Multifunctional Filtering Leaky-Wave Antenna Exhibiting Simultaneous Rapid Beam-Scanning and Frequency-Selective Characteristics Based on Radiative Bandpass Filter Concept

In this article, the concept of radiative bandpass filter (RBPF) is proposed and investigated for developing a class of multifunctional filtering leaky-wave antennas (LWAs) which exhibit the simultaneous rapid frequency-dependent beam-scanning and frequency-selective characteristics. A substrate-integrated waveguide (SIW) is periodically loaded with closed (nonradiative) discontinuities acting as a bandpass filter, where the lower and higher stopbands are, respectively, stemmed from the SIW natural cutoff and the Bragg effect bandgap or bandstop caused by periodic discontinuities. By adequately adjusting the periodicity of filter unit cells and loading effects of closed discontinuities, filtering and dispersion behaviors of the periodic SIW can be flexibly engineered. Open (radiative) discontinuities are then deliberately introduced into the bandpass filter to generate a controllable radiation leakage, thereby accomplishing the design of the RBPF, i.e., the proposed LWA. With this concept, both filtering/dispersion and radiation tasks can be independently managed by different modules for LWAs. For demonstration purposes, two kinds of closed discontinuities, namely nonradiative longitudinal slot-pair (capacitive) and iris (inductive), are separately exploited for periodic SIWs with bandpass and high dispersion characteristics, whereas transverse slot (open discontinuity) is mainly aimed for radiation leakage. Two RBPF-based LWAs are simulated, fabricated, and measured. The simulated and measured results are in a reasonable agreement, and both demonstrate the rapid beam-scanning and filtering behaviors, thereby validating the proposed concept.