A method to significantly improve the isolation of multiple-input-multiple-output (MIMO) antenna is presented in this paper. The proposed design consists of multiple patches arranged in the H-plane configuration. Satisfactory isolation is obtained by using microstrip lines that are positioned along the radiating edges of the patches. The function of the decoupled lines is to excite an orthogonal polarization mode on the non-excited patch. A two-element array is fabricated to demonstrate the effectiveness of the proposed decoupling structure. The experimental results illustrate that the isolation of the 2-element MIMO antenna can be significantly improved by about 26 dB with an extremely small element spacing of 0.017 λ ₀ . Besides, the antenna exhibits good diversity performances. The decoupling method is also applicable to a multiple-element MIMO antenna. Compared to other related works, the proposed design has the smallest element spacing while achieving high isolation. The antenna can be used for 5.2 WLAN applications.

Recently, helical antennas had been used as a very small implantable antenna in a capsule endoscopy system. For a helical antenna, a normal-mode helical antenna (NMHA) is promising because of its small size and the completeness of an antenna design method, which has already been established. However, in the human body, the effects of human tissues on the electrical characteristics of an NMHA were not clarified. The most important aspect is to determine the self-resonant structures. In this letter, a deterministic equation is derived for the self-resonant structures of an NMHA in the human body. By utilizing simulation results of an electromagnetic simulator, a capacitive reactance equation is deduced based on the electric field distributions around an antenna. An inductive reactance equation is obtained by modifying the equation of free space to the condition of inside a dielectric material. Finally, by equating the capacitive and inductive reactance equations, the self-resonant equation is determined. The accuracy of the equation is ensured through the agreements of the antenna structures given by equations and electromagnetic simulations. Moreover, by fabricating an NMHA and a human body phantom, the measured results are obtained. The self-resonant structure is ensured through the measured results.

Microstrip reconfigurable reflectarray antennas (RRAs) have great potential for advanced systems including satellite communications and the 6th generation (6G) wireless mobile communication networks. However, as a type of microstrip antennas, RRAs generally exhibit an intrinsic issue of narrow bandwidths. This issue is further deteriorated by complicated structures for phase shifting and DC supplying in RRAs. PIN diodes have been used in recent works to control the phases of RRA elements. However, modelling them is still costly and time consuming. In this work, a simple but novel method for modelling PIN diode SMP-1340-040 is developed by using waveguides and modified simulation approaches. Based on the obtained model, a broadband 1-bit unit cell using only one substrate is also proposed, and it achieves a simulated bandwidth of 40.6% and 33.8% for linear and circular polarizations, respectively. The experimental results show an excellent agreement with the simulation, which confirms the accuracy of the proposed PIN diode model. Moreover, the performances of the unit cell demonstrate that it can be used for designing RRAs in bands X and Ku.

This paper presents a multi-element multiple-input multiple-output (MIMO) antenna with self-isolation and flexible characteristics. The primary radiators of the proposed antenna consist of multiple ellipse-shaped patches arranged in an H-plane configuration. Self-decoupling is achieved by simultaneously different operating modes on the excited element (TM ₁₀ mode) and non-excited element (TM ₀₂ mode). The proposed method also shows strong extensibility. The measurements on the fabricated 4-element MIMO antenna demonstrate that the proposed decoupling method can improve the isolation by 14 dB. The antenna shows good MIMO diversity performances with respect to the envelope correlation coefficient and diversity gain. Additionally, the antenna also works effectively in when the substrate is bent, which contributes to significantly increasing the applicability of the proposed method in comparison with the other reported methods.

We develop a transmission line with a floating electrode (FE) arranged on a coplanar waveguide (CPW), and we propose using this transmission line to reduce the decay time of a microwave-band liquid crystal loaded device. Using the proposed CPW-FE structure makes it possible to control both the rise time and decay time by varying the applied bias field, thereby allowing the decay time to be reduced. In the 18 GHz band variable phase shifter we developed, we obtained a rise time of 75 ms and a decay time of 200 ms with a 500 μm wide CPW center conductor, a gap of 20 μm between the center conductor and ground plane, and a liquid crystal layer thickness of 50 μm. Under these conditions, the birefringence Δϵ′ of the liquid crystal was 0.23.