This paper presents a geometrically based method for the calculation of the node-to-node distance distribution function in circular-shaped networks. In our approach, this function is obtained from the intersection volume of a sphere and an ellipsoid. The method is valid for both overlapping and non-overlapping networks. Simulation results and comparisons with methods in the literature demonstrate the efficacy of the approach. The relation between networks geometric parameters and distance statistics is explored. As an application example, we model distance-dependent path loss and investigate the impact of channel characteristics and networks size on signal absorption. The aforementioned model is a useful and low-complexity tool for system-level modeling and simulation of mobile communication systems.

A highly birefringent four-hole fiber (FHF) with a pair of large air holes and a pair of small air holes are proposed for air/hydrostatic pressure sensing. The birefringence of the FHF can be up to 0.01 due to the rectangle-like fiber core surrounded by four air holes. Therefore, a FHF with a length of only several centimeters is required for high-sensitivity pressure sensing based on a Sagnac interferometer. Optical properties of the FHF such as effective index and birefringence are investigated. Pressure sensor based on the FHF depends on the pressure-induced refractive index change or pressure-induced birefringence. The stress distribution of the FHF subjected to an air/hydrostatic pressure is represented. Simulations show that the principal stress component parallel to the slow axis of the of the FHF under the air/hydrostatic pressure is greatly enhanced due to the existence of two large air holes, which consequently results in a high sensitivity of the FHF-based pressure sensor. Relationships between the pressure-induced birefirngence and the radius of the large air hole, the external diameter of the FHF, or the ellipticity of the elliptical FHF are investigated. The polarimetric pressure sensitivity of the FHF can be up to 607 rad/MPa/m.

Finite edge geometrical theory of diffraction (FEGTD) approach is a new and latest improvement in GTD technique. This FEGTD technique is applied to the H-plane and E-plane horn radiation problems with spherical source excitation. The horn patterns obtained with the FEGTD approach are found to be in good agreement with measured results.

Planar multiband bandpass filters are implemented based on the versatile multimode stepped-impedance resonators (SIRs). The resonant spectrum of a SIR can be calculated as functions of the length ratios for various impedance ratios of the high- and low-impedance sections. Thus, by properly selecting the geometric parameters and designing the input/output coupling structure, the SIRs are feasible to realize multiband multimode filters. Using a single SIR, a dual-mode dual-band, a dual-mode triple-band or a hybrid dual-/triple-mode dual-band bandpass filter can be realized. Emphasis is also placed on designing specified ratios of center frequencies and fractional bandwidths of the passbands. To extend the design flexibility, extra shunt open stubs are used to adjust the ratio of the passband frequencies. In addition, sharpness of the transition bands is improved by designing the input/output stages. Simulation results are validated by the measured responses of experimental circuits.

A compact printed and planar Multiple-Input Multiple-Output (MIMO) for Ultra Wideband (UWB) communications is presented. Two circular disc monopole antenna elements constitute the proposed UWB-MIMO antenna operating over the frequency band of 3.2-10.6 GHz. The isolation between the antenna ports has been enhanced to the value of more than 15 dB throughout the frequency band of interest. This enhancement is achieved by taking the advantage of an inverted-Y shaped stub that is being inserted on the ground plane of UWB-MIMO antenna. The insertion of the stub has also facilitated reduction of the size of the antenna, i.e., overall dimensions of the antenna are 40×68mm². The proposed antenna is investigated both numerically and experimentally.

The double and triple Langmuir probe diagnostic systems with their necessary driving circuits are developed successfully for the characterization of laboratory built low pressure inductively coupled nitrogen plasma, generated by 13.56 MHz radio frequency (RF) power supply along with an automatic impedance matching network. Using the DC properties of these two probes, the discharge plasma parameters like ion saturation current (I_io), electron temperature (kT_e) and electron number density (n_e) are measured at the input RF power ranging from 250 to 400 W and filling gas pressures ranging from 0.3 to 0.6 mbar. An increasing trend is observed in electron temperature kT_e and n_e with the increase of input RF power at a fixed filling gas pressure of 0.3 mbar, while a decreasing trend is observed in kT_e and n_e with the increase of filling gas pressure at a fixed input RF power of 250 W.

The planar metal particles, consisting of a multi-turn spirals, are studied with the aim of using them to realize high impedance surfaces or as an elementary cell to create an artificial material. These spirals present a resonant behaviour in a certain frequency band. To obtain miniature devices, a compromise between the surface and the efficiency of the resonance must be found. The compactness of the particles can be increased by using s spirals. However, the accuracy on resonant frequency of existing models is not sufficient for our applications. We present a simple analytical model that determines the resonant frequency from the geometric dimensions of the approximated model. This model is verified by electromagnetic simulations and by measurements.

Reflection from a planar DB interface placed in chiral and chiral nihility medium is studied. No difference between the two cases, regarding reflection chracteristics, is noted. No reflected backward wave is produced for DB interface placed in chiral nihility metamaterial. In this regard, DB interface may be considered as first known perfect reflector interface which yields non zero power when placed in chiral nihility medium.

A novel compact multi-band design of planar C-shaped monopole antenna with inverted L-shaped parasitic strip is proposed for IEEE 802.16m WiMAX system. The obtained impedance bandwidth across the 2.6/3.5/5.5 GHz operating bands can reach about 240/570/4470 MHz, respectively. Only with the antenna size of 15×30×0.8 mm³, the proposed monopole antenna has the compact operation with more than 50% antenna size reduction. The measured peak gains and radiation efficiencies are about 2.1/2.2/2.9 dBi and 91/96/94% for the 2.6/3.5/5.5 GHz operating band, respectively, with nearly omni-directional pattern in the XY-plane.

Spaceborne synthetic aperture radar (SAR) systems operating at lower frequencies, such as P-band, are significantly affected by Faraday rotation (FR) effects. This paper presents a novel algorithm for measuring system errors (channel imbalance and cross-talk) in the presence of Faraday rotation for spaceborne polarimetric SAR data. It uses four polarimetric selective calibrators (four polarimetric active radar calibrators [PARCs] or possibly two PARCs and two gridded trihedrals). Theoretical analysis and simulations demonstrate that the optimized calibration scheme puts tight constraints on the accuracy of the associated Faraday rotation if the cross-talk is to be accurately measured. There are also strong constraints on the allowable signal-to-noise ratio and average polarimetric noise associated with the calibration devices. The analysis suggests that, unless the calibration sites are at the magnetic equator, independent measurements of total electron content (TEC) from a direct ground-satellite line-of-sight dual-frequency system are also needed.

The method of connected local fields (CLF), developed for computing numerical solutions of the two-dimensional (2-D) Helmholtz equation, is capable of advancing existing frequency-domain finite-difference (FD-FD) methods by reducing the spatial sampling density nearly to the theoretical limit of two points per wavelength. In this paper, we show that the core theory of CLF is the result of applying the uniqueness theorem to local EM waves. Furthermore, the mathematical process for computing the local field expansion (LFE) coefficients from eight adjacent points on a square is similar to that in the theory of discrete Fourier transform. We also present a theoretical analysis of both the local and global errors in the theory of connected local fields and provide closed-form expressions for these errors.

The operation of a slab antenna with low-index metamaterial substrate is affected by a cluster of metallic cylinders positioned in the near-field area. A semi-analytical solution of the defined boundary value problem is obtained based on the small size of the rods. Several different configurations are found to possess beneficial features concerning the total radiated power and the angle of directive emission. The deduced diagrams are independently validated and discussed, revealing certain conclusions.

This paper presents the synthesis of a novel dual-band bandpass filter with improved out-of-band performance. The proposed circuit is constructed by cascading a dual-band filter using trisection stepped impedance resonators (SIRs) and an L-C ladder lowpass filter using open-circuited stubs. The dual-band trisection SIR can provide the desired dual-band response, and the lowpass filter can improve the out-of band performance by suppressing the harmonics and spurious responses. The proposed filter has been fabricated and measured. Simulation and measurement results are found to be in good agreement.

This paper presents an optimal power pattern synthesis procedure able to tackle the mutual coupling and platform effiects even for electrically large arrays. The novelty of the approach is due to its capability to account in the synthesis procedure for two different aspects at the same time: the coupling between the array radiating elements and the coupling between these elements and the array platform. The mutual coupling evaluation is based on the active element pattern method, and the active element pattern is numerically computed. The kind of synthesis problems here addressed belongs to the class of convex optimization problems. Therefore, the solution is found by means of very efficient convex programming tools, without requiring global optimization schemes, thus saving time and costs. The extension of the overall tool to adaptive arrays is also considered.

Breast cancer detection using Ultra Wideband Radar has been thoroughly investigated over the last decade. This breast imaging modality is based on the dielectric properties of normal and cancerous breast tissue at microwave frequencies. However, the dielectric properties of benign and malignant tumours are very similar, so tumour classification based on dielectric properties alone is not feasible. Therefore, classification methods based on the Radar Target Signature of tumours need to be further developed to classify tumours as either benign or malignant. Several studies have addressed the issue of tumour classification based on the size, shape and surface texture of the tumour. In general, these studies examined the performance of classification algorithms in primarily dielectrically homogeneous breast models. These relatively simplistic models do not provide a realistic test platform for the evaluation of tumour classification algorithms. This paper examines the classification of tumours under realistic dielectrically heterogeneous conditions. Four different heterogeneous scenarios are considered, with varying levels of heterogeneity and complexity. In this paper, the performance and robustness of tumour classification algorithms under these realistic conditions are examined and discussed.

Extraction of vegetation water content and soil moisture from microwave observations requires development of a high fidelity scattering model. A number of factors associated with the vegetation canopy and the underlying bare soil should be taken into account. In this paper, we propose an electromagnetic scattering model for a corn canopy which includes coherent effect due to the corn structure and takes advantage of recently advanced scattering models for dielectric cylinder of finite length, for thin dielectric disk with elliptical cross section, and for rough surface. The model results are validated at both L and C bands. At C band we acquired some RADARSAT-2 data of several test fields of corn canopy in Jiangsu Province, China, in 2009, and carried out simultaneous measurement campaigns to collect the in situ ground truth. A comparison is made between theory and RADARSAT-2 data. At L band because high quality AIRSAR measurement data are available along with detailed ground truth in the literature, a comparison is also made between theory and AIRSAR data.

By enabling both cavity modes and plasmonic resonance together in the designed two-handed metamaterial, we demonstrate a square-wave-like (SWL) bandpass filter with high-ratio bandwidth (HRB). Our results show that this metamaterial-based bandpass filter possesses high-ratio bandwidth of 30 GHz centered at 92 GHz, excellent transmittance beyond 87.5 %, sharp transition within 1.0 GHz from -3 dB to -20 dB as upper and lower band edge transitions, and dual-band behavior. Such an HRBSWL bandpass filter can be scalable and readily applicable for the commercialized unlicensed 60 GHz spectra with a bandwidth exceeding 7 GHz, solving the challenge of conventional passive bandpass filters to allow wide bandwidths and great quality factors simultaneously.

A novel compact open-ended L-shaped slot antenna with asymmetrical rectangular patch is demonstrated and designed for UWB applications. With the open-ended L-shaped slot and an asymmetrical rectangular patch fed by the micro-strip line, multiple resonant frequencies are excited and merged to form a measured widen operating bandwidth of 3.01~11.30 GHz with 10 dB return loss. The fractional bandwidth can be enhanced from previous 32% (3~4.15 GHz) to 112% (3~10.66 GHz) among three different antenna types in simulations. The details and vital parameters of the proposed slot antenna are also illustrated. In addition, the proposed slot antenna exhibits a small size of 22×25 mm², which makes it an excellent candidate for UWB systems and portable applications.

Image formation from squinted sliding spotlight synthetic aperture radar (SAR) is limited by azimuth spectral folding and severe two dimension coupling. This paper presents an Extended Wavenumber Domain Algorithm (WDA) for highly squinted sliding spotlight SAR data processing. This algorithm adopts azimuth deramping approach to overcome the azimuth spectral folding phenomenon. The chirp rate for azimuth deramping and the principle of choosing pulse repetition frequency (PRF) is presented to accommodate the characteristic of Doppler history. Subsequently, the full focusing is implemented by WDA. Instead of the conventional Stolt mapping in WDA, a modified Stolt mapping is introduced in order to enlarge the range extension of focused image and enable to update the Doppler parameters along range. To confirm the correctness of the implementation of modified Stolt mapping and the azimuth position of target in focused image, related compensation terms are developed. Point target simulation results are presented to validate the effectiveness of extended WDA to process highly squinted sliding spotlight SAR data.

An end-fire linear tapered slot antenna is presented in the terahertz band. The operation frequency goes from 0.6 THz to 2 THz, with symmetric radiation patterns from 1 THz to 1.7 THz, and gains up to 15 dB. The gaussicity of the beam is over 80% in the whole operation band and an efficiency at 1THz of 85%. This antenna gives enough directivity avoiding the use of a typical substrate lens, which introduce 30% of losses. This new design is a good candidate for new applications in the THz range in Radioastronomy and Imaging.