A broadband permeability measurement method based on the full-wave electromagnetic (EM) analysis of a non-reciprocal transmission line is presented. The dispersion diagram for the first significant modes inside the ferrite loaded section of the line is obtained. The presence of magnetostatic modes generated by the magnetized ferrite inside the line is verified. Using a mode matching technique, the theoretical scattering parameters (S-parameters) of the transmission line are calculated. The full-wave analysis is validated with measurements of material properties in limit cases.

A new design of reconfigurable sub-nanosecond pulse generator (PG) with pulse shape selection ability is presented in this paper. Step recovery diode is used as the pulse sharpening device and the pulse shaping circuit consists of a controllable RC differentiator in which a single PIN diode is embedded, which provides two different switchable pulse shaping performances. The realized PG has a compact (10 × 12 mm2) simple structure and is easy to implement while generating Gaussian and monocycle pulses with 510 and 660 ps pulse width, respectively. The proposed pulse shaping method is versatile and can be effectively modified and reconfigured to generate more complicated pulse shapes such as polycycle signals. The measured results reveal that the proposed reconfigurable PG is suitable to be used in systems with pulse shape modulation that require sub-nanosecond pulses at low pulse repetition rates.

This paper proposes and presents a millimeter-wave (MMW) fundamental and subharmonic hybrid mixer in a 65-nm CMOS technology. Based on a hybrid structure with two switching quads and a quasi-diplexer, the proposed circuit can function either as a fundamental mixer (FM) or a subharmonic mixer (SHM) for dual-band applications. An application of the MMW hybrid mixer in a concurrent dual-band receiver is also discussed, which indicates that the proposed mixer can operate at two different MMW frequency bands concurrently as long as the frequency conversion schemes are carefully designed. Measured results show that the 3-dB RF bandwidth of the MMW hybrid mixer ranges from 16 to 35 GHz for the FM mode and 30 to 53 GHz for the SHM mode, respectively.

In this paper, a 3 dB H-plane substrate-integrated waveguide (SIW) power divider/combiner with improved isolation is reported. By adding two isolated ports into the Y-junction, it will perform like a multi-port coupler, so that the isolation between its dividing ports can be effectively improved as the newly-added ports are properly matched. To verify the availability and effectiveness of this concept, two prototypes, one is terminated by coaxial terminations and the other is loaded with lumped resistors, are developed. Their measured results are separately in good agreement with their corresponding simulations. Meanwhile, isolations better than 16 dB with fractional bandwidth (FBW) of 35 and 25% are achieved, respectively, as well as low phase and amplitude imbalances. Compared with some reported similar SIW power dividers, the proposed ones exhibit wider FBW with similar isolation, insertion loss, phase, and amplitude balance performance.

In this paper, miniaturization of fractal geometry with defected ground structure (DGC) concept has been experimentally verified at S-band (2–4) GHz. The design starts with a self-symmetry structure using conventional Vicsek snowflake-box fractal antenna. The same has been used in third iteration to achieve miniaturization. This proposed microstrip patch antenna (MPA) is resonating at 2.12 GHz with acceptable gain and broadside radiation. The miniaturization of about 87.26% when compared to conventional fractal MPA is achieved. The fractal unit cell is optimized for miniaturization and bandwidth by carrying out parametric study and applying the DGS shapes like rectangular and U-shaped slot etched in the ground plane of Vicsek snowflake-box fractal microstrip antenna. A fractal microstrip antenna is designed for wireless applications at 3.95 GHz. The fractal microstrip antenna is simulated using HFSS-V15 simulator. It is observed that the maximum size reduction of 87.26% is achieved in the third iteration of the Vicsek snowflake-box fractal radiating patch. The proposed fractal patch antenna is designed and fabricated using epoxy substrate of FR-4 with dielectric constant of 4.4 and thickness of 1.6 mm. The simulated results are compared with the measured results.

This paper presents a compact ultrawideband slotted patch antenna for early stage tumor detection applications using microwave breast imaging systems. In order to reduce any reflections between the antenna and breast, the antenna is designed and optimized inside a coupling medium with electrical properties similar to that of normal breast tissue as a coupling medium. The wideband performance of the antenna is obtained by adding a rectangular slit and L-shaped sleeves on the ground plane. While the added rectangular slit mainly improves the matching, the L-shaped sleeves improve both the matching and the bandwidth. The antenna operates from 0.9 to 9.6 GHz with a fractional bandwidth of ~165$\%$, providing a good penetration and resolution. In addition, the proposed antenna has a very compact size of 16 × 16 mm2. Furthermore, an antenna array consisting of 31 antennas is formed around a realistic breast phantom in the simulation environment to demonstrate the imaging of a spherical tumor with a diameter of 5 mm inside the breast. The results confirm that the proposed antenna can be used for early stage breast tumor detection purposes.

This work proposes a novel, extremely miniaturized wideband linear–circular and linear–cross metasurface-enabled reflective polarizer. This design comprises a Meander-line structure with horizontal dipoles as the top frequency selective surface, printed on a 1 mm thin-grounded FR-4 substrate. The x/y-polarized incident electromagnetic wave is converted as circularly polarized from 10.60 to 10.92 GHz (LHCP/RHCP), 12.12 to 17.32 GHz (RHCP/LHCP), and 22.72 to 37.76 GHz (LHCP/RHCP) during reflection with 2.97, 35.33, and 49.74% Fractional Bandwidth (FBW). In addition, this design shows linear–cross conversion with a minimum 90% polarization conversion ratio from 11.41 to 12, 19.01 to 22.34, and 40.74 to 46.82 GHz with an FBW of 5.04, 16.11, and 13.89%. The device performance is considerably stable under different oblique incidences, and the polarizer's unitcell is compact with a structural periodicity of 0.089 × 0.064 $\lambda _L^2$, and ultra-thin low-profile substrate thickness of 0.035λL. The proposed prototype is fabricated, and the measured results are in good agreement with the simulated one. This article also mentions how this polarizer could be tuned for dual-band K- and Ka-band satellite applications. The authors believe that the design's novelty lies in the multiband conversion with circular-polarization orthogonality, a highly miniaturized unitcell's volume of 0.199 $\lambda _L^3$/1000, and better angular stability made this design a potential candidate for real-time satellite applications.

The paper presents a two-dimensional (2D) extended envelope memory polynomial model for concurrent dual-band radio frequency (RF) power amplifiers (PAs). The model is derived based on the physical knowledge of a dual-band RF PA. The derived model contains cross-modulation terms not included in previously published models; these terms are found to be of importance for both behavioral modeling and digital predistortion (DPD). The performance of the derived model is evaluated both as the behavioral model and DPD, and the performance is compared with state-of-the-art 2D-DPD and dual-band generalized memory polynomial (DB-GMP) models. Experimental result shows that the proposed model resulted in normalized mean square error of −51.7/−51.6 dB and adjacent channel error power ratio of −63.1/−63.4 dB, for channel 1/2, whereas the 2D-DPD resulted in the largest model error and DB-GMP resulted in model parameters that are three times more than those resulted with the proposed model with the same performance. As pre-distorter, the proposed model resulted in adjacent channel power ratio of −55.8/−54.6 dB for channel 1/2 and is 7–10 dB lower than those resulted with the 2D-DPD model and 2–4 dB lower compared with the DB-GMP model.

This paper presents a tradeoff between isoflux pattern quality and X-band antenna compactness for nanosatellite applications. Having an isoflux radiation and a circular polarization (CP) generally causes a large antenna size which is incompatible for these applications. A new design of an antenna is done with the following maximum antenna dimensions: a diameter of 90 mm and a height of 20 mm above the nanosatellite platform. The isoflux pattern is slightly degraded while a good CP and realized gain are kept. The structure is a compact choke horn. It presents an axial ratio lower than 3 dB and a RG close to 0 dB over a 400 MHz bandwidth (8.0–8.4 GHz). It has been realized and successfully measured.

We report on the development of a handheld three-dimensional (3D) terahertz scanning system with an aspherical telecentric 3D-printed f-θ lens using selective laser sintering. The lens covers a broader scan line of 50 mm with its larger aperture, compared to the 20 mm range in our initial work, which was presented at the European Microwave Week 2021. In order to evaluate the adaptability of the optomechanical components with different sensor units, two different integrated frequency-modulated continuous wave radar modules based on monolithic microwave integrated circuit technology, operating in W- and D-bands are tested within the measurement scheme. The optomechanical part consists of a galvanometer scanner mirror and the f-θ lens. The optical system enables B-scans perpendicular to the manual translational movement of the sensor unit by its user. An integrated guiding wheel system with rotary encoder makes it possible to correlate the measurement points to their respective locations, enabling complete 3D volumetric inspection of the corresponding structures, which is particularly useful for the inspection along cracks and welds.

A high gain antenna with Mu-near-zero metasurface (MNZ-MS) is introduced in this work. The proposed antenna can be utilized for future 5G applications. The patch antenna is designed on the upper face of the square substrate with a ground plane at the bottom face. To improve the antenna gain, a layer of MNZ-MS unit cells is placed above the antenna substrate with 0.48λ0 air space between the two layers, where λ0 is the wavelength in free space at the resonance frequency of 26.3 GHz. The MNZ-MS layer consists of four double-sided split square resonators. The overall thickness of the proposed antenna is 0.66λ0. To approve the execution of the proposed antenna, a prototype model is manufactured and tested. The outcomes fulfill a reflection coefficient lower than −10 dB over the frequency spectrum of 26–28 GHz. A gain improvement better than 5 dB is obtained compared to the gain of the reference patch at the center frequency of 26.3 GHz.

A compact quasi-Yagi antenna with a modified ground plane is designed for a through-wall radar on-chip. A slot-based ground plane modification in the proposed antenna results in significant miniaturization with an increase in the impedance bandwidth by 44.62%. The antenna has a high directivity of 9.02 dBi and a front-to-back ratio of 25.76 dB at 2.4 GHz. Based on experiments in real-world deployment scenarios, the performance of the proposed quasi-Yagi antenna is found to be comparable to that of a Vivaldi antenna and a commercial-off-the-shelf horn antenna. Spectrogram-based signatures of a moving person behind a wooden partition and a 40 cm thick masonry wall are successfully obtained using the designed antenna, demonstrating the suitability of the quasi-Yagi antenna for portable applications using a radar-on-chip.

Traditional near-field antenna measurements use the sampling theorem to reconstruct the antenna pattern perfectly. However, a large number of measurement points are required for this approach. To address this problem, in this study, we propose a technique to accelerate the near-field antenna measurement, which is achieved by sparse E-field sampling in the region where the E-field changes smoothly and dense sampling in the region where the field changes rapidly. Further, our approach ensures robustness of measurement; the E-field information need not be known before carrying out measurements. Our experimental results demonstrate that our technique can reduce the number of measuring points by at least 64.9% when measuring two different patterns (15-GHz horn antenna with θ = 0° and 10°).

A compact microstrip multi-stub loaded bandpass filter (BPF) with ultra-wide stopband is introduced and investigated. Lumped-equivalent circuit (LEC) method is adopted to analyze the characteristics of the in-band response based upon the low frequency LEC and even-odd mode analytical method. Besides, equivalent transmission line circuit method with even-odd mode analytical method are adopted to discuss the mechanism of the out-band rejection based upon the transmission poles and the transmission zeros analysis of the even-/odd-mode equivalent circuits. Accordingly, the design and the optimization procedures of this type of filters are summarized. To experimentally validate the proposed method, the filter is fabricated and measured. The measured results illustrate this BPF centered at f0 = 2.8 GHz, with −3 dB fractional bandwidth of 109.3%, the insert loss (IL) of less than 1 dB from 1.4 to 4 GHz, and the rejection level of 20 dB from 5.1 to 33.5 GHz(1.82f0 to 11.96f0).

We present a continuously tunable 52-to-67 GHz push–push dual-core voltage-controlled oscillator (VCO) in a 40 nm bulk complementary metal–oxide–semiconductor (CMOS) technology. The circuit is suitable for 60 GHz frequency-modulated-continuous-wave radar applications requiring a continuously tunable ultra-wide modulation bandwidth. The LC-tank inductor is used to couple the two VCO cores. The fundamental frequency of the VCO can be tuned from 26 to 33.5 GHz, which corresponds to a frequency tuning range of 25%. The second harmonic is extracted in a non-invasive way using a transformer. The primary side acts simultaneously as a second harmonic filter. The VCO achieves in measurement a low phase noise of −91.8 dBc/Hz at 1 MHz offset at 62 GHz and an output power of −20 dBm. The VCO including buffers dissipates in the dual-core operation mode 60 mA from a single 1.1 V supply and consumes a chip area of 0.58 mm2.

In this paper, we present a miniaturized ultra-wideband (UWB) bandpass filter (BPF) with multiple transmission zeros (TZs), which is based on transition technology of microstrip with short-circuited coplanar waveguide (CPW). The ground plane of the BPF contains a multiple mode resonator (MMR)-based CPW which is capacitively linked through the dielectric to two open-circuited microstrip lines on the top. The MMR is initially designed to allocate its lowest three resonant modes quasi-equally inside the designated UWB spectrum (3.1–10.6 GHz). This is followed by optimization of microstrip lines to provide a good broadband response possessing minimum insertion loss, two TZs at the lower and upper passband edges that improve selectivity and a wide stopband with appreciable attenuation. Later, multiple-folded split ring resonators are coupled to the BPF to inject dual passband TZs. The predicted theory in simulation is verified against measured result and is found to be in good agreement. The prototype covers a substrate area of only 14.6 × 9.2 mm2.

The temperature dependence of the dielectric parameters of tissues and tissue-mimicking phantoms is very important for non-invasive temperature measurement in medical applications using microwaves. We performed measurements of this dependence in the temperature range of 25–50°C using distilled water as a reference liquid commonly used in dielectric property studies. The results were compared with the literature model in the frequency range of 150–3000 MHz. Using this method, the temperature dependence of dielectric parameters of a new muscle tissue-mimicking phantom based on agar, polyethylene powder, and polysaccharide material TX-151 was measured in the temperature range of 25–50°C. The temperature dependence of the dielectric properties of this new muscle phantom was fitted to that of the two-pole Cole–Cole model and the deviation of the results between measured and modeled data was quantified.

Patch antennas with a meandering slot and different distributions of grounded metallic vias are presented in this paper. The meandering slot is adopted to stimulate dual-band operation, while the number and position of the grounded metallic vias are suggested to achieve different radiation performances. The characteristics are analyzed in detail where we find that the existence of the vias also improves the impedance matching. Four samples are designed, where dual-band with both linear polarization, dual-band with circular- and linear-polarization, and single band with linear polarization are obtained, respectively. The samples are finally fabricated and the measurement results agree well with the simulation results.

An increasing interest is arising in developing miniaturized antennas in the microwave range. However, even when the adopted antennas dimensions are small compared with the wavelength, radiation performances have to be preserved to keep the system-operating conditions. For this purpose, magneto-dielectric materials are currently exploited as promising substrates, which allows us to reduce antenna dimensions by exploiting both relative permittivity and permeability. In this paper, we address generic antennas in resonant conditions and we develop a general theoretical approach, not based on simplified equivalent models, to establish topologies most suitable for exploiting high permeability and/or high-permittivity substrates, for miniaturization purposes. A novel definition of the region pertaining to the antenna near-field and of the associated field strength is proposed. It is then showed that radiation efficiency and bandwidth can be preserved only by a selected combinations of antenna topologies and substrate characteristics. Indeed, by the proposed independent approach, we confirm that non-dispersive magneto-dielectric materials with relative permeability greater than unit, can be efficiently adopted only by antennas that are mainly represented by equivalent magnetic sources. Conversely, if equivalent electric sources are involved, the antenna performances are significantly degraded. The theoretical results are validated by full-wave numerical simulations of reference topologies.

A new band-reject frequency-selective surface (FSS) based on dual-band near-zero refractive index metamaterial (ZIM) design is presented in this paper. Consisting of a planar array of complementary dual-layer symmetry resonant ring, the proposed FSS exhibits a high-selective band-reject filtering response. From the viewpoint of effective medium, the subwavelength FSS is characterized by near-zero effective magnetic permeability and near-zero effective electric permittivity in two different operational bands, respectively. The corresponding resonant behavior and E-field distributions are analyzed in detail. A prototype of the proposed FSS working in X-band is fabricated and measured. The simulation and experiment results verify the effectiveness and correctness of the ZIM-based design method.