A Review on SIW and Its Applications to Microwave Components

Demonstration of bound states in the continuum in substrate integrated waveguides

Substrate integrated waveguides (SIWs) components play a crucial role in microwave devices fabricated by printed circuit board (PCB) technology. Bound states in the continuum (BICs) have high-quality factors that approach infinity. So far, there is little research on BICs in SIWs. Therefore, we studied a symmetry-protected BIC generated by the coupling between SIW and SIW resonators to fill this gap. Using the revised coupled mode theory (CMT), we explored the mechanism of resonance generation in this system. In addition, the effect of the geometrical parameters on the resonance is also investigated and higher Q3dB factors are obtained. The findings offer new insights into the design of BIC devices by traditional PCB technology, thus contributing to future applications in the integrated circuits field.

Textile Antenna Sensor in SIW Technology for Liquid Characterization

This study showcases the creation of an innovative textile antenna sensor that utilizes a resonant cavity for the purpose of liquid characterization. The cavity is based on circular substrate integrated waveguide (SIW) technology. A hole is created in the middle of the structure where a pipe is used to inject the liquid under test. The pipe is covered by a metal sheath to enhance the electromagnetic field's penetration of the tube, thus increasing the device's sensitivity. The resonance frequency of the proposed system is altered when the liquid under test is inserted into the sensitive area of the structure. The sensing of the liquid is achieved by the measurement of its dielectric properties via the perturbation of the electric fields in the SIW configuration. The S11 measurement enables the extraction of the electromagnetic properties of the liquid injected into the pipe. Specifically, the dielectric constant of the liquid is determined by observing the resonance frequency shift relative to that of an air-filled pipe. The loss tangent of the liquid is extracted by comparing the variation in the quality factor with that of an air-filled pipe after eliminating the inherent losses of the structure. The proposed SIW antenna sensor demonstrates a high sensitivity of 0.7 GHz/Δεr corresponding to a dielectric constant range from 4 to 72. To the best of our knowledge, this article presents for the first time the ability of a fully textile SIW cavity antenna-based sensor to characterize the dielectric properties of a liquid under test and emphasizes its differentiating features compared to PCB-based designs. The unique attributes of the textile-based antenna stem from its flexibility, conformability, and compatibility with various liquids.

Application of Compact Folded-Arms Square Open-Loop Resonator to Bandpass Filter Design

Folded-arms square open-loop resonator (FASOLR) is a variant of the conventional microstrip square open-loop resonator (SOLR) that facilitates further device size miniaturization by having the two arms of the conventional SOLR folded inwards. This paper highlights the benefits of this brand of compact SOLR by implementing a five-pole Chebyshev bandpass filter (BPF) using compact FASOLR. The test BPF is presented, with centre frequency of 2.2 GHz, fractional bandwidth of 10%, passband ripple of 0.04321 dB, and return loss of 20 dB. The design is implemented on a Rogers RT/Duroid 6010LM substrate with a dielectric constant of 10.7 and thickness of 1.27 mm. The filter device is manufactured and characterised, with the experimentation results being used to justify the simulation results. The presented measurement and electromagnetic (EM) simulation results demonstrate a good match. The EM simulation responses achieve a minimum insertion loss of 0.8 dB and a very good channel return loss of 22.6 dB. The measurement results, on the other hand, show a minimum insertion loss of 0.9 dB and a return loss of better than 19.2 dB. The filter component has a footprint of 36.08 mm by 6.74 mm (that is, 0.26 λg × 0.05 λg), with λg indicating the guided wavelength for the 50 Ohm microstrip line impedance at the centre frequency of the proposed fifth-order bandpass filter.

Inverted Microstrip Gap Waveguide Filtering Antenna Based on Coplanar EBG Resonators

A new simple design of an inverted microstrip Gap Waveguide filtering antenna integrated with two stopband filters is proposed in this work. In order to simultaneously provide filtering and radiating functions, we use the direct integration approach to cascade two periodic sets of coplanar coupled EBG resonators with a slot antenna. The analysis shows that the filters can be easily adjusted in the same feeding layer of the antenna, without extra circuitry and without modifying the lines. EBG-filters are compact and offer great flexibility in determining the frequency, width and selectivity of the rejected bands. Experimental results for an X-band filtering antenna prototype are provided showing a 7.3% transmission band centered at 10.2 GHz and a realized gain peak of 2.1 dBi. The measurements demonstrate the filtering capability of the proposed antenna, achieving rejection levels greater than 12 dB and 20 dB for the bands below and above the operation band. The proposed low-complexity design offers good performance as a filter and as an antenna, showing the essential advantages of the Gap Waveguide Technology, including low losses, self-packaging and limited cost. This work demonstrates the possibility of integrating the new coplanar EBG-filters into future Gap Waveguide antenna designs to avoid unwanted radiation, to reduce interfering signals or to provide high isolation in multiband systems.