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Microwaves, Antennas and Propagation, IEE Proceedings H

Issue 2 • Date Apr 1991

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Displaying Results 1 - 12 of 12
  • Analysis of a probe-fed microstrip disk antenna

    Page(s): 185 - 191
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    The input impedance of a probe-fed, annular-ring-loaded, circular-disk microstrip antenna is analysed using three methods of increasing complexity and sophistication. The first method uses a new variational formula which is more suitable for antennas driven by a voltage gap. The second method uses a mode-matching method where the field inside the coaxial line is expanded in terms of waveguide modes. The third method uses the mode-matching method with a diaphragm at the coaxial aperture. The mode-matching methods are identical to the variational formula under the single-mode approximation. However, when a diaphragm is present, the single-mode approximation is insufficient, implying that the variational formula is inaccurate when a diaphragm exists. The theory is used to study the effect of the gap capacitance at the coaxial aperture on the input impedance of the microstrip antenna. It is found that this gap capacitance is important when the dielectric substrate is thick. View full abstract»

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  • Phase measurements of millimetre wave antennas at 105-190 GHz with a novel differential phase method

    Page(s): 114 - 120
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    The application of conventional antenna phase measurement methods becomes increasingly difficult above 100 GHz. The main problems are the complexity of measurement set-ups and errors caused by the flexible cables or rotary joints needed in the system. To overcome these problems, a novel differential phase measurement method has been developed and used to measure phase centre positions and phase patterns of two corrugated horns at 105-115 GHz and 176-190 GHz. In spite of the simplicity, the differential phase method gives accurate results. Good agreement between the measured values and theoretical values, calculated with the modal matching technique, were obtained. View full abstract»

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  • Iterative calculation of ship-borne HF antenna performance

    Page(s): 151 - 158
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    The computer program NEC-2, which calculates the currents on wire-grid models by the method of moments, is modified to analyse structures which consist of a collection of disconnected substructures. The matrix equation for the currents is solved by means of iteration between the substructures using the Siedel method. The convergence is accelerated using an extrapolation technique. The program is used to calculate the impedance and radiation patterns of ship-borne antennas in the presence of a funnel, masts and other antennas, all on a perfectly conducting ground plane. Comparisons of the results obtained using the two codes show good agreement. In addition, a programme of electromagnetic measurements was carried out to validate the use of wire-grid computer codes in the simulation of antenna characteristics and scattering phenomena in the HF band. The results show favourable agreement. View full abstract»

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  • Flat-plate steerable antennas for satellite communications and broadcast reception

    Page(s): 159 - 168
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (892 KB)  

    Flat-plate steerable antennas have a number of potential uses; for example, X-band satellite communications to mobile terminals and K-band DBS television reception. A flat-plate array antenna design which could be used for these applications is described. The antenna consists of a printed element face, a polarisation converter, line distribution networks and a Rotman lens. The main beam of the antenna may be slewed in one plane. The second dimension of steering is achieved by rotating the array within its own plane. Two approaches to producing the slewed main beam are given; one uses a multiport lens and the other uses a lens with a single moveable beam port. View full abstract»

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  • Scattering of a transient electromagnetic wave by a dielectric sphere

    Page(s): 192 - 198
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    The transient scattered field from a lossless dielectric sphere is evaluated by the inverse Laplace transform of the frequency-domain solution. Two methods of obtaining the inverse transform are employed. In the first approach, direct numerical evaluation of the Bromwich integral is carried out. In the second approach, the asymptotically compensated singularity expansion method is employed. The numerical results obtained from both methods are in complete agreement. Reference to the physical origins of the various structures appearing in the time-domain response is made by considering the dependence of their magnitude and time of arrival on the permittivity. Verification of the various predictions previously given by frequency-domain analysis can be carried out in a different perspective with new physical insight. View full abstract»

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  • Low cost phased array antenna for land-mobile satcom applications

    Page(s): 131 - 136
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    Phased array antennas for use with land-mobile satcom services have been under development for several years. Owing to the relatively modest specification required of these antennas, it should be possible to produce them at an affordable price. A number of techniques aimed at minimising the cost of such arrays without significantly sacrificing performance are considered. A prototype 18-element array embodying these techniques is described, with theoretical predictions and experimental results to substantiate array performance. View full abstract»

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  • Multiple beam microstrip patch array with integrated beamformer

    Page(s): 176 - 184
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (636 KB)  

    A novel antenna concept that incorporates a beamformer and radiating array into a single, planar device is described. This integration of the beamformer and array components decreases the constructional complexity considerably. The beamforming action resembles that of the Blass matrix (1960), although the use of resonant arrays removes the need for directional couplers. The devices primary mode of operation is detailed and a number of performance capabilities are outlined. Results are given for a five beam experimental array realised in microstrip and operating at approximately 8 GHz. Peak gains of between 13 and 19 dB are achieved with a bandwidth of about 5%. Implementation of the concept in other transmission media seems possible and realisation in waveguide and suspended stripline are discussed as a means of increasing efficiency. View full abstract»

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  • Analysis of waveguide-fed thick radiating rectangular windows in a ground plane

    Page(s): 142 - 146
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    A moment method analysis of a radiating window in an infinite conducting plane excited by a rectangular waveguide is presented. The boundary conditions at the two interfaces are derived taking the effect of window thickness into account. The application of the moment method, using entire domain basis functions, transforms the integral equations representing the boundary conditions into matrix equations. The reflection coefficient seen by the feed waveguide is evaluated from amplitude coefficients determined from matrix inversion. Excellent agreement between theoretical and experimental values of complex reflection coefficient is obtained. View full abstract»

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  • Measurements of the direction of arrival of HF sky wave signals and single site location using a seven element wide aperture (294 m) interferometer array

    Page(s): 121 - 130
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    From measurements of the amplitude and phase of ionospherically propagated HF radio signals received at several spaced antennas, the direction of arrival (DOA) of the signal in both azimuth and elevation can be determined. Furthermore, by combining the DOA with reflection height measurements, the transmitter location can be estimated from a single receiving site. The direction of arrival has been measured for signals received from several European broadcast stations at distances of up to about 1400 km and the position fixes obtained are discussed. The performance of the system was severely affected by multimoded propagation and techniques for recognising periods of single moded propagation, when accurate measurements are to be expected, are described. Good position fixes were obtained when measurements were restricted to these periods provided that accurate height information was available. A period of data is also discussed for which the signal was found to be propagated predominantly by a 2-hop F-region reflection. View full abstract»

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  • Scattering by a perfectly conducting finite size vertical rectangular plate

    Page(s): 137 - 141
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    Expressions for the scattered field of a radio wave diffracted by a vertical, rectangular, perfectly conducting plate on a perfectly conducting flat ground, when it is illuminated by a vertical current element at ground level, are derived in closed form for all azimuthal positions of the receiving point. Experimental confirmation of the results for different sizes of the plate and different transverse positions of the plate is provided. The solution obtained is complementary to that using the geometrical theory of diffraction. View full abstract»

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  • Scalar wave scattering by a rough sphere: Bourret's approximation for the coherent field of a point source

    Page(s): 147 - 150
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    The average field of a point scalar source over a statistically rough sphere with a small surface impedance is analysed. The isotropic and statistically uniform inhomogeneities are assumed to be small and smooth. These assumptions allow the use of perturbation theory. All the values depending on spherical co-ordinates are represented as expansions of spherical functions. If substituted into the equivalent boundary conditions on the average surface, these expansions yield effective reflection coefficients for the spherical waves in the expansion of the coherent field. These coefficients depend on the effective impedance, the calculation of which is simple in the case of a large sphere. View full abstract»

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  • Scattering from an impedance cylinder embedded in a nonconcentric dielectric cylinder

    Page(s): 169 - 175
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    The electromagnetic scattering from an impedance cylinder embedded in a nonconcentric dielectric cylinder is derived rigorously by using a boundary value approach. The two cylinders are assumed to be infinite in length and of circular cross-section. The incident electromagnetic field is in terms of an electric or a magnetic field component parallel to both cylinder axes. The problem is two dimensional and the solution to either types of polarisation (TM or TE) can be found independently. Plane wave and line source excitations are considered in this analysis. The effects of various geometrical and electrical parameters (such as the cylinder's radii, permittivity, surface impedance and eccentricity) on the near field distribution and the far scattered field pattern are examined. Bistatic and monostatic scattering cross-sections of the composite cylinder which minimise or maximise the radar cross-section are also investigated. View full abstract»

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