# Passive Planar Microwave Devices
## 2 Contributions
Specifically, they investigated dielectric parallel plate waveguides periodically loaded with Jerusalem cross slots in three configurations: conventional, mirror, and glide symmetry. Out of these three configurations, they demonstrated that the glide-symmetric structure is the least dispersive and has the most isotropic response. Furthermore, the glide-symmetric structure achieved the highest effective refractive index, which enables the realization of a broader range of electromagnetic devices. To illustrate the potential of this glide-symmetric unit cell, a [PERSON] fish-eye lens was designed to operate at 5 GHz. [PERSON] et al. [9] developed a fully transparent multiband antenna for vehicle communications. The antenna is coplanar-waveguide-fed to facilitate its manufacture and increase its transmittance. An indium-tin-oxide film, a type of transparent conducting oxide, was selected as the conductive material for the radiation path and ground plane, with a sheet resistance of 8 ohms/square. The substrate is glass with a relative permittivity of 5.5. The proposed antenna meets the frequency requirements for vehicular communications according to the IEEE 802.11p standards. Additionally, it covers the frequency bands from 1.82 to 2.5 GHz for LTE communications applied to vehicular networks. [PERSON] et al. [10] proposed a multilayer bandpass filter with high selectivity. To this aim, the discriminating coupling formed by slot-coupled quarter-wavelength and half-wavelength resonators introduced a zero at 36 (\(f_{0}\) is the center frequency), while the second harmonic was also suppressed due to the quarter-wavelength resonators. As a result of the multilayer structure, source-load coupling was introduced to improve selectivity. Then, an extra coupled line path was added with the same amplitude as the discriminating coupling path while they were out of phase. Thus, signal cancelation produced three extra transmission zeros, with a further improvement in selectivity and suppression performance. The design was validated by a manufactured prototype bandpass filter centered at 2.49 GHz with a fractional 3 dB bandwidth of 8.1%. [PERSON] et al. [11] designed a microwave planar cutoff probe to measure the cutoff frequency in a transmission (S21) spectrum. For real-time electron density measurement in plasma processing, three distinct types of probes were demonstrated: point-type, ring-type (RCP), and bar-type (BCP). Moreover, the work includes a computational characterization of an RCP and a BCP with various geometrical parameters, as well as a plasma parameter, through a commercial three-dimensional electromagnetic simulation. Among the investigated parameters, the antenna distance was found to be the most important parameter for improving the accuracy of both RCP and BCP. Finally,Herraiz et al. [12] proposed a new wideband transition from the microstrip line (MS) to ridge empty substrate integrated waveguide (RESIW), with a dielectric taper based on the equations of the superellipse. The new wideband transition presents simulated return losses in a back-to-back transition greater than 20 dB in an 87% fractional bandwidth, while in the previous transition, the fractional bandwidth was 82%, which supposes an increase of 5%. Furthermore, the transition presented simulated return losses greater than 26 dB in an 84% fractional bandwidth, while the measured return loss was above 14 dB with an insertion loss lower than 1 dB throughout the band. Conceptualization, [PERSON]-R. and A.F. [PERSON]; Writing--original draft preparation, A.J.M. [PERSON] and [PERSON]; writing--review and editing, A.J.M.-R. and [PERSON]. All authors have read and agreed to the published version of the manuscript. This work was supported by Grant PID2020-116739 GB-I00 funded by MCIN/ AEI/10.13039/501100011033. The authors declare no conflict of interest.