Exposing the near field of an antenna to varying dielectric environment causes changes of the antenna input impedance and, thus, unwanted feed mismatch. Feeding such an antenna at different points, and selecting an appropriate feed for best match at a given scenario, may solve the problem. For the case of two scenarios of different dielectric environments and an antenna with two feed points, this work presents a passive power divider network, which keeps the antenna matched to the source in either scenario. Specific impedance transformations in the two branches of the divider network realize power transfer in a first scenario from the source to complex feed impedance at the first antenna feed, while in a second scenario, with now different antenna feed impedances, matched power transfer is from the source to the second antenna feed. Analytical formulae are derived for the design of the divider network. An experiment uses an example antenna with two feeds and a microstrip divider network, connected to a common 50 ohm port. Measurements are conducted with the antenna radiating, first, in air and, secondly, into butter. The measurements show antenna match at 1 GHz in either case and agree well with the analytical results.

A waveguide power divider based on ridge waveguide to microstrip line transition is presented in this paper. To improve the isolation performance, a probe insulator is inserted into the contact face from the center of the waveguide side wall, also two chip resistors are mounted on a planar substrate and connected with the probe to absorb the coupled energy. The impedance transformation is accomplished by ridge waveguide to microstrip line transition, which is hidden in the waveguide. This proposed power divider shows merits of waveguide power dividers and substrate-integrated waveguide power dividers simultaneously, i.e. planar output ports, compact size, and high isolation. For verification, a power divider operating at the Ka-band is simulated, fabricated, and measured. The obtained results show the return loss and isolation are better than 10 and 20 dB, respectively. The measured insertion loss is <1.5 dB, including the insertion loss of waveguide to microstrip line transitions at the output port in the range of 34.6–39 GHz.

Channel interference is a significant issue for many applications such as satellite communication, mobile communication, and RADAR communication. This paper presents co-channel interference analysis at faulty K band waveguide joints using the multi-cavity modeling technique. Numerical data obtained from multi-cavity modeling technique analysis has been compared with CST microwave studio simulated data and verified with measured data.

In this study, a novel microstrip antenna sensor with defected ground structure is investigated to detect the presence of other substances in liquid food samples. The proposed antenna sensor is rake-shaped which has been designed using time domain solver in three-dimensional simulation software Computer Simulation Technology Microwave Studio. The proposed antenna sensor has been fabricated using an FR4 material, having overall dimensions of 30 × 27 mm2 with dielectric constant 4.4, substrate thickness 1.57 mm, and loss tangent 0.0025. Furthermore, the Q-factor of the proposed antenna sensor is 485 showing a maximum sensitivity of 700 MHz and having accuracy 98%. In the present work, water and juice are considered as liquid samples in which the presence of foreign substances is detected in terms of reflection coefficient and shift in resonant frequency with the help of the suggested microstrip antenna sensor. Through experimentation, it has been observed that with the increase in the percentage of adulterant in the considered samples, the dielectric property of solution changes which results in shift of reflection coefficient and resonant frequency, thus making an allowance for the proposed antenna sensor a valid tool to detect adulteration in liquid samples.

A detailed dosimetry study of electromagnetic absorption and temperature rise under real scenarios is delivered when a mobile phone is used inside an elevator cabin. Numerically accurate human models of a 7th month pregnant woman and a 5-year-old female child are utilized as the exposed subjects. The female child acts as the phone user. The mobile phone is modeled in three talk positions (parallel, tilt, and cheek) operating at 1000 MHz and 1800 MHz. From the obtained numerical results for the specific absorption rate (SAR) and temperature rise induced by the mobile radiofrequency (RF) radiation, it is found that the child's RF exposure is significantly affected by the phone position and less affected by the relevant position of the human models. The exact opposite case applies for the pregnant woman model and its fetus. Almost all numerical investigations are carried out inside a metallic elevator cabin.

A small ultra-wideband (UWB) patch antenna for microwave breast imaging (MWI) applications is shown off in this paper. However, to improve the antenna performance relating to the bandwidth (BW), the radiating element of the suggested antenna is modified by adding slits in the patch as well as the ground plane. The proposed prototype has a relatively small size of 20 × 19 × 1.6 mm3 and it accomplishes a return loss below −10 dB (S11< −10 dB) at an overall BW of 7 GHz (4–11 GHz) with more than 3 dBi realized gain. The antenna is designed and simulated by using a finite integration technique-based simulator. In this way, the characteristics of the fabricated antenna are measured to examine the antenna performance. Indeed, the fidelity factor of face-to-face (FtF) and side-by-side (SbS) scenarios are also noticed for the same frequency range. In the final analysis, a simulation model of the antennas, that operate as a transceiver, and a breast phantom model with tumor sample is proposed for detecting cancerous tumor cells within the breast. Hence, the proposed approach is suitable for UWB based MWI applications in tumor cell detection.

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 presents a pattern diversity UWB antenna for Wireless Body Area Network (WBAN) communications. Pattern diversity antenna comprises two antenna elements with directional and omnidirectional patterns suitable for off-body and on-body communications respectively. Several broad-banding techniques such as Co-Planar waveguide, parasitic patches, and cavity resonant techniques are incorporated in microstrip antenna to achieve an ultra-wideband of 7.5 GHz (3.1 to 10.6 GHz) with a directional pattern. Monopole radiator topology is utilized to achieve a UWB frequency range of 2.6–10.6 GHz with an omnidirectional pattern. Pattern diversity is achieved using an orthogonal arrangement of the antenna elements in a compact size of 40 mm × 34 mm, maintaining the isolation >20 dB between the antennas. Gain varies from 2.2 to 4.6 dBi and 2.5 to 7.5 dBi for omnidirectional and directional antenna respectively. The simulated radiation efficiency for the directional antenna and the omnidirectional antenna are 74–86% and 52–66.5% respectively. The proposed design provides a good diversity performance in the entire UWB bandwidth with ECC<0.1 and a diversity gain of approximately 10 dB. SAR impact evaluated under various conditions is found to be <1.6 W/Kg for 1 gram of tissue.

Electromagnetic simulation software has become an important tool for antenna design. However, high-fidelity simulation of wideband or ultra-wideband antennas is very expensive. Therefore, antenna optimization design by using an electromagnetic solver may be limited due to its high computational cost. This problem can be alleviated by the utilization of fast and accurate surrogate models. Unfortunately, conventional surrogate models for antenna design are usually prohibitive because training data acquisition is time-consuming. In order to solve the problem, a modeling method named progressive Gaussian process (PGP) is proposed in this study. Specially, when a Gaussian process (GP) is trained, test sample with the largest predictive variance is inputted into an electromagnetic solver to simulate its results. After that, the test sample is added to the training set to train the GP progressively. The process can incrementally increase some important trusted training data and improve the model generalization performance. Based on the proposed PGP, two monopole antennas are optimized. The optimization results show effectiveness and efficiency of the method.

This paper describes a multiple-input multiple-output (MIMO) antenna for low millimeter (mm)-wave applications based on dielectric resonators. This is the first time that a filtering response is used in conjunction with an MIMO antenna operating at a low mm-wave frequency. The antenna is simulated using an asymmetrical U-shaped aperture and a microstrip line feed. The suggested filtenna has two distinguishing characteristics: (i) the diversity parameters of the proposed MIMO are increased by including pattern and spatial diversity, and (ii) the proposed feed mechanism of a dielectric resonator provides the filtering response. Between the two ports, a metallic plate tilts the radiation pattern by 45°. The anti-parallel locations of the ports increase the isolation value by >30 dB. To validate the performance of the suggested antenna, the proposed filtenna was built and confirmed. The proposed antenna operates between the frequencies 27.9 and 28.5 GHz. Within the operating frequency range, the observed gain is ~4.5 dBi. On the contrary, the gain suppression level beyond the operational frequency range is ~15 dB. The stable radiation properties and high diversity parameter values of the suggested filtenna make it an effective solution for 5G Internet of Things sensing applications.

In this study, a compact ultra-wideband (UWB) antenna with quintuple band-notched and wide-band rejection characteristics is studied. The proposed antenna mainly consists of a rectangular radiating patch, a microstrip feeding line, and a modified rectangular ground plane. The quintuple band-notched functions with narrow stop bands are achieved at WiMAX (3.3–3.7 GHz), WLAN (5.15–5.35 GHz and 5.725–5.825 GHz), C-band IEEE INSAT/super-extended (6.7–7.1 GHz) by using three modified inverted U-shaped slots and two symmetrical rectangular slots on the radiating path. Each stop band formed in the UWB antenna can be adjusted independently, and deep reflection zeros are formed between the adjacent stop bands. The formation of reflection zeros improves the band-edge selectivity of the stop band, and the notch characteristics are more prominent. To further study the wide stop band (C-band and X-band) with good selectivity characteristics, a pair of L-shaped open slot is added to the edges of two rectangular slots. Additionally, a pair of modified Rho-shaped resonators is located near the feeding line to realize band-notched characteristic at ITU service bands (8.025–8.4 GHz), thus a quintuple band-notched UWB antenna is achieved. The shape factor (ratio of the −3 dB bandwidth to the −10 dB bandwidth) of the wide stop band is 0.56, which indicates that the antenna has excellent band-edge selectivity. To verify the performance of the proposed design, both the time-domain and the frequency-domain characteristics of the antenna have been studied and analyzed. The simulated and measured results verify the design as a good candidate for various portable UWB applications.

This article presents a novel dual-fed triple-frequency bands antenna using quarter-mode (QM)/ Eight-mode (EM) substrate integrated waveguide (SIW) cavity resonators. A V-shaped slot is etched into the patch to divide the half-mode cavity into one QM and two EM cavities. One section of the EM cavity and QM cavity are excited with the help of individual micro-strip feedlines. This configuration yields two distinct frequency bands at 4.85 GHz due to TE110 mode of the EMSIW cavity and 5.87 GHz due to TE110 mode of the QMSIW cavity confirming the self-diplexing property. Later, when both the EM cavity sections are joined with the help of two metallic strips, an additional resonance appears at 7.34 GHz due to the excitation of TE120 mode. As compared to the conventional counterparts, the proposed structure is compact and simple. The footprint of the top patch is 0.6λ1 × 0.3λ1. To authenticate the proposed idea, the design is experimentally verified, and the measured results show a good covenant with the simulated results.

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).

An analytical and a numerical study on coupling in microstrip transmission line (MTL) are reported for different split-gap orientations of a single gap square-shaped split-ring resonator (SRR). Taking both magnetic and electric couplings and adopting Lagrangian formulation for this coupled system, mathematical relations are found for each orientation of SRR to determine the connection between coupling co-efficient and resonant mode frequency. It is shown that coupling results in higher resonance frequency when the SRR, with parallel split-gap, has the gap far from the MTL. But, a lower resonance frequency is obtained when the SRR is placed at shorter distances with parallel split-gap near to the MTL. Again, for perpendicular split-gap orientation of SRR, the resonant frequency is found in terms of an effective coupling co-efficient; at shorter distances it is found to be lower than the fundamental resonance frequency of uncoupled SRR and an opposite effect is obtained at longer distances. Using CST Microwave Studio, the resonance frequency for each split-gap orientation of SRR is also studied as a function of separation between MTL and SRR. It is observed that this phenomenon strongly depends on SRR side-length, substrate height, and separation between MTL and SRR.

The scattering by the perfectly electric conducting (PEC) half-plane and PEC zero thickness disk placed on parallel planes is considered. The fields are represented in the spectral domain, i.e. in the domain of Fourier transform. The operator equations with respect to the Fourier amplitudes of the scattered field are obtained. The kernel functions of these equations contain poles. After regularization procedure, which is connected with the elimination of the poles, operator equations are converted to the system of singular integral equations. The convergence of the solution is based on the corresponding theorems. The scattered field consists of the plane wave, reflected by the infinite part of the half-plane, cylindrical waves, which appear as a result of scattering by the edge of the half-plane, and spherical waves, which appear as a result of scattering by the disk and multiple re-scattering by the disk-half-plane. The total near-field distribution and far-field patterns of cylindrical waves are presented.

In the research of the natural ecological environment, environmental scattering is an important research content whose results are widely used. In order to fully study the relevant characteristics of the natural grassland environment, this paper established a grassland broadband clutter model, summarized the dominant and recessive laws of the grassland environment broadband clutter, and provided a new perspective for related environmental monitoring which would be helpful to solve the problem of target detection in complex environments. The main work of this paper is as follows: The dielectric constant model of the grass was established, and the curve of the dielectric constant with frequency was obtained. The Monte Carlo method combined with the Gaussian spectrum function was used to generate a two-dimensional Gaussian surface to simulate the actual grass surface. A broadband clutter model was established, and, considering the calculation efficiency and accuracy, the Sparse Matrix/Canonical Grid (SMCG) was used to calculate the surface scattering coefficient. Then, the environmental clutter amplitude with different radar bandwidth (10, 40, 80 MHz), surface roughness (h = 0.1 m, h = 0.2 m, h = 0.4 m) and grazing angle (30°, 60°) were calculated and the probability density function (PDF) was obtained. The results show that the higher the radar resolution, the larger the incident angle, and the rougher the interface, all of which will cause the tail of the PDF to become longer which will not only reduce the detection probability of the radar, but also the tracking accuracy. The research results can be used for civilian and military field.

The distorted Born iterative method (DBIM) is a widely used quantitative reconstruction algorithm to solve the inverse scattering problems of microwave imaging. The major mathematical challenges in solving such problems are non-uniqueness, non-linearity, and ill-posedness. Due to these issues, the optimization algorithm converges to a local minimum. This drawback can be overcome by selecting the correct initial guess solution, which helps to escape local minima and thus guides the inversion algorithm to a satisfactory result. This study uses a back-propagation algorithm to calculate the initial estimate, which significantly accelerates the rate of convergence and improves the accuracy of the standard DBIM approach. The results of this method are compared with zero initialization and Born-approximated initialization. For comparison, weak as well as strong scattering profiles of synthetic and experimental dataset are considered. The results suggest that the proposed method provides a significant improvement in terms of computing cost and efficiency. Furthermore, the proposed technique has the potential to successfully push the limits of reconstructible contrast.

A high gain antenna with Mu-near-zero metasurface (MNZ-MS) is introduced in this work. The proposed antenna can be utilized for future 5G applications. The patch antenna is designed on the upper face of the square substrate with a ground plane at the bottom face. To improve the antenna gain, a layer of MNZ-MS unit cells is placed above the antenna substrate with 0.48λ0 air space between the two layers, where λ0 is the wavelength in free space at the resonance frequency of 26.3 GHz. The MNZ-MS layer consists of four double-sided split square resonators. The overall thickness of the proposed antenna is 0.66λ0. To approve the execution of the proposed antenna, a prototype model is manufactured and tested. The outcomes fulfill a reflection coefficient lower than −10 dB over the frequency spectrum of 26–28 GHz. A gain improvement better than 5 dB is obtained compared to the gain of the reference patch at the center frequency of 26.3 GHz.

This paper reports an exhaustive review of recent research progress in the development of millimeter-wave absorbers. With the advancement in technologies, microwave absorbers have shown their evolution in several applications such as defense, security identification, stealth technology, and several more. The importance of these absorbers is increasing due to electromagnetic interference (EMI) effects. Primarily, an abundant amount of absorbers has been developed in lower frequency bands and with the increasing demand for 5G technology, the usage of millimeter-wave bands has gained attention. This in turn requires the development of millimeter-wave absorbers to provide EMI shielding in several applications. Out of several materials, polymers have grabbed attention in the mitigation of EMI. An absorber that combines carbonaceous elements with polymers offers large design flexibility and tunability per the filler concentration. This paper focuses on the classification of these absorbers based on geometry as well as that by using polymers with their design challenges, merits, and demerits with their industrial applications. Comparative studies of geometrically based absorbers and polymeric-based absorbers are also shown.