摘要:

The characteristics of the output and input couplers for a dielectric-slab waveguide grounded by a corrugated-conducting surface are investigated for the transverse electric mode, taking into account the small gain or loss in the dielectric. A pair of canonical equations valid for a distributed coupler with a guided wave, an incident wave and a radiated wave are derived, and all the coupling coefficients are expressed in terms of the physical parameters of the coupler. The coupling coefficients are shown to satisfy four general properties which lead to the principle of power conservation and reciprocity. The analyses of the couplers, based on the solution of the canonical equations subject to the appropriate terminal conditions, lead to the determination of the various design parameters such as the output coupling efficiency, and the optimum incident angle and grating length for the maximum input coupling efficiency. The effects of the gain or loss in the dielectric on the abovementioned parameters and on the amplitude profile of the radiated wave are investigated. The coupler with the grating on the conducting surface is compared with the coupler having the grating on the film-cover interface.

DOI:10.1049/ip-h-2.1985.0029

出版商:IEE    

年代:1985

数据来源: IET

摘要:

In the paper, a simple recurrence formula to obtain the Green's function for multilayered anisotropic structures, with rectangular boundary conditions involving electric and magnetic walls and open boundaries, allows us to present an unified variational approach in the spectral domain to find both upper and lower bounds on the mode capacitances of a large class of planar transmission structures. Very accurate results are obtained by using appropriate trial functions to approximate the surface charge density on the strips and the interface potential distribution for several significant MIC configurations.

DOI:10.1049/ip-h-2.1985.0030

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The circular-electric-mode hybrid coupler permits electromagnetic energy to be transferred from a circular waveguide, which supports a TE01mode, to a coaxial waveguide also supporting a TE01mode, or vice versa. The extent to which this transference occurs is controlled by a cylindrical-waveguide ‘drift’ region, which supports both a TE01and a TE02mode. The coupling mechanism is closely analogous to that which occurs in the more familiar rectangular-waveguide hybrid, or Riblet, coupler. The paper provides a theoretical description of such a coupler, the results of which are shown to be in agreement with measurement. The theory represents a new application of the moment method.

DOI:10.1049/ip-h-2.1985.0031

出版商:IEE    

年代:1985

数据来源: IET

摘要:

A large number of field problems cannot be solved exactly. Instead, an approximate solution is obtained by computation. The object of the paper is to draw attention to a method which gives an upper and a lower bound for the exact solution. The method, based on the fact that the basic equations of electromagnetism can be derived from a variational principle, is applicable to a variety of problems having a rather complicated geometry. The effectiveness of the method is illustrated by two characteristic examples.

DOI:10.1049/ip-h-2.1985.0032

出版商:IEE    

年代:1985

数据来源: IET

摘要:

In the paper we present the results of a modal analysis of the current distribution around the circumference of thin concentric rings arranged on both square and equilateral triangular lattices. The particular case of plane-wave illumination at 45° incidence is considered owing to its relevance to oblique-incidence diplexer systems. Measured and predicted transmission curves, together with computer curves illustrating the frequency dependence of various current-mode amplitudes, are plotted for selected concentric-ring structures, each with the same mean radius for the outer ring, but with different inner-ring radii. The results relate individual current modes to features in the observed transmission curves. They confirm that the copolar transmission and lower reflection bands can be modelled with only one current mode in each ring. Crosspolar effects are discussed for incidence on the square lattice in the planes ϕ = 0, 45° and 90°, where they are shown to be small for pure TE and TM.

DOI:10.1049/ip-h-2.1985.0033

出版商:IEE    

年代:1985

数据来源: IET

摘要:

With economical factors favouring the use of guyed structures for terrestrial microwave radio system towers of heights above 40 to 50 metres, situations are arising where information on antenna-pattern degradation due to guy wire scattering is required for route-design purposes. A qualitative understanding can be gained of the worst-case situations, where the wire runs near to, and directly in front of, the antenna, by regarding the illuminated section of guy as a long linearly phased cylindrical source. This produces a well-defined cone of maximum scattering, having the guy as its axis. Experimental measurements, and an approximate analytical study based on the above concept, show that within the cone region, antenna sidelobes may be degraded by as much as 20 dB. In the azimuthal plane the cone-region cuts can be quite narrow, so that interference with other cochannel terrestrial systems or repeaters will not always be significantly increased. However, co-ordination with satellite systems may often prove difficult, as a large fraction of the cone energy is radiated out into space, either directly, or after reflection from the ground.

DOI:10.1049/ip-h-2.1985.0034

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The action of electromagnetic applicators in hyperthermic cancer therapy is investigated, with specific reference to invasive wire probes and noninvasive slots, along with their ability to heat biological tissue at depth without creating unwanted hot spots. An analysis based on spherical eigenfunctions enables useful probe configurations to be analysed and the field penetration depth calculated as a function of frequency and probe size. Alternative methods for assessing power flow in the tissue are considered. The use of a water bolus for impedance matching and isolating hot spots is examined, along with a comparison of the performance for two types of probe shape. Computed results show that the ability of a given probe to dispense heat at depth is, on the whole, insensitive to the applied frequency, although performance is worsened for very short probes. Approximate calculations for a noninvasive planar applicator have enabled heating patterns in the tissue to be examined and confirm that good beam characteristics are formed only a small distance into the tissue, but near-field hot spots are again a consideration. It is concluded for both of the applicators analysed here that lowering the frequency will not result in a significantly increased penetration depth due to near-field effects, and the clinical inference is noted.

DOI:10.1049/ip-h-2.1985.0035

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The paper presents a spectral iteration technique for the analysis of linear arrays of unequally spaced dipoles of unequal lengths. As an example, the Yagi-Uda array is considered for illustration. Analysis is carried out in both the spatial as well as the spectral domains, the two being linked by the Fourier transform. The fast Fourier transform algorithm is employed to obtain an iterative solution to the electric-field integral equation, and the need for matrix inversion is circumvented. This technique also provides a convenient means for testing the satisfaction of the boundary conditions on the array elements. Numerical comparison of the input impedance and radiation pattern have been made with results deduced elsewhere by other methods. The computational efficiency of this technique has been found to be significant for large arrays.

DOI:10.1049/ip-h-2.1985.0036

出版商:IEE    

年代:1985

数据来源: IET

摘要:

The abrupt junction between a coaxial waveguide with hollow inner and a cylindrical waveguide has previously been analysed using a moment method for the case where the hollow inner has an infinitesimally thin wall. The paper describes modifications which permit a wall of finite thickness to be accommodated.

DOI:10.1049/ip-h-2.1985.0037

出版商:IEE    

年代:1985

数据来源: IET

摘要:

For small primary feeds the radiation field is determined numerically, using an integral-equation formulation for the surface currents and its solution by a moment method. The computed fields are used to determine the feed-phase centres, as defined to minimise the phase variation of the field over a selected angular region, or to maximise the reflector gain factor. Both circular and coaxial waveguides, with and without a corrugated flange, are considered. For the corrugation geometry, the commonly used rectangular shape and a trapezoidally-profiled one are studied. It is shown that the location and the uniqueness of the feed-phase centre depend on waveguide dimensions, the corrugation number, their location and shape. For an optimum phase-centre location, the resulting phase errors, over a selected angular region, are also determined.

DOI:10.1049/ip-h-2.1985.0038

出版商:IEE    

年代:1985

数据来源: IET