A novel compact Vivaldi Antenna (CVA) for short-pulse ground penetrating radar (GPR) systems is presented. Artificial materials lens (AML) and sidelobe suppressor (SSR) are loaded to improve GPR Antenna's radiation capability in the aperture and the flanks of the CVA. The simulation and experimental results indicate that the proposed CVA has a −10 dB impedance bandwidth of 100% (0.7-2.1 GHz) and a −3 dB gain bandwidth of 70.9% (1.0-2.1 GHz). Within the operating bandwidth of the CVA, AML primarily enhances the CVA's high-frequency gain (1.4-2.1GHz), while the SSR primarily enhances the CVA's lowfrequency gain (0.7-1.4 GHz). Moreover, the CVA loaded with two kinds of artificial materials (AMs) has an average gain of 1 dB and 2 dB in the low-frequency and high-frequency parts, respectively. In addition, the transmission response with small ringing in time domain makes the proposed CVA suitable for shortpulse GPR systems. AML and SSR effectively enhance the gain of the CVA with a compact and space-saving loading method, which provides a new idea to enhance the gain of the CVA by artificial material.

A three-layer multifunctional metasurface structure is proposed to achieve polarization rotation, perfect polarization conversion, and asymmetric transmission. The design consists of mutually perpendicular rectangular patches, metal pillars, and open-slit metal sheets. By propagating the current through the metal pillars and changing the surface current direction, the dipole can be orthogonally steered to accomplish polarization conversion. The metal in the middle layer can be used to both improve the polarization conversion ratio and ensure high transmittance. The operating band of asymmetric transmission is 8.3–14.7 GHz, where the conversion ratio is above 90% in all of 9–14.2 GHz. In order to verify the proposed concept, the related parameters are designed and measured, the final experimental results match with the simulation results, and the design can be used in the radome, electromagnetic stealth.

A kind of compound optical lens (COL) inspired by metamaterials whose unit cell is a closed symmetric S‐type resonator (CSSR) is designed to enhance the gain and directivity of the antipodal Vivaldi antenna (AVA). COL, composed of a plano‐convex lens and a double‐convex lens, can generate a very narrow beam with a half‐power beamwidth of 11.2° at 12 GHz. Traditional metamaterial lenses can only convert spherical waves into plane waves. Although the gain will increase, the beamwidth of the antenna is still very wide. COL can focus the plane wave transformed from the spherical wave, which makes the radiation beam extremely narrow. The proposed antenna has a −10 dB impedance bandwidth of 169.2% (1.0‐12.0 GHz) and a −3 dB gain bandwidth of 133.3% (2.0‐10.0 GHz) and a maximum gain enhancement of 5 dBi. The experimental results of the antennas agree with the simulation results. The proposed antenna is eventually a suitable candidate for wireless communications and radar applications.

A compact antipodal Vivaldi antenna (AVA) with metamaterial half-lens (MHL) for beam control is proposed. The proposed AVA has three different beam forms in the operating frequency band, including end beam from 3 GHz to 9 GHz, beam splitting at 12.2 GHz, and 30 ∘ beam deflection at 13 GHz. Furthermore, it can perform 18 ∘ beam scanning by adjusting operating frequency from 12.7 GHz to 13.5 GHz. The simulation indicates that the proposed AVA has a −10 dB impedance bandwidth of 143.6% (2.3–14.0 GHz) and a −3 dB gain bandwidth of 100% (4.5–13.5 GHz), which is consistent with the experimental results. Besides, the gain of the proposed AVA has an improvement of about 2 dB in the working band. As a new method to control the beam, the loading of MHL realizes the design of a small size and multi-function antenna, which can be widely used in wireless communication systems.

A dual-band MIMO antenna with enhanced isolation operating in 2.35-2.50 GHz and 5.13-5.88 GHz bands is investigated and presented. The proposed antenna system is deformed from two inverted-F antennas, and the distance between the antenna elements is only 0.104λ (λ- wavelength of 2.4 GHz). To enhance isolation and reduce mutual coupling, the metamaterial and slot structures are efficiently and innovatively designed on the ground plane for two bands. Both decoupling methods effectively improve the antenna isolation, with metamaterials acting on the lower band and slots acting on the higher band. The mutual coupling at 2.4 GHz and 5.5 GHz is reduced by 15.24 dB and 8.19 dB, respectively. Then, the optimized MIMO antenna can cover both 2.4 GHz and 5 GHz WLAN bands, and has the advantages of wideband, compact size, good radiation, enhanced isolation, and low ECC. The measured results agree with the simulated results, which shows that the proposed MIMO antenna system has potential application value in WLAN system.