In this paper, we introduce and validate signal processing techniques for the estimation of the individual rotation rates of multicopter’s Unmanned Aerial Vehicle (UAV), by exploiting a multistatic radar echoes. To validate the techniques, which have been introduced in our previous works, in this paper, we present a simulator for the multistatic radar echoes scattered by a UAV that integrates quadcopter’s aerodynamics with electromagnetic modeling to generate realistic radar return, characterized by blades rotating in different directions and with different rates depending on the flight trajectory to be traveled. This simulator enables the validation of signal processing.

We leverage the simulator to assess the effectiveness of autocorrelation and cross-correlation (XCF) techniques in separating multiple propellers, both in hovering and along a realistic flight trajectory. Simulated results confirm that XCF allows distinguishing counter-rotating propellers, while co-rotating ones remain unresolved due to their similar speeds. The simulator also demonstrates how variations in rotation rates can be used to infer the presence and weight of a payload. Experimental validation with a C-band continuous wave radar confirms the findings and highlights the impact of material properties on resolution. Finally, we exploit the simulator to investigate the effect of higher carrier frequencies, showing that increasing the operating frequency improves the ability to discriminate co-rotating propellers, supporting improved UAV classification, payload estimation, and trajectory prediction for anti-drone applications.

This paper presents an Substrate Integrated Waveguide (SIW) cavity-backed symmetric dual-beam self-diplexing slot antenna for short-distance multiuser point-to-point communications using mm-wave frequency bands. The antenna is fed by two capacitive-gap-coupled microstrip lines, which help the antenna to operate at two different frequency bands with a self-diplexing property. Independent frequency tunability at both the operating bands can be achieved by varying the capacitive gap position along the microstrip feed lines. To enhance port isolation and achieve dual-beam characteristics the design incorporates an L-shape folded slots, centrally located shorting via, W-slot, corrugated microstrip structures and mender line slot. The beams are directed at ± $\theta = \pm 43^\circ$ with a half-power beam width of 56∘ each. The antenna offers peak realized gains of 5.95 and 6.21 dBi at the lower and upper band, respectively. The antenna is fabricated and measured, which shows a good agreement between simulation and measurement, confirming its suitability for short-distance multiuser point-to-point communications

In this work, a wideband filtering antenna based on substrate integrated waveguide (SIW) cavities is proposed. The SIW cavities with zigzag topology excite multiple modes to increase the potential filtering bandwidth. The radiation slot etched on the cavity merges the resonant modes into a single frequency band, thereby enabling directional broadband radiation. Moreover, two supplementary slots are introduced to facilitate wideband impedance matching without increasing the overall size. Furthermore, both the cavities and the slots work together to create three radiation nulls, improving the filtering performance. The proposed SIW slot filtering antenna achieves good frequency selectivity and meets the increasing demand for wideband and integration of multifunctional devices. To validate the design, a prototype antenna was fabricated and tested. The measured results show that the prototype has an operating bandwidth of 10.1% at the center frequency of 11.16 GHz. The peak gain within the passband is 6.19 dBi, and the out-of-band radiation rejection level is better than 20 dB.

This paper elaborates the design and analysis of cross-aperture-coupled twin port ceramic radiator. Stimulation of alumina ceramic using a cross slot helps to produce circular waves within 7.35–7.8 GHz. The polarization diversity concept helps to improve the separation level by above 25 dB. Loading of double negative unit cell made metasurface (MS) improves the antenna gain over 11.5 dBi within the working spectrum. Machine learning (ML) techniques, i.e. Decision Tree and Random Forest are utilized to predict the |S11|/Axial ratio parameters. Experimental verification/ML prediction and optimized simulated consequences confirm that the structured radiator works efficiently between 7.21 and 8.2 GHz with over 25 dB isolation between the ports. Directive pattern and decent values of (MIMO) parameters make the radiator applicable for the 6G communication system.

This paper presents a low-profile miniaturized dual-band antenna utilizing the quarter-mode substrate integrated waveguide (QMSIW) structure. The two modes of TE110 and TE220 of a single QMSIW structure are employed, enabling a dual-band operation. The frequency ratio between the two bands can be tuned by loading a capacitive structure, which is comprised of a capacitive-loaded patch and a short circuit post, inside the QMSIW structure. By introducing parasitic QMSIW structures through magnetic coupling, a dual-band antenna with enhanced bandwidths is achieved. The antenna has dimensions of smaller than 400 mm2 (0.048λL2) with a uniform height of 1.4 mm (0.016λL). Measurement results indicate that the −6 dB impedance bandwidths of the antennas can cover the 5G N78 (3.3–3.6 GHz) and N79 (4.8–5 GHz) bands, and the average efficiencies is better than −2.5 dB. To the authors’ knowledge, the proposed designs offer dual-wideband operation while having the smallest planar dimension compared to the previously reported antennas. Furthermore, an extended electric coupling dual-band antenna configuration is also described and measured, which achieves similar bandwidth extension as the proposed antenna.

Acute respiratory distress syndrome (ARDS) is a critical lung condition caused by trauma or infection. This study explores the development and evaluation of human lung phantoms to investigate the feasibility of using microwave frequencies for ARDS detection. Both physical semisolid phantoms and their numerical models were developed in inflated and deflated states to replicate the dielectric properties of healthy and affected lungs. Three phantom sets with varying water and air content were fabricated to simulate different stages of respiratory distress. The geometric parameters of the phantoms were derived from CT scans of 166 ARDS patients. Dielectric permittivity and conductivity were measured using a Keysight N1501A dielectric probe over a 0.5–13 GHz range, showing strong agreement with IFAC’s reference data. To validate the models, horn antennas operating between 8.2–12.4 GHz were used to measure S-parameters (S11 and S21) in both physical and numerical phantoms. The results demonstrated consistent changes in transmission and reflection characteristics corresponding to variations in lung volume and dielectric properties. These findings support the potential of microwave imaging as a non-invasive tool for early ARDS detection by effectively distinguishing between healthy and distressed lung states based on measurable electromagnetic response.

In the advanced era of compact and convenient devices, electromagnetic microwave brain imaging systems have emerged as substitutes for large and bulky imaging devices such as X-rays, CT scans, MRIs, and ultrasounds for diagnosing brain disorders. This article introduces a compact monopole antenna specifically tailored for microwave imaging in brain stroke detection. The bidirectional antenna incorporates a triple hollow rectangular patch and a hexagonal slotted ground for enhanced performance. The antenna is constructed on an FR-4 substrate with a thickness of 1.6 mm. The design is finalized using CST, with parameters adjusted to achieve the desired bandwidth and gain performance. The antenna provides a bandwidth of 2.16 GHz, spanning from 1.35 to 3.51 GHz, with a return loss |S11| < 10 dB (VSWR < 2) and a peak gain of 5.1 dBi at 3.5 GHz, while maintaining stable radiation characteristics across the entire frequency range. Simulation results indicate that the proposed antenna is well-suited for microwave-based brain stroke detection and imaging applications. The fabricated antenna has been tested for brain stroke detection with an innovative setup in the lab. It is observed that the stroke models have been detected clearly.

In this work, a compact active integrated antenna based on a highly compatible antenna-in-package (AiP) solution is proposed. It consists of two sections, namely, a cover plate integrated with an antenna and a package backplane that carries a GaN power amplifier (PA) die. The proposed AiP solution not only provides efficient interconnection between the antenna and the GaN PA die while providing physical shielding, but also provides impedance compensation for the die to improve the matching performance. Besides, a plated through hole array is designed inside the package backplane to significantly improve heat dissipation performance. The proposed AiP solution is compatible with radio frequency integrated circuit (RFIC) dies with different pin arrangements. Two prototypes are fabricated and measured for validation. The first prototype is the active integrated antenna based on the GaN PA, which shows an impedance bandwidth of 25.7–28.7 GHz, a peak gain of 31 dBi, and a dimension of 8 mm × 8 mm × 1.7 mm. Another prototype is based on a GaN front-end module (FEM) die integrating the PA and low noise amplifier, which demonstrates better EVM and ACPR than the conventional design with separate antenna and FEM.

Due to the rising occupancy of the radio spectrum, new strategies for covering the ever increasing amount of data are necessary. This work presents a system for integrating data transmission into a frequency-modulated continuous wave (FMCW) radar by modulating the radar signal with frequency shift keying (FSK). The system offers a high chirp bandwidth of 5 GHz and uses the 60 GHz band. The FSK carrier frequency affects the noise level. A higher frequency leads to a lower noise floor due to 1/f-noise but requires a higher sampling rate. Therefore, 15 MHz was chosen as a compromise. A high data rate allows for a fast data transmission but requires a short chirp time, which leads to a noisier frequency chirp. The radar parameters are also affected by this choice. This leads to a baud rate of 20.8 kbit/s. With a higher order FSK, higher data rates are possible. This proves that the data transmission via FMCW radar signals is possible and a first choice if lower data rates are sufficient, because the hardware effort is comparatively low.

This paper presents a millimeter-wave end-fire dual-polarized (DP) array antenna with symmetrical radiation patterns and high isolation. The DP radiation element is formed by integrating a quasi-Yagi antenna (providing horizontal polarization) into a pyramidal horn antenna (providing vertical polarization), resulting in a DP radiation element with a symmetrical radiation aperture. To efficiently feed the DP element while maintaining high isolation, a mode-composite full-corporate-feed network is employed, comprising substrate-integrated waveguide supporting the TE10 mode and substrate-integrated coaxial line supporting the TEM mode. This design eliminates the need for additional transition structures, achieving excellent mode isolation and a reduced substrate layer number. A 1 × 4-element DP array prototype operating at 26.5–29.5 GHz using low temperature co-fired ceramic technology was designed, fabricated, and measured. The test results indicate that the prototype achieves an average gain exceeding 10 dBi for both polarizations within the operating band. Thanks to the symmetrical DP radiation element and mode-composite full-corporate-feed network, symmetrical radiation patterns for both polarizations are observed in both the horizontal and vertical planes, along with a high cross-polarization discrimination of 22 dB and polarization port isolation of 35 dB.

In this paper, we present the design, simulation, fabrication, and measurements of an on-chip dielectric resonator (DR)-fed millimeter-wave high-gain antenna system with in-antenna power combining capability. A low-profile resonant cavity antenna is fed by four spherical DR, showcasing the antenna’s multi-feed capabilities. Each DR is fed by two microstrip resonators located diagonally opposite on a planar circuit board and are excited via coaxial connectors. The design incorporates a printed partially reflecting superstrate, reducing the antenna’s overall size and profile while simultaneously enhancing directivity by approximately $10\,\mathrm{dB}$ at the design frequency of $30\,\mathrm{GHz}$. The antenna exhibits wideband matching. Key performance metrics, such as directivity, gain, beamwidth, and bandwidth, predicted by full-wave electromagnetic simulations align well with the results from experimental measurements.

This article proposes a hexagonal shaped circularly polarized (CP) antenna at ultra-high frequency (UHF) for radio frequency identification (RFID) and X-band applications. Initially, the antenna operates only in X-band and to convert this CP dual-band antenna asymmetric ground plane and four electromagnetic band gap structures are employed. A metasurface consisting of two complementary metamaterial structures is positioned above the patch at a 9 mm distance to enhance the gain and impedance bandwidth in both the bands. The presented antenna whose electrical dimension 0.48 λg × 0.48 λg × 0.02 λg achieves an impedance bandwidth of 796 MHz and of 4.24 GHz in UHF–RFID and X-band spectrum, respectively. The proposed antenna achieves circular polarization and has a bandwidth of 995 MHz and 796 MHz which spans 2.28–3.28 GHz and 10.44–11.24 GHz, respectively, with a 3 dB axial ratio. In addition to these, a stable radiation characteristic with an average gain of 6 dBi at both 2.45 GHz and 11.21 GHz are achieved which makes it suitable for RFID based real time logistic warehousing applications.

In this article, a simple model is proposed to compute the effective dielectric constant, resonant frequency, quality factors, input impedance, bandwidth and gain of a coaxial probe fed annular ring patch antenna loaded with several dielectric layers. This model is based on conformal mapping technique, cavity model and single resonant parallel R-L-C circuit. The computed values employing the present model are compared with experimental and simulation results. The present model shows good agreement with experimental and simulation results.

This research explores a circularly polarized (CP) multiple-input-multiple-output (MIMO) dielectric resonator antenna (DRA) designed specifically for 5G Sub-6 GHz and WiMAX applications. The antenna system utilizes a unique H-shaped feeding strip to excite each DRA element. This specialized feeding mechanism facilitates the activation of higher-order degenerate modes, including TE$_{\delta13}^x$ and TE$_{1 \delta 3}^{y}$, which are essential for achieving circular polarization. The antenna exhibits a reflection coefficient of −37.52 dB at 3.49 GHz, covering the entire CP passband and operating over a broad bandwidth of 1.35 GHz (3.40–4.75 GHz) yielding a return loss of 35.52%, making it suitable for Sub-6 GHz applications. An axial ratio bandwidth of 24.6% (3.4–4.2 GHz) is observed, with inter-port isolation of greater than −25.3 dB throughout the usable frequency band with a maximum efficiency of approximately 98%, indicating near-lossless power radiation. Additionally, the estimated gain is 5.95 dBic. The proposed MIMO design presented effectively reduces the intersecting spatial field components between antenna elements, leading to a lower envelope correlation coefficient and enhanced inter-port isolation. This diversity gain of the proposed antenna is a strong candidate for use in rich multi-path environments, helping to mitigate the effects of channel fading.. Initially, the proposed antenna design was examined using the time-domain solver of CST, followed by the fabrication of a prototype for experimental validation. The antenna exhibits a stable response, making it well-suited for 5G Sub-6 GHz and WiMAX applications.There is a satisfactory alignment between the results obtained from simulations and those observed experimentally.

A rigorous analysis of the scattering of plane and cylindrical waves from a strip loaded single near zero and double near zero (DNZ) metamaterial cylindrical object is presented. The proposed problem has been solved using integral equations derived from Green’s theorem and usual tangential boundary conditions. During the analysis, it was found that by loading a strip onto the metamaterial cylindrical objects, one can enhance or diminish the scattering under some specified conditions. It is shown that an enhancement in the back scattering occurs for a strip loaded DNZ metamaterial cylinder as compared to the back scattering of an unloaded DNZ metamaterial cylinder for both types of incident polarization. In the case of a specifically located electric line source, it is argued that by loading a strip onto a DNZ metamaterial cylinder, one can reduce the magnitude of the total field significantly at specific observation azimuth angles. For a specific location of a magnetic line source, the magnitude of total field of a strip loaded mu near zero (MNZ) metamaterial can be significantly enhanced as compared to unloaded MNZ cylinder in the specific observation directions. This parametric investigation is helpful in the designing of cylindrical metamaterial-based devices.

Wireless channel propagation parameter estimation forms the foundation of channel sounding, estimation, modeling, and sensing. This paper introduces a deep learning approach for joint delay and Doppler estimation from frequency and time samples of a radio channel transfer function.

Our work estimates the 2D path parameters from a channel impulse response containing an unknown number of paths. Compared to existing deep learning-based methods, the parameters are not estimated via classification but in a quasi-grid-free manner. We employ a deterministic preprocessing scheme that incorporates a multichannel windowing to increase the estimator’s robustness and enables the use of a convolutional neural network (CNN) architecture. The proposed architecture then jointly estimates the number of paths along with the respective delay and Doppler shift parameters of the paths. Hence, it jointly solves the model order selection and parameter estimation task. We also integrate the CNN into an existing maximum-likelihood estimator framework for efficient initialization of a gradient-based iteration, to provide more accurate estimates.

In the analysis, we compare our approach to other methods in terms of estimate accuracy and model order error on synthetic data. Finally, we demonstrate its applicability to real-world measurement data from a anechoic bistatic RADAR emulation measurement.

In this article, we discuss the behavioral modeling of the power amplifier (PA) for system-level simulations through its most advanced approach, named TPM model, based on a simplification of the Volterra series following the method of separation of the low and high frequency memory effects present in PA. The model, relying on frequency domain CW characterization of the PA, shows a limitation when applied to high-power radar applications, for which this article investigates an alternate solution based on time-domain pulsed RF characterization.

INCUS (INvestigation of Convective UpdraftS) is a NASA Earth Science mission scheduled to launch in 2026. The goal of the mission is to study in detail how water vapor and droplets move inside tropical storms and thunderstorms and understand their effects on weather and climate models. To carry out this study, the mission will use three almost identical SmallSats, each equipped with a Raincube-heritage Ka-band radar. The deployable mesh reflector antenna is a new 1.6 m design provided by Tendeg, which is fed using a seven-horn feed assembly to generate overlapping secondary beams. This paper discusses the approach used to design and fabricate the feed assembly and presents the measured and calculated RF performance parameters.