This paper presents two circuits for a high power GaN/AlGaN HEMT based self oscillating Active Integrated Antenna (AIA) using feedback topology. The first circuit, a fixed frequency high power source, is designed using a two-port T-coupled patch antenna in parallel feedback of a device. This circuit radiates 41 dBm power at 2.34 GHz frequency when being biased at Vgs = -2.1 V and Vds = 25 V. The second circuit, a frequency reconfigurable high power source, is designed using a frequency reconfigurable T-coupled two-port patch antenna in parallel feedback of a device. Frequency reconfigurability is achieved in the second circuit by adding one more strip and two pin diodes at both sides of centre patch of the two-port patch antenna. Change of biasing voltage of pin diodes changes the frequency of oscillation of the circuit. This circuit radiates 32.4 dBm power at 2.1 GHz when pin diodes are off and radiates 32 dBm power at 2.7 GHz when pin diode is on. To the best of our knowledge, the first circuit implemented radiates the highest power using single device whereas the second circuit is the first implementation of reconfigurable oscillating AIA in GaN and also delivers the same power in both states. Each circuit measures 80 mm x 80 mm.

The paper is focused on reliable analysis of the phenomena associated with the resonant and anomalous transformation of the field of a plane, density modulated electron beam, flying over the periodically rough boundary of a natural or artificial medium, in the field of bulk outgoing waves. The physical results presented here have been obtained as the result of numerical implementation of the rigorous mathematical models described in the two first papers of this series. The corresponding analytical constructions have been associated with the correct formulation of model problems and their algorithmization, with the provision of the possibility of a correct physical interpretation of the results of their numerical solution.

This paper introduces a method for efficiently eliminating false detections in coherent radar systems due to sea spikes. The proposed method employs scan-to-scan processing over a predefined number of successive antenna scans. Processing consists of matching estimated range-azimuth-velocity centroid associated with each radar plot extracted from a set of data detected within the current scan (initial plot) with centroids of radar plots generated in the previous scans. For each initial plot, the proposed method matches radar plots using a sequence of correlation windows generated in turn for each of the predefined previous scans. Each correlation window defines a range-azimuth region, with center and extent in range and azimuth adjusted from scan-to-scan. A group of matched plots is selected from all plots falling into a correlation window; these plots meet the velocity matching condition. Only the one radar plot, which minimizes the predefined overall matching criterion, is selected from the given group of matched plots for inclusion in the set of correlated plots associated with the initial plot. For each identified set of correlated plots, an overall correlation value is computed. If the correlation value exceeds a predefined threshold, the initial plot associated with that set of correlated plots is stored in memory for further processing and visualization. Otherwise, the initial plot is retained for plot rematching with modified velocity centroids. The modified velocities provide the detection of those targets of interest that may have been missed due to ambiguous radial velocity measurements. In contrast to known methods, the proposed method minimizes the correlation window area at a given probability of falling into the window for radar plots associated with a target corresponding to an initial plot. The proposed method efficiently eliminates the false detections while maintaining reliable detection performance for targets of interest; the detection performance is essentially improved compared to known methods. Additionally, the proposed method ensures reliable target detection when radial velocity measurements are ambiguous, a situation where known methods collapse.

The much-anticipated year of 5G deployment has lapsed, and yet much research is ongoing on the 5G New Radio (NR) interface. The quality of service and user experience is dependent on a stable and signal strength of the wireless communication link. To serve multiple users per sector accessing dedicated and unique services pose a challenge for passive antenna systems with omnidirectional beams. Smart 5G antenna technology with null forming and beamforming promises to serve mobile users well by offering a reliable wireless communication link. To address this need, we propose a 2 x 2 MIMO antenna capable of electronically forming electromagnetic beams in one direction and nullifying electromagnetic beams in any undesired direction. We demonstrate the usefulness of the proposed antenna by evaluating five cases that showed interesting insights, confirming the hypothesis that it is possible to implement beamforming in a 2 x 2 MIMO system with less computing power and minimum number crunching. What is novel and attractive about the proposed antenna are: (a) forming a beam with maximum directivity towards the desired user, while (b) simultaneously producing nulls towards an undesirable transmitter, and (c) a fast electromagnetic tracking module inbuilt into it so that the base station antenna may constantly track and maintain the communication link with the moving wireless transceiver or cell phone. While most wireless mobile systems use two separate software modules for beamforming and tracking the mobile station, the method presented here does electronic beamforming and tracking of the mobile user with a single low memory, computationally fast technique within the range of 10 ms to 19 s.

A compact folded-patch UHF RFID tag antenna (30 mm × 30 mm × 3 mm or 0.0912λ × 0.0912λ × 0.009λ) is proposed for metallic surface applications. Two large C-shaped slots, which can be easily tuned by adjusting their lengths, are incorporated into the folded-patch for providing tuning mechanisms that can be employed in the production line for tuning the tag resonant frequency on the fly. The slots are tactfully embedded into the patch structure so that they occupy no footprint. The slots are large enough so that their lengths can be easily adjusted by employing a penknife and some copper tapes. This provides an impromptu tuning mechanism so that the tag resonant frequency can be easily corrected in the production line. With reference to the effective isotropic radiated power of 4 W, the proposed tag antenna can be read from 10 m on metal. The read range is found to be able to go beyond 5.5 m when the tag is placed on a dielectric with permittivity ranging from 1 to 12.

Affected by multipath propagation as well as the receiving conditions of an actual array, a distributed source model considering array uncertainties/errors is more consistent with the realistic scenarios. In this paper, a new direction finding method for coherently distributed (CD) sources in the presence of array gain-phase errors is proposed. By exploiting partly calibrated uniform linear arrays (ULA), the gain-phase errors are first estimated according to the relationship of elements of array covariance matrix, and then a two-step iterative procedure is introduced to achieve a joint estimation of nominal DOA and angular spread from sparse recovery perspective. Performance analysis and related Cramér-Rao bound (CRB) are also provided. Numerical examples show that the proposed method can provide improved resolution and estimation accuracy, and performs almost independently of gain-phase errors.

In this paper, a design of dual band 10 × 10 antenna array for 5G Massive Multi-Input Multi-Output (MIMO) applications in the mobile phone is presented. The designed array is proposed to cover the sub-6 GHz bands (LTE bands 42/43 and LTE band 46). To realize MIMO operation in these three LTE bands, ten ring loop antenna elements are integrated into a limited space cell phone circuit board. Due to the implementation of spatial diversity techniques on the antenna elements, better isolation can be achieved. The proposed array was simulated, fabricated and measured. It achieved good MIMO performances, such as ergodic channel capacities higher than 27.1 bps/Hz and 57.6 bps/Hz for LTE bands 42/43 and LTE band 46 respectively. Also, the achieved Envelope Correlation Coefficient (ECC) is lower than 0.006. Moreover, it exhibited good isolation below -26 dB. The effects of user's hand phantom on the proposed array performance are also studied in two scenarios: Single Hand Mode (SHM) and Dual Hands Mode (DHM). The simulated results indicate that the proposed MIMO array can still achieve good MIMO performances in the presence of DHM and SHM. The Specific Absorption Rate (SAR) are also presented.

We here present a bivariate Chebyshev series method for the approximation of the experimental frequency and temperature dependent dielectric functions of materials. Within the framework of this method, the dielectric properties are modeled as a low-degree polynomial of the temperature variable (T), the coefficients of which have a frequency (variable f) dependency. This model is then rephrased in terms of the temperature coefficients which are given here as the rational functions of frequency. The principal merits of this method are that it produces a near-best polynomial approximation to the target function, rapidly improves with the order of approximation, and is easy to compute. The favorable features of our approach are demonstrated by considering the experimental wideband Cole-Cole models of animal tissues with the temperature-dependent parameters. The numerical results show the inferiority of the commonly used power-of-f representation of the polynomials concerned due to large rounding errors when the frequency range is large. This problem is ameliorated by expressing the appertaining coefficients as polynomials in the transformed frequency variable x(f) in the Chebyshev basis. Areas of application of the results of this article include the modeling of human exposure to radiofrequency fields, development of treatment and diagnostic procedures, and food processing technologies.

A self-quadruplexing antenna based on substrate integrated waveguide (SIW) is presented. A slot is engraved on its top surface of the SIW cavity, which generates four different resonant frequencies (around 6.54, 7.64, 8.30, and 9.60 GHz) when it is excited by four 50 Ω microstrip feed lines. Also, each resonant frequency can be controlled independently. Due to a quarter mode (QM) cavity, the antenna size becomes compact. The measured results show that the isolation between any two ports ismore than 32 dB, and the estimated gain is more than 7.8 dBi at the operating frequencies. The proposed design is simple to fabricate, compact, and easy to integrate with the planner circuits.

This paper presents an analysis of microstrip patch antennas with different dielectric/magnetic substrate profiles in an attempt to obtain operating frequency reduction. Initially, different ridge shapes in the substrate were examined. An in-depth investigation of the ridge shape and its dimensions on the antenna performance has been carried out. Subsequently an antenna with a magnetic-slab loaded in the prime magnetic-field region beneath the patch is proposed. The new magnetic loaded antenna design is aimed to reduce the resonant frequency of a conventional patch and reduce the profile of an earlier design with a substrate ridge. Various magnetic materials have been embedded within the original dielectric substrate of the patch antenna. Measured results validated the hypothesis that this frequency can be reduced by placing magnetic materials at the centre of the patch. The achieved gain is expected to be further enhanced by using forthcoming magnetic materials with improved performance.

A backward wave oscillator (BWO) operating at the high-order mode (HOM) with multiple inclined rectangular electron beams (IRBs) is presented in this article. The BWO operating at the HOM with multiple IRBs (HOM IRB BWO) is driven by multiple IRBs. Compared with typical BWOs, the slow wave structure of the HOM IRB BWO is an overmoded metal-grating rectangular waveguide (OGRWG). The mode competition of the slow-wave device operating at the HOM is analyzed according to the ohmic losses of different modes of the OGRWG slow wave structure and multiple beams exciting. The analysis is verified by simulation. Two kinds of HOM-fundamental mode converters (MCs) are designed for converting the HOM generated by the HOM IRB BWO into the fundamental mode. The beam-wave interaction of the HOM IRB BWOs with the HOM-fundamental MC is studied. The results show that the mode competition does not occur; frequency spectrums of output signals are pure; the HOM is converted into the fundamental mode effectively.

An investigation on using eco-friendly natural materials like coconut pith, rubber and charcoal powder for developing radio wave absorbers has been reported in this paper. Two absorbers named CoR (Combination of Coconut pith powder and natural Rubber latex) and CoRC (Combination of Coconut pith powder, natural Rubber latex and Charcoal powder) are made through proper mixing and drying. The absorptivity of these two absorbers (CoR and CoRC) is compared with the industrial standard polyurethane based absorber. The waveguide method is employed to measure the absorptivity of these absorbers in 3 different frequency bands. Band 1 (1.7-2.6 GHz) includes the mobile communication frequencies of 1.8 GHz and 2.4 GHz. Band 2 (4.9-7.05 GHz) is intended for sub 6 GHz band of 5G as well as WLAN frequencies while band 3 (8.2-12 GHz) is for higher frequencies of radar operation. The exact values of lower and upper frequencies of bands are determined by the physical dimensions of waveguides used. The absorption capability of the absorbers is found to increase as the frequency of operation increases. The CoR absorber has almost 63% average absorptivity in band 3, 56% in band 2 and 21% in band 1. The CoRC absorber has an average of 74% absorptivity in band 3, 63% in band 2 and 24% in band 1.

A low-profile compact uni-planar slot antenna design of size 26 mm × 26 mm is proposed, assisted with a metallic bottom reflector at a height of λ/6 (λ is the lowest CP frequency). The dual-band dual-polarization is observed at 6.2 GHz and 9.3 GHz, and polarization sense (LHCP and RHCP) is dynamically switched by introducing a pair of RF p-i-n diodes mounted at the confluence of right-slot (RS) and left-slot (LS). The metallic reflector of size 60 mm × 60 mm helps to improve overall impedance matching, enhance antenna gain and asserts uni-directional dual-polarized radiation with good back-lobe suppression. The proposed antenna operates at dual bands (5.46-6.76 GHz) with 21.27% IBW and (8.18-10.48 GHz) with 24.65% IBW for S₁₁ < -10 dB. The antenna gain reaches (7.82-8.75 dBi) for D1-OFF, D2-ON state with (9.2%, 15.63%) axial bandwidths and (6.42-7.0 dBi) for D1-ON, D2-OFF state with (7.53%, 16.04%) axial bandwidths with radiation efficiency ranging (75-87%). A prototype antenna is fabricated and measured, which shows good agreements with simulated performances and can be used for sub-6 GHz in 5G applications and X-band radar systems.

This letter shows a compact planar microstrip crossover. The crossover design employs a microstrip to coplanar waveguide transition. The crossover is fabricated on a low cost and readily available FR-4 substrate, and simulation and measurement responses in the low frequency band have been shown. The number of GND vias forming a quasi-coaxial section that confined the electric field around the signal via was increased to improve impedance matching. The core size of the circuit is as compact as 20 mm × 10 mm even in the low frequency band. The crossover operates in the low frequency band with insertion loss of less than 1 dB, return loss of more than 10 dB, and isolation of more than 15 dB.

A frequency reconfigurable antenna with conical radiation pattern is presented. The antenna is mainly composed of a suspended circular patch, eight shorting posts, and a ground plane. The circular patch is loaded with two concentric annular slots, and four varactors are placed across the outer annular slot to vary the resonant frequency of the antenna. Simulated results show that the resonant frequency can be tuned from 3.25 to 5.7 GHz as the capacitance of the varactors is varied from 0.2 to 12 pF, and conical radiation patterns are obtained when the antenna is operated at each resonant frequency. In the simulation, the reversed-bias circuit of the varactor is also included, and it is found that a bias tee or an inductor is not necessary for the proposed reconfigurable antenna. Experiments are also realized using two different varactors, and the measured results indicate that the peak gains of the conical radiation patterns occur around θ = ±40˚, and they are about 4.5 ± 1.5 dBi when the constructed prototypes are operated in the frequency range from 3.1 to 5.7 GHz.

Reflective interference caused by impedance discontinuities in the interconnect is a serious impediment to high speed serial link designs. The reflections can be addressed either through expensive equalization circuits or through interconnect redesign. Here a new technique for determining the most significant places to make changes in an interconnect design is presented. Through linearizing the S-parameter cascading process three unique reflection budgets are created based on 1) frequency domain insertion loss deviation, 2) time domain peak distortion analysis and 3) time domain reflectometry. Example analysis of a 25.8 Gb/s NRZ system identifies the connectors as the primary contributors to reflective interference and estimates that the interactions with the rest of the interconnect with the connector impedance discontinuities reduces the system eye height by 84 mV.

Uncertainty quantification and variability analysis are two domains of interest when looking at the efficiency of HPEM sources. Vircator is known to be a low efficiency high power microwave source subject to several generally volatile phenomena such as plasma expansion and shot-to-shot variability. In this study, a computationally low cost framework combining the Extreme Value Theory (EVT) and the Generalised Design of Experiments is proposed in order to study the peak power distribution of a Vircator obtained with a surrogate model. Following the pre-screening of random variables, the optimised parameters are introduced in 2.5D and 3D simulation tools, namely XOOPIC and CST-PS. It has been confirmed that the peak power output can reach a 40% increase. This shows that the EVT proves to be successful in classifying and quantifying random variables to influence the distribution tails.

A compact ultra-wideband antenna is presented for detecting malignant cells in the breast. The dimension of the proposed circular resonator-based antenna is 20 mm x 30 mm x 1.6 mm. The antenna sensor operates within the 3.1 GHz to 6.8 GHz (105.71%) range with peak gain 4.8 dB, radiation efficiency 89.2%, and an omnidirectional radiation pattern. Three types of breast phantoms (i.e., phantom without tumor, a phantom with a single tumor, and phantom with two tumors) arealso fabricated. The electrical properties of the malignant cells differ from non-malignant breast cells. S-parameters have been measured with phantom, then with the help of Principal Component Analysis (PCA), and normal and malignant breast phantoms are identified. Further, the tumor's locations in the breast phantom are find out by using the specific absorption rate (SAR) values.

In this paper, a UWB monopole antenna with triple band-notch characteristics using single TBMV-EBG (Triple band multi-via electromagnetic bandgap) unit cell is proposed and demonstrated. The antenna with a fork-type radiating patch with TBMV-EBG is simulated using Ansys HFSS. Measurement results show triple band-notches at 3.39, 5.78, and 8.60 GHz, respectively, which are in good agreement with simulation results. The proposed antenna has bi-directional pattern in E-plane and omnidirectional pattern in H-plane. Moreover, tunable characteristics of the proposed antenna using a single varactor diode are also presented. By changing the capacitance of varactor, the band-notched antenna is effectively tuned from 2.69-3.46, 5.71-7.84, and 8.40-8.50 GHz. The same antenna structure can be operated at different band notching modes depending upon the varactor's capacitance. Therefore, the proposed UWB antenna will prove to be a promising candidate wherein multi-band rejections using single TBMV-EBG unit cell and reconfiguration using one varactor diode are desirable.

In this work we present near-field image transmission and error vector magnitude measurement in rich scattering environment in metal enclosure. We check the effect of loading metal enclosure on the performance of SDR based near-field communication link. We focus on the key communication receiver parameters to observe the effect of near-field link in presence of rich-scattering and in presence of loading with RF absorber cones. The near-field performance is measured by transmitting wideband OFDM-modulated packets containing image information. Our finding suggests that the performance of OFDM based wideband near-field communication improves when metal enclosure is loaded with RF absorbers. Near-field EVM improves when the enclosure is loaded with RF absorber cones. Loading of the metal enclosure has the effect of increased coherence bandwidth. Frequency selectivity was observed in an empty enclosure which suggests coherence bandwidth less than the signal bandwidth.