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.

Several breast microwave sensing (BMS) systems have shown encouraging results as a potential breast cancer detection tool. The existing systems in the literature have diverse designs, equipment, measurement protocols, and analysis methods. However, there is relatively little investigation on the impact and performance of varying system designs. This work compares the impact of system design parameters on three existing BMS systems. The first system, a bed-based system, was designed for use in a permanent clinic. The second system, a bench-top system, was created for laboratory research. The third system, a portable system, was designed for use in low-income and remote communities. The bed-based system had the highest resolving capabilities, achieving a spatial resolution of 12.4 ± 0.5 mm. Additionally, the bed system had the highest signal-to-noise ratio of 26 ± 1 dB. The portable system had the least intensity dependence on polar positions within the imaging chamber. The bed system had the highest contrast between tumor- and adipose-mimicking materials. However, the contrast of tumor- and fibroglandular-mimicking materials was similar for each system. By comparing and evaluating the performance of multiple BMS systems, we improve our understanding of system design, allowing for potential studies into an ideal BMS system.

This paper presents a low-profile, triple-band elliptical coplanar waveguide-fed antenna designed using the split-ring resonator technique. An artificial magnetic conductor with three zero-phases of the reflection coefficient is incorporated as a reflector to improve the antenna gain. The results show a gain enhancement of 3.4, 5.65, and 1.5 dBi at the three frequency bands of interest centered on 2.45, 5.2, and 8 GHz, respectively. The first two operational bands are Industrial, Scientific and Medical bands (2.33–2.59 and 4.97–5.48 GHz) that can be particularly used for wireless local area network and Bluetooth applications, while the third band (7.48-8.59 GHz) is suitable for military and satellite communications. The proposed solution that is designed, fabricated, and tested exhibits a good agreement between measured and simulated results.

A circularly polarized broadband antenna is designed for Wi-Fi 7 applications. The patch antenna is modeled in the shape of G, and the feed position is adjusted to produce the arms with a length difference of λ/4. The G-shaped patch antenna has shown an impedance bandwidth of 5% (6.16−6.48 GHz) and a peak gain of 6.3 dBi. The metasurface is structured with a periodic array of 4 × 4 patches. The metasurface is sandwiched between dielectric substrates beneath the G-shaped patch. The outcome of these combinations has achieved an impedance bandwidth of 41% (4.85−7.37 GHz) and an axial ratio bandwidth of 26% (5.26−6.83 GHz), and the antenna achieved a peak gain of 7.45 dBic.

This paper presents a wideband dual-polarized in-band full duplex antenna which can also suppress the higher order modes. A dual differential capacitive feeding scheme is proposed to increase the isolation between the co-located transmitter and receiver ports. The proposed design uses λ/4 resonators in close vicinity of the radiating patch to provide spurious-free characteristics. Further, a parasitic patch placed above the radiating patch at height “h” is used to enhance the input matching, impedance bandwidth, and gain of the proposed design. The key features of the proposed structure are its wide impedance bandwidth (∼20%), high inter-port isolation (>58 dB) throughout the entire operating frequency range (2.26–2.76 GHz), and simultaneous suppression of higher order modes which makes it a suitable candidate for modern wireless application. Finally, a prototype is fabricated and measurement results are in good agreement with simulation results.

In this paper, a polarization-reconfigurable antenna fed by a coplanar waveguide (CPW) using a stepped structure is presented. The main parts of the proposed antenna consist of a CPW-fed monopole and four branches. After studying and analyzing the structure and mechanism of the antenna, it was found that different polarizations can be generated by adjusting the antenna’s structure. Based on the mechanism, four PIN diodes are utilized and inserted between the four branches and the monopole for the switching. By controlling the ON/OFF states of the four PIN diodes, the antenna can switch among left-hand circular polarization (LHCP), right-hand circular polarization (RHCP), and linear polarization (LP). The optimized antenna has been fabricated and measured. Measured results indicate that the antenna’s −10-dB impedance bandwidth for LP is 15.93%, covering the frequency range from 2.3 to 2.71 GHz. The overlap bandwidth of −10-dB impedance and 3-dB axial ratio for the LHCP mode is 18.96%, covering frequencies from 2.1 to 2.54 GHz. For the RHCP mode, the overlap bandwidth is 20.5%, covering frequencies from 2 to 2.52 GHz. At all the three polarization modes, the antenna is capable of covering the 2.4-GHz WLAN band (2400–2480 MHz) as well as the LTE TD 2300 band (2300–2400 MHz).

In this paper, we propose a hybrid sparse array design utilizing Delaunay Triangulation algorithm for element positioning and Convex algorithm for element excitation optimization. This Delaunay Triangulation algorithm yields a radiation pattern devoid of grating lobes. Then Convex algorithm is used to optimize the element excitations to further decrease side-lobe-level. The minimum inter-element distance is as large as 8 times of wavelength. The peak-side-lobe-level can be −17.3 dB. Furthermore, beam steering can be achieved with good performance within 80° field-of-view range.

This paper presents the design and implementation of a novel single-fed microstrip hexagonal patch antenna, which operates on 2.4 GHz by employing three-dimensional (3D) printing technologies for circular polarization (CP) with wide 3 dB beamwidth. It was fabricated using a thermoplastic polymer-based material through a 3D printer and subsequently coated with copper. The design of the antenna consists of identical hexagonal slots in mesh grid fashion. These slots are filled with air and perturbations are introduced, by partially filling them with rectangular chunks of the polymer. This produces asymmetry in the substrate layer which leads to the splitting of the degenerate modes of the patch antenna, thus producing CP waves. The presence of volume fraction of air influences the effective permittivity and as a result the axial ratio beamwidth enhances to 176∘. The substrate was created as a double layer, lightweight unit using fused deposition modeling. A copper layer was then added to the underside of the lower substrate to serve as ground. The 3D gain of the antenna is found to be 7.01 dB. The proposed low-profile antenna has the potential to be incorporated in IoT and smart devices, intelligent transport systems, and GPS tracking.

This paper presents a notched ultra-wideband antenna designed to suppress interference from narrowband communication systems. The antenna features a defected ground structure and a stepped microstrip feedline for improved impedance matching and enhanced bandwidth. A bent slot structure is incorporated into the radiating patch to achieve the band-notched characteristic. It has a wide tunable frequency range which allows for flexible adjustment of the notch frequency. Traditional optimization methods, such as numerical analysis, are computationally expensive and inefficient, while heuristic algorithms are less precise. To address these challenges, an improved one-dimensional convolutional neural network (1DCNN-IPS) model is proposed for optimizing the bent slot design more efficiently. The trained 1DCNN-IPS model can accurately predict the antenna’s electromagnetic parameters, reducing mean squared error and training times compared to traditional methods. This provides an efficient and precise solution for antenna structural optimization.

A reconfigurable leaky-wave antenna and its application capable of electronically steering the beam within the entire hemisphere is presented. The original antenna is designed as a 1D array of conducting patches on a dielectric substrate coupled by varactors in series with interdigital capacitors. The beam of this antenna is driven by a DC bias that controls the capacitances of the varactor diodes over a frequency range from 8 to 8.2 GHz. Simulations showed a change in the direction of the main radiation pattern within 55° at 8 GHz by varying the varactor capacitances in the range of 0.1 to 1 pF. The maximum gain is 10 dBi and the side lobe level is -10 dB. The fabricated antenna sample operates at an applied DC voltage between 0 and 12 V, which corresponds to varactor capacitances controlled in the range of 1 to 0.15 pF. This gives a range of elevation angles equal to 40°. The application of the antenna in a reconfigurable star-type structure is proposed. The direction of the main lobe of the radiation pattern in azimuth is controlled by switching between the centrally excited eight antenna arrays using PIN diodes. The direction of radiation in elevation is controlled by the DC bias of the varactors of a particular array switched to “ON”. This complex beam steering throughout the hemisphere represents a novel character of the presented antenna. The antenna has a planar structure. Low-cost printed circuit board technology was used for its fabrication.

This paper presents a vertically folded gap waveguide filter for use as the filter element for each antenna in an array of slotted waveguide antennas, at W-band. Loaded gap-waveguide resonators are used to reduce the footprint of the filter, and the filter is vertically folded to reduce the length. New input and output transitions are proposed, as well as inter-resonator coupling structures that conform to the basic gap-waveguide structure. A 7th order filter with a bandwidth of 10 GHz and a center frequency of 101 GHz is designed to meet geometric constraints of a transmitter system. A sensitivity analysis was performed on the structure to determine the required manufacturing tolerances. The filter was manufactured and measured yielding 10 dB of return loss in the passband and a detuning of the passband by 1 GHz. The return loss at 88 GHz peaked due to deviations in manufactured gap height in the gap waveguide. Deviations from the simulated response were accounted for with a parameter extraction from the measured results.

This paper proposes a compact coplanar waveguide-fed slot antenna for ultra-wideband wearable applications, featuring six notch bands. The antenna utilizes a flexible liquid crystal polymer substrate with a thickness of 0.1 mm. The antenna achieves six band-notched characteristics by incorporating a split concentric ring etched on the radiating patch and L-shaped branches loaded on the ground plane. The proposed flexible antenna has dimensions of 30 × 30 mm2(0.65λ0*0.65λ0,λ0 is the free space wavelength at 6.5 GHz.). Measurement results show an impedance bandwidth ranging from 2.37 to 13.7 GHz and a fractional bandwidth of 134%. The notch bands cover 2.9–3.77 GHz for WiMAX applications, 4.14–4.9 GHz for the ARN band, 5.09–5.55 GHz for the WLAN downlink band, 5.86–6.46 GHz for the C-band uplink band, 6.66–7.39 GHz for the C-band/INSAT/super-extended band, and 7.93–8.43 GHz for ITU-8 GHz. The maximum gain in the operating band is 6.5 dBi. The performances of the flexible antenna are analyzed under bending conditions. The ANSYS HFSS electromagnetic simulator was used for the design and simulation of the proposed antenna. The flexible antenna is suitable for wearable applications.

The antenna characterization from planar near-field (NF) measurements is generally realized by using the classical NF to far-field transform technique of plane wave expansion (PWE). This approach imposes strong constraints on NF sampling. To overcome these limitations, an equivalent model of the antenna under test (AUT) is created based on a distribution of infinitesimal dipoles. A reduced-order model (ROM) of the problem is constructed to obtain a decomposition basis defining the radiated field. The powerful ability of the ROM in determining the number of points needed for accurate NF measurements is demonstrated. Also, efficient non-conventional sampling strategies are applied to the case of planar NF measurements and the influence of these distributions on the reduction of the number of samples is studied. The global analysis of our approach on simulated and measured NF data shows that only 20% of the total number of points are needed with respect to the classical PWE technique to achieve an accurate characterization.

Multipath components (MPCs) are both the challenge and the resources to exploit in high-frequency wireless communication, especially in environments with complex reflections. On the one hand, late-arriving MPCs cause inter-symbol interferences in digital communication. On the other hand, techniques such as multiple-input multiple-output and rake receivers have been widely applied to utilize the information carried in the math-path components. To this end, identifying and clustering MPCs is the foundation for tackling the challenges and boosting the utilization of reliable and correct information. Past research focuses either on extracting the path information or on clustering the extracted components. In this paper, we propose a complete workflow that performs identification as well as clustering of MPCs. We extend our previous work in clustering algorithms to indoor propagation measurements of three different frequency bands, as well as multiple transmitter–receiver locations. We verify that the fast attenuation of terahertz-band signals results in clear separations of peaks in measurements, which in turn facilitates the identification and clustering solutions. The ease of application highlights the wide-applying potential of high-frequency communication.