A Superposition Method for Dual-Band Narrow-Wall Shorted-Slotted Waveguide Arrays at 3/4 GHz for Shared-Aperture ISAC Front-Ends

Abstract

This paper presents the design and implementation of a single-fed, dual-band narrow-wall shorted slotted waveguide array (SWA) operating at 3 GHz and 4 GHz within a shared aperture. Rather than treating the dual-band integration only as a geometric coexistence of two resonant slot families, this work introduces a coupling-aware multi-frequency formulation derived from the classical Elliott framework to interpret cross-family loading within a shared aperture. Within this formulation, the slot ensemble is partitioned into two frequency-selective families. Cross-family electromagnetic interactions are interpreted through a coupling perturbation term introduced within an extended multi-frequency impedance-matrix representation. The antenna is fabricated using a standard WR-284 waveguide platform and evaluated through full-wave simulation and experimental measurements. Results demonstrate that the integrated antenna maintains dual-band impedance matching with $S_{11}\lt -10~\text {dB}$ at both target bands. Furthermore, the proposed design achieves a peak realized gain of 15.7 dBi with a sidelobe level of approximately -19 dB at 3 GHz, and a gain of 14.5 dBi at 4 GHz, while preserving stable broadside radiation. In the compared set of representative dual-band SWA studies, the narrow-wall realization exhibits a higher reported aperture efficiency, reaching 87.6% at S-band and 57.3% at C-band. This combination of compact footprint and relatively high efficiency supports the usefulness of the proposed multi-frequency superposition interpretation and suggests that the architecture is promising for space-constrained sub-6 GHz ISAC front-ends.