The rapid advancement of the miniaturization techniques for high-frequency transceivers, radars, and communication systems operating in the D-band (110–170 GHz) has positioned circular dielectric waveguides (CDWGs) as a promising transmission-line alternative. Yet, their potential has not been fully exploited. This work fills this gap by introducing novel, compact CDWG-fed lens antenna solutions that deliver excellent gain and impedance matching performance. A low-loss, low-cost, and flexible CDWG made of low-density polyethylene is used to excite dielectric lens antennas of various sizes, contours, and materials, enabling a systematic evaluation of the impact of lens geometry on antenna performance. Through detailed electromagnetic simulations and experimental validations, lenses of different sizes and contours are designed. The proposed CDWG-lens configuration achieves measured broadband matching better than 17 dB and stable high gain across 115–130 GHz. Measured gains of 21–23 dBi for lenses with diameter of 10.6 mm and gain factor of 27–28 dBi for lenses with diameter of 20 mm confirm the high aperture efficiency and novelty of this approach. A strong agreement between the simulation and the measurement results is also observed. These compact and efficient lens antennas combined with the advantages of CDWG feed, can be integrated as a part of advanced system applications in the D-band frequency range like radar sensing and communications.

In this paper, we report an on-wafer High-Electron-Mobility transistor characterization method over a large frequency band [250 MHz–1.1 THz]. The transistor’s coplanar accesses were optimized to enable high-frequency measurement of the devices up to 1.1 THz. The characterization method implements an on-wafer multiline Thru-Reflect-Line calibration kit fabricated on indium phosphide (InP) substrate validated using comparisons between simulations and measurements of coplanar waveguide (CPW) devices. An 80-nm gate length InAlAs/InGaAs/InAs InP-HEMT was fabricated using the optimized transistor accesses then it was measured over the [250 MHz–1.1 THz] frequency band using the developed on-wafer characterization method. It is important to mention that the same transistor was measured on six different on-wafer test benches [250 MHz–110 GHz], [140–220 GHz], [220–325 GHz], [325–480 GHz], [500–750 GHz], and [750–1100 GHz]. The S-parameter measurement results show good continuity between the six measured frequency bands. Observations on the extracted gain measurements and a comparison between the measured and [250 MHz–110 GHz] extrapolated cut-off frequencies are also provided.

Acute respiratory distress syndrome (ARDS) is a critical lung condition caused by trauma or infection. This study explores the development and evaluation of human lung phantoms to investigate the feasibility of using microwave frequencies for ARDS detection. Both physical semisolid phantoms and their numerical models were developed in inflated and deflated states to replicate the dielectric properties of healthy and affected lungs. Three phantom sets with varying water and air content were fabricated to simulate different stages of respiratory distress. The geometric parameters of the phantoms were derived from CT scans of 166 ARDS patients. Dielectric permittivity and conductivity were measured using a Keysight N1501A dielectric probe over a 0.5–13 GHz range, showing strong agreement with IFAC’s reference data. To validate the models, horn antennas operating between 8.2–12.4 GHz were used to measure S-parameters (S11 and S21) in both physical and numerical phantoms. The results demonstrated consistent changes in transmission and reflection characteristics corresponding to variations in lung volume and dielectric properties. These findings support the potential of microwave imaging as a non-invasive tool for early ARDS detection by effectively distinguishing between healthy and distressed lung states based on measurable electromagnetic response.

In this paper, the design of frequency reconfigurable planar antenna by incorporation of metasurface superstrate (FRPA-MSS) is presented using an artificial neural network. The dual-layer radiating structure is created on a 1.524 mm thick Rogers RO4350B substrate board (εr = 3.48, tan δ = 0.0037). The candidate antenna is designed and analyzed using a high-frequency structure simulator (HFSS) tool. The transfer matrix method is employed for the successful retrieval of electromagnetic properties of the metamaterial. Frequency reconfiguration is achieved by placing the metasurface superstrate onto the rectangular patch antenna. A simplified ANN approach has been employed for the design of metasurface incorporated proposed antenna. Presented prototypes are characterized through experimental measurements. It is found from the practical observations that the proposed antenna effectively reconfigures the tuning range from 5.03 to 6.13 GHz. Moreover, the presented antenna operates efficiently with agreeable gain, good impedance matching, and stable pattern characteristics across the entire operational bandwidth. The experimental results obtained validate the simulated performance.

Coupled-mode theory is applied to obtain an analytic form of scattering parameters for a class of transmission line metamaterials with antisymmetric split-rings. The same structure is modeled with equivalent circuit, which includes electric and magnetic coupling with the line and inter-resonator coupling. Modified even/odd analysis is used to obtain scattering parameters from the equivalent circuit. These two methods are shown to be equivalent in a narrow band, and their constants related. The obtained results are compared with full-wave simulations and measurements, and it is shown that both methods give accurate approximation in one octave frequency band. The derived analytic expressions are suitable for study of resonant phenomena, with potential practical applications for filters, phase shifters, delay lines, and sensors.