Electrically tunable small microstrip antenna using interdigital plate loading for telemetry sensor applications

An electrically tunable small microstrip antenna for telemetry sensor applications in the UHF band (425 MHz) is presented. The proposed antenna is miniaturised by loading horizontal interdigital plates at both radiating edges. Varactor diodes are installed between the radiating edges and the ground plane to control the resonant frequency by adjusting the DC bias asymmetrically. The designed antenna is 65 × 50 × 20 mm³ in size (0.092λ × 0.071λ × 0.028λ). It is as much as 80% shorter than conventional microstrip antennas. The reconfigurable frequency range with a return loss of less than - 10 dB is 388.7- 462.8 MHz (74.1 MHz, 17.4%).