A Single-Layer Dual-Band Array at Low-Frequency Ratio With Concurrent Broad Fan Beam and Narrow Pencil Beam

A single-layer, dual-band, shared-aperture array with a broad fan beam in the lower band centered at 5 GHz and a narrow pencil beam in the adjacent upper band centered at 5.8 GHz is presented in this article. First, the schematic of a dual-band array with its beamwidth regulation capability is presented. Then, two key components, i.e., a novel dual-band patch antenna element and a compact filtering phase shifter (FPS) are developed. The antenna element has counterintuitive beam patterns with broad azimuthal half-power beamwidth (HPBW) of 183.3° in the lower band but much narrower azimuthal HPBW of 68.5° in the upper band, indicating its excellent ability in beamwidth regulation with a figure of merit (FoM) of 2.31. Meanwhile, the FPS serves as a band-stop filter in the lower band and a phase shifter in the upper band. Furthermore, a two-element series-fed subarray is designed by cascading two properly designed antenna elements through the FPS. Finally, a parallel-series-fed array consisting of four rows of the series-fed subarrays is implemented, and a prototype is fabricated and tested. The measured results, in good agreement with the simulated ones, have demonstrated that the array satisfactorily attains a broad fan beam with azimuthal HPBW of 156° and gain of 11.05 dBi at 5 GHz and a narrow pencil beam with azimuthal HPBW of 30° and gain of 16.23 dBi at 5.8 GHz under a shared aperture of
$1.37\lambda _{0} \times 3.53\lambda _{0} \times 0.05\lambda _{0}$
, indicating an enhanced FoM up to 4.48. The FoM and gain could be further improved by simply expanding the array’s dimension based on the developed array topology.