A novel compact dual-wideband, dual-sense, circularly polarized (CP), square slot antenna with the simple structure is presented in this communication. The right-hand circular polarization in the +z-direction for the lower frequency is mainly realized by an inverted L-shaped strip, and the left-hand circular polarization in the +z-direction for the upper frequency is mainly achieved by an offset feed structure. A parasitic matching stub is helpful to improve the input impedance matching. The overall dimension of the prototype is only 50×50×1 mm ³ . An optimized antenna is fabricated and measured. The measured 10 dB return loss bandwidth is 111% (1.82-6.36 GHz). Its measured 3 dB axialratio bandwidths in the broadside direction are 55% (1.91-3.36 GHz) at lower band and 29.3% (4.78-6.41 GHz) at upper band, which can fully cover all the wireless local area network and wireless fidelity bands. What is more, this antenna has stable antenna gain and good radiation patterns within these two CP bands.

Considering the diversity of uniformly distribution for the solutions of multi-objective optimization problems, we propose the multi-objective genetic algorithm based on fitting and interpolation (MOGA/F and MOGA/I). The selected operator is based on the optimal reference points uniformly distributed in the objective space, which is calculated by applying a fitting function or interpolation method from a finite set of objective values. After sorting the ranks of the population, the objective space for the last front can be easily calculated by using fitting and interpolation functions, and the uniformly distributed points can be obtained without parameter setting. The individuals with the shortest Euclidean distance to the reference points are chosen according to the error matrix. This method can maintain the diversity and spread of the solutions without destroying the convergence. In this paper, MOGA/F and MOGA/I are compared with the traditional methods, NSGA-II and MOEA/D, by optimizing the mathematical problems. The numerical examples show that MOGA/F and MOGA/I have a much higher performance in terms of diversity and convergence of the final solutions.

A novel dual-wideband antenna is designed for circular polarization (CP) diversity in this communication. It consists of a horseshoe-shaped slot, two L -shaped radiators, and two ports. The working principle of the horseshoe-shaped slot is half-wavelength slot mode, and the working principle of the L -shaped radiator is quarter-wavelength monopole mode. The slot mode is applied to produce two lower CP resonant frequencies of two bands and the monopole mode are used to generate two upper CP resonant frequencies of two bands. By narrowing these two modes of two bands, a dual-wideband CP antenna can be designed easily. When port 1 is excited and port 2 is matched, this antenna radiates left-hand CP wave at lower band and right-hand CP wave at upper band at the + z -direction. When exchanging the excited and matched ports, the radiation is reversed. The measured impedance bandwidths ( S ₁₁ <; -10$ dB) are 113% (0.7-2.52 GHz) and 60.2% (3.47-6.46 GHz). The measured 3 dB axial ratio bandwidths are 72.5% (1.17-2.5 GHz) and 56% (3.52-6.26 GHz). The isolation between the two ports is better than 15 dB.

A novel two-dimensional wide-angle scanning phased array antenna with ±45° dual-slant polarization is presented in this letter. The proposed dual-polarized antenna consists of two wide-beam dipole antennas with bent arms. To improve the active VSWR of the array antenna at large scanning angles, vertical metallic patches are applied to the four sidewalls of the dual-polarized antenna, which can effectively cancel out the total couplings on the antenna. In addition, metamaterial superstrates are placed on the antenna to further improve the active impedance matching performance of the proposed antenna. To validate the performance of the proposed antenna array, an 8×8 planar dual-polarization wide-angle scanning phased array antenna has been fabricated and measured. Within the operating frequency range of 5 to 6 GHz (18%), the levels of active VSWR are consistently below 2. The ±75° scanning capabilities of the proposed design are yielded in the xoz, yoz, and diagonal planes, with sidelobe levels below -9 dB, respectively. The measured results align well with the simulated. The proposed planar phased array exhibits a two-dimensional wide-scanning range under dual-polarization excitation, featuring a compact structure that is conducive to integration and suitable for wireless communication systems.

In this communication, a novel dual-band 0.9/2.45 GHz circularly polarized (CP) radio frequency identification (RFID) reader antenna with low-profile high-efficiency based on the polarization conversion metasurface (PCM) is proposed. At first, a dual-band linearly polarized (LP) bow-tie dipole antenna etched with two pairs of U-shaped grooves is designed as a radiator. The gradient microstrip balun feeding is employed to achieve excellent radiation performance and easy installation as a supporting structure. Then, a PCM is designed as a reflector, enabling polarization conversion and phase difference (including tracing phase difference) for CP radiation in dual frequency bands. Finally, the antenna has been manufactured and measured, resulting in an overall size of $0.42\lambda _{0} \times 0.42\lambda _{0} \times 0.09\lambda _{0}$ at 0.9 GHz. The measured impedance bandwidths for the lower and upper bands are 17.54% (0.78–0.93 GHz) and 4.94% (2.37–2.49 GHz), respectively. The axial ratio (AR) bandwidths are 6.67% (0.87–0.93 GHz) and 5.33% (2.37–2.50 GHz) in the corresponding bands. The proposed antenna can cover the UHF/2.45-GHz industrial scientific medical (ISM) dual bands of China, and the Federal Communications Commission (FCC) band of North America. Furthermore, the measured peak gains for right-handed circular polarization are more than 6.02 and 9.14 dB in the respective frequency ranges. Therefore, the antenna is very suitable for RFID applications in both UHF and 2.45-GHz ISM dual frequency bands.

To address the requirements of stealth platforms for low-profile antennas, this paper proposes an ultrathin low scattering circularly polarized (CP) slot array by integrating with a genetically-optimized 2-bit phase gradient metasurface (PGM). This approach achieves broadband RCS reduction (both in-band and out-of-band) under far-field illumination. The performance is robust for both LP and CP waves at incidence angles from normal to oblique, all while maintaining a 0.09 $\lambda _{0}$. low profile. Compared to periodic counterparts, the genetically-optimized aperiodic topology improves RCS reduction bandwidth and impedance bandwidth, with the bandwidth of RCS reduction of more than 8 dB is 13.1-23.5 GHz. The co-designed structure preserves circular polarization integrity and radiation efficiency from 10.48-13.46 GHz. Experimental validation demonstrates wideband RCS reduction by more than 4.5 dB is 96.8% (8.35-24 GHz). This work establishes a low-profile stealth antenna paradigm for conformal low-observable platforms.