This letter introduces a wideband circularly polarized (CP) array antenna for wireless communication application. The array consists of 2 Â 2 sequentially rotated symmetric antenna elements and a wideband weakly coupled feed network providing stable 90 phase difference. By using the proposed feed network and introducing the slot coupling feed, the CP array antenna can achieve a wideband CP performance with a low profile of 0.03 λ 0 (at 5.0 GHz). The proposed antenna exhibits the impedance bandwidth (IMBW) of 73.9%, axial ratio bandwidth (ARBW) of 53.6%, and 3-dB gain bandwidth (GBW) of 60% with the peak gain of 10.4 dBi and the maximum efficiency of 82%. The measured results are in good agreement with the simulated results, indicating that a promising application in compact wideband C-band wireless systems. K E Y W O R D S circularly polarized array antenna, sequential phase (SP), weakly coupled feed network, wideband 2 | DESIGN OF THE WIDEBAND CP ARRAY ANTENNA In this section, we design the wideband CP array antenna and analyze the mechanism of CP radiation. The

We presented a miniaturized patch antenna with enhanced bandwidth. Reactive Impedance Surface (RIS) was introduced instead of the traditional metal floor, and bandwidth enhancement is realized by loading slotted parasitic patches. The reference antenna and the antenna 1 loaded with the parasitic patch are designed, that impedance bandwidth changed from 8.5% to 23.6%, the peak gain and the front-to-back ratio was also improved by 2.2dBi and 7.8dB respectively; The metal floor of antenna 1 was instead by using RIS periodic structure to design Antenna 2. The absolute bandwidth of both antenna 1 and antenna 2 is about 1GHz. Antenna 2 is 22.4% smaller than the reference antenna and 28.6% smaller than antenna 1. The simulation results show that the proposed bandwidth enhancement and miniaturization methods are effective and ensure a certain improvement in gain.

A planar circularly polarized (CP) array antenna based on polarization conversion electromagnetic band-gap (PCEBG) and sequential phase (SP) feed network with wideband circular polarization and low radar cross section (RCS) is presented. The array is formed by 2 × 2 PCEBG elements. The CP performance is obtained due to the PCEBG, and the SP feed network contributes to the wide bandwidth and symmetric radiation pattern. The proposed array antenna, with an overall size of 64 mm × 64 mm × 2.008 mm (1.6 λ 0 × 1.6 λ 0 × 0.05 λ 0 at 7.5 GHz) has been fabricated and measured. The measured results are as follows, an impedance bandwidth of 42.90% (6.61-10.22 GHz), a 3-dB axial ratio bandwidth (ARBW) of 28.3% (6.65-8.83 GHz) and a 3-dB gain bandwidth of 23.7% (6.7-8.5 GHz). The antenna exhibits left-hand CP(LHCP) characteristics with a peak broadside gain of 14.1 dB. The proposed antenna achieves an in-band and out-band RCS reduction more than 8 dB under normal incidence. The measured results are in agreement with the simulated results.

A double-layer metamaterial with epsilon-near-zero (ENZ) properties is proposed loading on the patch antenna. The double-layer metamaterial that has two layers of the same material and structure is produced on FR4 substrate. The gain and radiation directivity of the patch antenna can be greatly improved covering with the proposed ENZ metamaterial. Simulation results show that by coating the ENZ superstrate, the gain of the patch antenna is increased from 5.99 dBi to 10 dBi, corresponding to 66.9% gain enhancement and greatly improved radiation directivity. While the performance of the patch antenna is improved, the working frequency and bandwidth of the patch antenna are not affected.