A low-profile dual-circularly polarized (CP) substrate integrated waveguide (SIW)-cavity-backed slot patch antenna with wide axial ratio beamwidths (ARBWs) is proposed. First, two orthogonal slots are etched on a square patch, and a SIW cavity is backed under the patch. Evolution of the SIW-cavity-backed cross-slot antenna is analyzed, and its beamwidths are enhanced by using the E-plane omnidirectional radiation of the slots. In order to broaden the ARBWs, four different SIW-cavity-backed slot patch antennas are also compared. Then, two rat-race couplers and two Wilkinson power dividers are skillfully cascaded together, and a novel six-port feeding network for the dual-CP antenna with high isolations is designed. Finally, a compact dual-CP slot patch antenna with dimensions of 0.53 λ ₀ ×0.53 λ ₀ ×0.035 λ ₀ is fabricated. Its measured results reveal that the antenna achieves 180°/194° left-handed CP ARBWs and 203°/200° right-handed CP ARBWs in two orthogonal principal planes at the center frequency of 5.2 GHz. Its measured isolation between two ports is greater than 16 dB in the entire bandwidth.

A wide axial-ratio beamwidth (ARBW) and half-power beamwidth (HPBW) circularly polarized (CP) antenna is realized by arranging two curved patch dipole pairs orthogonally in a cruciform contour that conforms with a hemispheric shell. First, two orthogonal curved dipole pairs are designed via step-by-step investigation of the evolution of traditional crossed dipoles. Then, an antenna with a wide CP working bandwidth and wide ARBWs and HPBWs is developed by enlarging the diameter of the curved arms, replacing the narrow arms with the wide patches and making these patches conformal with the shell surface; this improves the impedance bandwidth (IBW) and further reduces the antenna’s size. Finally, a prototype with reduced dimensions of $0.52\times 0.52\times0.15$ ( $\lambda _{0}^{3}$ ) is designed, fabricated, and measured. The resulting antenna exhibits a −10 dB IBW of 55.8% (1.06–1.89 GHz) and a 3 dB AR bandwidth of 70.9% (1–2.1 GHz), within which the ARBW and HPBW reach maximum values of 202°/196° and 113°/111° in the two orthogonal principal planes at 1.602 and 1.268 GHz, respectively. Furthermore, a 3 dB ARBW exceeding 100°, an HPBW exceeding 96°, and efficiency exceeding 60% are acquired within the 1.252–1.89 GHz (40.6%) target service coverage band.

A wideband and compact Fabry-Perot resonator antenna (FPRA) employing two layers of partially reflective surfaces (PRSs) is presented in this letter. The proposed PRSs with regular hexagonal units are used in wideband FPRA for the first time. Based on the compact arrangement of regular hexagon units and the addition of tripod branches, the size of FPRA is greatly reduced. Furthermore, the regular hexagonal units are arranged periodically along three directions on the 2-D plane, which means that one regular hexagon unit has six identical units around it. Therefore, there is a strong coupling between the PRS units, and units obtain a positive phase gradient in a wide range of 9.1-13.5 GHz, which is the basis for the formation of the wideband FPRA. The FPRA with dimensions of (2.2×2.2×0.6) λ ₀ ³ (λ ₀ is the wavelength of the center frequency) has a 3 dB gain bandwidth over 9.2-13 GHz, relatively 34.2%, with a peak gain of 14.2 dBi. The prototype has been fabricated and tested, and validate the simulated results.

A reconfigurable, planar, and end-fire circularly polarized (CP) antenna with wide beamwidth is presented, which exhibits the bidirectional radiation with the same sense by combining two pairs of identical CP elements placed in a back-to-back configuration. The design of the element includes a meandering phase delay line, which connects a printed electric dipole and a quarter-wavelength shorted microstrip patch. Then, eight p-i-n diodes are employed in the two dipoles arms to realize either left-handed CP (LHCP) or right-handed CP (RHCP) by manipulating the DC bias voltage across p-i-n. The prototype is designed to operate at a center frequency of 5.8 GHz with a size of 0.61 x 0.50 x 0.029 (lambda(3)(0)), where lambda(0) is the wavelength of the center frequency. Also, its end-fire beam is in parallel with its plane. Experimental results show that the overlapped bandwidth for 10-dB return loss and the 3-dB axial ratio (AR) of the bidirectional end-fire antenna is from 5.72 to 5.89 GHz for the two CP states. The half-power beamwidth (HPBW) in the horizontal and vertical plane are 95 degrees/115 degrees at the 5.8 GHz.