The manuscript reports on additively-manufactured (AM) coaxial-resonator-based bandpass filters (BPFs) and RF diplexers. A monolithic integration concept using stereolithography apparatus (SLA) is proposed and discussed in detail. Coupled-resonator-based synthesis alongside full-electromagnetic-based design methods is used for the design of the monolithic filters and RF diplexers. In particular, the paper discusses a new external coupling mechanism for dual-band BPFs that allow to independently control the coupling in each of the BPF passbands. Furthermore, a novel coaxial transmission line-type T-junction is proposed for the design of single- and dual-band RF diplexers. For practical validation purposes, multiple BPF and RF diplexer prototypes were designed, manufactured and tested at S- and C-band demonstrating the applicability of the proposed concept to low-cost, low-loss and low-weight RF components with complex geometrical features.

This contribution deals with array elements for K/Ka-band satellite communication terminals. It proposes an end-fire design realized in substrate integrated waveguide technology and featuring dual-band functionality, and dual circular polarization. The latter is achieved by means of a dual-band orthomode transducer. An extended hemispherical dielectric lens ensures good matching and radiation properties. The feed structure is composed of a multilayer printed circuit board and tapered superstrates. The design procedure of the components is explained in detail and three different variants of the antenna are compared. The measured scattering and far-field parameters validate the concept.

A superstrate loaded cylindrical dielectric resonator antenna is developed and demonstrated for dual-band circular polarization. The proposed antenna employs a microstrip-fed rotated cross-shaped slot coupling technique for exciting the dielectric resonator (DR). The design is developed in a straight forward way. Firstly, the DR is coupled with a conventional plus-shaped slot and operates in linear polarization mode at 7.4 and 11.2 GHz. Secondly, the slot is rotated by 10° to enable out-of-phase excitation and ensure circular polarization at the above-mentioned frequencies. In the third step, a square dielectric superstrate is placed above the DR which creates multiple reflection and enhance the gain up to ~8 dBi in both the frequencies without affecting other performances. The development stages are discussed in detail. The proposed design is demonstrated through prototype fabrication and characterization. This antenna can be used for X-band satellite communications.

This paper presents a new approach for improving the localization of passive ultra high frequency radio frequency identification (RFID) tags in line-of-sight channels using a received signal strength indicator (RSSI) technique. In practice, the complex propagation in the indoor channels and also the variability of some parameters of the RFID equipment itself introduces significant amount of errors when the operation of localization carries out the RSSI technique. Indeed, as the calculation is based on a trilateration, the incomplete knowledge of the propagation and some parameters of RFID tags leads to estimate distances which are wrong, and therefore the localization cannot be correct. In order to overcome this drawback, the proposed method takes into account the presence of unknown parameters relying on a dichotomous algorithm which includes probabilistic parameters. The presented simulation results are in good agreement with the expected theoretical results. Experimental results show that the proposed method strongly increases the accuracy of the estimated position of tags. Compared to other approaches based on the improvement of the RSSI technique, this method does not require too much complexity in terms of materials (no need for specific architecture or reference tags) and processing (fast and simple algorithm).

We present the realization of an frequency-modulated continuous-wave radar target simulator, based on a modulated-reflector radar system. The simulator, designed for the 24 GHz frequency band, uses low-cost modulated-reflector nodes and is capable to simultaneously generate multiple targets in a real-time environment. The realization is based on a modular approach and thus provides a high scalability of the whole system. It is demonstrated that the concept is able to simulate multiple artificial targets, located at user-selectable ranges and even velocities, utilized within a completely static setup. The characterization of the developed hardware shows that the proposed concept allows to dynamically and precisely adjust the radar cross-section of each single target within a dynamic range of 50 dB. Additionally, the provided range-proportional target frequency bandwidth makes the system perfectly suitable for fast and reliable intermediate frequency-chain calibration of multi-channel radar systems. Within this paper we demonstrate the application of the concept for a linear sweeped frequency-modulated continuous-wave radar. The presented approach is applicable to any microwave-based measurement system using frequency differences between transmit- and receive signals for range- and velocity evaluation, such as (non-)linear sweeped as well as pure Doppler radar systems.

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

This paper presents for the first time a wavetable-based coding scheme to generate a high-speed binary input signal for digital RF power amplifiers. The approach maximizes the utilization of the time domain handling capabilities of the pulse forming circuit. Key features are a greatly improved output spectrum purity in comparison with common digital modulators, the ability to adjust the modulator to any given pulse forming hardware and a built-in signal correction option that comes without additional computational cost. To give a first impression on the modulators behavior and its possibilities to adapt to different hardware constraints, simulations are carried out for different parameter variations and for different baseband bandwidths. Furthermore, the proposed concept is emulated with an arbitrary waveform generator to gather additional measurement data. For a 5 MHz wideband code division multiple access (WCDMA) signal (6.5 dB peak-to-average power ratio) at 900 MHz, an error vector magnitude (EVM) of 0.26% and better than >58 dB adjacent channel leakage ratio (ACLR) were recorded. To the authors’ knowledge, these are the best values achieved so far for a single-bit coding scheme without digital predistortion that still maintains maximum power coding efficiency.

This paper presents power results of L-band packaged hybrid amplifiers using InAlN/GaN/SiC HEMT power dies. The high-power densities achieved both in pulsed and continuous wave (cw) modes confirm the interest of such technology for high-frequency, high-power, and high-temperature operation. We present here record RF power measurements for different versions of amplifiers. Up to 260 W, i.e. 3.6 W/mm, in pulsed (10 µs/10%) conditions, and 105 W, i.e. 2.9 W/mm, in cw conditions were achieved. Such results are made possible thanks to the impressive performances of InAlN/GaN transistors, even when operating at high temperatures. Unit cell transistors deliver output powers of 4.3 W/mm at Vds = 40 V in the cw mode of operation at the frequency of 2 GHz. The transistor process is described here, as well as the amplifiers design and measurements, with a particular focus to the thermal management aspects.

A compact ultra-wideband (UWB) square and circular slot ground plane planar antenna with a modified circular patch for UWB communication is presented. This antenna has a low reflection coefficient and high gain in the range of 8.94 GHz, starting from 2.85 to 11.79 GHz. The proposed antenna demonstrates UWB behavior with electrically small dimensions of 0.18 λ0×0.14 λ0×0.015 λ0 (λ0 is the free-space wavelength at 2.85 GHz). The fractional bandwidth of the antenna is 122.1%, with stable radiations. The antenna's maximum gain stands at 2.79 dBi, and the antenna's peak efficiency stands at 72%, respectively. It is lightweight, compact, and easy to manufacture. Hence, it can be used for the complete range of UWB applications and covers Wi-Max/WLAN/ X-Band and Ku-Band.

We propose a compact, high-efficiency antenna configuration, which is 18 cm in diameter and has average gain of 24.1 dBi for automotive applications of satellite TV systems operating at Ku band. To achieve high aperture efficiency, hybrid microstrip, and waveguide feed network with low-loss microstrip-to-waveguide transition is designed and validated. The array antenna is wideband and covers entire downlink Ku-band frequencies (10.8–12.75 GHz) for simultaneous reception from multiple transponders. Vertical polarization panel is built and tested for reception quality. Carrier-to-noise ratio of 6.2 dB was observed the target transponder (42°E) at 11.9 GHz using intermediate frequency loop-out of the receiver. The antenna can be used on small vehicles or automobiles for satellite TV reception.

The wideband coherent-pulse radar provides high-resolution image of the target. The model of this image is a complex envelope superposition corresponding to signals diffracted by the point scatterers. The values of complex envelopes are distributed over the radar image coordinate plane in accordance with the point scatterer positions and their reflection coefficients. The radar image model consists of range and Doppler profiles. The parameters of the target point scatterers were defined by processing of two-dimensional (2D) data extracted from the complex 2D discrete Fourier transforms of the radar image. The proposed parametric system identification method performs the estimation of the model parameters for a short dwell time and the extrapolation of the radar data image beyond this time. The modified procedure of inverse synthesis aperture radar imaging applied to actual data showed a reduction of the Doppler smearing and some improvements of image resolution.

This article presents the design and performance analysis of a printed microstrip ultra-wideband (UWB) antenna consisting of the slots in the ground plane and radiating patch. A meandered S-shaped slot has been introduced on the patch and an inverted U-shaped slot has been incorporated in the ground plane to realize the band-notch effect for WiMAX (3.2–3.8 GHz) and WLAN (5.1–5.8 GHz) bands respectively. The total dimension of the proposed design is 44 × 44 mm2. The fabricated antenna exhibits wide impedance bandwidth of 10 GHz (2.4–12.4 GHz), i.e., 135% of center frequency. The design prototype is fabricated, and the measured results have good agreement with simulated values. The effects of the slots have been analyzed by simulated surface current distribution. The designed antenna shows almost omnidirectional radiation patter and stable gain. The proposed hexagonal antenna may be suitable for UWB applications removing WiMAX and WLAN bands.

A miniature dual-band bandpass filter with interlocked stepped-impedance resonators (SIRs) is presented in this paper, which was designed for the student design competition held in European Microwave Week 2019. This bandpass filter is required to have two concurrent passbands, namely, the first passband at 900–1000 MHz and the second passband at 1427–1518 MHz bands, which cover six designated bands in sub-6 GHz range of fifth generation (5G) New Radio Access Technology. Three stopbands are required at 500–850, 1050–1350, and 1600–2000 MHz, respectively. To achieve the best figure of merit, an interlocked configuration of two SIRs is proposed. One advantage is that the impedance ratio of the inter-locked SIR can be controlled to have two passbands at the required frequencies. Second, the coupling section of the interlocked SIR gives three transmission zeros distributed to every stopbands such that the stopband suppression are dramatically enhanced. The measured results show that the passband insertion losses are 2.16 dB at the first passband and 1.33 dB at the second passband, and the return losses are greater than 10 dB. The stopband suppression at the transmission zeros are greater than 38 dB. The circuit is very compact as 41.40 × 19.96 mm2, equivalent to $0.25 \times 0.12\,\lambda _g^2$.

In this article, analog fiber optic links (radio-over-fiber, RoF, links) are presented as a flexible, low-cost solution for in-house distribution of millimeter-wave (mmw) signals. Mode-locked laser diodes (MLLD) serve as inexpensive mmw sources for the downlink distribution of mmw signals across an optical fiber link. We compare the robustness of direct and external RF modulation for such MLLD-based RoF systems, whereas the error vector magnitude (EVM) of the received symbols serves as a figure of merit. On the eve of 60 GHz WLAN standardization, we experimentally investigate the transmission of narrowband WLAN (IEEE 802.11a) signals in the millimetric range at moderate data rates. We also demonstrate broadband transmission of multi-band orthogonal frequency-division multiplexing (MB-OFDM) ultra-wideband (UWB) european computer manufacturers association (ECMA 368) signals in the 60 GHz band for data rates of up to 480 Mbps.

Millimeter-wave (mm-wave) beam-steering antennas are preferred for reducing the disruptive effects, such as those caused by high atmospheric debilitation in wireless communications systems. In this work, a compact broadband antenna array with a low loss feed network design is introduced. To overcome the short-range effects on mm-wave frequencies, a feed network – with a modified Butler matrix and a compact zeroth-order resonance antenna element – has been designed. Furthermore, the aperture feed technique has been utilized to provide a broadside stable pattern and improve the delivered gain. A Fabry-Perot layer without the height of the air layer is used. Taking advantage of this novel design, a broadband and compact beam-steering array antenna – capable of covering impedance bandwidths (from 33.84 to 36.59 GHz) and scanning a solid angle of about ~94°, with a peak gain of 17.6 dBi – is attained.

This paper presents a two-elements based, dual polarized, single layer, patch antenna array with improved isolation between transmit (Tx) and receive (Rx) ports for 2.4 GHz in-band full duplex (IBFD) or simultaneous transmit and receive wireless applications. The differential feeding deployed at the Rx port effectively suppresses the coupling which is termed as self-interference from the Tx port to achieve high Tx–Rx interport isolation. A simple 3 dB/180° ring hybrid coupler with nice amplitude and phase balance characteristics has been used for differential Rx operation. The mathematical description for a differential feeding based self-interference cancellation mechanism is also presented for the proposed dual polarized IBFD antenna array. The measurement results for the implemented prototype of the antenna array demonstrate very nice levels of Tx–Rx interport isolation. The implemented single layer, compact antenna array presents 10 dB return-loss bandwidth of more than 50 MHz for both Tx and Rx ports. The prototype achieves >80 dB peak interport isolation and 75 dB (65 dB) isolation in 20 MHz (50 MHz) bandwidth.

The design and characterization of a new broadband small patch antenna, based on an innovative magneto-dielectric material and suitable for wearable applications at 868 MHz, is presented. To reduce antenna dimensions, while preserving its radiation and matching performance, a barium-strontium hexaferrite Ba0.75Sr0.25Fe12O19 has been synthesized as the antenna substrate to achieve magnetic permeability double than vacuum in the band of interest. First material realization is characterized and dispersive permittivity and permeability behaviors are included in the design of a small patch antenna with a shorting-plate. A button-size realization is obtained and its suitability for wearable applications is numerically and experimentally demonstrated on body with and without the presence of conductive shielding. Very good agreement with measurements is demonstrated for both matching and radiation performance of the antenna.

In this paper, the design analysis of a multi-way and high-power radial combiner is presented. This combiner incorporates a rigid stripline-type combining structure. This analysis, based on an equivalent circuit model and segmentation of the radial transmission line, provides simple design formulae. The developed methodology, after fine-tuning with the help of an electromagnetic full-wave simulator, is physically demonstrated by developing a high-power (16 kW average) and high combining-efficiency (98.9%) 16-way combiner at the center frequency of 505.8 MHz. Its efficient and repeatable performance, fabrication-friendly structure, and absence of the heat-related problem, caused by the isolation resistor, are the main features of this design.

In this paper, a novel multi-mode resonator is presented, which is formed by cascading several open-circuited transmission line sections with a coupled-line section. Owing to its symmetry, even- and odd-mode analysis methods are applied to analyze its resonance characteristic. Based on this resonator, a microstrip ultra-wide bandwidth (UWB) bandpass filter is designed, fabricated, and measured. The simulated and measured results show that its bandwidth can cover the desired UWB. Return loss in passband is better than −14 dB. This filter is featured by good selectivity and wide stopband. Stopband suppression as low as −40 dB can be achieved within frequency range from 12 to 16 GHz.

This paper proposes the novel application of three meta-heuristic optimization algorithms namely crow search algorithm, moth flame optimization, and symbiotic organism search algorithm for the synthesis of uniformly excited multiple concentric ring array antennas. The objective of this work is to minimize the sidelobe level (SLL) and maximize the peak directivity simultaneously. Three different cases are demonstrated separately with various constraints such as optimal inter-element spacing and/or optimal ring radii. Comparative study of the algorithms using common parameters such as SLL, directivity, first null beam width, best cost, and run time has been reported. Investigation results prove the superiority of case 3 over other cases in terms of directivity and SLL. This work demonstrates the potential of these algorithms.