International Journal of RF and Microwave Computer-Aided Engineering

In this paper, a convenient process for the fabrication of flexible liquid metal mesh films (LMMF) is proposed first. Then, the light transmittance and square resistance characteristics of LMMF are studied theoretically and experimentally. The light transmittance of the LMMF can reach 85% when the line width and spacing are 50 μm and 1000 μm, respectively. Furthermore, as an example of LMMF, a coplanar waveguide loop antenna is designed and fabricated that contains an LMMF with a line width of 50 μm and a line spacing of 500 μm. The measured square resistance and transmittance for the LMMF are 0.0456 Ω/sq and 72%, respectively. The measured peak gain of the antenna is 3.38 dBi while the average efficiency is 61%. The antenna’s working frequency covers most of the S-band, C-band, and X-band, as well as multiple channels of fifth generation (5G) communication. Therefore, the antenna can be used in fields such as radar and mobile communication. Uniquely, the fabricated antenna performs well in terms of light transmission, conductivity, and flexibility. In particular, it remains stable in stretching and bending deformation. As a highly light-transmissive stretchable flexible antenna, the antenna is equipped with various functions such as concealability, conformability, and reconfigurability. This LMMF-based antenna has good prospects for applications in the fields of flexible electronics and transparent electronics.

This paper presents a novel 3-D-printed circularly polarized (CP) open-ended waveguide (OEW) antenna array. It aims to provide a lightweight scheme for OEW array design and concurrently address the high fabrication complexity problem of conventional OEW arrays. To realize these, the proposed design adopts dielectric 3-D printing technology to build the main body of the array and employs electroplating to form the waveguide walls. To attain CP radiation, an in-built antipodal exponential groove polarizer is proposed and applied to a square waveguide. With the perturbation of the grooves, degenerate modes and can be excited simultaneously, and their differential phase can be 90 degrees, resulting in CP radiation. Moreover, a novel matching cube based on effective medium theory (EMT) is proposed for the antenna to mitigate the reflections at the waveguide aperture and therefore realize good impedance matching. To validate the design idea, prototypes for a single element and a 22 array were fabricated and measured. Experimental results show that their weights are 15 and 76 grams, and their axial ratio bandwidths (ARBWs) are 16% (5.45-6.4 GHz) and 11.1% (5.52-6.17 GHz), respectively.

In this paper, we investigate a low-scattering antenna array consisting of two different low radar cross-section (RCS) antenna elements. The low-scattering performance is achieved by broadband in-band absorbing with x (TM)-polarization and phase cancellation with y (TE)-polarization at normal incidence and a special shape design at grazing incidence. We demonstrate the effectiveness of the proposed antenna array through simulations and measurements. Compared with the reference one, the results show that it can achieve remarkable wideband monostatic RCS reduction from 3.3 to 8 GHz with a maximum reduction value of 23.5 dB at normal incidence and from 4.4 to 12.5 GHz with a peak reduction value of 15.3 dB at grazing incidence. Moreover, a low-RCS carrier is codesigned with the antenna array to verify the low-scattering property, which indicates that the proposed antenna array has a great potential for use in various application scenarios.

This paper presents a wideband dual-polarized filtering antenna with high suppression level and wide stopband. In the proposed antenna, the driven patch operates in a TM10 mode with an inherent radiation null caused by a higher mode TM12. Four dual-strip structures connected with the feeding probes are placed below the driven patch to achieve the capacitive coupling, thus resulting in a low-frequency radiation null with a sharp roll-off rate. The introduction of the parasitic patch and strips generates an in-band resonance and two high-frequency radiation nulls, which widens the upper stopband. Four slots are etched on the driven patch to excite the third resonance, thus achieving the wide operation band. The prototype of the proposed antenna is fabricated. With four controllable radiation nulls, the out-of-band suppression levels are above 29 dB in low-frequency band greater than 1 GHz and above 21 dB in high-frequency band up to 7 GHz, respectively. Due to the three in-band resonances, a wide impedance bandwidth of 2.93-3.96 GHz with a fractional band of 30% is obtained. With the rotational symmetry structure driven by differential probes, the proposed dual-polarized antenna has a cross-polarization ratio better than 28 dB, a high polarization isolation above 43 dB, and a good peak gain about 9.9 dBi.

A novel surface wave (SW) launcher design for power line fault detection is presented in this paper. The launcher is capable of converting TE₁₀ to TM₀ mode and exciting SW signal at 5.5 GHz frequency with high efficiency, on a single conductor line. The average attenuation of 2 dB/m and front to back ratio of 19 dB are observed and verified by simulation and experiments. Effect of bend, nearby obstacles, and extra wire connection on SW propagation is also investigated by experiments, and corresponding S-parameter results are presented. The optimization of launcher design with dielectric window and conical back plate is also demonstrated. The proposed launcher is compact and lightweight and can be easily installed without damaging the conductor line. Close structure makes it capable of withstanding outdoor environmental conditions. Using this launcher, microwave signal can be efficiently transmitted and received over existing conductor lines such as live power lines, pipes, and HVAC ducts, and it can be used in applications such as power line communication, fault detection, and permittivity measurement.

This paper presents a compact quadrature coupler with a tunable frequency and power-dividing ratio. Wide tunable frequency and power-dividing ratio are achieved by using the novel tunable unit instead of the transmission line sections in a traditional varactor-based quadrature coupler. Closed-form equations are derived for design parameters. For verification, a quadrature coupler is designed based on the given parameters, which demonstrate the tunable frequency of 2.0 GHz to 6.0 GHz and the tunable power-dividing ratio of -20 dB to 7.2 dB at 3 GHz. Finally, a microstrip tunable quadrature coupler is fabricated and measured. The measurements agree well with simulations. Under the frequency-tunable state, the measured 3-dB working frequency of this coupler can be continuously adjusted from 2.0 GHz to 4.7 GHz. And during the adjustment process, the return loss and isolation are always >15 dB. In the power-dividing ratio-tunable state, the adjustment range of the measured power-dividing ratio is from -14 to 6.0 dB at 3 GHz. Moreover, the return loss and isolation are always maintained at >20 dB.