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Microwaves, Antennas and Propagation, IEE Proceedings H

Issue 1 • Date February 1986

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Displaying Results 1 - 12 of 12
  • Variable-length cylindrical post in a rectangular waveguide

    Page(s): 1 - 9
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (973 KB)  

    The problem of a thin variable-length cylindrical post in a rectangular waveguide is investigated by an approach which permits the current distribution on the post to be determined accurately. This in turn permits the reflection coefficient to be evaluated accurately. The case considered is that where the frequency and waveguide dimensions are such that only the TE10 mode can propagate. Off-centred posts, little considered in previous studies, are specifically considered, as are the resonance characteristics of the post. An experimental study is also reported which demonstrates the accuracy of the theoretical predictions. View full abstract»

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  • Reradiation from a grating coupler for a grounded dielectric slab waveguide

    Page(s): 10 - 17
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (936 KB)  

    The reradiation characteristics of a grating coupler for a grounded dielectric slab waveguide are investigated for the transverse magnetic mode, taking into account the finite conductivity of the ground plane. A pair of canonical equations for the coupler are derived. Analyses based on the solution of the canonical equations show the effects of the finite conductivity on the minimum reradiation coefficient, the optimum modulation index of the grating, the optimum incident angle, and the sensitivity of the reradiation to the changes in the incident angle about the optimum value. The coupler with the grating on the conducting surface is compared with the coupler having the grating on the film-cover interface for both the transverse-magnetic and transverseelectric modes. View full abstract»

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  • Quasistatic characteristics of a coplanar waveguide with thick metal coating

    Page(s): 18 - 20
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (282 KB)  

    The variational expression of the line capacitance is derived for the coplanar waveguide (CPW) with thick metal coating for the first time. It is presented in the general form to be applicable to the case with uniaxially anisotropic media. An efficient and accurate numerical method is employed to calculate the line parameters, and it reveals the effect of the metalisation thickness of a CPW. View full abstract»

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  • Transient-field representation in terms of steady-improper solutions

    Page(s): 21 - 25
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (529 KB)  

    The transient-excitation problem of an open dielectric slab by the integral transform method is solved. The solution is represented by an expansion in discrete spectrum functions (so-called steady-improper or nonmodal complex oscillations) increasing in space when moving away from a slab surface. The physical interpretation of the improper complex oscillations is proposed. The space-time existence region of the solution is defined. The oscillation expansions are shown to describe a transient process in the structure. View full abstract»

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  • Antenna near-field measurements using directive probes

    Page(s): 26 - 33
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (694 KB)  

    A near-field/far-field transformation procedure is described which is based on cylindrical mode expansion techniques and provides the capability for dealing with probes of any directivity. The principle of the method is demonstrated by computer simulation and the approach is validated in practice by predicting the 2-dimensional far-field patterns of slotted waveguide arrays. The near-field data is acquired with directive probes of up to 9 wavelengths in size at ranges of 0.1 D2/¿¿ The effects of probe position errors are also discussed. View full abstract»

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  • Dynamic allocation of degrees of freedom in an adaptive antenna

    Page(s): 34 - 42
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1131 KB)  

    An algorithm to acquire a desired signal of unknown direction and waveform and to steer nulls to jammers by a process of sequential selection and testing of auxiliary beams in a sidelobe canceller is proposed. The receiver must be able to recognise the desired signal when its input SNR exceeds some given threshold of around 10 dB. For weak desired signals, the achievable output SNRs approach those obtained by the beamformer in the absence of jamming, but a saturation effect occurs as input signal power increases; output SNRs saturate relatively early and become dispersed in value, although remaining quite useable. Performance against jamming in diffuse multipath conditions typical of the urban environment is evaluated with fairly satisfactory results. Comparison is made with the competitive techniques of eigenvector steering and the use of a linearly constrained adaptive beamformer with an augmented sample correlation matrix diagonal. View full abstract»

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  • Blockage due to subreflector supports in large radiotelescope antennas

    Page(s): 43 - 49
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (660 KB)  

    In large Cassegrain antennas careful design is required to minimise the detrimental effects on the antenna performance caused by blocking of the radiation by the subreflector support. A study of the aperture blocking by some possible support structures has been carried out for the United Kingdom/Netherlands millimetrewave telescope antenna which has very stringent mechanical specifications. By examining the dependence of the blockage on the structural geometry and analysing the mechanical performance, an optimum structure has been achieved. Although the structure is required to support a secondary, which oscillates at up to 15 Hz without causing any spurious movements which are significant in comparison to the 0.4 mm shortest operating wavelength, the loss of gain has been kept down to 7.4%. View full abstract»

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  • Bibliography on propagation factors affecting microwave links operating in the 10 GHz to 30 GHz frequency range

    Page(s): 50 - 56
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (853 KB)  

    The paper presents a bibliography of approximately 150 References concerned with aspects of radiowave propagation affecting terrestrial line-of-sight microwave links operating in the frequency range 10 GHz to 30 GHz. The References cover the period 1971 to 1985 and have been classified by means of a matrix scheme, to allow the rapid selection of relevant papers. View full abstract»

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  • Synthesis of dual-offset shaped reflectors for arbitrary aperture shapes using continuous domain deformation

    Page(s): 57 - 64
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (979 KB)  

    The systematic synthesis of an optically shaped dual-offset reflector antenna with uniformly phased aperture and with source and aperture power distributions independently prescribed is reviewed. A recent paper showed that a method for dealing with circular apertures could be extended to noncircular apertures by the use of conformal mapping. In the paper we describe an alternative method in which the aperture boundary is continuously deformed to the required shape. Examples show that systems with elliptical apertures of high axial ratios (e.g. 4:1) can be successfully designed. The problem of interpolating points on the reflector surfaces has been addressed using bicubic splines. View full abstract»

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  • Recent developments in the analysis of reflector antennas. A review

    Page(s): 65 - 76
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1711 KB)  

    The basic methods used in the analysis of reflector antennas are discussed, with emphasis on recent developments. The current integration method and its various modifications is reviewed in detail. Also, the potential of the new sampling technique is illustrated. View full abstract»

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  • H11circular waveguide mode and back scattering cross-section along the axis of a thin walled tubular cylinder of finite length

    Page(s): 77 - 78
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    The back scattering cross-section along the axis of a thin walled, circular, tubular cylinder is measured. The cylinder has a length to inner diameter ratio of six to one. The ratio of the length of the cylinder to the wavelength of the incident field varies approximately from 1.8 to 6.3. Near and above the H11 cutoff frequency of the circular waveguide mode of the tubular cylinder, data are distinctly different from previously measured results using cylinders having a length to outer diameter ratio of six to one. The new data agree with theoretical predictions over the entire frequency range. It is concluded that the wall thickness of the cylinder under consideration can be neglected and that the internal (waveguide) modes of a scatterer contribute significantly to its scattering cross-section. View full abstract»

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