Active Sensor for Microwave Tissue Imaging with Bias-Switched Arrays

Abstract

A prototype of a bias-switched active sensor is developed and measured to establish the achievable dynamic range in a new generation of active arrays for microwave tissue imaging. The sensor integrates a printed slot antenna, a low-noise amplifier (LNA) and an active mixer in a single unit, which enables inter-sensor separation distance as small as 12 mm. The sensor's input covers the bandwidth from 3 GHz to 7.5 GHz. Its output intermediate frequency (IF) is 30 MHz. The sensor is controlled by a simple bias-switching circuit, which switches ON and OFF the bias of the LNA and the mixer simultaneously. It is demonstrated experimentally that the dynamic range of the sensor, as determined by its ON and OFF states, is 109 dB and 118 dB at resolution bandwidths of 1 kHz and 100 Hz, respectively.

The integration of an LNA on the same board with each antenna element is also studied. The LNA circuit dimensions have been reduced from 18.2 mm by 44.6 mm (the size of the evaluation board) to 6 mm by 8 mm in width and length, respectively. Simulations show promising results. Thus, fabrication and measurements can be carried out in the near future.