A thick metal microstrip diplexer is presented. The circuit is based on compact folded half wavelength resonators and uses a source/load-multi-resonator coupling method providing improved performance and greater design flexibility. Source/load coupling with multiple resonators introduces additional transmission zeros, and this coupling is enhanced by using high-aspect-ratio metal structures. Tall, narrow metal arms connected to the ports and extended to the non-adjacent resonators provide effective multi-resonator bypass coupling. The high-aspect-ratio diplexer fabricated using polymer-based deep X-ray lithography and 0.22 mm thick metal electroplating demonstrates the advantages of thick metal structures for coupled resonator applications.

To describe propagation of polarized electromagnetic wave within a disperse random medium a new Monte Carlo based technique with an adopted vector formalism has been developed. The technique has been applied for simulation of coherent backscattering of circularly polarized optical radiation from a random scattering medium. It has been found that the sign of helicity of circular polarized light does not change for a medium of point-like scatterers and can change significantly for the scatterers with the higher anisotropy. We conclude that the helicity flip of the circular polarized light can be observed in the tissue-like media. We find that this phenomenon manifests itself in case of limited number of scattering events and, apparently, can be attributed to the pulse character of incident radiation rather than to the specific form of scattering particles.

In this study, transmission characteristics of a novel THz wire waveguide --- conical metal wire with dielectric coating at 0.1-1 THz are studied. The investigation results show that the coated conical wire with virtually low attenuation and high energy concentration is a promising candidate as THz transmission medium. The calculation results agree well with that of simulation such as high frequency structure simulation (HFSS), which is based on the finite element method. In this paper, a novel transition from a coaxial line to the coated conical metal wire is designed. Although coaxial probe excitation has been used in microstrip lines and rectangular waveguides in microwave, millimeter-wave frequency domains, the present study shows that it is also an effective method to excite conical wire at THz frequency. As shown in the investigation results, the return loss of coax-conical wire transition is better than 20 dB from 0.1-0.5 THz, and the insertion loss is as low as 1 dB (the total length is 15 mm). It is a promising THz transition structure.

An accurate and flexible three-dimensional Volterra Time Domain Integral Equation (TDIE) algorithm is presented and implemented here to model the time-dependent electromagnetic field of arbitrarily shaped dielectric bodies. This development is motivated by the need for a modern high-resolution numerical tool that is capable of providing a full and comprehensive investigation of devices containing a diverse range of feature sizes or boundaries, in all three space dimensions plus time. Stability, accuracy and convergence of the algorithm are discussed and verified by means of canonical working examples.

This article presents a simple structure for reducing mutual coupling between two diversity planar monopole antennas for WLAN 5.2/5.8 GHz applications. The structure has two λ/4 (λ-wavelength in the substrate) slots cut into the ground plane between the two monopoles. In 0.5 λ_o (λ_o,-wavelength in the air) of the antenna spacing, mutual coupling was -33.3, -21.1 dB at 5.2, 5.8 GHz, respectively. The lowest mutual coupling of -33.3 dB was achieved at 5.2 GHz, which is 20.8 dB improvement over the reference.

A compact ultra-wideband microstrip-fed planar monopole antenna with dual band-notch characteristic is presented. Dual notched frequency bands are achieved by embedding an M-slot in the radiating patch and a W-slot in the ground beneath the feeding line. And the characteristics of the dual band-notched can be controlled by adjusting the length and position of the corresponding slot. Experimental results show that the proposed antenna, with compact size of, has an impedance bandwidth of 2.75~11.30 GHz for VSWR less than 2.0, except two notched bands of 3.25~4.20 GHz and 5.23~6.10 GHz. Moreover, this antenna exhibits good omnidirectional radiation patterns in the H-plane, stable antenna gains over the operation band, and perfect group delay in the time-domain.

The possibility of using non-Foster circuit to expand the bandwidth of a monopole antenna is investigated theoretically. Beginning with an inductor-loaded monopole antenna resonating at different frequencies by changing the value of the loaded inductor, we show that a frequency-dependent inductor is needed to enhance the bandwidth of the monopole antenna. The curve for the reactance of the frequency-dependent inductor versus frequency is fitted, which enlightens us to use a non-Foster reactive circuit to realize the frequency-dependent inductor. Based on the above studies, a monople antenna loaded with a non-Foster circuit is presented. Simulated results demonstrate that the input reactance of the loaded antenna becomes stable and approaches zero, which favors the impedance matching and extends the bandwidth to a certain extent. Finally, a passive (Foster) matching circuit is designed to improve the bandwidth further. A 0.69-m monopole antenna with 2.0:1 VSWR in the frequency range 30--150 MHz is designed and investigated.

This paper presents analysis and design of a Gaussian backscatter antenna with ring focus feed. The curvature of main reflector is Gaussian, and the subreflector is a portion of an ellipse. The antenna has axial symmetry. A backscattering technique is used with the main reflector to achieve wide beamwidth. The input parameters of the proposed antenna are derived in closed form. Physical theory of diffraction (PTD) is used to analyze the radiation pattern of the proposed antenna and verified with experimental results. The effects of the support structures on the radiation patterns of the proposed antenna have been investigated experimentally. The proposed antenna can produces high gain and wide beamwidth (coverage angle θ=±65°). This antenna can be used for realizing earth coverage beam in LEO satellite or indoor wireless LAN applications.

The paper describes pulse-based ultra-wideband (UWB) microwave imaging experiments for breast cancer detection using heterogeneous breast phantoms with dielectric properties mimicking the human breast. Three homogeneous and seven heterogeneous breast phantoms are used in tumor detection experiments. The phantoms have dielectric permittivity and conductivity higher than previously reported experiments, as well as clutters to represent the glandular tissue in human breast. The experiments are conducted in time-domain with pulse generator and real-time oscilloscope.

In this study, a general method for analyzing the multilayer optical planar waveguides with photonic metamaterial is presented. The propagation characteristics of TE waves guided by the film with both the permittivity and permeability less than zero are investigated theoretically. The formulae for the electric fields of TE modes in this structure have been proposed. Typical numerical results for dispersion characteristics are shown. The analytical and numerical results show excellent agreement.

This paper studies the left-handed behavior in conventional 2-port coupled line networks. The propagation parameters of 12 periodic structures, each has a different coupled line configuration, have been derived and the left-handed bands have been determined. Two structures were fabricated and measured to confirm the composite right/left handed (CRLH) characteristics. Measurements and EM simulations were in a very good agreement with the developed theory. In the light of the proposed theory, a geometrical circuit model was also proposed for split ring resonator (SRR). The model is capable to predict its performance over a wide band.

A dual-feed dual-polarized dielectric resonator antenna (DRA) with high isolation is proposed in this paper. The high isolation is achieved by using two hybrid feeding mechanism: one port having an H-shaped aperture coupled feed and the other with two out-of-phase probe feeds. The antenna is designed to operate at around 5.2 GHz for WLAN (Wireless Local Area Network) applications and experimental results show that it has more than 35 dB isolation over the entire impedance bandwidth. Good symmetric broadside radiation patterns with low cross polarizations are observed in the two principal planes, and in addition, the front-to-back (F/B) ratios for Port 1 and Port 2 are 10 and 18 dB, respectively.

A miniaturized microstrip-fed antenna composed of a broadside coupled split ring resonator and an excitation arc-shaped monopole is presented. Numerical and experimental results are presented for an antenna configuration of 1/25 wavelength in diameter (ka~0.126). The antenna size including the ground plane is 60×38.5 mm² and it is operating at 200 MHz. Its resonant frequency can be tuned over a good range of frequency without changing the antenna size, which can increase its usable bandwidth using reconfigurable antenna techniques.

In this letter, a novel high selectivity microstrip filter with source-loaded coupling is proposed using the dual-mode resonator. The resonator can generate one odd mode and one even mode in the desired band. The folded stepped-impedance open stub at the central plane can control the even mode resonant frequencies, whereas the odd mode ones are fixed. A transmission zero is created near the lower cut-off frequency due to the main path signal counteraction. Two additional transmission zeros attributed to source-loaded coupling are generated near the upper cut-off frequency and in the upper-stopband. A dual-mode filter prototype is simulated, fabricated and measured. The EM simulated and measured results are presented and excellent agreement is obtained.

Waveguide diplexer designs are widely used for telecommunications, space, and terrestrial applications. Although mathematical models and design procedures for waveguide filters are known, diplexer designs still remain complex and time consuming. This paper describes how to obtain an equivalent circuit network model and a complete design of non-contiguous diplexers using a computer-aided approach with a classic Y-junction. Results are satisfactory in terms of reduced design time and performance. Examples including physical dimensions are provided.

Low frequency imaging in radar domain can have applications for stealthy or buried targets. The transient scattering response from a ramp waveform is related to the profile function of the target, namely its transverse cross-sectional area along the line-of-sight, and thus provides information about the target size, orientation and geometrical shape. Such ramp responses can be used to generate a 3-dimensional image of the global shape of the target. Former imaging algorithm uses approximate limiting surfaces and is therefore limited to single convex objects. Here is proposed a new algorithm able to reconstruct non-convex as well as separated targets, from their ramp response signatures.

This paper is the third part of a series dealing with permanent magnet passive magnetic bearings. It presents analytical expressions of the axial force and stiffness in radial passive magnetic bearings made of ring permanent magnets with perpendicular polarizations: the inner ring polarization is perpendicular to the outer ring one. The main goal of this paper is to present a simple analytical model which can be easily implemented in Matlab or Mathematica so as to carry out parametric studies. This paper first compares the axial force and stiffness in bearings with axial, radial and perpendicular polarizations. Then, bearings made of stacked ring magnets with alternate polarizations are studied for the three kinds of polarizations, axial, radial and perpendicular. The latter correspond to Halbach structures. These calculations are useful for identifying the structures required for having great axial forces and the ones allowing to get great axial stiffnesses.

While designing wireless networks, it is crucial to obtain the maximum coverage by using minimum number of transmitting antennas. This paper proposes a new algorithm for determining the minimum number of transmitting antennas as well as their appropriate locations to provide the optimized wireless coverage in the indoor environment. The proposed algorithm uses a ray-tracing method to predict the signal distribution among the sampling points in the indoor area due to one or more transmitters and the genetic algorithm (GA) incorporated with the Breath First Search (BFS) terminology to determine the minimum number of transmitters and their corresponding locations to achieve the optimum wireless coverage. The proposed method outperforms the existing method in terms of both space and time complexities. The results obtained from this study also show that the computation time using the proposed algorithm is much less than that of the existing algorithm.

When employing computational methods for solving problems in electromagnetic scattering the resulting solutions are strongly determined by the geometry of the scatterer. Careful consideration must therefore be given to the computational geometry used in representing the scatterer. Here we show that the solution for a problem as simple as plane wave scattering off a PEC sphere is sensitive to the computational geometry used to represent the sphere. We show this by implementing 4 higher-order computational geometry schemes over 3 different tessellations resulting in 45 different representations of the sphere. Two methods for solving the scattering problem are implemented: the boundary-element method (BEM) based on the MFIE, and the physical optics (PO) method. Results are compared and insights are obtained into the performance of the various schemes to model surfaces accurately and efficiently. The comparison of the different schemes takes into consideration the required computational resources in implementing the schemes. Some unexpected results are discovered and explanations given.

A compact stack antenna consisting of square loop resonators, aperture couples, feed line and the perturbation for dual-band and circular polarization (CP) applications is proposed in this paper. This perturbation applies both dual-mode and orthogonal mode effects existing in the square loop resonator to present wide-band and CP characteristics simultaneously. The stack antenna presents the desired bands of 2.46 GHz with bandwidth (BW) = 160 MHz (6.58%) and 5.28 GHz with BW = 450 MHz (8.52%). The circular polarizations for dual-band are demonstrated with axial ratio (AR) spectrum and orthogonal modes. The proposed antenna is successfully simulated and measured with frequency responses, radiation patterns and current distributions.