This paper describes the design and development of a highly directive planar end-fire array using arc dipoles as the array elements. The inter element spacing, shape and size of the array elements are optimized for maximum directivity and gain. The array is printed on a substrate whose dimensions are also optimized for better performance. The overall length of the proposed six element array is 1.9λ, giving directivity and gain values as 12.0 dBi and 10.2 dBi respectively at 5.8 GHz.

In this paper, a highly directive small-cell waveguide antenna array for point to point wireless communication in E-band radio frequency systems is presented. The antenna array is designed and dedicated for the paired bandwidths 71-76 and 81-86 GHz. It is composed of 32 x 32 horn elements with a total surface of ~100 x 100 mm² to achieve a directivity ≥38 dBi, narrow beam (~2°) and low-level sidelobe ≤-26 dB. A compact stepped horn antenna element (SHE) (6.6 mm) is designed. It is 25% smaller than a standard horn element (in the same band) keeping the same aperture surface (3.4 x 3.4 mm²). Layer-by-layer micromachining process is employed for the fabrication. A compact feeding network (25 mm) is realized using ridged waveguide technique with a cut-off frequency of 55 GHz, much lower than standard WG one in the same band. A bow-tie multi-section waveguide polarizer rotator (±90°) is optimized and associated with the WG transitions to re-phase the fields applied to SHE elements. Electric discharge machining (EDM) process was used to manufacture a 4×4 sub-array prototype including the entire WG power-feed network. The antenna is characterized in an anechoic chamber, and experimental results are compared to 3-D electromagnetic simulations with good agreements over the two bands.

In this paper, the miniaturization of the slot antenna is presented for the first time with the use of high refractive index metamaterial. Based on the effective parameter extraction, the studies conducted on Single Ring Split Ring Resonator (SR-SRR) reveal that the unit cell can produce high values of positive refractive index. By taking the advantage of the principle of duality, the slot is loaded with two Complementary SR-SRRs (CSR-SRRs) on either side of it to create an effective HRI medium. With the partial loading of HRI metamaterial medium, the resonance frequency of the slot is brought down from 4.225 GHz to 2.5 GHz. The radiation characteristics of the loaded slot antenna were found to be almost similar to that of the conventional slot antenna. The simulated and measurement results were found in good agreement.

For the last half a century, neurophysiology relies on patch clamp which neutralizes the ions to sense a signal. The smaller the patch, the efficiency is better. However, the limit has not been reached yet, and we accomplish it here. We add a spiral and a ring antenna to a coaxial probe to significantly reduce its self-resonance as the tip filters the ultra-low vibrations of protein's sub-molecular parts (10^-18 watts to 10^-22 watts) in a living cell environment with 10-6-watt noise. A probe tip added by a cavity resonator & a dielectric resonator acquires four distinct ultra-low noise signals simultaneously from a biomolecule, which is not possible using a patch clamp. Protein transmits ions and small molecules. Our probe estimates the ionic content of the molecule. Simultaneously it also measures the dipolar oscillations of its sub-molecular parts that regulates ionic interaction. We experimentally measure signals over a wide frequency domain. In that frequency domain, we map the mechanical, electrical, and magnetic vibrations of the element and record the relationship between its electric and ionic conductions. Dimension wise it is the ultimate resolution, consistent both in silico & in real experiments with the neuron cells --- the atomic pen instantly monitors a large number of dynamic molecular centers at a time.

Characterization of the human body channel is a necessity to pave way for practical implementation of intrabody communication (IBC) in body area networks (BAN). In this paper, a circuit-coupled finite element method (FEM) based model is proposed to represent the galvanic coupling type IBC on human arm. In contrast with other models for IBC, both the finite element method and the parasitic capacitances between electrodes are taken into account in the modeling. To understand the characteristics of IBC, simulations with multiple frequencies, excitation voltages, channel lengths and values of parasitic capacitors are carried out using the model. The current density and electric field distribution in different human tissues reveal an insight into signal transmission path through the human body intuitively. The body channel gain presents a band-pass property after adding the parasitic capacitances into the model, while it performs an increasing characteristic with the frequency before the adding. Finally, a galvanic coupling IBC measurement setup is fulfilled, and the outcome shows a good agreement with the proposed model. It is indicated that the parasitic capacitances are the major factors to cause the band-pass and affect the bandwidth, and they should not be neglected in the real IBC applications.

This paper presents an overview and review of the fundamental implicit finite-difference time-domain (FDTD) schemes for computational electromagnetics (CEM) and educational mobile apps. The fundamental implicit FDTD schemes are unconditionally stable and feature the most concise update procedures with matrix-operator-free right-hand sides (RHS). We review the developments of fundamental implicit schemes, which are simpler and more efficient than all previous implicit schemes having RHS matrix operators. They constitute the basis of unification for many implicit schemes including classical ones, providing insights into their inter-relations along with simplifications, concise updates and efficient implementations. Based on the fundamental implicit schemes, further developments can be carried out more conveniently. Being the core CEM on mobile apps, the multiple one-dimensional (M1-D) FDTD methods are also reviewed. To simulate multiple transmission lines, stubs and coupled transmission lines efficiently, the M1-D explicit FDTD method as well as the unconditionally stable M1-D fundamental alternating direction implicit (FADI) FDTD and coupled line (CL) FDTD methods are discussed. With the unconditional stability of FADI methods, the simulations are fast-forwardable with enhanced efficiency. This is very useful for quick concept illustrations or phenomena demonstrations during interactive teaching and learning. Besides time domain, many frequency-domain methods are well-suited for further developments of useful mobile apps as well.

A periodic millimeter wave leaky-wave antenna (LWA), which has two different types of radiator elements that enable backward to forward radiation, is proposed. The unit-cell of the LWA consists of two quarter-wavelength microstrip lines and two corrugated substrate integrated waveguide (CSIW) cells with S-shaped quarter-wavelength open-circuit stubs. In addition to two parallel edge radiators, a single etched transverse slot with a tilt angle acts as an ancillary radiator, which ensures impedance matching in a large frequency range and achieves the backward to forward scanning. We analyze the proposed design through simulations, characterize a fabricated prototype and find it to have good radiation properties including broad impedance bandwidth. The measurement results show a high peak gain from 11 to 15.8 dBi with a large scanning angle range from -34° to +22° in the K-band operating frequency range.

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.