Wideband Frequency Tunable Concentric Circular Microstrip Patch Antenna with Simultaneous Polarization Reconfiguration

A wideband frequency tunable concentric circular microstrip patch antenna with simultaneous polarization reconfiguration is demonstrated by using four varactor diodes between a circular patch and a concentric ring patch around it. Both frequency tunability and polarization reconfigurability are controlled by a proposed feed network. Varying the capacitance value of the varactor diodes varies the operating frequency of the antenna from 1.17 to 1.58 GHz (around 30% tunability) with impedance matching better than S₁₁ = S₂₂ = -10 dB. Each set of the two varactor diodes provides vertical and horizontal linear polarizations excited using one of the feed ports at a time. Similarly, the right-handed circular polarization (RHCP) and left handed circular polarization (LHCP) radiation patterns are realized by employing all four varactor diodes and both feed ports with +90° time phase difference. The antenna is fabricated on a 120-mil-thick (3.05 mm) Arlon AD450 dielectric substrate (ε_r = 4.5, tanδ = 0.0035). The proposed feed network to control the excitation of ports for each of the polarizations is fabricated on 62-mil-thick (1.58 mm) FR-4 substrate material (ε_r = 4.4, tanδ = 0.02). A single-pole 4 through radio-frequency switch and two single-pole double through switches are used in this feed network for realizing the control circuitry. Simulated and measured impedance matching and radiation pattern results show good agreement with acceptable gain over the tunable frequency bands.