A Single-Layer Low-Profile Frequency-Reconfigurable Filtenna Without Extra Filtering Circuits

A single-layer low-profile frequency-reconfigurable filtenna (FRF) is proposed. It has a simple structure, which mainly consists of a driven patch and two parasitic patches. A lower radiation null is generated by etching a pair of narrow slots on the driven patch, and it can be flexibly regulated by changing the length of the extended part of the driven patch on both sides of the slots. The incorporation of the parasitic patches introduces an extra in-band resonance and an upper radiation null, thereby broadening the impedance bandwidth and enhancing the selectivity simultaneously. Five varactors were employed to realize the frequency adjustment, and only two sets of the bias voltages were supplied to realize the control, which reduces the antenna's complexity. A prototype was fabricated and measured to validate its feasibility, and the measured results demonstrated good agreement with the simulation ones. The proposed FRF has a size of 0.62 λ₀ × 0.62 λ₀ × 0.015 λ₀, a tuning range of 19.6% [(2.53 to 3.08) GHz], and a stopband suppression level exceeding 10 dB within this tuning range.