In this work, an optimized broadband method using multilayer transmission lines to characterize dielectric permittivity and loss tangent of material samples is presented. For this purpose, a microstrip line loaded with a piece of the selected dielectric to be characterized is used. From two-port measurements, and using different length lines, the propagation constant can be obtained. To minimize random errors and to improve the accuracy, an overdetermination of the method increasing the number of lines measured and a criterion to choose the optimal line lengths is considered. First, the measurement method itself is applied to uncovered microstrip lines and an accurate model of the substrate is obtained. Second, the lines are covered with several materials, made by fused deposition modeling (FDM) additive manufacturing technique, such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), high impact polystyrene (HIPS), thermoplastic polyurethane (TPU), copolyester (CPE), FLEX, polyethylene terephthalate glycol (PETG), and nylon. A model of the transmission line considering the cover is developed, and an electromagnetic (EM) simulator is used to indirectly determine the cover material electrical parameters. Results show excellent agreement with EM simulations in the 0.1-67-GHz frequency band, so they assess the suitability of the proposed method.

This paper explains the non-idealities that arise when using PIN diodes at millimeter-wave frequencies and the important limitations that they bring in classical configurations of 1-bit slotline reconfigurable unit cells. A robust solution is proposed where a single PIN diode is inserted inside a ring topology. The slotline unit cell is analyzed through a circuit-model approach. Its performance is compared with a unit cell based on a single slotline, which also includes a PIN diode, referred to as classical configuration. For experimental assessment, a circuit prototype is fabricated to verify the phase difference of both PIN diode states in each unit cell configuration. The measured results reveal that the slotline unit cell with ring configuration provides a 180° ± 20° reflection phase difference from 36.3 GHz to 45 GHz (21.4% relative bandwidth). Finally, the proposed slotline unit cell with ring topology is measured in a complete array to assess its performance in periodic and quasi-periodic environments. The measurements confirm the 1-bit behavior for both normal and oblique incidence with losses less than 2 dB. Therefore, this enables the design of wideband 1-bit reconfigurable reflectarrays and RIS in this frequency range.

The design of dual-band bandpass filters consisting of series short-circuited wire-bonded multiconductor transmission lines and shunt open stubs is thoroughly carried out in this paper. Two different configurations are studied, and closed-form analytical design equations are derived to synthesize Chebyshev filtering functions. A novel, simplified, and time-saving synthesis procedure to design dual-band filters with narrow or moderate broad bandwidths is finally presented, attending to the required final specifications and the physical and manufacturing limitations. The usefulness and validity of the proposed analytical equations are illustrated by designing, manufacturing, and measuring three different prototypes, showing an excellent agreement between analytical and measured results.

This work employs a new approach to analyze coupled-resonator circuits to design and manufacture a fully metallic dual polarization frequency selective surface (FSS). The proposed filtering structure is composed of a series of unit cells with resonators fundamentally coupled along the z -direction and then repeated periodically in the xy -plane. The fully metallic cascaded unit cell is rigorously analyzed within an infinite periodic environment as a coupled-resonator electromagnetic (EM) circuit. The convenient design of the EM resonators makes it possible to push the evanescent EM field through the metallic structure in the desired frequency band for both polarizations. An FSS prototype is manufactured and measured, and good agreement is found between the simulation results and the final prototype.

This manuscript introduces an analytical framework for the design of reconfigurable metasurfaces rooted in 2D periodic structures. Incorporating lumped elements into the model streamlines the design process for such devices, offering significantly improved efficiency compared to designs reliant on full-wave software. The theoretical framework, founded on Floquet modal expansions, also guarantees robust performance even under oblique incidence conditions, far beyond the onset of the first grating lobe. In practical applications, an absorber has been devised by integrating a resistor into the model. Nevertheless, circuit analysis extends the possibilities for crafting more intricate structures utilizing diodes or tunable varactors, enabling the design of phase shifters, polarizers, and reconfigurable intelligent surfaces (RIS).