Active Push-Pull Circular Patch Antenna

The paper presents a new design of an active self-oscillating circular patch antenna. The power radiated by the antenna was increased by using two bipolar transistors operating in push-pull mode. By using a circular instead of a rectangular patch the stability of the operating frequency was increased. The push-pull oscillator was integrated inside the patch resulting in small dimensions. Very linear frequency tuning has been obtained by changing transistor dc bias voltage. The measured radiated power was high. Measured co-polarisation radiation patterns showed no degradation due to patch modifications and active elements. Symmetrical active patch design resulted in low cross-polarisation levels. Clean free running spectra and stable operation have been observed. Injection locking characteristics have been verified.