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 low-cost, wideband PCB manufactured antenna is proposed in this letter for 5G/6G antenna-in-package (AiP) applications with wideband common-mode current (surface-wave) choking characteristics. The antenna is based on a grounded, wideband, high-efficiency electromagnetic structure (WHEMS) and a backing cavity, through both of which a radiating choke is introduced. By changing the choking condition of a quarter wave length widely applied in traditional low frequency baluns, wideband common-mode current suppression is achieved. The enclosing wall of the backing cavity is realized by a combination of isolated grounded vias and connected grounded vias based on current polarizations on the wall. Finally, a 22% impedance bandwidth (60-75GHz), and a relative gain of 8-10 dBi within the band is achieved.

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 multiband dual-polarized omnidirectional antenna for 2G/3G/LTE mobile communications is proposed in this paper, which consists of horizontal polarization (HP) and vertical polarization (VP) element with separate feeds. The VP element consists of three polygonal radiation patches with three equally-spaced legs shorted to the ground plane. The HP element consists of three wideband slot loop structures, which is nested on the top of the VP elements. Three slot loop structures enhance the bandwidth of HP, and the simulated and measured results both indicate that the frequency bands of 1650-2900 MHz for HP and 780-2700 MHz for VP can be achieved. Nesting improves the gain of the HP element at least 1dBi for the reflection of VP. The gain of HP element is more than 3 dBi for long term evolution (LTE), and the gain of VP element is more than 5 dBi in LTE band and 1.5 dBi in 2G band. Port isolation larger than 30 dB and low gain variation levels are also obtained. The proposed antenna can be applied in mobile communications.

In this letter, a low-profile wideband pattern diversity antenna based on metasurface (MTS) is proposed. Initially, based on the theory of characteristic mode (TCM), the two adjacent intrinsic modes, which correspond to the broadside and conical radiation pattern, respectively, are exploited to realize a wideband pattern diversity characteristic under a low profile. Then, by analyzing the modal current distribution on the MTS, the optimal locations, orientations and relative phases of the four L-shaped feeding probes are determined to excite the above two modes. However, the in-band high-order modes (HOMs) introduced by the feeding structure will deteriorate the radiation pattern. Therefore, chamfering corners on the MTS is used to suppress the HOMs for radiation pattern improvement. Finally, by combining TCM and MTS, the modes are manipulated to achieve a pattern diversity antenna with an extremely low profile of 0.06 λ0 (the free-space wavelength at the center frequency) and an isolation of better than 38 dB, which also maintains an operating bandwidth of 20.24%. Based on these excellent performances, the proposed antenna is an attractive solution for pattern diversity applications requiring low profile, especially in unmanned aerial vehicle communications.

A compact wideband high gain directional antenna is proposed in this paper for marine communications. The antenna consists of a back plane (reflector), a slot-loop antenna (driven element), and a director of rod. Based on the current distribution, the slot-loop antenna is equivalent to an array of three linear current dipoles. The dipole acts as an element of the director, which provides a high efficient director for slot-loop antenna according to theoretical analysis. Both the impedance bandwidth and the 1 dB gain bandwidth are 45% covering 1.7–2.7 GHz in this design. A gain of 11.2 to 12.2 dBi is obtained in the working band with only one set of directors. The directors have a dimension less than the antenna aperture in the H-plane, which can be seen as one director in the end-fire direction. Compared with the classic Yagi antenna with the same gain level, the newly proposed antenna is only half of the size in radiation direction, which is a breakthrough for the Yagi antenna design. This size reduction can significantly minimize the interference between ship-borne antennas. The antenna is fabricated using only metal of low cost, which is useful for the ship-to-shore/ship communicating applications and desirable for the large-scale deployment.