Self-detection performance of active microstrip antenna

Experimental results are presented for the (S+N)/N ratio of an active microstrip antenna operated as a selfoscillating detector. The antenna element uses a GaAs MESFET as the active device and is biased from a single sided DC supply (V_dc=3.77 V, I_dc=65 mA). The element oscillates at 10.03 GHz and produces approximately 4 mW of radiated power. It is shown that the (S+N)/N ratio produced by the active element when operated as a selfoscillating detector varies nonlinearly between 6 dB/30 Hz and 60 dB/30 Hz for synthetically generated Doppler frequencies between 500 Hz and 20 kHz, respectively. The effect of bias voltage control on self-detector performance is illustrated for a Doppler frequency of 1 kHz.