This paper proposes a hybrid, compact, low profile, and multi-port antenna system for Cognitive Radio (CR). This system consists of a CPW fed sensing UWB monopole (2-11 GHz) and three NB antennas, out of which one is standalone (7.355 GHz); one is dual-band (5.834 GHz and 8.786 GHz); and the other is reconfigurable (3.863 GHz, 4.664 GHz, 5.2 GHz, and 6.13 GHz) using switching mechanism. This antenna system exhibits less than -15 dB isolation over the operating band. The system is simulated using CST Microwave Studio, and a prototype is fabricated to verify the results. The simulated results are in good agreement with measured ones. The proposed antenna is suitable to operate in C-band, ISM/WLAN/Military application, mid-band 5G, maritime radio navigation, X-band satellite communication, and public safety wireless communications.

Microwave staring correlated imaging (MSCI) is a promising technique for remote sensing due to its ability to achieve high-resolution microwave imaging without the limitation of relative motion between target and radar. In practical applications, unsteady quasi-stationary platforms, such as tethered aerostat, are often used as carriers of MSCI radar. However, these platforms cannot keep ideally stationary during the imaging process. The platform's motion caused by atmospheric effects will cause time-varying inaccuracy of observation positions. Although navigation systems can measure the platform's motion to compensate for the errors of observation positions, the imaging performance of MSCI may still suffer from degradation due to the measurement errors of navigation systems since MSCI is sensitive to model error. This paper focuses on MSCI based on the quasi-stationary platform with motion measurement errors. First, the MSCI model based on the quasi-stationary platform with motion measurement errors is established under the assumption that the translation and the rotation of the platform are uniform during a coherent imaging interval. Then we propose a self-calibration imaging method for MSCI based on the quasi-stationary platform with motion measurement errors. This method iterates over the steps of target reconstruction and motion measurement errors correction until convergent conditions are met. Simulation results show that the proposed method can correct the motion measurement errors and improve imaging performance significantly.

In this article quad-band circular antenna is designed for multiband devices operated close to human body, and the investigation on parametric study for length of feed, width of feed, and length of ground is carried out. Specific absorption rate (SAR) is also evaluated and found to exceed standard limits for lower band. Further investigation to reduce the value of SAR leads to the design of an annular ring antenna with partial ground. Parametric study on the ratio of outer to inner ring radii is carried out to excite higher resonant modes and optimize the performance of annular ring antenna. SAR is evaluated for different bands, and 9{\%} reduction is observed for same dimensions of circular antenna with partial ground, but SAR still exceeds the limit for lower band. A novel approach of using dual feeds with half operating input power in magnitude and 180° out phase at each port for SAR reduction and performance optimization is presented in this work. Annular ring antenna with parametric study on variation in the ratio of ring radii and circular defect in ground structure is performed, and it leads to wideband operation, gain enhancement, and reduction in SAR. SAR reduction achieved is in the range of 66.93% to 82.15% in 1-gram of tissue and 64.43% to 82.20% in 10-gram of tissue at different bands and well within the limits for all the operating bands.

In order to provide high quality of service broadcasting systems, predicting the electric field strength in all the receiving points and generating the coverage map of the transmitter are svery important. Uniform Theory of Diffraction (UTD) based ray theoretical models could be used to predict the electric field and generate the coverage map in a short time. In order to eliminate the non-successive obstacles in the scenario and to reduce the computation time of UTD Model, Convex Hull (CH) technique is used for the first time. After this point, this model is named as Uniform Theory of Diffraction with Convex hull (UTD-CH) Model. Moreover, how operating frequency, obstacle height and the distance between the obstacles affect the coverage map of optimum base station location are researched by using UTD based models. In this study, UTD, Slope Uniform Theory of Diffraction (S-UTD), Slope Uniform Theory of Diffraction with Convex Hull (S-UTD-CH), and UTD-CH models are used for comparisons. Furthermore, computation times of UTD based models are compared.

The thinning methods were usually used to simplify the array complexity by turning off some of the radiating elements in large planar arrays which lead to unavoidable reduction in the directivity. In this paper, an alternative method is used to simplify the array complexity by partitioning a large array into two contiguous subarrays. The first subarray is in circular planar shape in which its elements are uniformly excited, while the second subarray in which its elements surround the circular subarray, and they have significant impacts on the array radiation features and are chosen to be adaptive. The desired radiation characteristics are then obtained by optimizing only the adaptive elements which are far less than the total number of the original array elements. Since the majority of the elements in the proposed array are uniformly excited, its directivity and taper efficiency are found very close to that of the benchmark solutions. Simulation results verify the effectiveness of the proposed array.

This paper considers utilizing radar multipath returns to locate a target in an L-shaped non-line of sight (NLOS) environment and proposes a NLOS target localization algorithm based on grid matching. The algorithm first establishes a multipath propagation model based on real data from an L-band single-input single-output (SISO) ultra-wideband (UWB) radar. Then, it calculates the times of arrival (TOAs) of each grid based on the multipath propagation model and matches the grid which is closest to the measured TOAs of round-trip multipath returns. Both simulation and real-data experiment results validate the effectiveness of the multipath model and the proposed localization algorithm.

Microwave Staring Correlated Imaging (MSCI) technology can obtain high-resolution images in staring imaging geometry by utilizing the temporal-spatial stochastic radiation field. In MSCI, sparse-driven approaches are commonly used to reconstruct the target images when the radiation fields are accurately calculated. However it is challenging to compute radiation filed with high precision due to existence of random phase errors in MSCI systems. Therefore, in this paper, a self-calibration method is proposed to handle the problem. Specifically, a two-step self-calibration framework is applied which alternately reconstructs the target image and estimates the random phase errors. In the target image reconstruction step, sparse-driven approaches are utilized, while in the random phase errors calibration step, an adaptive learning rate method is adopted. Moreover, the batch--learning strategy is utilized to reduce computation burden and obtain effective convergence performance. Numerical simulations verify the advantage of the proposed method to obtain good imaging results and improve random phase errors correction performance.

In this paper, a compact triple-band coplanar waveguide (CPW)-fed patch antenna with dual-polarization characteristics for wireless applications is proposed. The antenna is composed of an F-shaped patch, a grounded-C strip, a rectangular strip, and a horizontal rectangular grounded slot. The first circular polarized band is obtained by the F-shaped feed-line, and the second is achieved by the left C-shaped strip, while the right rectangle strip is responsible for the lower linearly polarized band. By inserting a slot at the right of the square slot, a notched band centered at 5.5 GHz is achieved. Both simulated and experimental results show that the antenna can generate three separate impedance bandwidths to cover frequency bands of 2.4/5.2/5.8-GHz WLAN band and X band. And the antenna is circularly polarized in the 5.8 GHz and 10GHz band. Furthermore, the antenna structure is extremely simple and occupies small space. The proposed antenna has its applications in compact and portable devices operating at multiple frequency bands like cellular phones, Tablets, Wi-Fi devices, etc.

We propose photonic crystal substrates that support microstrip structures to mitigate the problem of spurious harmonics in microwave devices. The wave propagation in microwave transmission lines can be controlled by employing substrates that have modulated dielectric constant such that there exist forbidden spectral regions, which are known as bandgaps in the photonic crystal terminology. With proper selection of crystalline geometry, these bandgaps can be designed to suppress the spurious harmonics. To show the existence of bandgaps in microstrip structures, we present Bloch analysis with a bi-layered photonic crystal configuration of high and low permittivities. For a practical microstrip structure that incorporates a bi-layered photonic crystal substrate, we show suppression of spurious harmonics via circuit analysis and transmittance measurements. Furthermore, a 2.5 GHz coupled-line filter is designed on a photonic crystal substrate, and 30 dB second harmonic suppression at 5 GHz is experimentally demonstrated. With the current trend multiple device integration on single platform, the photonic crystal substrates can potentially provide the noise suppression and spurious harmonic rejection needed for microwave components occupying close proximity.

This paper investigates the problem of wave propagation on periodic building façade with ray tracing method. Compared with the common practice, which is to replace a complex building structure with a flat surface and cause reduction in simulation accuracy, in this research, the Uniform Theory of Diffraction (UTD) is utilized with ray tracing method to include diffraction effects on building facades in propagation simulation. Two scenarios have been modelled which are Moore Hall's façade and Malaysia shop houses respectively. First, the façade models were created based on real buildings, and propagation simulations were conducted for flat surface and knife edge approximations. Then, for different approximations, the accuracy of simulation results was further examined, which varied with the degree of simplification and the frequency of the signal. Also, the computation time was evaluated to consider the speed of simulation. This study is beneficial to the improvement of accuracy in propagation prediction and supports the development of ray-tracing propagation prediction software and the design of wireless communication system.

Electromagnetic interference (EMI) is a crucial problem, and for solving this problem, absorbers especially very thin absorbers are used. Factors like frequency increasing in a device, high integration in electronic systems, higher power densities, and decreasing the size and thickness of PCB make it crucial. So, a novel ultra-wideband and thin metamaterial absorber is proposed in this paper. The absorber consists of metamaterial unit cells, which have a single FR4 layer, metallic ground, and four metallic spirals. A one hundred ohms SMD resistor is placed between two of the spirals. The size of the unit cell is 5.85×5.85×3.2 mm³. The proposed absorber is ultra-thin (λ₀/10), and the absorption occurs over a wide incident angle [0°-40°]. The reflection is less than -12dB in [6.5 GHz -12 GHz], and the absorption is more than 94% in this bandwidth. The structure is fabricated, and the outcomes of simulation and measurement are compared with each other. The values of front to back ratio of the fabricated measurements are -12.8, -7.31, and -15.36 dB at 8, 10, and 12 GHz, respectively. The values obtained from simulation are -13, -9.4, and -14 dB, respectively. There is a good agreement(accordance) between the simulation and measurement results of this absorber.

A differentially fed dual-polarized patch antenna with wide bandwidth is presented in this paper using Substrate-Integrated Waveguide (SIW) technology. The antenna comprises a circular patch radiator, a square SIW cavity and four symmetric arc-shaped slots. The circular patch is internally embedded in the square SIW cavity with a surrounded ring slot. Two pairs of differential L-shaped probes are used for the excitation of the differential signals. These signals excite the orthogonal linearly-polarized modes. The dominant resonant mode of the circular patch resonator (TM₁₁) and the modes of the SIW cavity (TE₁₁₀ and TE₁₂₀/TE₂₁₀) are employed to achieve effective radiation under these resonances. Besides, four symmetric arc-shaped slots are etched on the top surface of the cavity to enhance the impedance bandwidth. The resonant properties of these modes are studied based on the cavity model theory. Then, their resonant frequencies are discussed to provide information for designing and optimizing such an antenna. Finally, the feeding positions of the differential L-shaped probes are investigated for good impedance matching. The proposed antenna has been fabricated and measured. The measured results show that the proposed antenna achieves a wide impedance bandwidth of about 64.8% (4.37-8.56 GHz) and 64.2% (4.48-8.72 GHz) for horizontal and vertical polarization, respectively. High differential isolation of better than 30 dB and low cross-polarization are obtained by adopting the differential feeding mechanism. Due to the SIW cavity-backed structure, the antenna shows unidirectional radiation patterns and low back-lobe radiation, making it conveniently integrated with microwave differential circuits and applied in the base station systems.

In this paper, we discuss the spectral property of radiation of an electron moving in a bi-period harmonic undulator field with a phase between the primary undulator field and the harmonic field component. We derive the expression for the photons per second per mrad² per 0.1% BW of the radiation. A small signal gain analysis is also discussed highlighting this feature of the radiation. A bi-period index parameter, i.e., Λ is introduced in the calculation. According to the value of the index parameter, the scheme can operate as one period or bi-period undulator. It is shown that when Λ = π, the device operates at the fundamental and the third harmonic. However, when Λ = π/2, it is possible to eliminate the third harmonic.

This paper describes an innovative technique for the quantitative reconstruction of the dielectric and conductivity distribution of objects in a microwave tomography framework using sparse data. The proposed method tries to extract information about the size, shape, localisation and dielectric distribution of various inclusions within the object under study using an iterative reconstruction methodology in the sparse domain. The proposed algorithm combines the Distorted Born Iteration method (DBIM) and a convex optimization technique for solving the inverse ill-posed problem. The Re-weighted Basis Pursuit (RwBP) algorithm is chosen as the convex optimization technique in this work. The performance of the proposed algorithm has been compared with the TV-norm method, and the results obtained are highly encouraging. The proposed method produces a significant reduction in the reconstruction error as compared to the TV norm method with an error value of 0.083 as against 0.32 in the case of TV norm in the presence of 25 dB noise. By accurately preserving the edges of the inclusions the proposed technique is found to provide an overall improvement in the reconstruction in terms of tissue differentiation (permittivity and conductivity), dimensions of inclusions, resolution, shape, size and coordinate localisation of inclusions. The proposed algorithm converges within 10-12 iterations as compared to other complex imaging algorithms available in the literature. Further, this proposed technique is validated using experimental data from an actual breast imaging setup. The three inclusions of 10 mm, 6 mm, and 3 mm have been localised with errors of 0.052, 0.04, and 0.09, respectively The results obtained from the real-time data show the applicability and feasibility of the proposed algorithm in breast tumor imaging application

Wearable antennas have received a great deal of popularity in recent years owing to their enticing characteristics and opportunities to realize lightweight, compact, low-cost, and versatile wireless communications and environments. These antennas must be conformal, and they must be built using lightweight materials and constructed in a low-profile configuration when mounted on various areas of the human body. These antennas ought to be able to function close to the human body with limited deterioration. These criteria render the layout of wearable antennas demanding, particularly when considering factors such as investigating the usability of textile substrates, high conductive materials during fabrication processes, and the effect of body binding scenarios on the performance of the design. Although there are minor differences in magnitude based on the implementations, several of these problems occur in the body-worn deployment sense. This study addresses the numerous problems and obstacles in the production of wearable antennas, their variety of materials, and the techniques of manufacturing alongside with bending scheme. This is accompanied by a summary of creative features and their respective approaches to address these problems recently raised by work in this area by the science community.

Microwave Imaging (MI) is a new technique for detecting breast cancer using electrical property difference between the non-malignant and malignant tissues present in the breast. Numerous studies show that detecting the depth of the tumor is the essential measure in determining additional management. Developing evidence in many of the literature surveys illustrate that detecting tumor depth is a precise parameter for identifying the affected area. Thus, Ground Penetrating Radar (GPR) algorithm is applied successfully to detect the exact depth of the malignant tissue. Generally, GPR is originally conceived for archaeological investigations, building condition assessment, detection of buried mines, etc. But here an effort has been made to apply GPR to Radar-based breast cancer detection. The simulated bandwidth of the proposed UWB antenna starts at 2.4GHz and ends at 4.7 GHz. The electromagnetic wave reflected due to dielectric property variation is used by GPR algorithm to identify the depth of the tumor. Before applying a depth migration technique, preprocessing steps like Cartesian form transformation, Hermitian Signal Processing, and Inverse Fast Fourier Transform (IFFT) have to be followed in the backscattered signal to convert positive frequency data into time-domain data. Depth details can be noticed in the migrated image, after applying the migration procedure. Results show that GPR algorithm can be effectively used for detecting the tumor embedded in the depth of the breast tissue. To understand the effectiveness of this imaging scheme, an experimental analysis is done using a combination of wheat flour and water-petroleum jelly. The measured impedance bandwidth of the UWB antenna ranges from 2.8 GHz to 4.48 GHz. The observation is done for a known spherical tumor of diameter 13mm which is placed at different depths from the skin layer. While applying the algorithm in the received backscattered signal, we were able to detect correctly the tumor at a depth of 45mm embedded in the breast tissue. The experimental results are compared with simulation ones to validate the aptness of a microwave imaging approach for detecting the depth of the tumor.

In this paper, we extend our previously published hybrid analytical model for estimation of shielding effectiveness of a dual-cavity structure with an aperture array to generalize the model for a wider range of applications. The aperture array in the center and off-center, higher order modes, and multi-cavity are taken into consideration, respectively. At last, comparations of the results calculated by the extended hybrid analytical model with those obtained by the simulation software CST are given. The results show that the extended hybrid analytical model for shielding effectiveness prediction of a three-cavity structure with numerous apertures has high precision and high efficiency.

Stub-loaded step-impedance resonator (SLSIR) is a multi-mode resonator and can be applied to implement multi-band or wideband filters. In this paper, odd- and even mode impedance analysis is used to resonant properties of the SLSIR. Only two SLSIRs are applied to design a quint-band bandpass filter (BPF). To find the required five resonant modes, the frequency ratios of the high order modes to the fundamental mode of the SLSIR are calculated depending on the impedance ratio and the length ratio of the SLSIR. Several coupling types of the SLSIRs are considered first to have enough energy for all the five passbands. When forming the quint-band, a pair of the SLSIR are coupled electrically and connected with 0o feeding input/output structure. The center frequencies are designed at 1.38 GHz, 2.58 GHz, 3.69 GHz, 5.36 GHz, and 5.8 GHz, corresponding to the different communication applications. The filter is designed, fabricated, and measured. Simulated and experimental results are in agreement, verifying the design concept.

Different optimization strategies to reduce the earth resistance in a high resistivity soil are discussed in this work and illustrated with a practical example. Finite Element simulations reproducing real-world conditions in terms of structure design and soil profiles have been made to evaluate the improvements that should be adopted to minimize earth resistance. We analyze an example of an earthing system of an array of four identical telescopes installed on high resistivity (k­¢m order) soils with two different behaviors. In the first one, current dissipation occurs in an uniform soil. In the second one, a terrain with four layers of different resistivities is considered. This situation corresponds to a real world case of an observatory constructed in a volcanic terrain. It was found that the best strategy in each case differs: extend horizontal electrodes as far as possible from the foundation in the first case and combine these electrodes with buried vertical electrodes that connect with deep high conductive layers in the second. The results are discussed in terms of the achieved improvements depending on the modifications introduced in the main structure.

An eight-element ultra-wideband multiple-input multiple-output antenna system is proposed for the 5G mobile terminals. Each radiating branch is composed of a Loop and a monopole antenna. The ultra-wideband characteristics of the antenna are obtained by a T-shaped feed branch coupling a radiation branch. Furthermore, the isolation is lower than -15 dB by introducing a T-shaped neutralization line structure. The results of simulation and measurement show that the antenna system can cover 3.3-5.6 GHz, and the antenna efficiency is 45%-80%. At the same time, the envelope correlation coefficient between any two elements is lower than 0.03. Therefore,the proposed antenna in this study is very suitable for the eight-element MIMO antenna system as a reference.