Realization of highly-selective multiband filtering antennas with tunable and reconfigurable characteristics

Abstract

This article presents planar multiband filtering antennas with frequency tunable and reconfigurable features. A highly-selective bandpass filter is initially designed using a pair of square open-loop resonators (OLR). To implement a dual-band filter, an open-ended stub is loaded at the center of each resonator. Varactor diodes are introduced to enable continuous tuning of the second band while keeping the first band fixed. Utilizing this approach, a quad-band filter with tunable higher bands is designed and measured. The proposed filter exhibits a wide frequency tuning range of 654 MHz (16.86%) and 930 MHz (21.8%) for the two higher bands, while the first two lower bands remain fixed at 2.74 GHz and 3 GHz. Subsequently, by co-designing the multiband filter with a wideband linear tapered slot antenna (LTSA), multiband filtering antennas are realized. Varactor diodes and PIN diodes are employed to demonstrate multiband filtering antenna with tunability, reconfigurability, and a combination of both. All the filtering antennas are fabricated and validated. The measured results demonstrate stable end-fire radiation patterns, low cross-polarization levels, and high selectivity characterized by two radiation nulls on both sides of each passband in the gain response. All the measured results correlate well with the simulation results.