This paper presents a new design of a reconfigurable miscrostrip patch antenna based on a substrate-integrated waveguide (SIW). The antenna is resonant at the millimeter-wave (mmWave) 5G spectrum. The tuning technique consists of using a nematic liquid crystal (K15). An adjustable frequency band from 30.191 to 32 GHz is obtained, giving a tunable range of Δfr = 1.809 GHz. The maximum gain and efficiency reach the values of 7.61 and 9.07 dBi and 93 and 94%, respectively. The proposed SIW antenna loaded with liquid crystal was fabricated and tested. The experimental results correlated well with the simulation; however, the measured reflection coefficient plot shows a shift of the tuning range of 284 MHz, which is an acceptable outcome compared to simulation. A new approach of adopting the magnetic field as a technique to tune the resonance frequency has been used. The structure is characterized by its design simplicity, compactness, and fabrication process. The proposed antenna proves that the liquid crystal improves the performance of the antenna in the Ka band for 5G applications and satellite communication systems.

In this paper, flexible substrate integrated waveguide (SIW) resonators have been designed and fabricated on polyimide substrates for humidity sensing applications. The proposed SIW resonant cavity allows the resonator to obtain the maximum humidity sensitivity and meet the demand for flexible microwave sensing detection. Meanwhile, the humidity response performance can be further significantly enhanced by introducing nanodiamond (ND) sensing material. Three prototypes of ND-coated SIW sensors with different bending radii are measured to analyze their humidity sensing performance. The experimental results demonstrate that the proposed ND-coated SIW sensor with the minimum bending radius can achieve a maximum humidity sensitivity of 1.09 MHz/% relative humidity (RH) in the high RH region (>75.3% RH) and a low humidity hysteresis of 1.8% in the range of 11.3–97.3% RH. This study provides a promising candidate to realize flexible microwave sensors with excellent sensing performance.

A compact microstrip to substrate integrated waveguide transition feed tapered slot antenna array (1 × 4) with the elliptical patch is proposed and analyzed. The new approach is presented, employing a parasitic patch in the flared aperture to generate more radiation in the end-fire direction and improve field coupling between the arms. It boosts gain while maintaining overall size and low-frequency performance without using electrically thin dielectric substrates. To validate the designed approach, the proposed structure is fabricated and measured. The measured results show that the array provides impedance bandwidth of 40%, peak measured gain of 9.14 dBi, and radiation efficiency is 90% over the 8.5–12.5 GHz frequency band. A four-way feed network is also fabricated with the insertion loss of −6 ± 0.9 dB; the reflection coefficient is below −15 dB over the desired frequency range and only ±4° phase imbalance. The overall dimension of antenna array is 50 × 54 × 0.813 mm3 or ~1.6λ × 1.8λ × 0.027λ at 10 GHz.

A substrate integrated waveguide (SIW) based self-quadruplexing antenna and its design approach in Ku-band (12–18 GHz) is presented in this paper. This consists of splitting of TE220 mode of square-shaped SIW cavity by incorporating the two diagonal arrays of metallic vias. Accordingly, four orthogonal dominant mode triangular shape SIW cavity (DMTC) resonators are formed. This methodology ensures enhanced isolation. To achieve the broadside radiation, the cavity structure is fed using microstrip lines and rectangular slots are loaded on the top layer of each DMTC. The length and position of each rectangular slot being chosen such that quad-resonances are achieved at 13, 13.5, 14.3, and 15 GHz for the respective DMTC. The equivalent circuit model of the proposed design is also developed, and the tuning of each frequency band is analyzed without affecting the others. The proposed antenna is producing high isolation (>28 dB) among all four ports and a unidirectional radiation pattern with a high front-to-back ratio (>26.8 dB).

In this paper, a novel SIW microwave sensor is designed to accurately determine the broadband complex permittivity of medium loss and dispersive liquids using a number of higher order modes in 11–20 GHz. To achieve a higher accuracy in characterization, the sensor is equipped with some methods such as Photonic Band Gap method, slow-wave via, and a new feedline, which enhances the quality factor for the higher order TE1,0,n modes. The operating principle of this sensor is based on the cavity perturbation technique, in which the resonant properties of the cavity are utilized to extract the dielectric properties of liquid under test. To provide a method to decrease the LUT consumption, a winding microfluidic channel is designed and embedded in the cavity. The channel increases the interaction between the induced electric field and the LUT. The accuracy of different perturbation technique for determination of permittivity is compared with each other.

A novel tri-beam slot antenna array based on substrate integrated waveguide (SIW) technology is proposed in this paper. The beam forming network is a 3 × 3 Butler matrix consisted of three couplers and four phase shifters. A 1.76 dB coupler is located between two 3 dB couplers, with this arrangement; the input signal can be divided into three parts with the same amplitude and certain phase differences. Two parallel slots are cut off broadside of SIW transmission line, which constitutes the basic unit of the antenna array. A 3 × 2 slot antenna array is connected with this circuit. Three beams with the directions of −30, 0 and 30° are produced when different ports are excited, respectively. The S parameters, radiation patterns, and gains are simulated and measured, which show that it can be a candidate for multi-beam wireless communication systems.

The orthogonal LSM10 and TE10 modes that are supported by the image SINRD (iSINRD) guide and substrate integrated waveguide (SIW) is exploited to develop a planar millimeter-wave hybrid orthogonal-mode transducer (OMT) within the same dielectric substrate. The two output arms are iSINRD guide and an SIW. The proposed co-layered planar OMT belongs to a narrowband acute angle class. The design process is explained and measurements at 94 GHz are presented. No septa or step changes in thickness are required. Both modes are excited using WR10 transitions, where the transition of one mode is orthogonal to the other. Therefore, the OMT is fabricated as a back-to-back 4-port OMT; two inputs and two outputs for each mode respectively. The lateral dimensions of all guiding arms are 0.6 × 0.635 mm2. An insertion loss of around 1.2 dB is obtained for both LSM10 and TE10 modes, while isolation better than 17 dB is obtained for both modes (30 dB for the LSM10 mode).