Current Research Projects:
Millimeter-Wave Front-End Electronics

I. 154 GHz Subharmonic Receivers for Next Generation Automotive Radars
II. 94 GHz Monopulse Receivers: Single and Dual Polarized Designs
III. Planar High Efficiency Millimeter-Wave Doublers
IV. Planar Millimeter-Wave Mixers and Transceivers

I. 154 GHz Subharmonic Receivers for Next Generation Automotive Radars

A 150 GHz Schottky-diode subharmonic receiver based on a coplanar-waveguide (CPW) fed double folded-slot antenna is presented. The double folded-slot antenna is placed on an extended hemispherical high-resistivity silicon substrate lens to achieve a high directivity and a high coupling to a Gaussian beam efficiency. The uniplanar receiver results in a 12 dB measured DSB conversion loss at 144-152 GHz for a 8-10 mW LO power at 77 GHz, and has a wideband <13 dB conversion loss over 30 GHz of bandwidth (140-170 GHz). The measured conversion loss includes silicon lens absorption and reflection losses, as well as IF mismatch losses. The applications are in new small aperture (7.5 cm lenses) collision avoidance radars at 150 GHz.

- G.P. Gauthier, J.-P. Raskin and G.M. Rebeiz, "A 140-170 GHz low-noise uniplanar suhbharmonic Schottky-receiver," Accepted for publication in the IEEE Trans. Microwave Theory Tech. To appear July 2000. (File: pdf 240 K)

Figure: Picture of the subharmonic mixer-receiver with a double-folded slot antenna for 154 GHz reception. The receiver is placed on a dielectric lens.

II. 94 GHz Monopulse Receivers: Single and Dual Polarized Designs

PRESS HERE FOR SOME COOL PICTURES ON MONOPULSE RECEIVERS. (120 K)

The two papers below summarize the work of Raman and Barker on the development of planar monopulse receivers. The idea is based on IF processing of the 4 signals from the monopulse antenna, that is, downconvert the signal from 94 GHz to 2-4 GHz, and then do the accurate sum and difference processing at the IF. The receiver is based on four slot-ring antennas on a dielectric lens which feed four planar subharmonic mixers. The slot-ring antenna is capable of supporting two orthogonal modes offering the possibility of dual/multiple receive polarizations. The measured two-port isolation of the dual-polarized slot-ring antenna is better than -25 dB from 86-92 GHz. The design center frequency is 94 GHz and the IF bandwidth is 2-4 GHz. The measured conversion losses of the individual receiver channels is 14.5 dB at an LO frequency of 45.0 GHz and an IF of 1.4 GHz. This includes the lens reflection and absorption losses, backside radiation, RF feedline loss, mixer conversion loss, and IF distribution loss. The four IF signals are taken to an IF processing network for the sum and difference patterns. Excellent monopulse patterns are achieved with better than 45 dB difference pattern nulls using IF monopulse processing. This translates to sub-milliradian angular accuracy for a 24 mm aperture. Better than 25 dB nulls are possible over a 600 MHz bandwidth. The receiver is robust with respect to RF frequency. Potential applications are compact, low-cost millimeter-wave tracking receivers with fixed or variable polarization capabilities.

Also, Barker developed a very wideband planar monopulse processing network on a Si chip with excellent difference nulls in the azimuth and elevation planes. Check his paper for a neat idea!

- S. Raman, S. Barker and G.M. Rebeiz, "A W-band dielectric-lens-based integrated monopulse radar receiver," IEEE Trans. Microwave Theory Tech., Vol. 46, pp. 2283-2288, Dec. 1998. (File: pdf 480 K)

- N.S. Barker and G.M. Rebeiz, "An octave bandwidth monopulse process," IEEE MTT-S Int. Microwave Symp., Denver, CO, pp. 405-408, June 1997. (File: pdf 240 K)

Figures: 94 GHz Monopulse Receiver on a dielectric lens (front and back view).

III. Planar High Efficiency Millimeter-Wave Doublers

Two different planar doubler designs for mm-wave applications have been developed. The doublers are fabricated on quartz for low loss operation, and using two Schottky varactor diodes in series for high power operation. The high-Q design (Q = 6) results in a conversion loss of 6.4 dB at an output frequency of 72-73 GHz. The low-Q design (Q = 1.6) results in a conversion loss of 9.6 +/- 0.7 dB from 64-78 GHz at -2 V bias, and delivers 71 mW at 74 GHz for an input power of 490 mW (conversion loss of 8.4 dB at optimal bias of -7 V). The output power shows no sign of saturation, and is limited to 71 mW due to the input source power. The results are quoted "on-chip" and are state of the art for mm-wave planar multipliers. The application areas are in automotive collision avoidance radars and mm-wave communication systems.

- G.-L. Tan and G.M. Rebeiz, "High-power millimeter-wave planar doublers," IEEE-MTT Int. Microwave Symp., Boston, June 2000. (File: pdf 360 K)

Figure: The mm-wave planar doubler on a quartz substrate. The dimensions are 3 mm x 1 mm.

IV. Planar Mixers and Transceivers

This section represent some of the work which has been done on planar mixers at mm-wave frequencies. This is different from the quasi-optical (antenna coupled) mixers that are presented in the Completed Research section. In this case, the mixers are MMIC-based on a GaAs or Si substrate (with GaAs diodes) and the measurements are done on a probe station.

A. W-Band Subharmonic Mixers:

A uniplanar subharmonic mixer has been implemented in coplanar waveguide technology using back-to-back Schottky diodes*. The circuit is designed to operate at RF frequencies of 92-96 GHz, IF frequencies of 2-4 GHz, and LO frequencies of 45-46 GHz. Total circuit size excluding probe pads and transitions is less than 0.8 x 1.5 mm. The measured minimum SSB conversion loss is 7.0 dB at an RF of 94 GHz. The LO power is only only 4-6 mW of LO power without any LO matching networks, and 2-3 mW with an LO matching network. This represents state-of-the-art performance for a planar W-band subharmonic mixer. The mixer is broadband with a SSB conversion loss of less than 10 dB over the 83-98 GHz measurement band. The measured LO-RF isolation is better than -40 dB for LO frequencies of 45-46 GHz. The DSB noise temperature measured using the Y-factor method is 725 K at an LO frequency of 45.5 GHz and an IF of 1.4 GHz. Potential applications are millimeter-wave receivers for communication systems and automotive collision avoidance radars.
(*Diodes obtained from the University of Virginia)

- S. Raman and G.M. Rebeiz, "A high-performance uniplanar W-band subharmonic mixer," IEEE Trans. Microwave Theory Tech., vol. MTT-45, pp. 955-962, June 1997. (File: pdf 240 K)

Figure: The W-band subharmonic mixer using back-to-back GaAs Schottky diodes.

B. Balanced Silicon-Diode Mixers for Automotive Transceivers:

A new balanced mixer using a ratrace coupler and two flip-chip Schottky Silicon diodes was developed. Silicon diodes were used for low-noise mixer performance in FMCW radars. In contrast to a conventional ratrace mixer, in this special type of mixer, a part of the local oscilla-tor signal is fed through the mixer to the antenna. This is achieved by using a mismatch at the Schottky diodes. Since the developed transceiver section is going to be used within a MMIC-based radar system and since available W-band MMICs are not capable of providing high power levels, the mixer is optimized for a low LO power level. For the measurements of conversion loss, a typical LO power of only +6 dBm was applied. Diode biasing turned out to significantly enhance mixer performance. Under appropriate bias conditions (about 1.6 mA per diode), the 77 GHz mixer resulted in a SSB conversion loss of about 13 dB (including the targeted transmission/feed-through from LO port to RF port of about ­3 dB; thus, the effective conversation loss compared to a standard mixer would be 10 dB). This represents state-of-the art performance for mm-wave mixers using Si Schottky diodes.

More detail will be placed in this section in Summer '00.

- B. Schoenlinner, T.V. Kerssenbrock, P. Heide, G.M. Rebeiz, "77 GHz Transceiver Module for Millimeter-Wave Radar Sensors," To be presented at the European Microwave Conference, Paris, October 2000.