W-BAND GaAs HEMT MMIC SUBHARMONICALLY PUMPED DIODE MIXERS FOR ARRAY OF MICROWAVE BACKGROUND ANISOTROPY (AMiBA) RECEIVERS Yuh-Jing Hwang (1), Ming-Tang Chen (2), Ta-Hsiung Chu (3), Huei Wang (4), Ming-Shung Ho (5), Russell G. Gough (6) and Malcolm W. Sinclair (7) (1) Institute of Communication Engineering, National Taiwan University and Academia Sinica Institute of Astronomy & Astrophysics, P.O. Box 23-141, Taipei, 106, Taiwan. Email: [email protected] (2) Academia Sinica, Institute of Astronomy & Astrophysics, P.O. Box 23-141, Taipei, 106, Taiwan. Email: [email protected] (3) Department of Electrical Engineering and Institute of Communication Engineering, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei, 106, Taiwan. Email: [email protected] (4) As (3) above, but e-mail: [email protected] (5) Department of Physics, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei, 106, Taiwan. Email: [email protected] (6) Australia Telescopes National Facility, P.O. Box 76, Epping, NSW, Australia. Email: [email protected] (7) As (6) above, but e-mail: [email protected] ABSTRACT Two different W-band subharmonically pumped (SHP) diode mixers are designed for fixed LO frequency operation. For the first circuit, on-wafer measurement shows that the conversion loss is about 10 to 14 dB across the 78-114 GHz, as a 10 dBm 48 GHz LO signal is pumped. Both the simulation and measurement results are shown in good agreement. The second circuit shows that the conversion loss is about 10 to 13 dB across 85-105 GHz, as an 8-dBm 42-GHz LO signal is pumped. The SHP mixers are integrated into a wideband HEMT-based heterodyne receiver, which is designed for millimeter-wave telescope array for cosmic microwave background anisotropy observation. INTRODUCTION Low-Noise HEMT LNA based heterodyne receiver for millimeter-wave astronomy is more common in the past few years, for example, the Microwave Anisotropy Probe Satellite , SEQUOIA for Five-College Radio Astronomy Observatory , and DASI . In those HEMT-LNA based heterodyne receivers, low-loss mixer are essential to down-convert the amplified RF signal into IF frequency for correlation and detection. Compared to the fundamental mixers, SHP mixers have the advantage of LO noise cancellation , better RF-LO isolation, separate RF/LO input path, and lower LO frequency to make LO signal distribution more easy. In this paper, we present the design and measured performance of the two different wideband, low-conversion-loss subharmonically-pumped (SHP) mixers. The SHP mixer is used as the receiver down-conversion devices of Array of Microwave Background Anisotropy (AMiBA) , a 3-millimeter-wavelength cosmic background anisotropy compact array. CIRCUIT DESIGN The mixers utilize anti-parallel connected HEMT diode pairs to mix the second harmonic of fixed-frequency LO with the broadband signal. The first and second iteration mixer designs are fabricated by the TRW GaAs PHEMT MMIC process on 4-mil substrate, using 0.15um gate length, 20um total periphery diodes and 0.1um, 16um total periphery diodes, respectively. The mixer circuit structures is adapted from the previous research done by S. Raman  and A. Madjar , but our designs emphasize the RF and LO circuit symmetry near the diode pair to suppress the higher-order mode excited by the asymmetric microstrip tee junctions. In order to ensure the design accuracy, we do not use spiral inductors in the circuit. The MIM capacitor is used only for IF low-pass network because of its higher-frequency fringing capacitance and distributed model limitation. The critical circuit structures, such as the RF parallel coupled line bandpass filter and microstrip tees were analyzed numerically. The MMIC chip layouts are with the size of 1.5 mm x 2.0 mm and 1.5mm x 1.0mm, as shown in the Figure 1, respectively. Fig. 1. W-band SHP diode mixer chips. Left: P/N WSHM3, chip size = 1500 µm x 2000 µm, 78-114 GHz RF passband. Right: P/N WSHM2, chip size = 1500 µm x 1000 µm, 85-110 GHz RF passband. CIRCUIT PERFORMANCE The on-wafer measurement results for the first iteration design, P/N WSHM3, show that the conversion loss is 10 to 14 dB across 78 to 114 GHz, as a 10.0 dBm 48.0 GHz LO signal is pumped, as shown on Figure 2. Measurement on the RF, LO and IF return loss shows a good agreement with the simulation results. We also design a split mixer blocks with WR-10 waveguide RF input  and coaxial LO and IF ports to packaged the MMIC SHP mixer chips. The packaged module measurement shows 8.5-13dB conversion loss under the same test condition. Table 1 shows that the simulation and measurement results of first iteration mixer design are shown in good agreement. The simulation results for the second iteration mixer design, P/N WSHM2, show that the conversion loss is about 9 to 11.5 dB across 85-105 GHz, as a 5.0 dBm 42.0 GHz LO signal is pumped. TABLE 1 SUMMARY OF SHP MIXERS PERFORMANCE MMIC Chip P/N RF Frequency Range LO Frequency Conversion Loss RF Matching LO Matching IF Matching LO-RF Isolation RF-LO Isolation Simulation 75-115GHz 48GHz 10-17dB < -3dB < -12dB < -12 dB 30dB 20dB WSHM3 On-wafer Test 78-114GHz 48 GHz 10-14dB < -7dB -5dB (*1) -8-10dB 20.5dB 5dB (*2) Module Test 85-104GHz 42GHz 8-13dB <-6dB (N/A) <-5 dB (N/A) (N/A) Notes: (*1) measured under small-signal conditions. (*2) measured without RF/LO frequency diplexer. WSHM2 Simulation 85-110GHz 42 GHz 8.5-11.5dB < -5dB < -12dB < -12 dB 30dB 20dB Fig. 2. (a) Simulated and measured results of conversion loss for WSHM3 over 78-114 GHz with 48 GHz, 10 dBm LO power. (b) measured conversion loss for 5 pieces of WSHM3 packaged modules over 85-105 GHz with 42 GHz, 12 dBm LO power RECEIVER PERFORMANCE In order to verify the SHP mixer performance as a receiver component, the packaged devices are integrated with corrugated horn antennas, wideband orthomode transducers, W-band low-noise amplifiers, wideband isolators and IF broadband amplifiers to form the prototype receivers for the Array of Microwave Background Anisotropy. Local oscillator sources are provided from a 21GHz DRO whose frequency is doubled by active frequency doublers and amplified by mmw power amplifiers. Fig. 4 shows the block diagram of the receiver. Table 2 shows the estimated noise-gain budget of the receiver. Hot/cold measurement was chosen to determine the system noise and gain of the receiver under room temperature and cryogenic temperature, using a HP-8970V noise figure meter system and a power meter with high-sensitivity power sensor. The room temperature test results show its system noise temperature is around 700-900k. The cryogenic test results show that the optimized noise temperature of the receivers is around 125-350K, with 65-80dB conversion gain. Fig. 4. Left: System block diagram of the prototype receivers for the Array of Microwave Background Anisotropy. Right: the receiver vacuum chamber under assembling. Fig. 5 The noise temperature and conversion gain measured results of the W-band receivers. The receivers consist all the components describe in Fig. 4 except the IF broadband amplifier. CONCLUSION The design, test and application to heterodyne receivers of W-band wideband SHP MMIC diode mixers using GaAs PHEMT process are presented. The measured mixer conversion loss, receiver noise and gain show a good performance over the W-band. ACKNOWLEDGMENT This work is sponsored by Ministry of Education, ROC, under Grants 90-N-FA01-4-1. The authors would like to thank Dr. Y.Z. Juang in CIC for the coordination effort on providing excellent TRW GaAs MMIC foundry service and Dr. John Archer of CSIRO for providing the measurement facilities. REFERENCES  M. W. Pospiezalski, E. J. Wollack, N. Bailey, D. Thacker, J. Webber, L. D. Nguyen, Minh Li and Mark Lui, “Design and performance of wideband, low-noise, millimeter-wave amplifiers for microwave anisotropy probe radiometers,” IEEE MTT-S Symp. Digest, Boston, MA, June 11-16, 2000.  N. R. Erickson, R. M. Grosslein, R. B. Erickson and S. Weinreb, “ A cryogenic focal plane array for 85-115 GHz using MMIC preamplifiers,” IEEE Trans. Microwave Theory Tech., Vol. MTT-47, No. 12, pp. 2212-2219, Dec. 1999.  N. W. Halverson, J. E. Carlstrom, M. Dragovan, W. L. Holzapfel and J. Kovac, “DASI: a degree angular scale interferometer for imaging anisotropy in the cosmic microwave background,” Proceeding of the SPIE conference on advanced technology MMW, Radio and Terahertz Telescope, pp 416-423, Kona, Hawaii, March 1998.  P. S. Henry, B. S. Glance, and M. V. Schneider, “Local-oscillator noise cancellation in the subharmonically pumped down-converter,” IEEE Trans. Microwave Theory Tech., Vol. MTT-24, No. 5, pp 254-257, May 1976.  M.T. Chen, Y.-J. Hwang, T.-H. Chu, S. C. Lu, K. Y. Lo, R. N. Martin, Huei Wang, M. Kesteven, M. Sinclair, W. Wilson, J. Payne, and J. Peterson, "Receiver for AMiBA: prototype concepts," the 2001 Asia-Pacific Radio Science Conference, Tokyo, Aug 1-4, 2001.  S. Raman, F. Rucky and G. M. Rebeiz, “A high-performance W-band uniplanar subharmonic mixer,” IEEE Trans. Microwave Theory Tech., Vol. MTT-45, No. 6, pp. 955-962, June 1997.  A. Madjar, “A novel general approach for the optimum design of microwave and millimeter wave subharmonic mixers,” IEEE Trans. Microwave Theory Tech., Vol. MTT-44, No. 11, pp. 1997-1999, Nov. 1996.  Y.-C. Leong and S. Weinreb, “Full Band Waveguide-to-Microstrip Probe Transitions,” 1999 IEEE MTT-S Int. Microwave Symp. Dig., June 1999.