circuit. The reflection 
coefficient at the circulator terminal calculates the circular 
function. The reactance of the mirror is determined by the 
thickness of the substrate and the spacing from the grid. 
1058 
1 
-j Circular Function -
Unit Circle - - - - - -  
-90 -60 -30 0 30 60 90 
Angle, degrees 
Fig. 6. Saturated circular function, C, of the grid. the 
oscilation criterion is satisfied at 44.3 GHz, where C=l. 
beam. The oscillation frequency is 43 GHz, about 3% 
lower than the design frequency, 44.3 GHz. The highest 
effective radiated power (ERP) is 200mW. The effec- 
tive transmitter power (ETP) defined by Gouker [lo] 
is low, only 5mW. The total dc power supplied was 
272 mW. 
The far-field radiation patterns of the grid were mea- 
sured and are shown in Fig. 8. The theoretical patterns 
are for a uniformly excited array of 36 short dipoles 
spaced 2.75 mm apart in the H-plane and 2.25 mm apart 
in the Eplane and placed 5.8" in front of a mir- 
ror. Both E and H-plane patterns have side lobes 
about lOdB lower than the main beam. No evidence 
of substarte-modes is seen. By changing the position 
of the mirror and the tuning slab the oscillator can 
20 
d 
g 10 
ra 
0 
-20 -10 0 10 20 
Frequency offset, h5Hz 
Fig. 7. Oscillation spectrum. The center frequency is 
42.94 GHz. 
- 3 0 1 " " " " 1 " " ' " ' ~ ~ ' 1 ~ ' ' ~ ~  
I I 
-90 -60 -30 0 30 60 90 
Angle, degrees 
(b) 
Fig. 8. Measured E-plane (a) and H-plane (b) patterns 
(solid lines) with 6mm mirror spacing and theoretical pat- 
terns (dashed lines) with 5.8 mm mirror spacing. 
be tuned to operate at other frequencies and different 
power levels. These tuning curves are shown in Fig. 9. 
The ERP and frequency repeat at  half-wavelength in- 
tervals. 
IV. CONCLUSIONS 
A 43-GHz 36-element grid oscillator has been demon- 
strated with an ERP of 200mW. The grid was de- 
signed to reduce substrate-mode excitation. This grid 
also demonstrated that hybrid circuit techniques can be 
used for quasi-optical grids at  millimeter-wave frequen- 
cies. The electrical thickness and the geometry of the 
array (spacing of the devices) can control the excitation - . -  
1059 
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$ 42.8 
t 4 
I ( , ,  , , , 
I ’ I ’ I ‘  
I ’ I  I I I I I I I I I I I 
3 4 5 6 7 8 9 10 
Mirror distance from the grid, mm 
Fig. 9. Frequency and power tuning of the grid as a func- 
tion of mirror position. For these measurements a dielectric 
slab was placed 6.5” in front of the grid. 
of substrate modes. 
V. ACKNOWLEDGMENTS 
We appreciate the support of the Army Research 
Office and the Physical Optics Corporation. We would 
like to thank Freddie Williams for his help on mounting 
and wire-bonding the devices to the grid. 
VI. REFERENCES 
[l] Z.B. Popovic, R.M. Weikle, M.Kim, D.B. Rutledge, 
“A 100-MESFET Planar Grid Oscillator,” IEEE 
Trans. Microwave Theory Tech., MTT-39., pp. 193- 
200, Feb. 1991. 
[2] J.B. Hacker, M.P. DeLisio, M. Kim, C.-M. Liu, S.- 
J. Li, S.W. Wedge, D.B. Rutledge, “A 10-Watt X- 
Band Grid Oscillator,’’ 1994 IEEE MTT-S Int. Mi- 
crowave Symp. Dig., pp. 823-826, 1994. 
M.P.De Lisio, D.B. Rutledge, “A 35 GHz HBT Mono- 
lithic Grid Oscillator”, Proc. SPIE, 17th Int. Conf. 
on Infrared and Millimeter Waves, R.J. Temkin, 
[4] M.Kim, “Grid Amplifiers,” Ph.D. Thesis, California 
Institute of Technology, Pasadena, CA, 1993 
[5] D.W. Griffin, “Monolithic Active Array Limitation 
Due to Substrate Modes,” 1995 IEEE AP-S Int. 
Symp. Dig., pp. 1300-1303, 1995. 
L.E. Larson, M.J. Delaney, M.A. Thompson, R.A. 
[3] M. Kim, E.A. Sovero, R.M. Weikle, J.B. Hacker, 
Ed., pp. 402-403, 1992. 
[6] M. Matloubian, L. Jelloian, A S .  Brown, L.D. Nguyen, 
Rhodes, J .E. Pence, “V-Band High-Efficiency High- 
Power AlInAs/GaInAs/InP HEMT’s,” IEEE Trans. 
Microwave Theory Tech., MTT-dl . ,  pp. 2206-2210, 
Dec. 1993. 
[7] M. Matloubian, L.D. Nguyen, A.S. Brown, L.E. 
Larson, M.A. Melendes, M.A. Thompson, “High 
Power and High Efficiency AlInAs/GaInAs on InP 
HEMTs,” 1991 IEEE MTT-S Int. Microwave Symp. 
Dig. Vol. 2, pp. 721-724, 1991. 
[8] R.M. Weikle, “Quasi-optical planar grids for Mi- 
crowave and Millimeter-wave Power Combining,” 
Ph.D. Thesis, California Institute of Technology, 
Pasadena, CA, 1992 
[9] R.D. Martinez, R.C. Compton, “A General Ap- 
proach for the S-Parameter Design of Oscillators 
with 1 and 2-Port Active Devices,” IEEE Trans. 
Microwave Theory Tech., MTT-do., pp. 569-574, 
March 1992. 
[lo] M.Gouker, ‘(Toward Standard Figures-of-Merit for 
Spatial and Quasi-Optical Power-Combined Arrays,” 
IEEE Trans, Microwave Theory Tech., MTT-43., 
pp. 1614-1617, July 1995. 
1060 


A 43-GHz AlInAs/GaInAs/InP HEMT grid oscillator

A 10-Watt XBand Grid Oscillator,’’

A 100-MESFET Planar Grid Oscillator,”

A General Approach for the S-Parameter Design of Oscillators with 1 and 2-Port Active Devices,”

Amplifiers,” Ph.D. Thesis,

High Power and High Efficiency AlInAs/GaInAs on InP HEMTs,”

Monolithic Active Array Limitation Due to Substrate Modes,”

Quasi-optical planar grids for Microwave and Millimeter-wave Power Combining,”

Standard Figures-of-Merit for Spatial and Quasi-Optical Power-Combined Arrays,”

https://authors.library.caltech.edu/3184/1/PREims97.pdf

A 43-GHz AlInAs/GaInAs/InP HEMT grid oscillator

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