Radio-Wave-Propagation Modeling in the Presence of Multiple Knife Edges by the Bidirectional Parabolic-Equation Method

Fast full-wave computation of fields is the main reason for a radio system planner to apply the parabolic-equation method (PEM) for radio-coverage prediction. In this paper, the capability of PEM for the determination of backward electromagnetic-field scattering by single and multiple knife edges is investigated. For the wave equation, a suitable solution is considered. Contrary to the available formulations for the PEM, the proposed method includes a backward-propagating term. For both the forward and backward terms, the split-step algorithm is employed. Similar to the terrain-masking method, the effect of edges is exerted by the Fresnel-Kirchhof approximation into the forward-propagating wave. For the backward field, a similar algorithm is derived. Then, an iterative marching algorithm is developed for modeling radio wave propagation over multiple knife edges. Numerical results are compared with those of Uniform Theory of Diffraction (UTD) and finite-difference time-domain methods for the single-knife-edge problem. In addition, the effect of the backward-propagating field on radio wave propagation is investigated. The effect of edge locations and heights on the backward scattered field and number of computational iterations is studied. It is seen that, for the single knife edge, the backward scattered field depends on the height and location of the edge. The intensity of the backscattered field is a monotonic increasing function of the edge height. In addition, by increasing the edge height, the beam width of the backward scattered field increases. In ranges far from the knife edge in front of it, the field spreads, and its amplitude decreases. For multiple knife edges, it is seen that, in addition to the single backward scattered field, radio-wave-propagation modeling requires multiple forward-backward terms between successive edges. The geometry of the problem determines the required number of terms for sufficient accuracy     

Design of impedance transformers by the method of least squares

The method of least squares is applied to the theory of small reflections of transmission lines to develop numerical algorithms for the design of stepline and tapered line impedance transformers to match two impedances over a frequency band. The transformer characteristic impedance function is expanded by polynomials, pulse functions, approximate operators, and piecewise linear functions to construct an error function for the input reflection coefficient which, after minimization, gives the line impedance and length. The computer programs could be used to design a transformer under the specified conditions and then to optimize the design under the constraints of a problem     

Wideband Frequency-Reconfigurable Antenna for Airborne Applications

Wireless Personal Communications - One of the important objectives of underwater acoustic sensor network is to extend the lifespan of a network which depends on the topology control mechanisms....     

Miniaturization and dual‐banding of an elevated slotted patch antenna using the novel dual‐reverse‐arrow fractal

A novel fractal geometry called dual‐reverse‐arrow fractal (DRAF) is introduced and compared with various versions of Koch fractals for application to triangular patch antennas. It is shown that DRAF results in the reduction of antenna size and tends to maintain its bandwidth. The presented DRAF is applied for the reduction of size of an elevated triangular patch antenna for the dual band operation in WLAN. This DRAF antenna has achieved 40% size reduction compared to a simple triangular patch antenna. For the provision of required bandwidth in the second frequency band (4.9‐5.9 GHz), a stepped U‐shaped slot is cut in the triangular patch. This antenna is more compact than similar antennas reported in the literature but maintains its fractional bandwidth (%25). The optimized design of the proposed DRAF antenna with air gap and slot is fabricated and tested, which verifies its expected specifications.     

Novel application of a new metamaterial complementary electric LC resonator for the design of miniaturized sharp band‐pass filters

In this article, we introduce a new metamaterial complementary electric LC resonator (CELC) and investigate its operational mechanism, characteristics, and potentialities for application in microwave components and devices, such as filters. We consider the excitation of CELC by the electric and magnetic fields of microstrip lines and its resonance characteristics by the diagrams of effective permittivity (ε_eff) and permeability (μ_eff). A circuit model is obtained by the consideration of its coupling with the loaded microstrip line. We then realize a novel left‐handed (LH) cell by the combination of the CELC resonator and a short circuited stub. It is designed by the least mean square method. We finally use the cascade connection of such LH cells for the design of a miniaturized narrow‐band band‐pass filter with high out of band rejection. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Zeros of f(z) = (az-b)npm (cz-d)n

The zeros off(z) = (az - b)^{n} pm (cz - d)^{n}are found to lie on a circle of radius|(ad - cb)/(|a|^{2} - |c|^{2})|with its center atz = (a^{ast}b - c^{ast}d)/(|a|^{2} - |c|^{2}), wherea, b, c, anddare complex numbers andnis assumed real. When|a| = |c|the locus of the zeros is a straight line perpendicular to the line joining the pointsb/aandb/cand intersecting it atz = 0.5(b/a + d/c). The zeros are found analytically and constructed geometrically.     

Application of grooved substrates for design of unequal wilkinson power dividers

Application of the grooved substrate is presented for the design of an unequal Wilkinson power divider. The grooves are applied along one of its strips which requires high characteristic impedance for the purpose of overcoming its conventional narrow width. The grooves are oriented parallel to the strip and just next to it. The groove depths are selected such that, for a suitable width of the strip, the desired characteristic impedance is achieved. A 4:1 unequal Wilkinson power divider is designed, fabricated and tested, which verify the design specification of power division.     

Application of the Rotating Angle Parabolic Equation Method for the Solution of Scattering Problems

In this paper the rotating angle parabolic equation method (PEM) is presented for the solution of scattering problems. Separate spectral domains for the incident and scattered fields are obtained and their sum is substituted into the wave equation. Considering the satisfaction of wave equation by the incident and scattered fields, the solution of wave equation changes into the solution of two separate parabolic equations for the incident and scattered fields. The paper continues with the development of an algorithm for the determination of back scattered fields from knife edges and scattered fields from the slope and slope discontinuities. It will be seen that the results of the proposed algorithm agree with those of other methods for the solution of aforementioned problems.

Novel circuit topologies for active distributed frequency multiplexers and demultiplexers

In this work, a novel circuit topology is introduced for the implementation of multiplexers and demultiplexers, called “active distributed (de)multiplexers.” The desired characteristics of active distributed (de)multiplexers as being wideband, planar and active are realized by the proposed microwave circuit. A numerical methodology is presented for its design. An active distributed detriplexer is designed, simulated, fabricated, and measured by the proposed numerical procedure. Computer simulation and measurement results show the effectiveness and suitability of the proposed topology as a detriplexer. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2010.     

Mathematical formulation for zero reflection from multilayer metamaterial structures and their notable applications

The behaviour of bilayer structures composed of common materials and metamaterials (MTMs) under oblique incidence of plane waves is investigated by exact analytical methods. The TE, TM and elliptical polarisations are analysed. There are several combinations of double positive (DPS), double negative (DNG), epsilon negative (ENG) and mu negative (MNG) media for the bilayer structures, but only DPS?DPS, DPS?DNG and ENG?MNG bilayers with TE, TM and circular polarisations are analysed in detail. For homogeneous and isotropic MTM media, exact mathematical relations are derived for the design of reflectionless bilayer structures as a function of their geometry (thickness) and electric and magnetic parameters. Frequency dispersion is included in the formulations. It is shown that bilayers composed of common materials are not effective for the construction of zero reflection bilayer surfaces, whereas the application of MTMs is required to realise reflectionless phenomena. For the design of zero reflection bilayer structures, their thicknesses and values of ε and μ are determined. Finally, the performance of forward and backward notch filters observed by MTM bilayer structures are studied in detail and their designs and applications are investigated. The bandwidth of lossy MTMs increases considerably.