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)
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]
Academia Sinica, Institute of Astronomy & Astrophysics, P.O. Box 23-141, Taipei, 106, Taiwan. Email:
[email protected]
Department of Electrical Engineering and Institute of Communication Engineering, National Taiwan
University, 1 Roosevelt Rd., Sec. 4, Taipei, 106, Taiwan. Email: [email protected]
As (3) above, but e-mail: [email protected]
Department of Physics, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei, 106, Taiwan. Email:
[email protected]
Australia Telescopes National Facility, P.O. Box 76, Epping, NSW, Australia. Email:
[email protected]
As (6) above, but e-mail: [email protected]
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.
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.
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.
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.
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.
RF Frequency Range
LO Frequency
Conversion Loss
RF Matching
LO Matching
IF Matching
LO-RF Isolation
RF-LO Isolation
< -3dB
< -12dB
< -12 dB
On-wafer Test
48 GHz
< -7dB
-5dB (*1)
5dB (*2)
Module Test
<-5 dB
Notes: (*1) measured under small-signal conditions.
(*2) measured without RF/LO frequency diplexer.
42 GHz
< -5dB
< -12dB
< -12 dB
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
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.
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.
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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