Microwave reflection amplifier for detection and tagging applications

A reflection amplifier module with up to 14 dB gain at 21 GHz is described, which is capable of direct detection of amplitude modulated incident signals at K band. The module consists of a single pseudomorphic high electron mobility transistor (pHEMT) transistor gallium arsenide integrated circuit attached to a microstrip patch antenna. Experimental sensitivity characteristics for the module are given for several bias conditions. These results show that the module is capable of direct detection of signals as low as -75 dBm. In addition, reflection gain control through d.c. bias modification is used to directly encode amplitude modulated backscattered information onto the amplified signal returned by the reflection amplifier tag. The authors also show how the incorporation of an ultra- thin absorber with the tag can be used to increase its re-transmitted signal performance characteristics.