ALTHOUGH RF PHASE shifting can be realized in a CMOS variable phase shifter, it is very difficult to achieve a large tuning range. To tackle this problem, a receiver based on the subsector beam-steering technique has been developed by Ting-Yueh Chin, Sheng-Fuh Chang, Jen-Chieh Wu, and Chia-Chan Chang from Taiwan's National Chung Cheng University. Thee compact, CMOS phased-array-receiver front end performed continuous beam steering with 21 dB receive gain while consuming just 30 mW.

The beam-steering range is divided into five subsectors from four characteristic beams of the Butler matrix. In each subsector, the receive beam is steered by a weighted combination of the received signals from array antennas. If the beam-steering network simultaneously excites any two beam ports with appropriate weighting factors, a new beam will be formed by the linear combination of two excited characteristic beams. The new main beam angle will then be determined by the ratio of the weighting factors. By controlling the weighting factors, the beam can therefore be steered across the full spatial range.

Once the four-element, phased-array-receiver monolithic microwave integrated circuit (MMIC) was implemented, its performance was measured by an on-wafer vector network analyzer. A realistic measure of receive gain and noise figure were then obtained when the receiving beam was steered. When implemented in 0.13-m CMOS, the phased-array MMIC offers 17 to 21 dB receive gain with 8.9 to 10.7 dB noise from 25 to 26 GHz. It consumes less than 20 mW. The receiver, which is housed in a chip that is just 1.43 mm2, performed continuous beam steering from -90 to +90 deg. See "A 25-GHz Compact Low-Power Phased-Array Receiver with Continuous Beam Steering in CMOS Technology," IEEE Journal Of Solid- State Circuits, Nov. 2010, p. 2273.