Miniaturized-element frequency selective surface assisted dual-polarized broadband high-gain resonance cavity antenna

Resonant cavity antenna (RCAs) can provide highly directive radiations with planar and compact configuration but suffers from a narrow bandwidth surrounding the resonance frequency. A recent method based on replacing the ground of a conventional RCA (see Fig. 1(a)) with a spherical modified ground (SMG) (see Fig. 1(b)) [1] achieves wideband performance by simultaneously exciting three cavity modes. However, a few drawbacks are suffered, which include (i) a tall cavity height of one-wavelength, (ii) the fabrication complexity of the SMG and (iii) limitation to single polarized operation.
In this work, we present a planarized wideband RCA (see Figs. 1c-d) that mimics the working principle of [1] but mitigates the aforementioned drawbacks. We replace the ground of a conventional RCA with a planar metasurface inside the cavity that mimics, over a wide bandwidth, the electromagnetic property of the SMG. We used a ground-plane-backed MEFSS metasurface unit cell [2] to implement an equivalent lowpass filter. Such a filter provides a linear phase, and hence a constant time delay, over a broad bandwidth [3]; in this work we design the cells to achieve frequency-independent time delays from 12 GHz to 16 GHz, which enable us to replace the curved SMG with a flat metasurface. We demonstrate that placing this metasurface inside the cavity leads to the excitation of the higher-order cavity modes, broadening the gain bandwidth of the RCA and reducing the cavity height. Further, we show that the excitation of higher-order cavity modes does not depend on the polarization of the incident wave; hence a high-gain dual-polarization RCA is constructed. Figure 1c shows how the metasurface replaces the SMG. Figure 1d shows a side view of the MEFSS RCA; the insets show the side-view of a unit cell and a top view of the entire metasurface. The proposed RCA offers a peak gain of 17.6 dB (for both the linear and circular polarizations) and shows a gain variation of about 4 dB from 11.8 GHz to 14.84 GHz range. The antenna also has low return loss and shows consistent radiation characteristics and low side-lobes levels across its entire band of operation. The proposed antenna can find strong application in high-gain, polarization insensitive wireless environments such as satellite and long range communication.