This paper presents a wideband, low-cost, high-performance, and continuous phase shifter for millimeter-wave (mm-wave) phased array systems. Its operational principle is based on modifying the propagation mode of a grounded coplanar waveguide (GCPW) line by placing a high dielectric constant slab over the GCPW line. The propagation constant and hence the phase shift is varied by changing the air gap height between the GCPW line and the dielectric slab. As a proof of concept, a piezoelectric transducer is used to precisely control this air gap height. A printed circuit board-based phase shifter prototype has been designed, fabricated, and tested at two different frequency bands (19–21 and 28.5–30.5 GHz), which are the downlink and uplink bands, respectively, of the Ka-band two-way satellite communication system. A continuous and almost linear phase–voltage characteristic has been achieved experimentally with average phase shift variations 170° and 260° over the two bands, respectively. The footprint of the proposed phase shifter is 2.1 mm×3 mm, which is quite small and suitable for low-profile mm-wave applications. The average insertion losses over the two bands are <0.53 and 2.35 dB with very low variations±0.22 and ±0.35 dB, respectively.

Different configurations of leaky-wave antennas (LWAs) based on graphene metasurfaces are studied. The electronic properties of a graphene metasurface in the low THz range are investigated in details in order to discuss the reconfigurability features of the presented structures. Simple exact formulas for evaluating the ohmic losses related to the surface plasmon polariton (SPP) propagation along a suspended graphene sheet, and the relevant figures of merit of SPP propagating over a generic metasurface are given. Such formulas allow us to explain the low efficiency of reconfigurable antennas based on SPPs along graphene metasurfaces. Then, the radiative performance and relevant losses of graphene Fabry–Perot cavity antennas (FPCAs) based on non-plasmonic leaky waves (LWs) are investigated and compared with previous solutions based on SPPs. In particular, a single-layer structure, i.e. a grounded dielectric slab covered with a graphene metasurface, and a multilayered structure, i.e. a substrate–superstrate antenna in which the graphene metasurface is embedded at a suitable position within the substrate, are considered in detail. The results show that the proposed LW solutions in graphene FPCAs allow for considerably reducing the ohmic losses, thus significantly improving the efficiency of the proposed radiators.

We review the main results of the development of whispering gallery mode (WGM) resonators and their unique applications due to their quasi-optical functionality. Several types of advanced WGM resonators are proposed by the authors. The theoretical results are described for the resonators with an analytical solution of the electromagnetic problems. Special emphasis is given to the interaction of moving charged particles and waves of cylindrical resonators. Important aspects are described concerning the developed sapphire resonators, for which an exact solution can only be found by using specially designed computer program products. A separate section of the paper is devoted to application aspects of the WGM resonators. In particular, it describes advanced solutions for overcoming the problems of measuring the small microwave (MW) surface impedance of unconventional superconductors in the form of large-area thin films and small samples under study. In addition, a demonstration of accurate complex permittivity measurements of small volumes of lossy liquids is provided. Special emphasis is given to highly stable MW signal sources, namely Ka-band transistor-based feedback oscillator and solid-state maser WGM oscillators. Recently obtained results are presented of experimental studies of the auto-oscillatory system developed on the basis of the WGM resonator with relativistic electron beam.

This paper presents a new class of quasi-elliptic pass-band filters in substrate-integrated waveguide technology, which exhibits compact size and modular geometry. These filters are based on mushroom-shaped metallic resonators, and they can be easily implemented using a standard dual-layer printed circuit board manufacturing process. The presented filters exploit non-resonating modes to obtain coupling between non-adjacent nodes in the case of in-line geometry. The resulting structure is very compact and capable of transmission zeros. In this work, the singlet configuration is preliminarily investigated, and a parametric study is performed. The design of three-pole, four-pole, and higher-order filters is illustrated with examples and thoroughly discussed. A four-pole filter operating at the frequency of 4 GHz has been manufactured and experimentally verified, to validate the proposed technique.

A robust and tuneless micromachined waveguide diplexer operating in the frequency range 71–86 GHz is here presented. The diplexer is based on multiple coupled cavities and it is manufactured using micromachining technology on two staked silicon layers. The diplexer consists of two filters combined to a common waveguide port via an E-plane T-junction. The two eight-order band-pass filters are centered at 73.5 and 83.5 GHz. The fractional bandwidths for two bands are 8.8 and 7.8% at higher- and lower-band, respectively. The measured insertion loss is below 0.7 dB for both the filters and the diplexer isolation is better than 55 dB, as required. The proposed technology allows for a very compact device (<20 × 20 × 1.5 mm) and the first prototypes were proved to be very robust to manufacturing tolerances and environmental tests, thus leading to an excellent tuneless manufacturing yield in future production. The diplexer will be employed in next generation terrestrial radio-link communications front-ends.

This paper proposes a compact, low-loss, and low-cost phase shifter for millimeter-wave/sub-THz applications. The basic idea is to perturb the propagation constant of a high resistivity silicon image guide by high-dielectric constant barium lanthanide tetratitanates (BLT) ceramic loading. Three different BLT ceramic samples have been tested. The measured maximum phase-shift variation reaches 150° at 100 GHz with an average insertion loss of 2.85 dB and an insertion loss variation <0.7 dB for a sample of a 5-mm length. The proposed phase shifter has a bandwidth from 95 to 105 GHz. A low-cost fabrication technology has been developed and used to realize this phase shifter.

A tunable substrate-integrated waveguide phase shifter using low-temperature co-fired ceramic (LTCC)-technology is presented in this paper. By changing the effective permittivity in the liquid crystal (LC)-filled waveguide, the differential phase can be tuned continuously. This is achieved by means of an analog signal applied to the electrodes, surrounding the LC. The design allows for precise tuning of the differential phase, which is proven with a Monte Carlo measurement resulting in phase errors of less than 3° at 28 GHz. Besides that, the ambient temperature dependency of the module is shown. The phase shifter has a high integration level and can be included into a complete and lightweight single-phased array antenna module. The phase shifter is realized with a high level of integration which is available through the multilayer process of the LTCC. It has a length of 50 and provides a differential phase shift of more than 360° at 28 GHz. The figure of merit for tunable phase shifters is >40°/dB.

In this paper, we present the first ridge-gap waveguide resonator made with a polymer base. It is designed for the frequency range 220–325 GHz, and is fabricated solely using a Au coated two-layer SU8-based process. The design is based on previous work done with Si. The new process has advantages such as fewer and cheaper process steps. The SU8 ridge-gap waveguide resonator is made in order to obtain attenuation characteristics via the measured Q-factor of the resonator. The ridge-gap waveguide resonator has the same dimensions as the previous one fabricated in Si, and the same thickness of the Au coating. The SU8-based resonator shows an attenuation loss of 0.41 dB/mm at 282.2 GHz compared to the Si-based resonator with an attenuation loss of 0.043 dB/mm at 283.5 GHz. This makes the SU8 process a more cost-effective alternative to the Si process

The paper presents millimeter-wave (mm-wave) signal sources using a hetero-integrated InP-on-BiCMOS semiconductor technology. Mm-wave signal sources feature fundamental frequency voltage-controlled oscillators (VCOs) in BiCMOS, which drive frequency multiplier–amplifier chains in transferred-substrate (TS) InP-DHBT technology, heterogeneously integrated on top of the BiCMOS wafer in a wafer-level bonding process. Both circuits are biased through a single set of bias pads and compact low-loss transitions from BiCMOS to InP circuits and vice versa have been developed, which allows seamless signal routing through both technologies exhibiting 0.5 dB insertion loss up to 200 GHz. One VCO operates at 82 GHz with a tuning range of 600 MHz and an output power of approximately 8 dBm. A frequency doubler combined with this VCO circuit delivers 0 dBm at 164 GHz and a frequency tripler with a similar VCO delivers −10 dBm at 246 GHz. Another hetero-integrated W-band doubler–amplifier circuit demonstrates 12.9 dBm saturated output power with 5.9 dB conversion gain at 96 GHz. A direct comparison of the TS InP-DHBT MMIC with either silicon or traditional AlN carrier substrates shows the favorable properties of the hetero-integrated process discussed here. The results demonstrate the feasibility of hetero-integrated circuits operating well above 100 GHz.

New wireless wearable monitoring systems integrated in professional garments require a high degree of reliability and autonomy. Active textile antenna systems may serve as platforms for body-centric sensing, localisation, and wireless communication systems, in the meanwhile being comfortable and invisible to the wearer. We present a new dedicated comprehensive design paradigm and combine this with adapted signal-processing techniques that greatly enhance the robustness and the autonomy of these systems. On the one hand, the large amount of real estate available in professional rescue worker garments may be exploited to deploy multiple textile antennas. On the other hand, the size of each radiator may be designed large enough to ensure high radiation efficiency when deployed on the body. This antenna area is then reused by placing active electronics directly underneath and energy harvesters directly on top of the antenna patch. We illustrate this design paradigm by means of recent textile antenna prototypes integrated in professional garments, providing sensing, positioning, and communication capabilities. In particular, a novel wearable active Galileo E1-band antenna is presented and fully characterized, including noise figure, and linearity performance.

In this paper, the design methodology of a flat reflector composed with standard dielectric material and using transformation electromagnetics (TE) is presented. First, the mathematical relation between a flat reflector and a parabolic one is described. The TE principle is then described. Some realization issues are highlighted, leading to approximations and compromises in order to design a more realistic structure. In this way, a flat reflector made only with standard dielectric materials is presented, using an original method to achieve the desired spatial permittivity variation. The simulation results of different configurations for the flat reflector are presented and compared to classical solutions in order to prove the thickness reduction and the improvement of radiation characteristics in terms of gain and half-power beamwidth.

The silicon/porous silicon (PS) hybrid substrate is an interesting candidate for the monolithic integration of radiofrequency (RF) circuits. Thus, passive components can be integrated on the insulating PS regions close to the active devices integrated on silicon. Regarding silicon, hybrid substrates allow the improvement of RF circuits performances. To demonstrate it, coplanar waveguides have been integrated on glass, silicon, and localized PS substrates. The characterization results show that the substrate losses are reduced with PS.

This paper presents a novel technology for the implementation of substrate-integrated waveguide (SIW) structures, based on a paper substrate and realized by an inkjet-printing fabrication process. The use of paper permits to implement low-cost microwave structures and components, by adopting a completely eco-friendly implementation technology. SIW structures appear particularly suitable for implementation on paper, due to the possibility to easily realize multilayered topologies and conformal geometries. In this paper, SIW passive components, and antennas (including straight interconnects, band-pass filters, and slotted-waveguide antennas) are proposed for the first time. The design of the components, the steps of the fabrication process, and the experimental characterization of the prototypes are reported in this paper.

Emerging intrinsically tunable film bulk acoustic wave(BAW) resonators allow the development of new generation reconfigurable and agile microwave circuits. In this paper, we demonstrate the enhancement of tunable performance of the high Q-factor BaxSr1−xTiO3 BAW – solidly mounted resonators (BAW–SMR) by varying Ba concentration. The Ba0.5Sr0.5TiO3 BAW–SMR reveal tunability of series resonance frequency up to 2.4%, electromechanical coupling coefficient up to 7.5% and rather high Q-factor, up to 250 at 5.3 GHz. Correlations between the measured electroacoustic parameters are analyzed using the theory of dc field-induced piezoelectric effect in paraelectric phase ferroelectrics. Higher coupling coefficient and tunability of resonance frequency of the Ba0.5Sr0.5TiO3 BAW–SMR are associated with higher tunability of permittivity. Strong anisotropy in field-induced piezoelectric effect is predicted with highest coupling coefficient in (001) direction of the BaxSr1−xTiO3 films. It is also shown that the tunability of series resonance frequency of Ba0.5Sr0.5TiO3 BAW–SMR is limited by relatively high and negative nonlinear electrostriction coefficient which is found to be m ≈ −4·1010 m/F. The BAW–SMR Q-factor is limited significantly by extrinsic acoustic loss associated with wave scattering at reflection from relatively rough top interface. The results of analysis show possible ways of further improvement of the performance of tunable BAW–SMR.

We present detailed results of the self-consistent analysis of carbon nanotube (CNT) field-effect transistors (FET), previously extended by us to the case of multi-walled/multi-band coherent carrier transport. The contribution to charge transport, due to different walls and sub-bands of a multi-walled CNT, is shown to be generally non-negligible. In order to prove the effectiveness of our simulation tool, we provide interesting examples about current–voltage characteristics of four-walled semi-conducting nanotubes, including details of numerical convergence and contribution of sub-bands to the calculation.