摘要:

A new algorithm for separating and tracking multiple directional sources in a linear power-inversion array is proposed and investigated. In this algorithm, the sources are separated by using an adaptive beamformer whose responses consist of perfect steerable nulls. By using the LMS algorithm for adaptive processing of the beamformer outputs to minimise the array output power and examining the adaptive weights employed, these nulls can be adjusted to track the sources individually so that the beamformer outputs will be due to different sources in the steady state. With this algorithm, the problem of incidental cancellation is eliminated and the enhancement of multiple moving sources becomes a natural process. Also, since the sources are individually tracked and the beamformer is only updated occasionally when significant changes in the environment are detected, the algorithm possesses fast tracking behaviour and its implementation complexity is comparable with that of beamformer-based adaptive arrays using the LMS algorithm.

DOI:10.1049/ip-h-2.1992.0086

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Biconical microstrip antennas having a conical patch over a conical substrate are investigated. Analytical expressions for the field distribution inside the conical cavity are developed in a spherical coordinate system and used to determine the eigenvalues of the resonant modes. It is found that, in addition to the axially symmetric modes,TEmodes can also resonate which are asymmetric and dependent on the azimuthal angle. For coaxial probe excitation of the cavity its analytic expressions for the field components are determined and used to investigate the antenna input parameters and radiation patterns. The special case of a conical patch microstrip antenna with a planar substrate is also studied. It is shown that, in comparison with circular disc microstrip antennas, a conical patch yields a wider impedance bandwidth and higher gain.

DOI:10.1049/ip-h-2.1992.0087

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper describes the application of the finite-difference method in the time domain for obtaining the cutoff frequencies of TE and TM modes in waveguides of arbitrary cross-section. Maxwell's equations are discretised in a two-dimensional space. The application of the discrete Fourier transform also provides the spatial distribution of the modes in the cross-section of the waveguide. The method is validated against rectangular and a circular waveguides, each with a known cutoff spectrum. Finally, the method is applied to determine cutoff wavelengths and modal field distributions in a square coaxial waveguide.

DOI:10.1049/ip-h-2.1992.0088

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The monostatic radar cross-section spectra of a rotating-fan array, with tilted blades, are investigated. The high-frequency theoretical treatment of a slowly rotating and electrically large scattered is based on the quasi-stationary method with the physical optics/physical theory of diffraction (PO/PTD) technique. Only theθθpolarisation case is considered here, although theψψpolarisation case can be treated in the same way. The solution is applicable to any observation angles, and, except for the condition of the same rotational velocity, each fan need not have the same number of blades and dimensions or the same spacing. An example, a linear array with two synchronously rotating fans, each with three identical tilted blades, is presented. The agreement between the theoretical and experimental results is acceptable.

DOI:10.1049/ip-h-2.1992.0089

出版商:IEE    

年代:1992

数据来源: IET

摘要:

This paper presents a modified theory for the measurement of the surface resistivity of thin films, deposited on either thin or thick dielectric substrates; in addition the formulations for the measurements of thin dielectric substrates is derived. The reflection coefficient of a probe in contact with the surface is used to calculate the surface resistivity of the film or else the dielectric constant of the dielectric substrate. The expression giving the reflection coefficient in terms of the surface resistivity of a film on a thin substrate is developed by matching the electromagnetic fields at the aperture of the coaxial line. Experimental results of conductive thin films on thin substrates (indium tin-oxide thin film deposited on polyethylene substrates) and dielectric substrates without films are reported from DC to 4 GHz. The experimental results calculated with the derived expressions and the measured reflection coefficients are in agreement with surface resistivity values quoted by the manufacturer of the various test samples used.

DOI:10.1049/ip-h-2.1992.0090

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A further study is made of the reconstruction of permittivity profile by using the spectral inverse scattering scheme with the moment-method procedures. Based on earlier works, the reconstructed profiles have been affected by large errors even with a negligible random noise of the measured field. One of the intuitive approaches to reduce these errors has been implemented successfully by employing a polynomial basis function to the induced field on each enlarged cell in conjunction with a suitable weighting function. Another method is presented which adopts a low-pass filter to the spatial- Fourier transform of the equivalent source distribution induced in a dielectric object. The accuracy and validity of the spectral filtering are assured by a number of numerical simulations for a simple test geometry.

DOI:10.1049/ip-h-2.1992.0091

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Propagation properties of elementary beam modes are derived and used to examine the structure of the focal region of a focused aperture. Some general features of the field structure are obtained by approximating the field with a suitable fundamental Gaussian beam. The parameters governing the beam are found to be closely related to the Fresnel number of the system. It is then shown how the equations describing the fundamental mode are also applicable to a complete set of modes. The relationship between an analysis based on beam modes and a Fourier treatment is shown. Numerical results are presented which show the accuracy of field reconstruction for finite numbers of modes.

DOI:10.1049/ip-h-2.1992.0092

出版商:IEE    

年代:1992

数据来源: IET

摘要:

In the paper a self-calibration technique is proposed to handle the bearing estimation problem involving unknown perturbed sensor location. This calibration technique is applied on the MUSIC estimator in finding the direction of arrival (DOA) of plane waves in white noise. The basic idea of the technique is to maximise the total output power from the MUSIC estimator in the directional or frequency regions of interest while imposing constraints on the length of projection of the signal position vector (SPV) on the noise subspace. This technique exhibits relatively stable performance over other existing techniques in the sense that it converges to the required solution consistently. However, this is achieved at the expense of heavy computational load. This is illustrated with numerical results obtained from the computer studies conducted.

DOI:10.1049/ip-h-2.1992.0093

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Following an outline of established optical techniques for the generation and distribution of reference and control signals for phased array antennas, two novel approaches are put forward: (i) a ‘nondispersive prism’, controlling agile single beams or monopulse patterns, and (ii) a ‘lens fed model array’, which can control multiple, independent antenna beams. The prospects of fibre-optic transmission for other functions in the array are also considered.

DOI:10.1049/ip-h-2.1992.0094

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A coupled integral equation formulation of analysing a generalised multilayer frequency selective surface is described. An iterative spectral technique has been adopted for the calculation of the induced currents, aperture fields and the plane wave transmission coefficient. In this scheme, the error is minimised using variational expressions for the element current in each of the unit cell areas of the multilayer structure. The effect of the distance separating the arrays and state of incidence to the rate of convergence and the transmission coefficient is discussed. The analysis described in the paper is not restricted to identical element geometries.

DOI:10.1049/ip-h-2.1992.0095

出版商:IEE    

年代:1992

数据来源: IET