A low-profile broadband dual-circularly-polarized metasurface antenna is proposed. The antenna consists of a modified cross-slot coupling antenna with a lattice of 4 × 4 square metallic patches. A characteristic mode analysis is used to investigate the operating mechanism of the metasurface antenna. Then, the desired modes are chosen and excited by the modified slots. The modified slot introduces a new resonance to achieve broadband characteristic. Two orthogonally placed microstrip lines are used to achieve both right-hand circular polarization and left-hand circular polarization in the same frequency band. The final prototype, with an overall size of 100 mm × 100 mm × 6 mm (0.71 λ ₀ × 0.71 λ ₀ × 0.04 λ ₀ at 2.15 GHz) is measured. The measured results show that the proposed antenna has an axial-ratio bandwidth of 31.3% and an impedance bandwidth of 52.5%.

Joint communication and radio sensing (JCAS) in millimeter wave (mmWave) systems requires the use of steerable beam. For analog antenna arrays, a single beam is typically used, which limits the sensing area to within the direction of the communication. Multibeam technology can overcome this limitation by separately generating package-level direction-varying sensing subbeams and fixed communication subbeams and then combing them coherently. In this paper, we investigate the optimal combination of the two subbeams and the quantization of the beamforming (BF) vector that generates the combined beam. When either full channel matrix or only the angle of departure (AoD) of the dominating line-of-sight (LOS) path is known at the transmitter, we derive closed-form expressions for the optimal combining coefficients that maximize the received communication signal power. For quantization of the BF vector, we focus on the two-phase-shifter array where two phase shifters are used to represent each BF weight. We propose novel joint quantization methods by combining the codebooks of the two phase shifters. The mean squared quantization error is derived for various quantization methods. Extensive simulation results validate the accuracy of the analytical results and the effectiveness of the proposed multibeam optimization and joint quantization methods.

Multibeam technology enables the use of two or more subbeams for joint communication and radio sensing, to meet different requirements of beamwidth and pointing directions. Generating and optimizing multibeam subject to the requirements is critical and challenging, particularly for systems using analog arrays. This paper develops optimal solutions to a range of multibeam design problems, where both communication and sensing are considered. We first study the optimal combination of two pre-generated subbeams, and their beamforming vectors, using a combining phase coefficient. Closed-form optimal solutions are derived to the constrained optimization problems, where the received signal powers for communication and the beamforming waveforms are alternatively used as the objective and constraint functions. We also develop global optimization methods which directly find optimal solutions for a single beamforming vector. By converting the original intractable complex NP-hard global optimization problems to real quadratically constrained quadratic programs, near-optimal solutions are obtained using semidefinite relaxation techniques. Extensive simulations validate the effectiveness of the proposed constrained multibeam generation and optimization methods.

This paper includes a design of a four-port stacked patch antenna with band enhancement for multi-in multi-out application. The proposed stacked patch antenna consists of two collocated microstrip patches printed on the upper and lower substrates. Through the analysis of characteristic modes, we find that eight desired modes forced to resonant at the operating band. By exciting the resonant modes on the lower patch, four different radiation patterns are achieved. For each radiation pattern, there are three resonance frequencies at interested frequency band-two parallel resonances and one series resonance-which have been combined to form a wider operating band. The proposed antenna is operating at 2.6 GHz frequency band with at least 7.3% in simulated and 6.5% in measurement impedance bandwidth for each port with low profile. A high port isolation (>24.5 dB) and low correlation (<;1e-3) have been achieved. Numerical and experimental results illustrate the validity of the design.

This paper presents a method of designing filtering metasurface (MTS) antennas, which is to excite the candidate in-band modes and suppress the out-of-band interference ones. The candidate modes are selected depending on the expected radiation patterns and operating band, and excited by choosing a reasonable feeding structure. The suppression of interference modes is achieved by controlling the modal currents with the aid of characteristic mode analysis (CMA). As a result, the MTS works as a radiator and filter simultaneously. A 3×3 array MTS antenna is implemented to demonstrate the concept. Targeting the broadside radiation pattern and 5G operating band, two candidate MTS modes are selected. A ground slot is used to excite them and introduce an extra slot mode. The out-of-band interference modes are eliminated by removing specific patches and etching a split slot on the central patch of the MTS. Moreover, to improve the selectivity at the lower band edge, a probe is added at the center of the antenna. The antenna has a simulated -10-dB impedance bandwidth of 25%, covering the 5G n77 band (3.3–4.25 GHz). The out-of-band suppression level exceeds 27 dB. Thin-band peak gain is 10.9 dBi while the peak efficiency reaches 95%.

In this communication, conformal concave and convex bent dielectric resonator antennas (DRAs) with curving ground plane are proposed and investigated. Their resonant frequencies and field distributions are theoretically analyzed through the eigenmode method and single-mode approximation with approximate models containing various boundary conditions. This method shows good accuracy for both concave and convex bent DRAs. Then, radiation performance of bent DRAs is studied and compared with that of rectangular DRAs and bent microstrip patch antennas. Bent DRAs exhibit superior or flexible performance in terms of bandwidth, gain, and beamwidth. Finally, a prototype is fabricated and measured to validate the research. This work paves the way for DRAs to the area of conformal, flexible, and wearable antennas.