摘要:

The paper first examines the issue of the beampattern dependency on the choice of phase centre location, when a narrow band beamformer is subjected to directional and spatial derivative constraints. It is shown that the norm of the weight vectors for a zero-plus-first and zero-plus-first-plus-second derivative constrained beam-formers, under white noise conditions, is a quadratic and a quartic function of a parameter which specifies the phase centre location. The paper then presents a technique based on a power response approach, for deriving a new set of constraints for controlling the beampattern spatial derivates. The new set of constraints ensure that the array beam-pattern is independent of the choice of the phase centre co-ordinate origin. It is shown that for the first-order case, the constraint is linear, but for the second-order case, the constraint is quadratic. The paper then presents a technique for approximating the effect of the quadratic constraint by two linear constraints. It is shown that by using these two sets of linear constraints, the dependency of the beampattern on the choice of the phase centre co-ordinate origin cannot be totally eliminated, but the effect has been very much reduced. Finally, the paper presents a technique for optimising the beampattern with respect to the choice of the phase centre location, when the quadratic constraint is being approximated with linear con-straints. Numerical results showed that the optimised version has a better performance in terms of maintaining beamwidth broadening and capability of rejecting interferences.

DOI:10.1049/ip-h-2.1988.0086

出版商:IEE    

年代:1988

数据来源: IET

摘要:

The propagation of the guided modes in a cylindrical waveguide with imperfectly conducting walls and with the radius having a weak harmonic variation in the axial direction is investigated using the expansion of the fields in terms of the ideal normal modes. The theory is applied to the design of a mode convertor that selectively transforms the power in the TEOrmode to the TEOsmode. The spectral response of the mode convertor is analysed and the possible improvements of the basic design of the mode convertor are discussed.

DOI:10.1049/ip-h-2.1988.0087

出版商:IEE    

年代:1988

数据来源: IET

摘要:

A method for characterising two-port matching networks at the input and output ports of a GaAs MESFET at a single frequency is described. Two steps are involved. First, measurement of the input reflection coefficient of the overall circuit with the transistor drain voltage equal to zero and for different values of the gate voltage. Secondly,S-parameter measurements of the overall circuit for two sets of transistor drain and gate bias voltages. Equations are presented which make possible the calculation ofS-parameters of the passive matching networks from these measurements, provided that the transistorS-parameters are known for each of the bias points.

DOI:10.1049/ip-h-2.1988.0088

出版商:IEE    

年代:1988

数据来源: IET

摘要:

A large microwave open resonator is operated over a wide bandwidth requiring the application of a microcomputer. The design of a resonator system which achieves the wide band-width operation is described. Illustrative applications which demonstrate the scope of the technique are given for the measurement of extinction cross-sections of resonant scattering objects, where considerable detail in behaviour occurs.

DOI:10.1049/ip-h-2.1988.0089

出版商:IEE    

年代:1988

数据来源: IET