This paper presents a simulation approach of optical heterodyne systems by using the equivalent circuit representation of a distributed feedback laser (DFB) in the electrical domain. Since the electrical representation of the DFB laser is developed from the rate equations, its characteristics such as non-linearity, relative intensity noise (RIN), and phase noise can be predicted precisely for various biasing conditions. The model is integrated in a heterodyne radio over fiber (RoF) system where two DFB lasers are used to generate a millimeter-wave (mm-wave) signal. An optical phase-locked loop is also introduced to reduce the phase noise on the mm-wave signal. The optical phase noise contribution of individual lasers to the mm-wave signal is evaluated and compared with theoretical results. It is shown that the phase noise of the mm-wave is reduced considerably depending on the loop bandwidth and propagation delay. With the circuit simulation approach proposed, optical and mm-wave phase noises can be studied together with other circuit environments such as parasitic effects and driver circuits.

In this paper, a miniaturized elevated-coplanar-waveguide-fed antenna with a slotted ground plane is proposed. This antenna has a compact size of 25 mm × 25 mm × 1.6 mm where the ground plane is reduced by etching a trapezoidal slot along with two extended slits. A −10 dB wide-impedance bandwidth of 126% ranging from 2.8 to 12.4 GHz is achieved for the proposed antenna. The proposed antenna is successfully manufactured and experimentally investigated. The measurement shows a good agreement with the simulation. The measured radiation characteristic shows a stable and nearly omnidirectional pattern over the operating bandwidth region. The effects of various parameters on the antenna performance are analyzed and discussed as well.

A substrate integrated waveguide (SIW) based self-quadruplexing antenna and its design approach in Ku-band (12–18 GHz) is presented in this paper. This consists of splitting of TE220 mode of square-shaped SIW cavity by incorporating the two diagonal arrays of metallic vias. Accordingly, four orthogonal dominant mode triangular shape SIW cavity (DMTC) resonators are formed. This methodology ensures enhanced isolation. To achieve the broadside radiation, the cavity structure is fed using microstrip lines and rectangular slots are loaded on the top layer of each DMTC. The length and position of each rectangular slot being chosen such that quad-resonances are achieved at 13, 13.5, 14.3, and 15 GHz for the respective DMTC. The equivalent circuit model of the proposed design is also developed, and the tuning of each frequency band is analyzed without affecting the others. The proposed antenna is producing high isolation (>28 dB) among all four ports and a unidirectional radiation pattern with a high front-to-back ratio (>26.8 dB).

This paper presents a circuit architecture for a new integrated on chip test method for microwave circuits. The proposed built-in-self-test (BIST) cell targets a direct low-cost measurement technique of the gain and the 1 dB input compression point (CP1) of a K-band satellite receiver in the 18–22 GHz frequency bandwidth. A signal generator at the radiofrequency (RF) front end input of the device under test (DUT) has been integrated on the same chip. To inject this RF signal, a loopback technique has been used and the design has been accommodated for it. This paper focuses on the design of the most sensitive block of the BIST circuit, i.e. the RF signal generator. This circuit, fabricated in a SIGe:C BiCMOS process, consumes 10 mA. It presents a dynamic power range of 17 dB (−41; −24 dBm) and operates in a frequency range of 5.6 GHz (17.5; 23 GHz). This BIST circuit gives new perspectives in terms of test strategy, cost reduction, and measurement accuracy for microwave-integrated circuits and could be adapted for mm-wave circuits.

In this paper, we propose a machine-based classification technique using the scattering parameters obtained using a wearable wideband textile antenna to diagnose breast tumors. The breast phantom is formed following the dielectric properties of the human breast tissues and characterized to ensure the resemblance with a actual tissue model for the range of frequencies from 3 to 10 GHz. A biocompatible textile antenna is fabricated and embedded on an artificial breast phantom model to capture the variation of the reflection coefficient S11 and the transmission coefficient S21 for frequencies 3–10 GHz for different locations and sizes of tumors within the phantom model. Support vector machine is used to classify the healthy tissues from the malignant tumors based on the variation of the scattering parameters owing to the variation of the dielectric characteristics of the breast phantom model. The proposed method offers 84% and 89% accuracy while using S11 and S21 parameters alone for the analysis. However, the results further improve up to 93% as a combination of S11 and S21 signals is considered.

This paper illustrates the different possibilities given by additive manufacturing technologies for the creation of passive microwave hardware. The paper more specifically highlights a prototyping scheme where the 3D-printed plastic parts can be used as initial proofs of concept before considering more advanced 3D-printed parts (metal parts, for instance). First, a characterization campaign has been made on common plastics used by a 3D printer using the fused deposition modeling and material jetting (Polyjet©) technologies. The impact of the manufacturing strategy (high-speed or high-accuracy) on the part roughness, as well as on the dielectric material permittivity and loss tangent, has been specifically studied at 10 and 16 GHz. Based on a specifically optimized and deeply explained characterization method, the conductivity of a coating based on silver paint has also been characterized on such plastic parts at 10 and 40 GHz. These plastic materials and coating have been used for the creation of quasi-elliptic and tuning-free bandpass filters centered at 6 and 12 GHz and compared with a similar filter made of stainless steel by selective laser melting. Finally, a compact rectangular TE10 to circular TE01 mode converter also undergoes one prototyping step out of plastic before moving to an advanced part made out of stainless steel. This mode converter, which is made in a single part, is designed to operate from 28 to 36 GHz as a tuning-free final demonstrator.

In this paper, a 10 W ultra-broadband GaN power amplifier (PA) is designed, fabricated, and tested. The suggested design technique provides a more accurate starting point for matching network synthesis and better prediction of achievable circuit performance. A negative-image model was used to fit the extracted optimum impedances based on source-/load-pull technique and multi-section impedance matching networks were designed. The implemented amplifier presents an excellent broadband performance, resulting in a gain of 8.5 ± 0.5 dB, saturated output power of ≥10 W, and power added efficiency (PAE) of ≥23% over the whole bandwidth. The linearity performance has also been characterized. An output third-order intercept point (OIP3) of ≥45 dBm was extracted based on a two-tone measurement technique in the operating bandwidth with different frequency spacing values. The memory effect based on AM/AM and AM/PM conversions was also characterized using a modulated WiMAX signal of 10 MHz bandwidth at 5.8 GHz. Furthermore, a broadband Wilkinson combiner was designed for the same bandwidth with very low loss to extend the overall output power. Excellent agreement between simulated and measured PA performances was also achieved.

In this paper, a miniaturized open-ended dual-band band-pass filter with stepped series capacitance and shunt meandered line inductance for microwave frequency applications has been designed and discussed. In order to offer ease of fabrication and uniplanar configuration, coplanar waveguide feeding arrangement has been used. Zeroth order resonance, a special phenomenon of composite right/left handed transmission line has been utilized to miniaturize the filter size. The designed filter structure offers miniaturization with overall footprint size of 0.26λg × 0.19λg, where λg is the guided wavelength at the center frequency of 1.46 GHz. It offers 58.90% (1.03–1.89 GHz) and 25.93% (2.55–3.31 GHz) measured −3 dB fractional bandwidth with respect to the center frequencies of 1.46 and 2.93 GHz, respectively. Dispersion plot has been utilized to discuss the metamaterial properties for the proposed dual-band band-pass filter. In addition to above, the proposed filter structure presents almost flat group delay curve within both passbands. The proposed filter structure can be suitably utilized for distinct wireless applications, for example global navigation satellite system (1.559–1.610 GHz), GSM1800 (1.7–1.8 GHz), Wi-MAX (2.5–2.7 GHz), and naval radar and air traffic control (2.7–2.9 GHz).

A compact monopulse comparator with complete nulling in all DELTA channels is designed and fabricated. The proposed comparator has small dimension and consists of interconnections of four broadband branch-line couplers and several 90° phase shifters with multistage Schiffman coupled-lines. This comparator has been characterized by its eight-port S-parameters to generate the SUM and DELTA channel frequency responses. Over 30-dB null depth was achieved in DELTA channels across the SUM channels in pass band from 14.8 to 18.2 GHz frequency range.

This work focuses on the circuit modeling and full-wave analysis behavior of circular split ring resonator (SRR). We investigate an equivalent circuit model that allows calculating the resonant frequency from the geometric parameters. Equivalent LC parameters of inductance and capacitance are derived using conformal mapping and constitutive equations. Lumped element equivalent circuit models of resonator are investigated highlighting the behavior of inductance and capacitance. In order to validate our proposed analytical LC model, a comparison of theoretical and simulation results has been performed and a good agreement is achieved with a maximum error of 4.23% and a minimum error of 0.52%, which supports the validity of the equivalent model.

A circularly polarized ring cylindrical dielectric resonator antenna (ring-CDRA) of wideband impedance bandwidth is presented in this article. The proposed ring CDRA consist of an inverted rectangular (tilted rectangular) shaped aperture and inverted L-shaped slotted microstrip feed line. The tilted rectangular shaped aperture and inverted L-shaped microstrip feed line generate two-hybrid mode HEM11δ and HEM12δ while ring CDRA and slotted microstrip feed line are used for the enhancement of impedance bandwidth. The proposed ring CDRA is resonating between 6.08 and 12.2 GHz with 66.95% (6120 MHz) impedance bandwidth. The axial ratio (AR) bandwidth of 6.99% (780 MHz) is obtained between 10.76 and 11.54 GHz with a minimum AR value of 0.2 dB at a frequency of 11 GHz. The proposed geometry of ring CDRA has been validated with measurement performed by VNA and anechoic chamber. The operating range of the proposed radiator is useful for different applications in X-band.

In this study, a new microstrip patch antenna with wideband radar cross-section (RCS) reduction is presented. The RCS of the proposed antenna was reduced by subtracting the current-direction slots of the patch, with the radiation performance sustained not only for the current-direction subtraction, but also for the no modification in the ground plane. Modified and reference antenna were fabricated and measured. The simulation and measurement results showed that the modified antenna reduced the in-band and out-band RCS simultaneously with no detriment to the radiation performance. In the frequency band from 3.9 to 8.1 GHz, the RCS of the modified antenna was reduced in the whole band compared with the RCS of the reference antenna. The maximum RCS reduction was 7 dB at a frequency of 6.7 GHz.

Two coaxial waveguide bend mode converters that transform coaxial transverse electromagnetic mode to TE11 coaxial waveguide mode are presented in this paper. Both converters are designed and optimized on the basis of the strictly derived mode coupling coefficients. Conversion efficiencies of both converters are over 99% and the power-handling capacities reach a gigawatt level. The combined dual-bend mode converter is fabricated and tested. The experimental results coincide well with the theoretical calculations and simulations, which demonstrates the feasibility of the designed converter.

The electrical modeling of power packages is a major issue for designers of high-efficiency hybrid power amplifiers. This paper reports the synthesis and the modeling of a packaged Gallium nitride (GaN) High electron mobility transistor (HEMT) associating a nonlinear model of the GaN HEMT die with an equivalent circuit model of the package. The extraction procedure is based on multi-bias S-parameter measurements of both packaged and unpackaged (on-wafer) configurations. Two different designs of 20 W packaged GaN HEMTs illustrate the modeling approach that is validated by time-domain load-pull measurements in S-band. The advantage of the electrical modeling dedicated to packaged GaN HEMTs is to enable a die-package co-design for power matching. Internal matching elements such as Metal oxide semiconductor (MOS) capacitors, Monolithic microwave integrated circuits (MMICs), and bond wires can be separately modeled to ensure an efficient optimization of the package for high power Radio frequency (RF) applications.

The design of agile active antennas requires an efficient modeling methodology in order to quantify the impact of other components on the array radiation pattern, and especially the influence of power amplifiers (PA). Therefore, the performance prediction of PA on TX chains is of prime importance. This article describes two different approaches for active antenna applications. The first one concentrates on PA macro-modeling, which takes into account a large output load impedance mismatch with a voltage standing wave ratio up to 4:1. A PA behavioral model based on nonlinear scattering functions was developed and extracted from CW measurements. The model validity was checked by comparison with the measured data. The second one describes a novel technique for synthesizing a given radiation pattern, whereas taking into account the mutual coupling and calculated matching impedances (ZL ≠ 50 Ω) of each antenna in the array according to frequency and pointing angle.

Doubled frequency optical two-tone generation and optical single sideband (SSB) modulation by the dual-electrode-type electro-optic (EO) modulator with a single Mach–Zehnder (MZ) interferometer were considered. We theoretically showed that redundant spectrum components in the modulated optical signals, which are caused by the imbalance of light splitting ratio between the two arms of the interferometer, are significantly suppressed by controlling the input power ratio of RF modulation signals applied to each electrode. This effect was confirmed by the experiment, where an optical two-tone with the redundant components 49.8 dB lower than the primary two-tone components in intensity level was obtained. This method is also valid for suppression of undesired frequency components of RF signals that are generated at a photo detector from the optical two-tone waves propagated through a dispersive optical fiber.

In this article, an angle-independent wideband metamaterial microwave absorber (MMA) for C (4–8 GHz) and X (8–12 GHz) band frequency is presented. The unit cell of the proposed MMA consists of outer and inner structure associated with lumped resistors. The outer structure consists of rectangular split-ring resonator, whereas the inner structure consists of circular split-ring resonator. The structure is made up of three layers, in which top and bottom layers are made up of copper acting as a conducting material. The middle layer is made up of FR-4 acting as a dielectric substrate. The resonating structure at the top is designed in such a way that wideband absorption is achieved in the range from 6.11 to 13.52 GHz. The wideband absorption within the range approaches almost unity having a bandwidth of 7.41 GHz. Three different peaks are considered in the range of interest having maximum absorption of 0.94, 0.94, and 0.99 at frequencies of 6.76, 11.15, and 13.07 GHz, respectively. The structure is analyzed with respect to the effective parameters, i.e., effective permittivity (${\varepsilon _{{\textrm{eff}}}}$) and effective permeability (${\mu _{{\textrm{eff}}}}$), to prove that the structure acts as a metamaterial. Electric field and current distribution are plotted at three different peaks to prove the mechanism of wideband absorption. Normal and oblique incidence are plotted to determine that the structure is behaving as an angle independent. The simulated structure is fabricated on FR-4 substrate and measured inside an anechoic chamber. Finally, to prove the novelty of the work, the proposed structure is compared with the already reported MMA. The proposed MMA finds practical applications in radar cross section reduction, terrestrial communication, keyless entry system, space communication, radar, and baby monitor.

In this work, microwave planar resonators are printed with silver nanoparticle inks using two printing technologies, inkjet printing and aerosol jet printing, on polyimide substrates. The microwave resonators used in this paper operate in the frequency band 5–21 GHz. The printing parameters, such as the number of printed layers of silver nanoparticle inks, drop spacing, and sintering time, were optimized to ensure repeatable and conductive test patterns. To improve the electrical conductivity of silver deposits, which are first dried using a hot plate or an oven, two complementary sintering methods are used: intense pulsed light (IPL) and laser sintering. This paper presents the results of different strategies for increasing the final quality factor of printed planar resonators and the trade-offs (sintering time versus final conductivity/unloaded Q) that can be reached. Improvement of the resonator unloaded quality factor (up to +55%) and of the equivalent electrical conductivity (up to 14.94 S/μm) at 14 GHz have been obtained thanks to these nonconventional sintering techniques. The total sintering durations of different combinations of sintering techniques (hot plate, oven, IPL, and laser) range from 960 to 90 min with a final conductivity from 14.94 to 7.1 S/μm at 14 GHz, respectively.

Systems based on secondary surveillance radar (SSR) downlink signals, both with directional and with omni-directional antennae (such as in multilateration), are operational today and more and more installations are being planned. In this frame, high-density traffic leads to the reception of a mixture of several overlapping SSR replies. By nature, SSR sources are sparse, i.e. with amplitude equal to zero with significantly high probability. While in the literature several algorithms performing sources separation with an m-element antenna have been proposed, none has satisfactorily employed the full potential of sparsity for SSR signals. Most sparsity algorithms can separate only real-valued sources, although we present in this study two algorithms to separate the complex-valued SSR sources. Recorded signals in a live environment are used to demonstrate the effectiveness of the proposed techniques.

With the increasing demand for smarter antenna design in advanced technology applications, well-designed antennas have been an important factor in enhancing system performance. Most traditional antenna design requires multiple iterations and extensive testing to produce a final product. Machine learning (ML) algorithms have been used as an alternative to predict the optimal design parameters, but the outcome depends highly on the ML model efficiency. With recent development in machine learning algorithms and the availability of data for antenna design, we investigated different machine learning algorithms for optimizing the output strength of three basic antennae by analyzing the signal strength of the antenna for various antenna parameters. Different regression-based ML models were used to learn the behaviors and efficiency of three different antennas and to predict the output strength (S11) for different ranges of frequencies. The experiment compared and analyzed these ML regression algorithms for three different antennas: shot antenna, patch antenna, and bowtie antenna. In addition, the paper also provides comparison of ensemble ML models for performance analysis using the best three ML algorithms from the preliminary study. This study optimizes antenna parameters and quicker and smarter antenna design procedure using ML algorithms as compared to traditional design methods.