A Wideband Multiple Reflection Zeros and Radiation Nulls Dual-Band Filtenna Analyzed Utilizing Filter Coupling Matrix Theory

This communication proposes a dual-band filtenna composed of six in-band reflection zeros (RZs) and eight controllable radiation nulls (RNs) with a wide overall bandwidth. The complete dual-band filtenna is analyzed by decomposing it into several fundamental filtering components using the filter coupling matrix (CM) theory. Based on the field distribution relationships of the in-band modes obtained through full-wave simulations, the signed coupling matrices are derived. The spectral expressions for the RNs are formulated, followed by inequality analysis to predict their positions. The parameters contained in these expressions can guide the adjustment of the RNs. A resonator-loaded strip (RLS) feeding structure is introduced to enhance the bandwidth and generate RNs. It is a modified resonant probe feeding scheme with higher parameter degrees of freedom. The initial applications of the patch with embedded SIW cavity and the cavity-backed slot antennas were to broaden the bandwidth and enhance the gain. In this work, they are repurposed not only for their original functions but also for dual-band filtering characteristics. The final dual-band filtenna operates within 4.45–5.03 GHz and 6.10–7.05 GHz, with a fractional bandwidth (FBW) of 12.24% and 14.45%. It exhibits a higher number of RZs/RNs and significant bandwidth advantages compared to other dual-band filtennas of the same type. It exhibits good out-of-band suppression levels and low cross-polarization.