A low profile broadband circularly polarized (CP) microstrip antenna with wide beamwidth is proposed for global navigation satellite system (GNSS). Four claw-shaped parasitic branches are placed on the corners of the ground to widen the impedance bandwidth and half power beam width (HPBW) simultaneously. Several slots are etched on the radiation patch to obtain impedance matching. The proposed antenna is fabricated and measured. The experiment results show that the impedance bandwidth (IBW) for VSWR${\leq}$2 is 72.5% from 1.02 to 2.18 GHz and the 3-dB axial ratio bandwidth (ARBW) is 54% from 1.15 to 2GHz. The HPBW is beyond 100° overall CP bandwidth. Its dimension is 70mm×70mm×12mm, (0.35×0.35×0.06) $\delta_{0}^{3}$, where $\delta_{0}$ is the wavelength of the center frequency.

A dual-linearly polarized leaky-wave antenna (LWA) with low cross-polarization levels is proposed. The LWA with 14 circular patches is fed by symmetrical spoof surface plasmon polariton (S-SSPP) lines. When the S-SSPP lines are excited by a common mode, z-components of the magnetic fields are out-of-phase, and those of the electric fields are in-phase, due to the symmetrical structure. The radiation generated by the magnetic couplings (M-couplings) between these two SSPP transmission lines and the patch array strengthens each other, while the cross-polarized radiation produced by the electric couplings (E-couplings) cancels each other out. From another perspective, the M-couplings excite the horizontally-polarized (H-pol) TM11 mode. The E-couplings excite the TM21 mode, thus the E-couplings mainly appear at higher frequencies. As a result, the M-coupling and E-coupling mechanisms are separated successfully. Specifically, the LWA radiates H-pol waves with high purity. On the contrary, with the differential-mode excitation, the E-coupling patch array radiates vertically-polarized waves. Finally, a dual-linearly polarized LWA with frequency-controlled scanning beams and suppressed cross-polarization levels is designed. Measured results show that the dual-linearly polarized beams scan from backward to forward. In the whole band, the cross-polarization levels are less than -30 dB in the scanning plane.

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 novel composite right/left‐handed substrate integrated waveguide (SIW)‐based leaky wave antenna (LWA) is proposed. Square‐ring‐slot radiators are adopted to introduce series capacitor as well as the energy leakage, and four grounded vias within the slot ring contribute to part of the shunt inductor. Moreover, low cross‐polarisation levels in the beam scanning plane are achieved due to the differential excitations of the radiators located along the centre line of the SIW working at TE10 mode. The antenna is fabricated and measured. Both simulated and measured results show that the proposed antenna is a balanced LWA operating in the frequency band 13.5–17.8 GHz. Continuous beam scanning characteristic is acquired within the scanning region −57° to +30°. In addition, low cross‐polarisation levels less than −27 dB are obtained, and measured results are in good agreement with simulated ones.

A novel broadband circularly polarized (CP) squarering-loaded slot antenna with flat gains is proposed in this letter. The antenna is fed by an L-shaped microstrip line with tapered section for impedance matching. A square ring is also loaded, and a new resonant frequency with the minimum axial ratio (AR) is produced, broadening the CP bandwidth of the original slot-coupled microstrip-fed antenna. The antenna is successfully designed and fabricated. Measured results show that its 10-dB return-loss bandwidth is 3.94 GHz (4.56-8.5 GHz with the center frequency 6.53 GHz) and that its 3-dB AR bandwidth can reach 3.7 GHz (4.75-8.45 GHz with the center frequency 6.6 GHz). The antenna occupies an overall volume of 0.8λ ₀ × 0.8λ ₀ × 0.13λ ₀ with respect to 6 GHz. Its peak gain is 4.4 dBic, and the gain variation within 4.75-8.2 GHz band is less than 1 dBic, which means a good flat gain feature in the broad frequency band. The measured results agree well with the simulated ones.

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.