Axial Ratio Bandwidth Enhancement of DBDCP Fabry-Pérot Cavity Antenna for Vehicular MIMO Communications and Sensing.

This paper presents the axial ratio (AR) bandwidth enhancement of a dual-band dual-circularly polarized (DBDCP) antenna. It utilizes a novel polarization-independent partial reflective surface (PRS) unit cell, which consists of two same metallic patterns with a relative 90o rotation on both surfaces of a substrate. Each metallic pattern is composed of a C-shaped arc and a circular patch. The LP field from the feeder is transformed into two different circularly polarized (CP) field at two respective bands by the unit cell. Due to the asymmetric structure and separated topology of two C-shaped arcs, a slight resonant deviation appears in AR for different polarized waves. Moreover, both x- and y-polarized waves are produced simultaneously by using Fabry-Pérot cavity (FPC) structure when a y-polarized feeder is used. Thus, the AR bandwidths for both x-and y-polarized incident waves are close to each other and combined deliberately into wide AR bandwidth. To validate the design concept, a prototype of the proposed MIMO antenna is fabricated and measured. The measured voltage standing wave ratio (VSWR) of less than 2 covers from 11.55 GHz to 14.8 GHz, and the LHCP pattern and RHCP pattern are realized in low band of 12-12.6 GHz (4.88%) and high band of 14.1-14.61 GHz (3.55%), respectively. The maximum gain is 13.5 dBi (13.1 dBi) at the low-band (high-band). Besides, the port isolation is better than 40 dB, and the ECC is less than -80 dB. With these performances, the proposed MIMO antenna can be employed for vehicular MIMO communications and sensing at Ku-band.