Compact, Co-Polarized, and In-Band Filtering Cavity-Backed Slot-Antenna Pair Based on Multifunctional Metasurface Diaphragms

A cavity-backed slot-antenna (CBSA) pair is designed in a shared cavity inserted with the multifunctional metasurface diaphragms (MSDs). The CBSA pair is co-polarized and in-band, and meanwhile exhibits the good features of a wide working band, good in-band decoupling, and enhanced out-of-band filtering performance, which are rarely achieved in other reported CBSAs. The customized MSDs in this design can introduce desired reflection/transmission properties and provide shorting paths in the cavity, which play an important role in adjusting the frequencies of the resonance modes to expand the working bandwidth, allowing proper transmission magnitudes and phases at different frequency points to enable the high isolation level, and generating filtering responses to introduce the radiation nulls (RNs) and enhance the out-of-band suppression. The proposed CBSA pair was analyzed, and then fabricated and measured. The total electrical size at the lowest working frequency $\text{f}_{L}$ is $0.76\times 0.58\times 0.16\lambda _{L} ^{3}$ . The overlapped fractional impedance bandwidth is $\sim $ 11.1%. The peak realized gain (RG) reaches 6.4 dBi, and the isolation is greater than 15 dB. The three introduced RNs guarantee the out-of-band suppression level is better than 14.6 dB in 6–15 GHz. The proposed CBSA pair is a good candidate for the compact, co-polarized, in-band, and high-efficiency multiple-input-multiple-output (MIMO) CBSAs.

I. Introduction

Cavity-backed slot antenna (CBSA) has been widely applied due to its advantages of easy integration with planar circuits, directional radiation, high mechanical strength, high-power-handling capability [1], [2], [3], [4], [5], [6], [7], [8], etc. The filtering CBSAs with enhanced anti-interference performance are further developed by introducing the filter design strategies into the CBSAs, e.g., adjusting the multiple intrinsic high-Q cavity modes [9], etching slots on cavities [10], adding shorting vias [11], [12], [13], [14], cascading multiple cavities [15], [16], [17], [18], [19], utilizing modes cross-coupling [20], [21], applying frequency selective surfaces [22], tuning coupling between the cavity and the parasitic patch [23], etc.