Resonant frequency tunable range is an important character for active frequency selective surfaces (AFSSs), especially when building electronically steerable antennas based on AFSS. In this communication, a broadband tunable bandpass AFSS is presented. The tunable ability is achieved by the varactors mounted on the surface. The proposed design has zigzag resonant current flows through multiple unit cells. Thus, the magnetic field coupling between unit cells is enhanced and the resonant frequency tunable range is extended. The measured resonant frequency tunable range is from 935 MHz to 2.405 GHz. Another advantage of this design is that no additional bias grid is required. Furthermore, this design has stable response under different angles of incidence because it has subwavelength dimensions.

An ultra-wideband (UWB) antenna with butterfly-like coupling slot for 4-element multiple-input multiple-output (MIMO) applications is introduced in this letter. In the design of the UWB antenna unit, the proposed butterfly-like slot is adopted to improve the impedance matching and achieves the operating bandwidth of 3-12 GHz. At the same time, a symmetrical T-shaped meandering strip etched on the ground and connecting with the patch through via produces a notch at 5.1-5.37 GHz, which suppresses the signal interference in WLAN band simultaneously. The results show that the proposed antenna array consisting of four orthogonal elements realized good isolation of lower than -15 dB without any additional decoupled structures. Also, the proposed design exhibited good diversity performance in terms of envelop correction coefficient (ECC9.92 dB). The gain reaches a maximum value of 6.8 dBi. Simulated and Measured results are in good accordance. All of this reveals the effectiveness of the proposed antenna in MIMO system and it can be suggested as a suitable candidate for UWB applications.

This paper proposes a monostatic backscatter communication system with enhanced isolation between excitation and receiver. This enables a mechanism akin to simultaneous co-frequency full-duplex operation, allowing the receiver to effectively amplify and quantify the weak reflected backscatter signals, subsequently demodulating them to extract valid data. Compared to RFID systems, which also employ monostatic backscatter communication, this approach can substantially extend the effective communication range. Furthermore, the exciting source and receiver are integrated in the same system, which makes the base-station system's framework compatible with a common WiFi router. Meanwhile, the communication power consumption of the remote node is significantly decreased

In this paper, we proposed a beamforming antenna, which is realized using an omnidirectional antenna in the center surrounded by a cylindrical smart dome. The smart dome is made of 16 active frequency selective surface columns of which the amplitude and phase response can be continuously tuned by varying the bias voltages of the employed varactors. Thus, the performance of the proposed antenna could achieve higher gain, better nulling level, and more agility than many switch methods-based cylindrical reconfigurable antennas. Moreover, in order to overcome the unavailable analytical synthesis caused by complex mutual coupling between columns, we develop a genetic algorithm based optimization system and conducted a serial of experiments to evaluate the high-gain, nulling, continuously steering, and frequency-invariant ability. The results show that, during the frequency tunable range of the AFSS (2.0 GHz to 2.7 GHz), the antenna can offer an additional gain of up to 6.57 dB and nulling level of −56.41 dBi. For the high-gain modes, the −3 dB beam widths are 26°–34°, which offers enhanced angular resolution compared with other reported beam-sweeping work. Furthermore, the radiation pattern is continuously steerable.

In this article, an 8×8 MIMO antenna system with multidecoupling structures is proposed for the fifth-generation (5G) terminal applications. First, an antenna element consisting of an L-shaped open slot with dimensions of 5.6×5mm² and two bent-L-shaped monopoles with dimensions of 12.7×6.1mm² is introduced. Due to coupling feed technology, the initial open slot owns a wide bandwidth from 3.62GHz to 4.82GHz. For broadening the bandwidth of the initial antenna element, two bent-L-shaped monopoles are added to the open slot to adjust the input impedance. By optimizing the parameters of monopoles, the proposed antenna element has been finally determined and the bandwidth of the antenna element has been broadened (2.82GHz to 5.23GHz). Second, a dual antenna pair is constructed by placing the two antenna elements with an edge-to-edge distance of 27mm in a mirror image placement; the 8×8 MIMO antenna system is brought about by symmetrically disposing four such antenna pairs with an edge-to-edge distance of 47mm. Moreover, the isolation of two closely placed antenna elements is achieved by the parasitic strip-loading technique and defective ground techniques. Due to the decoupling techniques used in the 8×8 MIMO antenna system, the average isolation has been optimized from 13.2dB to 21.9dB and the total efficiency of each antenna element has been improved from a worst 20 to over 45. Besides, the calculated mean efficiency gain is less than 1dB, and the calculated envelop correlation coefficient (ECC) is lower than 0.01 for desired frequency bands. Furthermore, the proposed 8×8 MIMO antenna system has the measured broadband bandwidth from 3.28GHz to 5.05GHz (covering N77, N78, and N79 bands) and a compatible dimension for ultra-thin mobile phones. The simulated results of this work are all obtained from EM software CST STUDIO SUITE 2019. In general, the proposed 8×8 MIMO antenna system with a high-isolation property provides a hopeful solution to 5G ultra-thin mobile phones.