Ultrawideband (UWB) microwave imaging is a promising emerging method for the detection of breast cancer. Fibroglandular tissue has been shown to significantly limit the effectiveness of UWB imaging algorithms, particularly in the case of premenopausal women who may present with more dense breast tissue. Rather than trying to create an image of the breast, this study proposes to compare the UWB backscattered signals from successive scans of a dielectrically heterogeneous breast, to identify the presence of cancerous tissue. The temporal changes between signals are processed using Support Vector Machines to determine if a cancerous growth has occurred during the time between scans. Detection rates are compared to the results from a previous study by the authors, where UWB backscatter signals from a single scan were processed for cancer detection.

Japanese terrestrial broadcasting was completely converted to digital television (DTV) broadcasting on 470--710\,MHz as of July 2011. However, fading phenomenon resulting from standing waves is a factor in quality deterioration in TV and mobile communication technologies. Suppression of this is needed for many kinds of technologies. A broadband single-feed planar antenna composed of two antenna components, a Broadband Planar Monopole Antenna (B-PMA) and a Broadband Planar Slot Antenna (B-PSA), is proposed for reducing deterioration of reception due to the fading across the DTV band. Reflection coefficients and radiation patterns analyzed by the Finite Difference Time Domain (FDTD) method and compared with measured results indicate that the proposed antenna is broadband compared with a conventional antenna studied previously. A field experiment is conducted in the DTV band. The results of the field experiment indicate clearly that the proposed antenna efficiently suppresses fading resulting from standing waves across the band.

A comprehensive study is performed to investigate the performance of a non-uniform circular array interferometer in a real time 3-dimensional direction finder. The angular range of view is supposed to be 65 degrees vertically and 120 degrees horizontally, which is suitable for airborne applications. Interferometer is designed to work in the S, C and X bands. Regarding optimization process, the interferometer employs an eight element non-uniform circular array along with a phase reference antenna at the center of the array. Several quantities and parameters are studied, e.g., frequency behavior, origins of phase measurement errors, Signal to Noise Ratio (SNR) effect on phase measurement, and the effect of the phase measurement error on direction finding performance. The proposed interferometer is able to tolerate at least 35 degrees of phase measurement error. Radius of the array is determined to be 22 cm in order to have good frequency response in the desired frequency band. Both Generalized Regression Neural Network (GRNN) and Maximum Likelihood (ML) estimation are applied for mapping the phase relationships between antennas to the Direction of Arrival (DoA). The results of two methods are well matched, and therefore validation is performed.

The microwave transmission of hexagonal arrays consisting of patches of equilateral aluminium triangles has been experimentally studied as a function of metal occupancy (triangle size). As one would expect, at low frequencies the microwave transmission drops on passing through the connectivity threshold (50%) when the disconnected hexagonal array of metal triangles switches to a disconnected hexagonal array of equilateral holes. However, for higher frequencies resonant phenomena cause a complete reversal in this behaviour such that the transmission, on passing through the connectivity threshold, increases substantially.

Electromagnetic properties of conventional radar absorbing materials (RAM) make it difficult to use them to provide remarkable surface electromagnetic waves (SEMW) attenuation with thin thickness at low radar frequencies such as in the UHF and L bands. In this paper, a composite structure realized by a grounded RAM slab covered by a resistive sheet is proposed. The use of a resistive sheet results in a significant increase of SEMW attenuation performance at low frequency, but almost no increase in its thickness. The electromagnetic scattering properties for a target coated with the RAM with/without covered by a resistive sheet are considered for interpreting the improvement of SEMW attenuation with resistive loading. Using a method-of-moments (MoM) computational scheme, we explore the performance of the proposed composite structure as radar backscattering suppression for a metal slab at low radar frequencies. It is found that the RAM with resistive loading has significantly increased SEMW attenuation at low frequencies, and advances the large incidence angle or grazing angle mono-static radar cross section (RCS) reduction of the coating slab further than the RAM without resistive loading case.

A compact ultra-wideband (UWB) slot antenna based on a mesh-grid structure is designed. A Boolean differential evolution (BDE) algorithm is used to optimize the mesh-grid structure as well as other parameters of the proposed antenna for good impedance matching in the UWB band. The optimized UWB antenna has a compact size of 24.2 × 32.2 mm and is fabricated and measured. According to the measured results, the proposed antenna yields a wide bandwidth, defined by S₁₁ < -10 dB ranging from 2.8 to 11.2 GHz. And it shows that the BDE algorithm is an effective method for antenna design.

A novel, tri-band, planar plate-type antenna made of a compact metal plate for wireless local area network (WLAN) applications in the 2.4 GHz (2400-2484 MHz), 5.2 GHz (5150-5350 MHz), and 5.8 GHz (5725-5825 MHz) bands is presented. The antenna was designed in a way that the operating principle includes dipole and loop resonant modes to cover the 2.4/5.2 and 5.8 GHz bands, respectively. The antenna comprises a larger radiating arm and a smaller loop radiating arm, which are connected to each other at the signal ground point. The antenna can easily be fed by using a 50 Ω mini-coaxial cable and shows good radiation performance. Details of the design are described and discussed in the article.

A novel compact printed antenna for dual band applications is presented. The antenna consists of two monopole elements and operates within the ISM 2.4 GHz and 5.2/5.8 GHz frequency bands. The proposed antenna provides a bandwidth of 403 MHz (2.184 GHz-2.587 GHz) in the lower frequency band and 4004 MHz (3.880 GHz-7.884 GHz) in the upper frequency band, respectively. Thus, it can cover multiple standards such as: HIPERLAN, 5.5 GHz WiMAX, and 2.4/5.2/5.8 GHz WLAN. Moreover, the lower resonant frequency of the proposed antenna can be easily tuned within 2.15 GHz to 3.22 GHz with almost no effect on the upper resonance. Additionally, the small ground plane size of the proposed antenna makes it suitable for almost any portable device.

A compact planar 4 x 4 microstrip Butler matrix is proposed in this paper. It is a wideband beam-forming network with the advantages of compact size, low cost and ease of fabrication. Three-branch line couplers with lumped-distributed elements are adopted to reduce the size, and multi-U-shaped coupled-line Schiffman phase shifters are designed to get good transmission and phase performances. The Butler matrix is fabricated and measured, and a good agreement is found between the simulated and measured results, which makes it very attractive for wideband multi-beam antenna applications.

In a previous paper, we proposed and tested a robust and efficient three-dimensional (3-D) subgridding algorithm for the FDTD solution method of the Maxwell's curl PDEs system. Its characteristic feature is the straight, non-recursive, embedding of Yee grids - refined by factors of 3, 5, 7 and even larger - within coarser ones. There, the algorithm's implementation was described with the traditional serial programming approach. In the present paper, we propose and test its parallel programming implementation. The goal is to make it suitable and efficient for large scale electromagnetic simulations.

A slotted-ground-plane meandered-slot resonator with multi-resonance characteristics and a compact lowpass filter (LPF) by using the resonator are demonstrated in this paper. The meandered slot provides a wideband resonator with low insertion loss and very sharp cutoff frequency response. Unlike conventional design of cascading bandstop slotted-ground-plane resonators in the literature, the introduced LPF is presented, which consists of a modified-meander slot in the ground plane, a spurred C-like slot, and a uniform microstrip transmission line with constant characteristics impedance. Two rectangular-head slots, giving an increase in the inductance, are added at the two terminals of the meandered slot for purpose of frequency reduction. An arm aperture is embedded to form another resonant path so that an additional transmission zero could be generated. In order to increase rejection capability, the slot width of one section of the meandered-slot resonator is widened. Meanwhile, a C-like slot with a spur slit is also etched inside the meandered slot to improve rejection performance. The measured insertion loss at a passband is below 0.7 dB, and the rejection band over 20 dB is from 2.9 to 12.0 GHz.

Vivaldi antennas have broad applications in real practice due to the ultra wideband properties. However, their gain and directivity are relatively low. In this paper, a new method is presented to improve the gain and directivity of Vivaldi antennas in a broad band using inhomogeneous and anisotropic (IA) zero-index metamaterials (ZIM). ZIM have the ability to enhance the antenna directivity; anisotropic ZIM with only one component of the permittivity or permeability tensor approaching to zero can make impedance match to improve the radiation efficiency; and IA-ZIM can broaden the frequency bandwidth. Single- and multiple-layered planar IA-ZIM have been analyzed, designed, and fabricated, which can be embedded into the original Vivaldi antenna smoothly and compactly. The IA-ZIM-based Vivaldi antennas have good features of high gain, high directivity, low return loss, and broad bandwidth. Compared to the original Vivaldi antenna, the measurement results show that the gain has been increased by 3 dB and the half-power beam width has been decreased by 20 degrees with the reflection coefficient less than -10 dB from 9.5 GHz to 12.5 GHz after using IA-ZIM.

A computational technique is presented for efficient and accurate time-domain analysis of multiport waveguide structures with arbitrary metallic and dielectric discontinuities using a higher order finite element method (FEM) in the frequency domain. It is demonstrated that with a highly efficient and appropriately designed frequency-domain FEM solver, it is possible to obtain extremely fast and accurate time-domain solutions of microwave passive structures performing computations in the frequency domain along with the discrete Fourier transform (DFT) and its inverse (IDFT). The technique is a higher order large domain Galerkin-type FEM for 3-D analysis of waveguide structures with discontinuities implementing curl-conforming hierarchical polynomial vector basis functions in conjunction with Lagrange-type curved hexahedral finite elements and a simple single-mode boundary condition, coupled with standard DFT and IDFT algorithms. The examples demonstrate excellent numerical properties of the technique, which appears to be the first time-from-frequency-domain FEM solver, primarily due to (i) very small total numbers of unknowns in higher order solutions, (ii) great modeling flexibility using large (homogeneous and continuously inhomogeneous) finite elements, and (iii) extremely fast multifrequency FEM analysis (the global FEM matrix is filled only once and then reused for every subsequent frequency point) needed for the inverse Fourier transform.

The diffraction field asymptotics on the edges of a slot in the plane conducting screen and of a complementary strip is considered using the exact solutions of corresponding stationary diffraction problems, which have been derived before on the bases of the slot (strip) field expansions into discrete Fourier series. It is shown that as nearing the slot (strip) edges, the fields decrease or increase indefinitely in magnitude by the power law with an exponent of modulus less than unity, so the given exact diffraction solutions yield finite value of electromagnetic energy density in any point of space.

A RF directional modulation technique using a switched antenna array is proposed for communication and direction-finding applications. The main idea is that a baseband modulation signal is transmitted by the switched antenna array. The phase center of the transmit signal is moved by the feeding line of each element from the left to the right. In this way, the data information and Doppler frequency shift information are modulated into a transmit signal constellation simultaneously. Therefore, this constellation is a scrambled constellation compared with traditional baseband modulation signal, which varies with the azimuth angle information of the receiver. For the receiver with a single antenna, a differential correlation algorithm is employed to demodulate the data information, and an azimuth angle estimation algorithm is also developed to extract the azimuth angle information from this scrambled constellation. Simulation results show that this RF directional modulation technique offers a comprehensive scheme for communication and direction-finding from the point view of RF modulation technique.

The imaging quality of tomography SAR is limited by the low number of flight tracks and their non-uniform distribution. In this paper, a new 3-D imaging algorithm is proposed for tomography SAR based on the improved interpolated array transform. The key point of the proposed algorithm is the introduction of the projection technique into the interpolated array transform, which can reduce the energy of the interference signal and improve the imaging quality. Performance analysis under different scenarios is carried out via the simulations. And the results demonstrate that the sidelobe performance can be significantly improved by the proposed algorithm.

A novel RCS (radar cross section) reduction configuration for a reflectarray antenna, employing the appropriate FSS (frequency-selective surface) as a ground, is proposed. The performance of a reflectarray element backed either by a solid metal ground plane or a frequency-selective surface is compared. To optimize the performance of the designed frequency-selective surface, a parametric study is carried out using Ansoft HFSS. Then, a prime-focus FSS-backed reflectarray is fabricated and tested. The measurements demonstrate that the gain of a FSS-backed reflectarray is about 0.5 dB lower than its counterpart backed by a solid ground plane. The RCS is nearly the same at the operating band of 10 GHz, while out of this band the FSS-backed reflectarray reduces the RCS strongly, especially at 1 GHz with the reduction up to 20 dB. Compared with the RCS reductions obtained in the other papers, the FSS-backed reflectarray using a ring element can also obtain a good result.

This paper presents a rigorous approach for the propagation of electromagnetic (EM) fields along a helical waveguide with slab and rectangular dielectric profiles in the rectangular cross section. The main objective is to develop a numerical method for the calculation of the output fields, for an arbitrary step's angle and the radius of the cylinder of the helical waveguide. The other objectives are to present the technique to calculate the dielectric profiles and their transverse derivatives in the cross-section and to demonstrate the ability of the model to solve practical problems with slab and rectangular dielectric profiles in the rectangular cross section of the helical waveguide. The method is based on Fourier coefficients of the transverse dielectric profile and those of the input wave profile. Laplace transform is necessary to obtain the comfortable and simple input-output connections of the fields. This model is useful for the analysis of helical waveguides with slab and rectangular dielectric profiles in the metallic helical waveguides in the microwave and the millimeter-wave regimes. The output power transmission and the output power density are improved by increasing the step's angle or the radius of the cylinder of the helical waveguide, especially in the cases of space curved waveguides.

A new type of elevated coplanar waveguide structure is described which uses airbridge technology to suspend CPW traces above a ground plane resting on a high permittivity substrate. The transmission line is effectively shielded from the substrate and is equivalent to conductor backed CPW with an extremely thin, air substrate. It is, therefore, insensitive to parasitic substrate effects such as surface waves and the effect of dielectric loss tangent. In comparison with other forms of CPW with typical lateral dimensions, the structure exhibits no high frequency roll-off at frequencies of around 240 GHz and above. Measured results show 2.5 dB/mm insertion loss at 320 GHz for a 51 Ω line. In order to demonstrate the performance of the new line at mm-wave frequencies, several passive components have been fabricated, measured and their performance compared with CPW counterparts. The experimental results, which are in close agreement with simulation results, for short and open circuited matching stubs, and band-pass and band-stop filters, clearly show improvements in terms of loss and in the characteristics of the frequency response. Also, in order to make some qualitative assessment of the variation in performance with elevation, results for elevations of 6 μm and 13 μm are compared. Low loss and a simple, MMIC compatible, fabrication process make grounded elevated CPW a promising transmission media for MMIC applications at the very high end of the millimeter-wave frequency spectrum.

Fourier transform of discontinuous functions are often encountered in computational electromagnetics. A highly accurate, fast conformal Fourier transform (CFT) algorithm is proposed to evaluate the finite Fourier transform of 2D discontinuous functions. A curved triangular mesh combined with curvilinear coordinate transformation is adopted to flexibly model an arbitrary shape of the discontinuity boundary. This enables us to take full advantages of high order interpolation and Gaussian quadrature methods to achieve highly accurate Fourier integration results with a low sampling density and small computation time. The complexity of the proposed algorithm is similar to the traditional 2D fast Fourier transform algorithm, but with orders of magnitude higher accuracy. Numerical examples illustrate the excellent performance of the proposed CFT method.