In this paper, design, implementation, and experimental results of efficient, high-power, and multi-octave gallium nitride-high electron mobility transistor power amplifier are presented. To overcome the low optima source/load impedances of a large transistor, various topologies of a broadside-coupled impedance transformer are simulated, implemented, and measured. The used transformer has a flat measured insertion loss of 0.5 dB and a return loss higher than 10 dB over a decade bandwidth (0.4–4 GHz). The transformer is integrated at the drain and gate sides of the transistor using pre-matching networks to transform the complex optima source/load impedances to the appropriate impedances of the transformer plane. The measurement results illustrate a saturated output power ranged between 80 and 115 W with an average drain efficiency of 57% and gain of 10.5 dB across 0.6–2.6 GHz.

In this article, the design of a new dual-band impedance transformer with ultra-high transforming ratio (UHTR) is presented. The closed-form expressions are derived analytically using a lossless transmission-line theory. To practically validate the proposed design concept, two examples of dual-band transformer working at smaller and larger frequency ratios are designed for different load impedance of 500, 1000, and 1500 Ω. Finally, three prototypes of dual-band transformer with UHTR are designed, fabricated, and tested. For all these prototypes, different frequency ratios (two operating frequencies can be chosen arbitrarily) are considered. The measured return loss of the prototypes is better than 15 dB at all the operating frequencies. The measured results are matched very closely with the simulated results. This design is then extended to match a complex load at two different frequencies. The multi-band characteristic is obtained by decomposing a shorted stub into a stepped impedance section of the proposed structure. With the necessary derivation and analysis, a tri-frequency matching network is designed for a transforming ratio of 10.

Since last decades, microwaves have received tremendous attention as an interesting tool for material characterization. In general, standard microwave measurement methods require cutting and polishing of samples to put it in a suitable waveguide or cavity. However, several methods have been developed in order to permit a non-destructive measurement. A well-known method is based on coaxial open-ended waveguide, which is used as a sensor for dielectric characterizations. Moreover, with the requirement of new forms, developing mathematical model for each one is not convenient. Indeed, the complex structures required in the industrial field can be perfectly designed with high-performance three-dimensional software. Many attempts have been done to solve the conversion problem by proposing different algorithms. Nevertheless, they are sensitive for complex structure that contains transition part. In this paper, we propose a dielectric measurement method based on the use of coaxial waveguide. A novel algorithm for dielectric characterization of complex structures is also presented, which is based on the joint use of artificial neuronal networks and finite element method. The proposed algorithm aims to find the dielectric characterization for complex structures. Experimental evaluations applied to solid and liquid dielectrics confirm the validation of the proposed algorithm.

In this manuscript, serial-shunt of square ring resonators with step-impedance open circuited stub resonators to produce a new on-off switchable bandpass to bandstop response in the same ultra-wideband microstrip filter structure is proposed. The closed ring of series-shunt square ring resonators with a combine stubs are introduced to excite the bandpass response while bandstop characteristic excited when gaps are embedded in the corners of the square ring resonators. The main advantage of this microstrip filter is its capability to switch from bandpass-to-bandstop operation using open-short gap, respectively. A microwave simulator is utilized to show the switchable case by replacing Skyworks radio frequency diodes (RF-PIN) instead of those gaps. The entire filter models have been simulated using the computer simulation technology (CST) Microwave Studio. The computed results for the proposed filters were compared with the measured results of the both prototype structures (bandpass- and bandstop-filter). The codes also showed good agreement between them. Other advantages include being small in size, and low in effective cost.

This paper presents a new artificial neural network (ANN)-based radar data processing approach for the detection of breast cancers located inside fibro-glandular tissues. The aim is not the breast imaging but detecting tumors through ANN processing of data extracted from the radar signals measured around the breast. The proposed approach has been assessed using several realistic two-dimensional breast geometries derived from the models provided by the numerical breast phantom repository of the University of Wisconsin Cross-Disciplinary Electromagnetic Laboratory (UWCEM). The pulsed radar system was assumed to operate in the mono-static configuration. The obtained results showed the abilities of the proposed approach to detect, for any single radar trace, tumors located inside the fibro-glandular tissues with a sensitivity of 93%, a specificity of 90%, and an overall accuracy of 92%.

A miniaturized substrate-integrated waveguide (SIW) power divider with embedded filter response and arbitrary power-dividing ratio loaded by open complementary split-ring resonators (OCSRRs) is presented. In the proposed power divider, the miniaturization and filtering response are realized by a pair of OCSRRs, which are etched on the metal cover of the SIW structure. The design procedure indicates that the power division ratio can be adjusted by changing the locations of the output ports. In this study, three miniaturized filtering SIW power dividers with different power division ratios (1:1, 1:4, and 1:8) are implemented to evaluate the performance of the proposed structure on the size reduction. These power dividers (1:1, 1:4, and 1:8) have the overall sizes of 0.31λg × 0.14λg, 0.25λg × 0.17λg, and 0.25λg × 0.18λg, respectively. The measured results also agree well with the simulated results.

A novel small-size filtering power divider (PD) featured four-function integration is proposed. These four integrated functions are high-selectivity filtering, inherent DC block, high all-frequency isolation, and high-power applications. Using single-layer planar circuit technology, this proposed PD can be implemented easily. The measured results of a prototype show that it can operate at 2 GHz with a −10 dB matching bandwidth of 6% and all-frequency −15 dB isolation.

This paper is focused on explaining the radiation test in temperature performed on the Engineering and Qualification Model of the Medium Gain Antenna Radiofrequency (MGA-RFA) Assembly of ESA's BepiColombo mission. The goal of this program is to observe and study Mercury and its surroundings in a very demanding environment in terms of temperature and radiation. The MGA is an X-band two-axis steerable horn, which provides bidirectional communications between spacecraft and Earth as backup of the High Gain Antenna and also operates as primary communication link at several mission stages or conditions. The paper presents the measurement set-up for the qualification campaign of the antenna, where it was necessary to characterize the antenna in a representative thermal environment, and the results obtained from this test. Results of test up to 150°C show how gain and radiation pattern shapes are slightly affected by thermal stress, but without jeopardizing mission requirements. In addition, by analyzing correlation of this test with RF analysis in the same thermal conditions, it becomes possible to accurately extrapolate the MGA-RFA behavior up to temperatures of more than 500°C. This fact allowed the successful space qualification of this model.

This paper presents a wideband band-stop filter (BSF) structure designed by using planar technology. The proposed filter consists of a modified conventional band-stop structure with open stubs, inner T-inverted shape, and two input/output feed lines. Based on series of optimization and a specific design method, two compact filters with good electrical performance are obtained. In order to characterize the frequency response of the proposed filters, the performance is carried out numerically using two different solvers (Advanced Design System -Momentum and CST-MWS). Furthermore, in order to validate the conception approach, two circuits are designed, fabricated, and tested. Additionally, an equivalent circuit of the wideband BSF is built to estimate the electromagnetic simulation results for practical realization. The features of the design have a reduced size, wideband rejection, and higher insertion losses, which can be performed by adjusting the L-shaped stubs (23.25 × 2.2 mm2) toward the 50 Ω input and output ports. Two filters are designed, fabricated, and tested; one can be operated between an fractional bandwidth (FBW) of about 50% at a center frequency of 1.8 GHz, and the other can be switched from an FBW of 43.38% at a center frequency of 1.82 GHz. In addition, good agreement between the simulation and the measured results is achieved. The overall size of each filter is 43.4 × 34.5 mm2.

This paper proposes a novel T-shape electromagnetic bandgap (EBG) structure to suppress simultaneous switching noise (SSN) in mixed-signal systems. Noise is generated due to simultaneous switching multiple drivers in the digital ICs. It is called as SSN. It could propagate between power and ground planes of underlying PCB platform and interfere with the functionality of nearby RF/Analog ICs. So, the RF modules are isolated from the digital module for proper functioning of entire mixed-signal system. A high-impedance surface, called T-shape EBG has been implemented between digital and RF modules. It will exhibit the characteristics of bandgap for a wide frequency range to suppress the propagation of switching noise. A single unit-cell of T-EBG is periodically patterned over one side of the PCB and the other side is kept continuous. In this paper different characteristics of T-EBG have been simulated and verified with the measurement results. A 3 × 3 T-EBG layout provides an isolation of −40 dB from 0.72 to 6.39 GHz. A scaled version of T-EBG is used to shift the bandgap towards higher frequency range from 2.22 to 7.19 GHz. Also, a novel layout methodology has been proposed to broaden the bandgap from 2.02 to 18.84 GHz without reducing the thickness of dielectric substrate.

This paper compares the noise performance of two different types of time-domain microwave detection systems: a pulsed system and a pseudo-random noise sequence system. System-level simulations and laboratory-based measurements are carried out in the study. Results show that the effect of timing jitter is more significant on the measurement accuracy of the pseudo-random noise sequence system than that of the pulsed system. Although the signal power density of the pseudo-random sequence system is tens of dBs higher than that of the pulsed system over the frequency band of interest, the signal-to-noise ratio difference between these two systems can be just a few dBs or even smaller depending on the jitter level.

A meandered-dual-antenna structure is proposed for UHF radiofrequency identification (RFID) tag. It is composed of two independent antennas printed on the one side of the substrate board. One of the antennas is exclusively used for receiving and harvesting sufficient energy to the tag chip having the complex conjugate impedance of the receiving antenna. The other is for backscatter to enhance maximum differential radar cross-section with purely real input impedance, to enhancement the read range. The receiving antenna is formed by a rectangular loop and a parasitic meandered line. The rectangular loop is used as a feeding element for the meandered line. The backscattering antenna is made using a meandered dipole along with a thin rectangular strip. The input impedance of the receiving antenna is designed to be conjugate matched to the chip impedance (13.5-j110 Ω), whereas the input impedance of backscattering antenna alternatively switched to open and short circuit for modulating the backscattered field. The input impedance of receiving and backscattering antennas is measured using differential probe technique. The simulated and measured results are found in good agreement. It is also demonstrated that the read range of UHF RFID system increased considerably by using the dual-antenna structure.

A miniaturized Bagley Polygon power divider based on composite right/left-handed transmission line is presented. The composite right/left-handed transmission line and conventional microstrip transmission line are utilized to realize the 0° phase shift transmission line, which is used to replace the 180° transmission line of the conventional Bagley Polygon power divider. As a result, miniaturization is realized, without deteriorating the isolation between the output ports. The design equations are presented. This power divider shows advantages compared with other miniaturized ones. For verification, a miniaturized Bagley Polygon power divider is designed and fabricated. The 58.2% length reduction of the counterpart is realized. The measurement and simulation results show good agreement.

In this paper, a novel compact microstrip low-pass filter (LPF) with ultra wide stop band and sharp roll off, is proposed. In the proposed structure, a high impedance transmission line is loaded by compact microstrip resonant cells, which results in ultra wide stopband. The −3 dB cut-off frequency of filter is 1.5 GHz and the maximum insertion loss is <0.1 dB in the passband. The proposed LPF presents extremely wide stopband from 1.68 to 44 GHz, with more than the −20 dB attenuation level, which suppresses the 2nd to 29th harmonics with high rejection levels. The size of the proposed LPF is only 0.1 λg × 0.19 λg, which shows excellent size reduction. There is a good agreement between the simulated and measured results.

This paper outlines a new class of quad-band amplifier (QBA) realized using extended composite right- and left-handed coupled lines. The design procedure to reach the QB CLs with predefined frequency operations and characteristic impedance of their ports is clearly presented. Designed and fabricated QBA operation frequencies are $f_{b_{1}} = 2.9\,GHz$ and ${\rm \;} f_{b_2} = 4.3\,GHz$ (output port B) ${\bi \;} \; f_{f_1} = 3.8\,GHz\; $ and $\; \; f_{f_2} = 5\,GHz\; $ (output port C) and the proposed structure exhibits a matching (−10 dB) bandwidth of over 300 MHz in each operation frequency bands. In addition, the insertion loss is smaller than 1 dB. The length and the width of the proposed QBA are approximately 7.7 and 2.4 cm, respectively. To further demonstrate the idea, a QBA is successfully designed and fabricated. The simulated and measured results of the proposed QBA are presented to verify the proposed idea.

This paper presents a position gauging system of welding joints. While the principle measurement concept was already introduced by Schrattenecker et al. in 2014, here it is focused on different types of practically used welding materials. The sensor used is based on the frequency-modulated continuous-wave principle operating in the W-band. Position estimation (PoE) of different welding geometries is carried out with polarimetric scattering effects introduced by geometrical discontinuities. For the real-time calculation of the signal models a field simulation tool we developed is used. Aside from a variety of geometries, we introduce a geometrical optimization approach that increases the achievable accuracy of the measurement concept. The optimization and PoE of the different welding materials were examined in various simulations and the results were verified by measurements in the laboratory and in an industrial environment. Simulation and measurement were in good agreement.

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.

In this paper, we designed and developed a novel internal compact printed loop antenna for WWAN/WLAN/ISM/LTE smartphone applications. The proposed antenna is composed of a meander loop antenna and a capacitively coupled feeding line. It has a planar structure, with an overall dimension of 120 × 60 mm2, the antenna portion occupying a size of 20 × 60 mm2, which makes it suitable for practical smartphone applications. The results of our measurement reveal that the prototype antenna can provide two wide frequency bands of 712–1078 and 1757–2930 MHz, which cover multi-band for GSM850/GSM900/DCS1800/PCS1900/UMTS2100/IMT2000/WLAN2400/ISM2450/LTE700/LTE2300/ LTE2500. The antenna also shows good radiation characteristics and gain peaks for frequencies over the desired operating bands. We also studied the specific absorption rate (SAR) of the proposed antenna placed at the bottom of a mobile phone. The obtained SAR values are all below the SAR limit of 1.6 W/kg for the 1 g head tissue and 2.0 W/kg for the 10 g head tissue. We used CST Microwave Studio and Ansoft HFSS for the simulation and the design of the antenna and present in this paper the details of the design considerations, as well as the results on the reflection coefficient, the surface current distributions, the radiation characteristics, and the gain of the proposed antenna.

In this work, an electromagnetic (EM) model and a small-signal (lumped-element) model of a wafer-level encapsulated (WLE) radio frequency microelectromechanical systems (RF-MEMS) switch is presented. The EM model of the WLE RF-MEMS switch is developed to estimate its RF performance. After the fabrication of the switch, the EM model is used to get accurate S-parameter simulation results. Alternative to the EM model, a small-signal model of the fabricated WLE RF-MEMS switch is developed. The developed model is integrated into a 0.13 µm SiGe BiCMOS process technology design kit for fast simulations and to predict the RF performance of the switch from a pure electrical point of view. The 0.13 µm SiGe BiCMOS embedded WLE RF-MEMS shows beyond state-of-the-art measured RF performances in D-band (110–170 GHz) and provides a high capacitance Con/Coff ratio of 11.1. The results of the both EM model and small-signal model of the switch are in very good agreement with the S-parameter measurements in D-band. The measured maximum isolation of the WLE RF-MEMS switch is 51.6 dB at 142.8 GHz with an insertion loss of 0.65 dB.

In this paper, a new kind of admittance inverter and design of a switchable microstrip bandpass filter using composite right/left-handed (CRLH) cells has been presented. The proposed filter has two states (or passbands). One of the two passbands, is accessible at each time by on/off state of three PIN diodes. This filter is a three-pole, coupled resonator filter, composed of short-circuited shunt resonators. These resonators are coupled using admittance inverters. With regard to the characteristics of the equivalent circuit of CRLH cells, a new structure of admittance inverter (J-inverter) has been introduced. This novel J-inverter has PI-section equivalent circuit and it consists of both inductive and capacitive elements. In our work, the proposed J-inverter was mathematically studied and the switchable filter was simulated and implemented. The results of simulations for the first and second state of the filter, which are frequency bands of (Δ1 = 0.11 and f1 = 1.26 GHz) and (Δ2 = 0.12 and f2 = 1.5 GHz), are verified by measurements.