摘要:

An efficient moment solution is given for the problem of electromagnetic scattering from an arbitrarily shaped, three-dimensional conducting body coated with a thin layer of lossy magnetic material. The surface equivalence principle is used to replace the conductor with a surface electric current, and the volume equivalence principle is used to replace the coating with a magnetic volume current. The behaviour of the field in the thin coating justifies approximating the volume current by a surface magnetic current residing next to the surface electric current. The boundary condition on the tangential component of the total magnetic field is used to express the magnetic surface current in terms of the electric surface current. The boundary condition on the tangential component of the electric field is then used to obtain an integral equation for the surface current. The method of moments is used to solve this equation approximately. The computed numerical results are in excellent agreement with the exact data for the case of a spherical scatterer.

DOI:10.1049/ip-h-2.1993.0036

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A new type of periodical chirowaveguide is proposed in the paper. A numerical approach for solving the problem, which is a combination of the mode expansion method and the least-squares boundary residual method, is developed. Canonical examples are presented to show the validity and usefulness of the method. The novel features of the new type of waveguide are also shown. To help design band-reject filters and leaky-wave antennas, some theoretical curves and useful conclusions are presented.

DOI:10.1049/ip-h-2.1993.0037

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The paper proposes an analysis method of nonlinear microwave circuits referred to as the frequency-domain-continuation intermodulation balance method (FDCIBM). This technique introduces a generalised complex matrix to represent (in the frequency domain) the steady-state variables of the nonlinear circuit with multifrequency large-signal excitation. In terms of this generalised complex matrix and a generalised complex-matrix convolution operator defined here, the frequencydomain- balance equation of the nonlinear circuit is a system of complex-variable nonlinear algebraic equations, that is solved using the continuation method. As an example, the intermodulation analysis of a GaAs MESFET amplifier is given.

DOI:10.1049/ip-h-2.1993.0038

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A reflector illuminated by a small phased array is an attractive antenna configuration for systems requiring reconfigurable contoured beams. The use of a shaped reflector can provide control of the feed power distribution and antenna geometry. A systematic reflector synthesis technique based on geometric optics is formulated, using complex coordinate notation and illustrated by application to a simple design requirement. Results demonstrate that geometric shaping can be successfully applied to systems with distributed sources, and that significant beam reconfiguration can be achieved by phase-only control of the feed array.

DOI:10.1049/ip-h-2.1993.0039

出版商:IEE    

年代:1993

数据来源: IET

摘要:

On the basis of a modified form of Meis integral equation, which includes dielectric effects using the quasistatic approximation theory proposed by Popovic, the input impedance and the radiation patterns of several quadrifilar helical antennas with axial or normal mode are investigated. The theoretical results agree quite well with experiment.

DOI:10.1049/ip-h-2.1993.0040

出版商:IEE    

年代:1993

数据来源: IET

摘要:

Various eight-port comparator circuits are synthesised by using transmission lines to connect certain ports. The most common type can be synthesised using λ/4 and 3 λ/4 100 Ω lines to connect the coupled ports.

DOI:10.1049/ip-h-2.1993.0041

出版商:IEE    

年代:1993

数据来源: IET

摘要:

By making use of rigorous solution to the problem of electromagnetic wave propagation as given by the compensation theorem, a qualitative justification for the existence of a number of models in which the prominent terrain features are replaced by simple geometrical shapes and for which canonical solutions exist is presented. The paper presents an alternative derivation of the recently introduced cascaded cylinder model, which considers propagation by diffraction over a cascaded arrangement of circular cylinders. The model predictions are compared with experimental data, and with Vogler's multiple halfplane function.

DOI:10.1049/ip-h-2.1993.0042

出版商:IEE    

年代:1993

数据来源: IET

摘要:

An algorithm is presented which makes use of a topographical and a morphological terrain database to simulate the terrain profile along the great cricle path between a transmitter and a receiver by a cascaded arrangement of circular cylinders. This idealised representation is used by the recently introduced cascaded cylinder diffraction model to predict the propagation loss along the geodesic path. Prior to making use of the terrain data, it is corrected for the earth's curvature and for the atmospheric radio refractive index. An approximate but efficient interpolation scheme, using bi-cubic B-splines is employed to compute terrain surface heights and their first and second-order derivatives. Using these tools, a technique for detecting the prominent terrain obstacles along the geodesic profile is presented. Finally, each identified terrain feature is simulated by an optimum cylinder fit. Verification of the model is presented by comparing its predictions with experimental results.

DOI:10.1049/ip-h-2.1993.0043

出版商:IEE    

年代:1993

数据来源: IET

摘要:

Multilayer surfaces, consisting of stacked inductive and capacitive strips or grids, have been used to design wideband filters in the 5–40 GHz range, with rapid transitions between reflection and transmission. For singly polarised applications, transmission bandwidths of 70–100% and edge transition ratios of 1.1–1.3 are realisable at 45° TM incidence using 4–8 layers of capacitive and inductive strips. Factors which constrain the passbands are highlighted. In dual polarised designs using doubly periodic grids, the widths are restricted to 35–40% by TE incidence grating responses at the upper passband edge. In TM they are even more restricted by a TE11mode resonance. Wider passbands require high inductances to reduce the low frequency edge, implying very fine conductors.

DOI:10.1049/ip-h-2.1993.0044

出版商:IEE    

年代:1993

数据来源: IET

摘要:

In an indoor environment, channel variations which occur most frequently are due to the movement of personnel near the transmitting or receiving antennas and/or local movements of the terminals around a given location. Such spatial and short time variations in the indoor radio channel are studied and determined by performing wideband propagation experiments in line of sight and nonline of sight environments at 910 MHz. The database is divided into two classes: spatial and short time variations. Spatial variations deal with the changes in the radio channel, observed over a short time and space, at different locations in an environment. The short time variations address changes induced over time, by human traffic close to the fixed transmitter/receiver or by manually shaking the antenna on its base. The statistics of RMS delay spread and the received power in the multipath profiles are computed and compared for these experimental variations.

DOI:10.1049/ip-h-2.1993.0045

出版商:IEE    

年代:1993

数据来源: IET