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 [1], SEQUOIA for Five-College Radio Astronomy Observatory [2], and DASI [3]. 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 [4], 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) [5], 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 [6] and A. Madjar [7], 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.

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: yjhwang@asiaa.sinica.edu.tw

(2) Academia Sinica, Institute of Astronomy & Astrophysics, P.O. Box 23-141, Taipei, 106, Taiwan. Email: mchen@asiaa.sinica.edu.tw

(3) Department of Electrical Engineering and Institute of Communication Engineering, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei, 106, Taiwan. Email: hueiwang@ew.ee.ntu.edu.tw

(4) As (3) above, but e-mail: thc@ew.ee.ntu.edu.tw (5) Department of Physics, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei, 106, Taiwan. Email:

westho@asiaa.sinica.edu.tw (6) Australia Telescopes National Facility, P.O. Box 76, Epping, NSW, Australia. Email:

russell.gough@atnf.csiro.au (7) As (6) above, but e-mail: msinclai@atnf.csiro.au

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 [8] 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 WSHM3 WSHM2 Simulation On-wafer Test Module Test Simulation RF Frequency Range 75-115GHz 78-114GHz 85-104GHz 85-110GHz LO Frequency 48GHz 48 GHz 42GHz 42 GHz Conversion Loss 10-17dB 10-14dB 8-13dB 8.5-11.5dB RF Matching < -3dB < -7dB <-6dB < -5dB LO Matching < -12dB -5dB (*1) (N/A) < -12dB IF Matching < -12 dB -8-10dB <-5 dB < -12 dB LO-RF Isolation 30dB 20.5dB (N/A) 30dB RF-LO Isolation 20dB 5dB (*2) (N/A) 20dB

Notes: (*1) measured under small-signal conditions. (*2) measured without RF/LO frequency diplexer.

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.

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