Frequency-reconfigurable single- and dual-band designs of a multi-mode microstrip antenna

Frequency-reconfigurable designs of a probe-fed multi-mode H-shaped microstrip antenna are presented. The reconfigurability is achieved by symmetrically loading the antenna with varactor diodes. The design approach for the proposed antennas is to control the propagating modes by matching a specific mode or two modes while mismatching the other modes in order to achieve single-band or dual-band operation, respectively. The key to such approach is the careful selection of the varactors´ positions and type. Two single-band designs are proposed where each tunes a different resonant mode of the H-shaped microstrip antenna. The two designs are only different in the type of the used varactors. One of these designs achieves 41% tuning range (2.22-3.37 GHz), while the other achieves 16% (3.77-4.45 GHz). A dual-band design is proposed where one of the bands is fixed at 2.728 GHz while the other is tunable. The dual-band antenna achieves a 32% tuning range (1.89-2.6 GHz) for the tunable mode. All of the designs are implemented on 80 × 80 × 1.57 mm³ substrate with ε_r = 2.2. Good agreement between the measured and simulated results of these designs is observed.