This paper describes a small unmanned aerial vehicle (UAV)-based synthetic aperture radar (SAR) system using low-cost radar (5–6 GHz), position (GNSS/RTK) and attitude (IMU) sensors for the generation of high-resolution images. Measurements using straight as well as highly curved flight trajectories and varying flight speeds are presented, showing range and cross-range lobe-widths close to the theoretical limits. An analysis of the improvements obtained by the use of attitude angles (roll, pitch, and yaw), to correct for the relative offsets in antenna positions as the UAV moves, is included. A capability to generate SAR images onboard with the back-projection algorithm has been implemented using a GPU accelerated single-board computer. Generated images are transmitted to ground using a Wi-Fi data link.

The paper presents a 1 × 2 B-shaped antenna array for dual-band operation at 4 and 8 GHz. The antenna design consists of a rectangular patch with two annular-strip lines fabricated on the top layer and finite ground plane on the bottom layer. The array is formed by designing an optimum T-shaped microstrip line for impedance matching. The dimensions of the antenna array are 78 × 36 × 1.6 mm3. Full-wave simulations have been conducted and the measured results are in good consent with the simulated results. The measured impedance bandwidth (reference −10 dB) has been observed at 3.84–4.16 and 7.78–8.38 GHz. Measured peak gain and radiation efficiency at 4 and 8 GHz are 8.3, 9.4 dB and 82.5 and 81.2%, respectively.

Two configurations of a modified feather-shaped antenna element are proposed for super wideband (SWB) multiple-input multiple-output (MIMO) applications. The antenna element geometry comprises of a circular slot-loaded feather-shaped radiator and rectangular notch-loaded quarter elliptical coplanar waveguide ground plane. An operating bandwidth of 4.4–51.5 GHz with inter-port isolation, S21 ≥ 15 dB for spatial diversity configuration, and 3.8–51.5 GHz with S21 ≥ 15 dB in pattern diversity configuration are achieved. The footprints of the antenna configurations are 17 × 33 and 31 × 31 mm2. Both configurations exhibited an envelope correlation coefficient of <−20 dB. The proposed MIMO configurations are fabricated and experimentally validated. The designed antenna configurations are SWB and compact.

In this paper, non-uniform meandered line shunt capacitive RF-MEMS switch is presented at an elliptical patch etched with a split-ring resonator (SRR) for satellite communication applications. The non-uniform meander line shunt capacitive is a fixed-fixed type of RF-MEMS switch that is introduced in this model antenna. The proposed antenna design is resonated at 10.46 GHz with the return loss of −37.6 dB. The performance evolution of the proposed antenna design is evaluated with and without integrated RF-MEMS switch on the proposed antenna SRR. It is observed that the proposed model at the ON-state switch resonates at 10.57 GHz frequency with the return loss of −30 dB. Similarly, at the OFF-state switch, it resonates at 10.53 GHz frequency with the return loss of −43 dB. Al3N4 (aluminum nitride) is used for the switch as a dielectric material, hence the switch attains higher isolation. The actuation voltage of 7.9 V is required for the switch to actuate from ON to OFF state. The switch attains minimum insertion and return loss which is discussed in further sections. The proposed antenna is fabricated and tested by a vector network analyzer; there is a good agreement between the simulated and measured results.

This paper presents a low-profile multi-slotted patch antenna for long term evolution (LTE) and fifth-generation (5G) communication applications. The studied antenna comprised of a stepped patch and a ground plane. To attain the required operating band, three slots have been inserted within the patch. The insertion of the slots enhances the capacitive effect and helps the prototype antenna to achieve an operating band ranging from 3.15 to 5.55 GHz (S11 ≤−10 dB), covering the N77/N78/N79 for sub-6 GHz 5G wireless communications and LTE bands of 22/42/43/46. The wideband antenna presented in this paper offers omnidirectional stable radiation patterns, good gains, and efficiency with a compact size which make this design an ideal contender for wireless fidelity (WiFi), wireless local area network (WLAN), LTE, and sub-6 GHz 5G communication applications.

Phase retrieval algorithm is an effective method to reconstruct the surface distortions for reflector antennas. As the traditional Fourier iterative algorithms usually stagnate at local minima, we previously proposed a global phase retrieval algorithm, named CMAES-HIO, based on the hybridization of hybrid-input-output algorithm and covariance matrix adaptation evolution strategy. We address the problem of selection of the Zernike order used in the phase parameterization for CMAES-HIO algorithm in this paper. By introducing a hybrid evaluation parameter, which combines the algorithm accuracy and time consumption, we utilize the Monte-Carlo method to simulate the algorithm performance under different random surface distortions. Simulation results show that for an unknown surface distortion, a Zernike order of 5 or 6 is probably the optimum for the comprehensive algorithm performance with respect to time and accuracy.

A compact co-planar waveguide (CPW) fed planar elliptical antenna has been designed and presented for super wideband (SWB) characteristics. The designed antenna has an overall size of 30 × 30 × 1.57 mm3, and it consists of an elliptical patch radiator fed using a modified 50 Ω CPW-fed tapered microstrip feed line. By using a semi-ring shaped structure with a tapered feed line, an impedance bandwidth of 180.66% has been observed from 1.27 to 25 GHz with a ratio bandwidth of 19.68:1. To validate simulation results, the designed antenna has been fabricated and measured, and a reasonable agreement has been observed between simulated and measured results. It has also been observed that the designed antenna offers good radiation properties over the entire operating bandwidth. The simulated average gain and radiation efficiency of the proposed SWB antenna is noted to be 4.3 dBi and 95.77%, respectively; while the measured average gain and radiation efficiency is 3.8 dBi and 94.69%, respectively.

In this article, a dynamically switchable ultra-wideband (UWB) planar monopole antenna employing defected ground structure (DGS) with a folded stepped impedance resonator (SIR) that can operate as either a UWB mode or the single band-notched mode is introduced. The UWB monopole antenna contains a novel whirligig-shaped radiating patch and a chambered conductor as a partial ground plane. The switchable UWB antenna uses one PIN diode as switching elements in the DGS-SIR structure without any biasing network. When the state of diode is OFF, the planar monopole antenna changes to the UWB mode, and when the diode is turned ON, a frequency notch is created at 5–6 GHz. The state of diode is set to the “ON” state dynamically in the presence of a 5–6 GHz RF signal that is detected by using a wireless power management unit (PMU) that contains a broadband rectenna and a DC-DC passive booster. The rectenna consists of a novel cypress-shaped monopole antenna as a signal receiving part and two sub-rectifiers which are connected to a 3 dB branch-line coupler with a grounded isolation port. The antenna switches from UWB to single band-notched when an RF input signal (≥8.5 dBm) in the 5.25 GHz is sensed by the RF PMU with a conversion efficiency of 26% and DC output voltage of 0.36 V, and it fades immediately in real time when the external RF signal is eliminated. In the three-tone signals, the efficiency and input signal improvements are about 10% and −5.5 dBm in the low-power levels, especially, and so develop and enhance the performance of the dynamic reconfigurability.

The 5th generation new radio (5G NR) standards create both enormous challenges and potential to address the spatio-spectral-temporal agility of wireless transmission. In the framework of a research unit at TU Ilmenau, various concepts were studied, including both approaches toward integrated circuits and distributed receiver front-ends (FEs). We report here on the latter approach, aiming at the proof-of-principle of the constituting FEs suitable for later modular extension. A millimeter-wave agile multi-beam FE with an integrated 4 by 1 antenna array for 5G wireless communications was designed, manufactured, and verified by measurements. The polarization is continuously electronically adjustable and the directions of signal reception are steerable by setting digital phase shifters. On purpose, these functions were realized by analog circuits, and digital signal processing was not applied. The agile polarization is created inside the analog, real-time capable FE in a novel manner and any external circuitry is omitted. The microstrip patch antenna array integrated into this module necessitated elaborate measurements within the scope of FE characterization, as the analog circuit and antenna form a single entity and cannot be assessed separately. Link measurements with broadband signals were successfully performed and analyzed in detail to determine the error vector magnitude contributions of the FE.

This study presents a new design of a four-element multiple-input multiple-output (MIMO) antenna, which is suitable for X-band applications. The circular polarization (CP) operation in this work is attained by using Tai Chi-shaped patches and L-shaped feeds. The proposed four-element MIMO antenna achieves two resonant frequencies, the first one at around 7.75 GHz and the second one with CP radiation is at approximately 10.15 GHz frequency. The measured isolations between ports with 46.7 × 46.7 mm2 total dimensions are <−20 dB. Due to the experiments, the envelop correlation coefficient for the orthogonal and parallel ports of the proposed MIMO antenna is <0.003 and 0.005, respectively. Additionally, the presented antenna has a circularly polarized performance in the frequency band of 9.75–10.41 GHz and the average realized peak gain almost 2 dBic. The investigated antenna in this work is fabricated and tested in which the results are in a good agreement.

This communication reports significant isolation improvement utilizing planar suspended line (PSL) technique in ultra wideband (UWB) antenna for Multiple Input Multiple Output (MIMO) application. The antenna exhibits dual-band notched characteristic in Wireless Local Area Network (WLAN) band covering 5.45–5.85 GHz range; and in 7.15–7.95 GHz range for X-band downlink operations in satellite communication. Band-notching characteristics have been obtained by employing a single Elliptical Split Ring Resonator (ESSR) placed adjacent to each microstrip feed line of the radiating element and duo of “Y”-shaped strips employed within the circular ring of individual radiating elements. Two elements antenna occupy a compact space of 20 × 36 × 1.6 mm3 exhibiting huge measured impedance bandwidth (S11/S22 < −10 dB) covering 3.1–11.5 GHz and significant isolation of >21 dB in the almost entire band of operation. The electrical performance of antennas has been analyzed in terms of various MIMO parameters. Measured results demonstrate good accord with simulated results proving the competency of proposed antenna in high-density package systems and massive MIMO applications.

In this paper, a low profile 4 × 4 multiple input and multiple output (MIMO) antenna is proposed and designed for wireless local area network (WLAN) application using a square split-ring resonator. Initially, a single square-patch antenna is designed with square-shaped split-ring slot. Subsequently, the two-element MIMO antenna is designed and it is extended to four-element MIMO antenna. Finally, the defected ground structure (DGS) is implemented in order to enhance antenna performance. The antenna elements are placed opposite to each other. The mutual coupling between the antennas elements is reduced by DGS. The proposed single, two and four-element antennas operate at 5.8 GHz for WLAN. The overall performance is measured in terms of S parameter, radiation pattern, and envelope correlation coefficient. The simulated results are verified through measurements. The simulated and measured results demonstrate that the proposed 4 × 4 MIMO antenna is the most suitable for WLAN applications.

In this study, the problem of backward heating in microwave ablation technique is examined and an electromagnetic solution based on the use of high impedance graphene material is presented for its mitigation. In this context, a one-atom-thick graphene layer is added on the coaxial double slot antenna. In addition to the electromagnetic behavior, thermal effects caused by the graphene-covered antenna are emphasized. The graphene's conductivity being highly dependent on its chemical potential and the relaxation time, a parametric study is performed to determine a range of tolerances within which the graphene-coated antenna outperform a typical graphene-free antenna. The range of values is found to be 0 < μc < 0.5 eV and τ < 0.4 ps, for the chemical potential and the relaxation time, respectively. The backward heating problem being prevented, the ablation region is ensured to be spherical around the tip of the antenna. Effects of the graphene layer to the heat dissipation in the tissue, the necrotic tissue ratio (damage to the cancerous tissue of the caused by electromagnetic energy), and the treatment time using the coaxial double slot antenna were examined. The results show that the heat dissipation is concentrated around the slots (region of cancerous tissue) and a higher necrotic tissue ratio can be achieved with a graphene-covered double slot antenna in a shorter time.

Achieving robust and fast two-dimensional adaptive beamforming of phased array antennas is a challenging problem due to its high-computational complexity. To address this problem, a deep-learning-based beamforming method is presented in this paper. In particular, the optimum weight vector is computed by modeling the problem as a convolutional neural network (CNN), which is trained with I/O pairs obtained from the optimum Wiener solution. In order to exhibit the robustness of the new technique, it is applied on an 8 × 8 phased array antenna and compared with a shallow (non-deep) neural network namely, radial basis function neural network. The results reveal that the CNN leads to nearly optimal Wiener weights even in the presence of array imperfections.