The authors implemented a directionally-constrained adaptive array system in an audio-frequency range. This system has a good prospect of applications since it does not require a rigorous a priori knowledge of the desired signal. Its algorithm contains matrix calculation, for which some technique has to be devised in implementation. For this, data are sampled and A-D converted so that the necessary processing for feedback control may be done by a microcomputer in digital form. The signal path remains in analog form, which will allow us to extend the system to higher frequency range. The performance of the system is demonstrated through the experiments. Effects of hardware errors are found: (1) Nulling behavior against the interference is not affected at all by virtue of the feedback control. (2) A little deviation from the constrained response to the desired signal is perceived. The behavior against a wideband interference is investigated analytically and experimentally. It was found that the final SIR becomes lower with wider frequency bandwidth.

Millimeter-wave monolithic low noise amplifier modules using 0.15 µm AlGaAs/InGaAs/GaAs pseudomorphic HEMTs have been developed at V- and W-bands for the Advanced Microwave Scanning Radiometer. To achieve low noise and high gain of V-band single-stage and W-band two-stage monolithic amplifiers, a reactive matching method is employed in the design of input noise matching and output gain matching circuits based on the results of on-carrier S-parameter measurements up to 50 GHz and noise parameter measurements at 60 and 90 GHz. A V-band four-stage monolithic amplifier module has been mounted on a hermetically-sealed package with microstrip interface and has achieved a noise figure of 3 dB with a gain of 42.2 dB at 51 GHz. A W-band six-stage amplifier module has been mounted on a hermetically-sealed package with waveguide interface and has achieved a noise figure of 4.3 dB with a gain of 28.1 dB at 91 GHz. These results represent the best noise figure performance ever achieved by multi-stage monolithic low-noise amplifier modules.