This paper describes progress in the ongoing development of a radar for rotorcraft that utilizes new CMOS ICs that were development for automotive applications. The radar design is discussed, including a lens-based focal plane array that is fed by patch antenna subarray elements. Measured detection pattern data indicates sensitivity sufficient to detect a 1 m2 RCS object at 200 m with a 13dB SNR. Detection pattern data vs. azimuth angle are presented, which indicate a 2.1 deg 3dB beamwidth. Sidelobes are reduced to 30dB below the beam peaks using digital beamforming techniques.
This paper describes the design and demonstration of a 1024 element coded aperture subreflector array, implemented with single-bit phase shifters that utilize GaN HEMTs to modulate signals upon reflection. An active reflect-array enables digital beamforming using a single 235 GHz radar transceiver. Wafer level fabrication and assembly allows large arrays to be tiled up while maintaining reasonable costs.
HRL Laboratories has been developing a new approach for high resolution radar imaging on stationary platforms. High angular resolution is achieved by operating at 235 GHz and using a scalable tile phased array architecture that has the potential to realize thousands of elements at an affordable cost. HRL utilizes aperture coding techniques to minimize the size and complexity of the RF electronics needed for beamforming, and wafer level fabrication and integration allow tiles containing 1024 elements to be manufactured with reasonable costs. This paper describes the results of an initial feasibility study for HRL’s Coded Aperture Subreflector Array (CASA) approach for a 1024 element micromachined antenna array with integrated single-bit phase shifters. Two candidate electronic device technologies were evaluated over the 170 - 260 GHz range, GaN HEMT transistors and GaAs Schottky diodes. Array structures utilizing silicon micromachining and die bonding were evaluated for etch and alignment accuracy. Finally, the overall array efficiency was estimated to be about 37% (not including spillover losses) using full wave array simulations and measured device performance, which is a reasonable value at 235 GHz. Based on the measured data we selected GaN HEMT devices operated passively with 0V drain bias due to their extremely low DC power dissipation.
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