This article describes numerical solutions for the electromagnetic interactions, known as `wakefields', of a proton beam with an RF cavity and a beampipe. Using FDTD calculations, time-varying electromagnetic solutions are obtained. Unlike modal expansion methods, FDTD allows to compute transient wakefields due to proton beam passing through the structures. A popular time-frequency analysis approach, the short-time Fourier transform (STFT), is applied to the electromagnetic fields inside a resonant cavity and past an open-ended beampipe. STFT enables a more explicit interpretation of the transitions between the fields radiated by moving charges and the resonant modes. The described time-frequency analysis is useful to engineers and accelerator physicists who analyze proton beam dynamics. As an extension of electromagnetic simulations using an extended proton bunch, a numerical Green's function approach is proposed in order to account for the wakefields due to individual superparticles.

Partially dielectric-filled empty substrate integrated waveguide (PFESIW) is introduced for millimeter-wave application alongside partially dielectric-filled ESIW filter by using inverter and resonators technique. The new design presents good transition implementation in order to introduce a waveguide compatible with planar integrated circuits. The main goal of introducing the new transmission line PFESIW is to control characteristic impedance without changing the cutoff frequency. The presented transmission line is analyzed by calculating attenuation constant α, phase constant β and characteristic impedance Z. The PFESIW is used to build a resonator with high-quality factor. The filter based on the combination of of ESIW and PFESIW is proposed. Furthermore, the designed filter showed very good performance in terms of bandwidth and cost. Transmission line and filter prototypes are manufactured using standard printed circuit board fabrication. Partially dielectric-filled ESIW measurement displays very good results in terms of phase constant β, attenuation constant α, return loss (S₁₁) and insertion loss (S₁₂). Measured return loss (S₁₁) and insertion loss (S₁₂) for waveguide and filter agree very well with simulation.

A modified compact microstrip resonance cell (CMRC) low pass filter (LPF) with ultrawide and deep stopband using novel fractal patches is presented. The proposed filter has low insertion loss in the passband, good selectivity, ultrawide and deep stopband. The experimental results show a 3-dB cut-off frequency of 2.85 GHz and out-of-band rejection up to 67 GHz with 181.5% relative stopband bandwidth.

In this paper an ultra-wideband band (UWB) pass filter is introduced. The filter is composed of multiple shorted shunt stubs and defected ground structure (DGS). The defected ground structure is composed of some circular-shape defects and diagonal-line patterns. The bend-shaped defected-ground structure is thoroughly studied and compared to some other defected structures. The filter features a simple structure and small dimensions (12 × 22 mm²). Meanwhile, a systematic design method is presented. The analysis method is based on numerical methods and is verified by a commercially available EM simulator. The 3 dB passband of the proposed wide band filter is between 2 GHz and 10 GHz.

Through-the-wall imaging (TWI) of human vital signs by bioradar is a hot research topic in recent years. Unknown wall parameters (mainly thickness and dielectric constant) are huge challenges for TWI. Ambiguities in wall parameters will degrade the image focusing quality, lower signal-to-noise-clutter ratio (SNCR) of vital signs, cause vital signs to be imaged away from their true positions and blur the close vital signs from multiple humans caused by the imaging resolution declination. A through-the-wall propagation model of vital signs for multiple-input and multiple-output (MIMO) bioradar is first built to analyze the influence of wall on imaging. In order to obtain focused image of vital signs quickly, an imaging model and a novel autofocusing imaging method of vital signs are proposed in this paper. Since vital signs of human are weak and sensitive to interferences, the SNCR-enhanced imagery of vital signs after change detection (CD) is applied to evaluate the focusing quality of image. Reflections of wall in the stationary targets imaging result are line structure approximately, so Hough transform is used to extract the positions of the front edge and rear edge of wall automatically. Propagation time in the wall of electromagnetic waves is estimated and used to build the constraint relationship of wall parameters. The number of unknown parameters is reduced to only one and the efficiency of autofocusing imaging improves. Several cases, including the case of single human, multiple human objects close to each other and the case of non-human objects, are simulated. The magnetic resonance imaging (MRI) image of human chest is put into simulation scene. And then the simulation data of human vital signs are calculated by the finite-difference time-domain (FDTD) method. The results show that the proposed method can effectively estimate the wall parameters and improve the focusing performance of human vital signs. And also the kurtosis of image can be used as a feature to efficiently decide the human vital signs are existed or not. Thus the SNCR of vital signs and resolution of imaging are improved, which are beneficial for detection of vital signs. The position errors of human vital signs are also corrected.

An array of rectangular holes pierced through a conducting screen is treated herein by a rigorous full-wave modal analysis using the moment method entailing Green's functions for rectangular cavities and planar multilayer structures in the spectral domain. Unexpectedly strong diffusions of incident plane waves are observed even at frequencies where the size of each hole is considerably less than the wavelength, posing a transmission efficiency that exceeds unity and thus leading to extraordinary transmission since this defies classical aperture diffraction theory. This paper fortifies the present understanding of the role surface plasmon polaritons (SPP) play in explaining this phenomenon, by using surface-wave dispersion and Floquet lattice diagrams to link up with the peaks in the transmission spectra. The incidence angle and polarization of the irradiation are taken into account in this work.

This paper describes the design of a broadband, fixed-IF, high efficiency single subharmonic mixer at Ka-band. The co-simulation between HFSS and ADS is applied to the modeling of the mixer. In order to improve the accuracy of simulation, the diode model is divided into passive linear model and active nonlinear model. On this basis, a global accurate equivalent circuit model of mixer is proposed and verified by testing data. The circuit of the presented mixer printed on the substrate of Rogers RT/Duroid 3003 is mounted in a waveguide block. When the fifixed IF frequency is set at 1.5 GHz, measured results show that the conversion loss is less than 8 dB over the RF bandwidth from 25 GHz to 39 GHz with 12 dBm of local oscillator power. The minimum conversion loss of 6.2 dB is measured at 28 GHz. The measured isolation between LO and IF, LO and RF is over 23 dB. The measured isolation between IF and RF is over 20 dB. Good isolation is achieved.

Satellite communication links operating at higher frequency bands suffer from signal outages due to rain attenuation. Site diversity technique is one of the rain fade mitigation techniques that can be employed over earth-satellite links to improve on system availability. In this study, we use 5-year rainfall rate statistics and the queuing theory approach to investigate the attributes and behavior ofintense rain storms along an earth-space link over Durban, South Africa (29˚52'S, 30˚58'E), a sub-tropical climate. Thereafter, a comparison is made with results obtained in a related study in Jimma, Ethiopia (7.6667˚N, 36.8333˚E), which is a tropical climatic region. Verification of the best fit distribution is done through the application of the root mean square error (RMSE) and CHI squared statistics. Results of these analysis tools confirm the suitability of the proposed distributions with RMSE error margin in the range 0.0024 to 0.0128, and a χ² statistics value of 0.4070. The spike service time for such rain storms is found to follow Erlang-k distribution in both regions of South Africa and Ethiopia as opposed to earlier determined exponential distribution. In addition, the analysis shows that there exists a power law relationship between the rain spike maximum rain rate and its diameter. This relationship is further utilized in the development of the rain cell sizing model that can be used for site diversity fade mitigation. Furthermore, the Markov chain techniqueis employed to determine the occurrence behavior of shower and storm rainfall regimes, and their contributions to rain attenuation over a slant path radio link.

In this paper, a circularly polarized (CP), high gain and wide bandwidth metal plated microstrip antenna (MSA) using partially reflecting surface (PRS) and artificial magnetic conductor (AMC) layers is proposed. The bandwidth of MSA is increased primarily, using AMC layers and gain is increased by placing the antenna in a Fabry-Perot cavity (FPC) resonator. The two slotted AMCs are designed to resonate at two frequencies which electromagnetically couple to provide wide bandwidth. The FPC antenna with PRS and AMC layers provides higher gain, more impedance bandwidth, less gain variation and more miniaturization than the antenna without AMC layers. The proposed antenna provides S₁₁ < -10 dB, axial ratio (AR) < 3dB and 17.4 dBi peak gain with gain variation < 3 dB over 5.725 GHz to 6.4 GHz frequency band. Broadside radiation patterns have side lobe level (SLL) < -20 dB, cross polarization (CPL) < -16 dB and front to back (F/B) lobe ratio > 20 dB. The overall antenna dimensions are 2.83λ₀ × 3.23λ₀ × 0.49λ₀, where, λ₀ is the free space wavelength corresponding to the central frequency of 5.725-6.4 GHz. The proposed structure is fabricated, and the measured results agree with simulation ones.

In this paper, a compact wideband circularly polarized (CP) crossed-dipole antenna with wide half-power beamwidth (HPBW) and broad 3 dB axial ratio beamwidth (ARBW) is proposed. The antenna is composed of crossed bowtie dipoles, four pentagonal parasitic elements and eight vertical metallic plates. A double vacant-quarter printed ring with orthogonal bowtie dipoles is designed for CP radiation and broadband characteristics of impedance and 3 dB axial ratio (AR) bandwidths. Parasitic elements and vertical metallic plates are utilized to increase bandwidth and broaden beamwidth further. The total size of the proposed antenna is 0.4λ×0.4λ×0.16λ. Simulated results are in good agreement with the measured ones which demonstrate an impedance bandwidth 88.4% and a 3 dB AR bandwidth 73.1%. The HPBW of more than 120° is 70.0%. The 3 dB ARBWs of more than 120° in E-plane and H-plane are 63.1% and 37.5%, respectively. With both the excellent CP performance and compact size, the proposed antenna is attractive for modern wireless communications.

A compact planar double inverted-F antenna (IFA) is proposed in this work. The antenna, composed of a shared short arm and two L-shaped open arms, has three operating bands, 1.7-1.9 GHz, 2.25-2.48 GHz and 5.33-5.8 GHz for Wi-Fi and LTE applications. It has the length of 80 mm, width of 23 mm and height of 1.6 mm. Near omnidirectional coverage of radiation patterns in x-y and x-z plane, are realized with peak gain of 3.3 dBi, 2.1 dBi and 4.1 dBi at 1.8 GHz, 2.4 GHz and 5.5 GHz, respectively. Based on reflection coefficients with different dimensions and current distributions, the functions of arms and via holes are analyzed in detail, which provide a useful guidance for design of multiband PIFA antennas.

In this paper, a novel and simple solution for generating vortex electromagnetic wave and reducing divergence simultaneously in a wideband is presented. Based on phase gradient metasurface, we design a metasurface that can convert an ordinary electromagnetic wave into a vortex one and focus the vortex wave in X-band. Double layer rectangular metal patch units of different sizes are arranged in a certain order to compose the metasurface. The phase introduced by the metasurface is superimposed by the vortex phase and focusing phase. Compared to a general vortex wave metasurface, the simulation results show that the divergence of the reflected vortex wave generated by our designed metasurface is dramatically reduced in the frequency range from 8 GHz to 12 GHz. It is indicated that the designed metasurface has a highly efficient focusing effect, and it is also in a good agreement with the theoretical analysis. The proposed reflective metasurface paves an effective way to reduce the divergence of vortex electromagnetic wave for OAM-based system in microwave and radio frequency.

We revisit the standard electromagnetic problem wherein wave propagation within a uniform, lossless dielectric is interrupted by a dissipative slab of finite thickness. While such a problem is easily solved on the basis of interface field continuity, we proceed to treat it here under the viewpoint of radiative self-consistency, with effective current sources resident only within the slab interior and gauged by ohmic/polarization parameter comparisons against those of the reference, exterior medium. Radiative self-consistency finds its natural expression as an integral equation over the slab interior field which, once solved, permits a direct, fully constructive buildup, both up and down, of the reflected/transmitted field contributions, without any need for ascertaining such quantities implicitly via the enforcement of boundary conditions. The persistent cadence of solution steps in such integral-equation problems asserts itself here, too, in the sense that it leads, first, to an exact cancellation, left and right, of that interior, unknown field, and second, that it brings in still other contributions of a reference medium variety, of which it is required that they, and only they, balance the incoming excitation. Balancing of this latter sort provides indeed the linear conditions for slab field determination. The two-step solution pattern thus described may be regarded as a manifestation at some remove of Ewald-Oseen extinction, even though the analytic framework now on view differs fundamentally from proofs elsewhere available. We go on to solve the several balancing equations by direct, vector manipulation avoiding all recourse to large, unwieldy determinants, and then offer a partial confirmation by exhibiting a canonical, boundary value counterpart in the special case of perpendicular incidence. Following all of this, in an appendix, we allow the receptor, downstream half space to differ from that wherein the excitation had been launched and which continues to serve as the reference medium. Effective currents are now found not only within the slab proper, but also throughout an entire half space, necessitating a suitable generalization of the underlying integral equation, and a provision, during its solution, of cross-talk, both up and down, between slab and the half space now contributing as a radiation source. We provide in this appendix a fairly accelerated presentation of these generalized features, but with all logical details nevertheless fully displayed in plain view. The integral equation radiative self-consistency method is, to our way of thinking, physically far more satisfying than the prevailing method of scattered fields guessed as to their structure and then fixed by boundary conditions. Its analytic themes, moreover, are far, far more elegant.

Because traditional eigen-subspace projection (ESP) methods cannot cancel the main lobe interference, an improved ESP algorithm and an orthogonal array of antenna are proposed to overcome this problem. Based on the orthogonal antenna array, the proposed algorithm combines ESP with ICA and signal blocking methods, which implements the extraction of part of the main lobe interference and optimized the estimation of the interference subspace. Both simulation and experiment results show that the improved ESP algorithm provides robust cancellation capability of main lobe and sidelobe interference for super low frequency (SLF) communication.

This paper presents the design and realization of a 4 × 4 broadband circularly polarized microstrip antenna as subarray element for airborne C-band circularly polarized synthetic aperture radar (CP-SAR). The main objective of this work is to optimize impedance bandwidth, axial-ratio bandwidth, gain, and radiation pattern of a CP-SAR array antenna due to the limitation in the available space for a large array antenna installation on airborne platform. Various patch separations in uniformly 2 × 2 subarray configuration have been simulated to investigate characteristics of impedance bandwidth, axial-ratio bandwidth, gain, and radiation pattern. In order to broaden the impedance bandwidth, the proposed antenna is constructed by stacking two thick substrates with low dielectric constant and dissipation factor. The measured 10-dB impedance bandwidth is 0.91 GHz (17.2%), spanning from 4.83 GHz to 6.01 GHz. A simple square patch with curve corner-truncation is applied as the main radiating patch for circularly-polarized wave generation. The radiating patch is excited by single-fed proximity coupled strip-line feeding. The improvement of axial-ratio bandwidth in 2 × 2 and 4 × 4 subarray is employed by a feeding network with serial-sequential-rotation configuration. Experimental result shows the 3-dB axial-ratio bandwidth achieved 1.18 GHz (22.17%) from 4.8 GHz to 5.71 GHz. Other characteristic parameters such as gain and radiation pattern of the 4 × 4 subarray antenna are also presented and discussed.

A miniature patch antenna for handset mobile communication is studied by loading an H-shaped patch associated with fashionable mushroom structures. The mushroom structures work as effective high index metamaterials while the H-shape can lengthen the current path on the patch. They both contribute to reduce the patch length. To verify the conceptual method, an H-shaped patch meta-antenna is demonstrated in full wave simulations and experiments. Good agreement has been observed. A compact patch is achieved for the antenna with a size of 0.15λ₀×0.15λ₀. The measured antenna gain is acceptably high as 4.2 dBi.

This paper presents an ultra-wideband (UWB) high temperature superconducting (HTS) bandpass filter (BPF) based on a ring resonator loaded with a pair of symmetrical cross-shaped stepped-impedance open stubs. The main advantages are that two transmission zeros are introduced to improve passband selectivity, and high mode suppression is achieved by adjusting the impedance ratio of the cross-shaped stubs and using a pair of parallel-coupled lines. The filter is designed on double-sided YBCO/MgO/YBCO HTS films with a thickness of 0.5 mm and dielectric constant of 9.8. At 77 K, the measured 3-dB bandwidth of the filter covers 1.63 GHz~6.03 GHz. Due to the use of superconducting material, the insertion loss at the center frequency of 3.83 GHz is 0.12 dB, and the rejection is greater than 36 dB in the lower stopband, and the upper stopband with 20 dB attenuation level is extended to at least 8.5 GHz.

In this paper a compact planar dual band-notched ultra-wideband (UWB) multiple input multiple output (MIMO) antenna is presented for universal synchronous bus (USB) dongle application with pattern diversity characteristic. The MIMO configuration has orthogonally placed elements with overall size of 16×37.6 mm², and the common ground plane of the MIMO antenna is further extended by 20 mm for its practical use. The measured and simulated reflection coefficients of the antenna show good impedance bandwidth matching over the range from 3 GHz to 12 GHz excluding the dual notched bands. Both elements show good band-reject property at the notched bands. The simulated results are verified through measurements and calculations. Moreover, absence of decoupling network makes circuit less complex and very compact. Radiation pattern of the MIMO antenna is almost omnidirectional. Furthermore, diversity performance of MIMO antenna is validated with its envelope correlation coefficient (ECC) and pattern diversity characteristic. These characteristics demonstrate its candidacy as a compact dual band-notched UWB MIMO antenna for USB dongle application.

Distributed antenna arrays are arbitrarily large groups of neighboring nodes which are controlled to form virtual antenna arrays for both transmission and reception. Distributed beamforming (DBF) is widely used in wireless sensor networks (WSNs) and distributed massive Multi-Input Multi-Output (MIMO) systems. The research in DBF has been divided into four major research trends: radiation pattern analysis, optimization of power and lifetime, nodes synchronization, and array design. In this paper, a new algorithm is introduced to synthesize the radiation pattern of an arbitrarily distributed array using reduced number of distributed nodes. In this context, the reduction in the number of nodes results in minimizing the synchronization complexity between the synthesized array nodes and in minimizing the number of RF front ends. Thus, the overall system cost is reduced. In this algorithm, the three antenna array parameters (number of nodes, nodes locations, and nodes excitations) are properly adjusted to construct a close copy of the original array pattern. Different nodes selection ways are utilized to select the nodes required to synthesize the array for a desired radiation pattern. Also, uniform feeding and non-uniform feeding scenarios are introduced. In simulations, the proposed algorithm is applied to the synthesis of pencil-beam patterns. The simulation results reveal that the synthesized radiation patterns highly agree with the ordinary distributed array pattern in the case of non-uniform feeding. Also, the proposed algorithm can be applied to the synthesis of shaped-beam patterns via controlling the three aforementioned antenna array parameters and taking the shaped-beam pattern as the desired pattern in the algorithm.

In this paper, a high power, air suspended stripline (SSL) T junction power divider at L band microwave frequencies is introduced. The power divider operating frequency is centered at 1.3 GHz. In this new configuration, the only dielectric used is air to have maximum power handling capability. An excitation transition from coaxial cable to the SSL transmission line is explained. The SSL was fabricated using alumi-num sheets to gain the advantage of low cost. The power divider design was validated using circuit and 3D full wave simulations and confirmed using experimental measurements with all agreements. It has been proved that the power divider attenuation has sharp rejection characteristic at the designed frequency (-20 dB at 1.3 GHz). The power divider can be used as a feeder for devices used in high power applications.