摘要:

The boundary value problem of a circular waveguide that is completely filled with a homogeneous, lossless and isotropic chiral medium is solved and the axial phase constant is determined from a numerical solution of the characteristic equation. The electric and magnetic field components in the transverse plane are determined and subsequently used in the radiation integrals to obtain the far-field components. The variation of such radiation characteristics as the halfpower beamwidths in the principal planes and directivity are studied as functions of the electrical radius and normalised chirality admittance parameter. Some comparisons are made between the different propagating hybrid modes in the chirowaveguides.

DOI:10.1049/ip-h-2.1992.0001

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A method based on vector spherical mode expansion (VSME) for solving radiation and scattering problems is developed. Combined with numerical methods such as MoM or FDTD, three dimensional electric and magnetic current sources are theoretically analysed according to image theory and equivalence principles. The electric and magnetic VSME coefficients introduced are written in terms of the electric and magnetic current densities with space sinusoidal and Legendre functions. By using these coefficients and the correct choice of the co-ordinates, the electromagnetic fields can be constructed with a minimum number of modes.

DOI:10.1049/ip-h-2.1992.0002

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A general method of antenna pattern synthesis using weighted least squares is presented. The special case of linear equal spaced arrays is analysed, and three design examples are given. This design technique is compared with Woodward synthesis and with the method of Orchard, Elliott and Stern. An example using unequal spacing is also presented. The method can also be used on nonlinear arrays, for arrays with different element patterns on each element, and for near-field pattern synthesis.

DOI:10.1049/ip-h-2.1992.0003

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper presents a method for the analysis of generalised wire antennas and scatterers, consisting of right truncated cones of circular cross-section interconnected in an arbitrary manner. The integral equation for current distribution is derived starting from the local and extended boundary conditions for the electric field, enabling the efficient analysis of both hollow and solid cones. An entire domain current expansion for a series connection of n ≥ 1 truncated cones is proposed, that enables curved wires to be approximated by any number of straight segments without increasing the number of unknown coefficients. A method for obtaining the expansions starting from arbitrary function sets which satisfy the continuity equation at the segment interconnections and ends is also presented. With such basis functions, the solution of the integral equations by means of the Galerkin method is shown to require(a) A remarkably small number of unknowns per wavelength (e.g. two with the combined polynomial/trigonometric current expansion)(b) A remarkably short time of evaluation of the impedance matrix.The results obtained by the method are in good agreement with available experimental and numerical results.

DOI:10.1049/ip-h-2.1992.0004

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper presents a new approach to the design of a uniform linear array with partial adaptivity. The technique uses the symmetric and skew-symmetric eigenvectors of a certain symmetric Toeplitz matrix to form the fixed weighting vector for the main beam and the transformation matrix for the cancellation beam. This approach allows the adaptive dimension of the processor to be reduced to about half of that of the full processor without prior knowledge of the interference field. Eigendecomposition is performed on matrices of dimensions that are half that of the number of elements. Numerical results show that the new approach is effective in designing partially adaptive uniform linear arrays.

DOI:10.1049/ip-h-2.1992.0005

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The work investigates the use of phaselocked loops (PLLs) as phase shifters in the control of a phased antenna array. The phase error of a PLL can be altered by adding a DC offset voltage to the output of the phase detector. If a digital phase detector, with its inherently linear response, is used, then the phase error, and hence the relative phase shift, will vary linearly with applied control voltage. Such phase shifters can act on their own at VHF or they can provide an IF reference signal to a mixer to create a linear phase shifter at microwave frequencies. Four prototype phase shifters, fed in series, have been built, driving a linear array of four monopoles, in transmit mode at 1.5 GHz. By use of a single common control voltage, a single main beam can be swept through 180° with an accuracy of better than±2° within the range±70°.

DOI:10.1049/ip-h-2.1992.0006

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A method for the transient analysis of frequency-dependent interconnections and planar circuits terminated with nonlinear loads is presented. The frequency-dependent portion of the system is first analysed to obtain theS-parameters and hence the impulse responses. Two different methods are used to get the scattering parameters: the three-dimensional finite-difference timedomain method and an analytical procedure. The nonlinear convolution equations governing the overall system are then derived and solved numerically. The transient responses of a pair of coupled dispersive microstrip lines, a corner discontinuity, and a microstrip switching circuit are presented.

DOI:10.1049/ip-h-2.1992.0007

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The possibility of reconstructing the distribution of the dielectric characteristics of unknown inhomogeneous dielectric objects contained inside a fixed investigation volumeV, where the scatterers can be placed at arbitrary positions is considered. It is assumed that the localisation of the scatterers and the determination of their surface shapes can be accomplished through the reconstruction of the equivalent current density, following a previously proposed approach. The method is based on an inverse-scattering formulation, and makes use of the moment method, together with a pseudoinversion algorithm, to face the problems associated with ill-conditioning. The approach does not require any plane-wave illumination or first-order approximations. It can potentially be used even in the case of strong scatterers. The advantages of using suitable thresholds for the reconstruction of the equivalent current density is considered. The capabilities and limitations of the approach have been assessed by means of numerical computer simulations, for which even data strongly affected by Gaussian noise have been used.

DOI:10.1049/ip-h-2.1992.0008

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Measurements from a 131 km precipitation scatter experiment at 11.2 GHz are described. The experiment had two scatter geometries (forward and backward) and the observations made over three years are reported. Forward and backward scatter differ in many respects and these are compared and contrasted. Comparisons are also made with the CCIR report 569-3 prediction method to assess its validity. On a few occasions, a 3 GHz dual-polarisation radar was used to scan along the plane of bistatic scatter. The radar data were used to simulate the bistatic experiment. Estimated power levels compared favourably with the direct measurements.

DOI:10.1049/ip-h-2.1992.0009

出版商:IEE    

年代:1992

数据来源: IET

摘要:

In generalising Green's function approach based on the Hertz dipole, a precise determination of the electromagnetic field generated by a system made up of any given number of microstrip patches is provided. The interaction of the number of elements (circuit theory), and the influence of various parameters (work frequency, dielectric constant and thickness, length and width of patches and antenna cells, the number and spacing of the plates etc.) are taken into account. The results obtained in the case of one or two microstrip patch antennas are in excellent agreement with those already published. Examples of antenna electromagnetic field radiation patterns in rectangular multimicrostrip elements up to 512 (32×16) and even 1024 (32×32) in a given circuit are presented.

DOI:10.1049/ip-h-2.1992.0010

出版商:IEE    

年代:1992

数据来源: IET