Worldwide adoption of fourth-generation wireless (4G) long-term evolution (LTE) smartphones and the actual transition to fifth-generation wireless(5G) is the main driving engine for semiconductor industry. 5G is expected to reach high data rate speeds (1 Gbps) and low latency (<1 ms). 5G requires more RF bandwidth and therefore an increase in the number of components such as RF switches, acoustic filters, and power amplifiers integrated in few RF front-end modules. Also, there is an increase in the number of RF radio transmitters and receivers operating at the same time. This paper presents new architecture elements for 5G RF front-end modules. Circuit details and measurements are presented to reduce the RF noise, improve the efficiency, and help the coexistence of multiple radio transmitters. These circuits will help extend the 5G applications with radar-like sensing applications, remote medicine, and autonomous driving.

This paper describes the design and implementation of a 39 GHz 256-element hybrid active phased array antenna system with 16 individual digital transceivers, and its wireless multi-user, multi-input, multi-output verification. An earlier version of this paper was presented at the 2021 51st European Microwave Conference and was published in its Proceedings [1]. Using the prototype device, a single carrier transmission test assuming a mobile backhaul link and a MU-MIMO transmission test using a zero-forced orthogonal multi-beam based on channel reciprocity assuming an access link was performed. As a result, an EIRP of 43 dBm and a data rate of 5.5 Gbps in 1 GHz bandwidth single carrier 128QAM operation and an estimated total throughput of 2.4 Gbps by 3GPP TS38.214 [2] in 100 MHz bandwidth OFDM 8 MU-MIMO operation were achieved, respectively. As far as the author knows, this is the first demonstration for integrated access and backhaul (IAB) application that uses the 39 GHz band.

This paper describes the experimental investigation of orthogonal time-frequency space (OTFS) modulation using a 28 GHz multi-user distributed multiple-input multiple-output (D-MIMO) testbed in over-the-air (OTA) and mobility environments to enhance cell throughput in a millimeter-wave band. We build the D-MIMO testbed having newly developed OTFS modulator and demodulator, and measured OTFS signals and orthogonal frequency-division multiplexing (OFDM) signals with up to four user simultaneous connections on an actual office floor. Additionally, the Doppler effect on OTFS signals is mathematically analyzed and is confirmed in the measurements. OTFS indicates higher robustness in time-variant channels than OFDM. The error vector magnitude (EVM) and system throughput of OTFS are −22 dB and 1.9 Gbps with 100 MHz signal bandwidth, respectively. To our knowledge, this is a first paper describing the OTA measurements of EVM, throughput, and spectral efficiency using OTFS modulation on the 28 GHz coherent beamforming system.

Modern radar sensors are gaining more and more relevance for several industrial measurement applications. To achieve the required range resolution and measurement accuracy, the use of higher frequencies beyond 100 GHz is beneficiary. A commonly used signal generation concept in fully integrated radar transceivers is to use a fundamental oscillator with subsequent frequency multiplication. Depending on the overall system concept, this type of signal generation suffers from a fundamental feed-through signal which generates false targets in frequency modulated continuous wave operation. Additionally, those unwanted signal components radiated by the sensors might be problematic for legal conformity or electromagnetic (EM) interference compliance. This paper presents a novel concept for frequency filtering dielectric lens antennas, to suppress unwanted signal components at harmonic frequencies based on interference filtering effects. Besides the EM simulations to theoretically prove this concept, multiple prototypes of filtering lens antennas were fabricated by conventional mechanical and additive manufacturing. Using a self-developed, ultra-compact radar sensor, measurements were taken to compare the lens antenna prototypes in terms of filtering performance and how the material characteristics affect the filtering performance. Within these measurements, the successful suppression of false targets caused by fundamental feed-through signals is demonstrated.

Digital radar waveforms such as orthogonal frequency-division multiplexing (OFDM) often have the disadvantage that they require high sampling rates if fine range resolutions have to be achieved. The frequency comb OFDM radar scheme offers a possibility to overcome this drawback and to improve the range resolution without increasing the sampling rate. Simultaneously, the high unambiguous velocity, which is one of the advantages of digital radar waveforms, is retained and due to the simple generation of orthogonal transmit signals, it is well suited for multiple-input multiple-output (MIMO) applications. To prove all these features of the frequency comb OFDM radar scheme, a suitable 4 × 4 MIMO demonstrator including frequency comb generation as well as up- and downconversion with these combs has been set up. Its functionality has been validated with real measurements in an anechoic chamber in conjunction with a radar target simulator to emulate very high velocities.

Due to their periodic nature, metasurfaces used to perform anomalous reflection raise parasitic harmonic reflections. We show a classical synthesis example of such a structure and highlight its limitations. Floquet analysis and its associated simulation environment are exploited to understand the origin of these parasitic reflections and to mitigate them. The proposed method is based on the optimization of the metasurface periodic pattern: the supercell. A predictive method is built to calculate radar cross-section patterns from supercell Floquet simulation, avoiding dealing with heavy simulations. The proposed model, the optimization outputs, and the general results are exposed in details. Different cases are also discussed to prove the repeatability of the proposed method. An earlier version of this paper was presented at the European Microwave Conference and was published in its proceedings.

With increasing demands on resolution and flexibility in current and future radar applications, the focus is moving to digital radar systems such as orthogonal frequency-division multiplexing (OFDM) radars. To achieve high bandwidths and consequently a high range resolution, high sampling rates are needed. To overcome this constraint, an approach called frequency comb OFDM radar has been developed. This paper presents a novel, hardware efficient implementation of such a frequency comb OFDM radar including a novel way of comb generation. Special attention is put on the suppression of unwanted frequency components. Measurements which demonstrate the functionality of the hardware efficient radar system in combination with the frequency comb OFDM technique are presented.

Short-channel Gallium Nitride (GaN) high-electron-mobility transistors (HEMTs) often utilize T-shape gates due to their large gate-line cross-sectional area and subsequent fMAX increase. In this paper, we report the linearity trade-offs associated with varying the T-gate geometries of AlGaN/GaN HEMTs on Si, specifically the gate extensions which serve as field plates and their impact on the large-signal performance. Small-signal characterization and modeling, in addition to TCAD, provide initial guidelines for the optimal dimensions for the gate field plates using the ratio of fT and the product of the gate resistance and the gate-to-drain capacitance. We utilize various characterization methods, including 6 GHz non-linear vector network analyzer characterization in addition to load-pull, to quantify the amplitude and phase distortion and their subsequent impact on the large-signal metrics of the devices under differing matching conditions and bias points. We deduce that the influence of the gate field plates on the amplitude and phase distortion is non-negligible, particularly under matched conditions.

This contribution presents miniaturization techniques for folded circular substrate integrated waveguide (FCSIW) cavity filters. The cavities support dual-mode operation. Two of these cavities are combined to form a fourth-order filter. Two filter designs are implemented. The first one serves as a reference and exhibits good manufacturability. For the second one, the cavity is modified, which leads to $50\%$ more compactness. The designs are experimentally verified with 10 GHz bandpass filters. Even though the achieved level of compactness requires higher technological effort, the measurements validate the miniaturization concept. The out-of-band rejection exceeds 40 dB between 11.2 and 30 GHz for the reference filter and between 11.3 and 33 GHz for the miniaturized one. The implemented components are compared with state-of-the-art filters.

This work introduces a method for plasma state supervision, based on a frequency-modulated continuous wave radar sensor and a suitable signal evaluation enabling a continuous supervision method for the plasma state. Highly precise phase evaluation of the signal allows us to detect and visualize smallest changes in the plasma state. Assuming the plasma to act like a frequency-dependent dielectric material, the propagation of the electromagnetic wave depends on the plasma state and hence, also the measured phase. Broadband measurements are carried out at center frequencies of 80 and 140 GHz in a low-pressure plasma. The radar-based setup can be used for a very flexible application, capable for spatially resolved measurements in the plasma bulk. At the same time, the high measurement rate allows for quasi real-time monitoring, so that transient processes in the plasma are recorded. Due to the simple setup, this approach is most suitable for industrial applications to improve process control. The chosen different frequencies will show a change in the influence of the plasma on the electromagnetic wave demonstrating the advantages of multi-frequency approaches in future applications.

Radio telescopes are among the applications with the highest demands on a local oscillator (LO), which is used to receive and process the signals coming from the sky. Therefore the modules providing the required LO signal have traditionally been big and complicated. To overcome this disadvantage, we implement our own integrated frequency synthesizer inside a small LO module in this article. With this synthesizer we are able to achieve a jitter of only 50 fs integrated from 10 Hz to 2.5 GHz offset at a carrier frequency of 75 GHz. This is in part achieved by a very low in-band phase noise of −111.8 dBc at 10 kHz offset. The stabilizable frequency range is 62–88 GHz. Thus achieving promising results to fulfill this very demanding task with integrated frequency synthesizers in the future.

Metamaterial lenses are appealing thin alternatives to conventional dielectric lenses. In this contribution we describe their design and application in two exemplary 77 GHz automotive radar sensors operating in monostatic and bistatic modes. The frontends are built around commercially available MMICs and small feed antennas are used in coordination with the six-layer printed circuit board-based realizations of metamaterial lenses. The design follows the principles of dielectric lenses, while the required local phase shift is obtained from a set of metasurface bandpasses. Their design uses a novel interpolation procedure to extract layout parameters for a given phase shift. Despite the small structural sizes due to the high frequency, the fabricated frequency-selective surfaces show very good performance in the required frequency range. Verification measurements were conducted on single bandpasses as well as on metamaterial lenses mounted on the radar frontend. The results agree very well with the simulation and confirm the applicability of thin lenses operating at mm-wave frequencies for automotive radar applications.

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.

Terahertz technologies for non-destructive testing (NDT) are continuing to find their way into the industrial sector in the context of very specific inspection tasks. Part of this development is the capability to adapt terahertz systems in such a way that they can meet the sometimes harsh challenges and requirements of real-world industrial scenarios. One such scenario is the inspection of components with limited available measurement space. In particular, we show here the terahertz NDT inspection of the mica insulation of generator bars of turbogenerators at power plants, where an early on-site detection of defects and cracks in the insulation can be crucial, but where only few centimeters of space between adjacent bars are available. To address this problem, we have developed a measurement system combining a 100 GHz all-electronic terahertz transceiver with a low-loss dielectric waveguide antenna with 90 degree tip. We achieve sub-wavelength image resolution by scanning the waveguide antenna's tip over the surface of the generator bars in a near-field measurement setup. Employing a frequency-modulated continuous wave technique, we obtain depth-resolved, volumetric terahertz images of the objects under test. We discuss here the implementation and performance of the implemented measurement system for terahertz NDT inspection. keywords: terahertz, non-destructive testing, dielectric waveguides, frequency-modulated continuous wave, millimeter waves, power generators

In this work, the use of a configuration of a reflective metasurface (MS) layer is employed to design a highly directive wideband Fabry–Pérot cavity (FPC) antenna. With the use of only one MS layer and along with the achieved high directivity, the antenna's wide bandwidth, and antenna low size/cavity thickness profile are all optimized so that they are still competitive which is the main contribution of our work. The highly reflective MS layer is placed as a superstrate of a low-cost FR4 microstrip patch antenna, as the primary radiator, at a height of half-wavelength cavity condition. Thanks to the employed MS layer, most of the power is transmitted and a very small reflected power to the primary patch. The antenna is designed to serve the 28 GHz band of 5G wireless applications. At 28 GHz, the FPC antenna has a good directivity performance, with a peak simulated directive gain of 15.46 dB and measured directive gain is 14.3 dB which is a 9 dB enhancement in directivity compared to a conventional microstrip patch antenna. The antenna has a wide impedance bandwidth of 2.9 GHz which is almost three times the microstrip patch antenna bandwidth. The achieved results are for the same size of FPC antenna whose height is almost half wavelength and its overall size 2.33λ × 2.33λ.

This paper presents an analysis of the radiated susceptibility of multiconductor shielded cables within complex structures following a hybrid method using moments (MoM) circuit models. The MoM code was used to compute the currents on the shielding induced by an external electromagnetic field and incorporated into a circuit model. The proposed method can be employed for nonlinear loads. The method was tested on two cases: coaxial shielded cables inside a cavity and a car with complex wiring, including a coaxial cable, a twinax cable (a cable with two parallel wires), and a triaxial cable (a cable with three parallel wires), all of which are excited by an incident plane wave. The proposed method provides high accuracy and significant speed gain, and its results are in good agreement with those obtained in other studies.

This paper presents a novel method to improve the working bandwidth and radiation intensity of piezoelectric antenna by using external circuit. This method makes the piezoelectric antenna combined with roles of high radiation intensity and multiple resonant frequencies without changing the structural size of the piezoelectric antenna. The experimental results show that, compared with the original piezoelectric antenna, the tuning range of the resonant frequency of the piezoelectric antenna caused by the series capacitance and inductance is +13.6 and −24%, respectively. The series inductance will produce new resonance frequency, which provides a new method for the multi-band operation of the piezoelectric antenna. The LLC (series and parallel circuit) composite circuit can increase the number of resonant frequencies of the piezoelectric antenna from 1 to 3, and the S11 at the resonant frequencies are all lower than −10 dB, and the radiated magnetic field of the piezoelectric antenna is increased by 42.3% at least. This method makes the piezoelectric antenna have the dual functions of high radiation intensity and multi-band, which has great significance for broadening the application field of piezoelectric antenna.

This work represents a circularly polarized implantable patch antenna operating at the ISM band (2.4–2.48 GHz) for biomedical applications. The presented patch antenna has a compact volume of 50 mm3 i.e., 10 × 10 × 0.5 mm3. All the Simulations have been carried out within homogeneous skin phantom and head scalp phantom. Miniaturization of antenna and enhancement of bandwidth is achieved by using various techniques described in this work. The designed patch antenna has wide axial ratio bandwidth of 20.08 and 15.44% inside scalp phantom and homogeneous skin phantom, respectively. Obtained impedance bandwidths are 56.79 and 49.75% inside scalp phantom and homogeneous skin phantom, respectively. At 2.45 GHz, obtained peak gains are −25.18 and −28.12 dB, respectively. The proposed antenna is enclosed in a biocompatible material to avoid direct contact with the human tissue. For patient safety concerns, simulated maximum specific absorption ratio values are also investigated and are under the limits of the IEEE standard. The allowable input power is also calculated in this work. Link budget analysis is used in this work to determine the far-field communication range of the designed antenna.

E-plane sectoral horn antenna based on printed ridge gap waveguide (PRGW) technology is designed for 5G applications. It is implemented on the top plate of the PRGW structure to avoid the losses and dispersion associated with conventional feeding mechanisms. The quasi-transverse electromagneticPRGW-based antenna is excited through a planar microstrip transition. First, the single horn antenna element is introduced with the microstrip feeding section. It shows an impedance bandwidth of fractional bandwidth 26% from 45.7 to 55.4 GHz with the realized gain of 12.7 dBi and radiation efficiency of 90%. In order to maximize the realized gain, a four-element linear horn array is introduced. The same impedance bandwidth is maintained with the array having a gain of 18.6 dBi from 45.7 to 55.4 GHz. The overall antenna array performance in the entire operating frequency range is stable with a radiation efficiency around 85%. Three matching sections are implemented to achieve better impedance matching. One is used to match the horn with the feeding aperture via the PRGW line. Another section is designed to match microstrip transition with PRGW ridge. Finally, two-stage quarter wavelength transformers are required to match the power divider with the array feeding network. A prototype of single-element horn antenna was fabricated to verify the concept of the design. Simulated and measured results show that the proposed antenna can operate in the frequency band of 45–55 GHz with good agreement of radiation performance. Moreover, the proposed designs are implemented and simulated using two microwave simulation tools (CST and HFSS) to verify the radiation performance, which exhibits good agreement. The design of an E-sectoral horn antenna and its array with high gain based on PRGW is demonstrated for the first time which is considered a novel issue. It can be integrated with other passive and active elements in communication systems. Thus, it can be a valuable component in 5G communication due to its high gain, compact size and ultra-wide band.