ESPAR antenna RF nonlinearity reactive-field measurement - mitigation of distortion by anti-series varactor diode pairs

摘要

Harmonic and intermodulation distortion of a recently developed lightweight film-type ESPAR antenna is investigated experimentally. These distortions arise from the nonlinearity of the varactor diode circuitry used to control the antenna's radiation pattern. Therefore, the presented results will apply to all types of ESPAR antennas that utilize the same varactor circuitry. Reactive-field measurement technology that employs low interference probes within an ultra small anechoic box is used to reduce experimental cost. Anti-series varactor diode pairs (ASVP) are introduced and compared with the conventionally used single varactor diode. ASVP showed remarkable suppression of the nonlinear distortion. In particular, the second harmonic is reduced by more than 20 dB when compared to the single varactor diode. The second and third harmonic levels are better than -80dBe when using an input power of +28dBm (640mW). The third order intermodulation intercept points vary between +43dBm～+48dBm (20～63W) for different control bias voltages.