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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 1 • Date Feb 1995

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Displaying Results 1 - 15 of 15
  • Modelling studies of microstrip reflectarrays

    Page(s): 78 - 80
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    Modelling studies of microstrip reflect-arrays are presented in this paper. A highly efficient full-wave analysis technique-a combination of the CG-FFT method and the complex discrete image technique-has been developed for the analysis of microstrip reflectarrays. Based on the technique, some trial designs have been implemented. Experimental and theoretical results are compared and found to be in good agreement View full abstract»

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  • Linear phase arrays based on slitted asymmetric ridge waveguides

    Page(s): 47 - 51
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    The analysis of linear phase arrays based on the slitted asymmetric ridge waveguide: a structure that is, at the same time, easy to manufacture and very flexible in terms of electrical characteristics is presented. Scanning is obtained in leaky-wave fashion (frequency scan) in elevation (longitudinal plane), and by phase shifters in azimuth (cross-plane). The analysis is based on the development of an accurate transverse equivalent network and on the derivation of a dispersion relation which gives the complex longitudinal propagation constant in terms of the structural parameters. Both cases of air-filled and dielectric-loaded ridge waveguide are studied. The effects of mutual coupling between the various line sources of the array are taken into account using the unit-cell approach. A detailed parametric analysis is carried out showing how the real and imaginary parts of the complex propagation constant, which are related to the radiation characteristics, can be controlled with a good degree of independence from each other. Moreover, no blind spots are introduced in the scanning process. While the grating lobes an avoided, due to the choice of the cross-section. This approach has been applied to two other linear phased arrays of leaky-wave line sources, based on an asymmetric NRD guide and on a printed-circuit version of an offset groove guide View full abstract»

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  • General scheme for electromagnetic reflection and transmission for composite structures of complex materials

    Page(s): 52 - 56
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    A time-harmonic electromagnetic planewave obliquely incident on a stratified composite structure consisting of different types of complex (bianisotropic) media is considered. A modified invariant imbedding method is used to calculate the reflection and transmission, and the internal fields are calculated through a Green function approach. A characteristic feature of the approach is that it is based on a wave splitting that is not related to the media which make up the composite structure, but is always defined with respect to a vacuum. Several advantages of this approach are identified and it is compared to other approaches. Numerical results for the co- and cross-polarised reflection and transmission coefficients for TE and TM modes for a composite structure are presented View full abstract»

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  • Comparative study on electrical performance of normal and superconducting multiconductor lines for high-speed interconnects and uniplanar MICs

    Page(s): 71 - 74
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    A comparative study of electrical performance is made between normal and superconducting multiple conductors, for applications in high-speed, high-density VLSI interconnects and uniplanar MICs. The self-consistent electromagnetic analysis is presented, which can handle the multiconductors as normal dielectrics, with high real or complex conductivity in the electromagnetic simulation. Examples of interconnecting lines and multiple uniplanar waveguides are shown for dispersion and losses. Extremely low losses and dispersion of superconducting multiple lines, over a very wide frequency range, demonstrate promising potential for high-speed interconnects View full abstract»

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  • Supergain printed arrays of closely spaced dipoles made of thick film high-Tc superconductors

    Page(s): 26 - 34
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    Closely spaced dipoles in an array configuration, if properly excited, may result in end-fire superdirectivity. Albeit at the expense of transmission bandwidth and radiation efficiency. Efficiency of superdirective arrays can be considerably improved if a high-Tc superconductor (HTS) is used in the realisation of the radiating elements and the feeding and matching network, resulting in practical supergain radiators. Basic feeding configurations, which in printed dipole arrays may induce superdirective excitation, an explored and characterised in terms of their efficiency and bandwidth. Superdirective and supergain array designs, operating at frequencies around 1 GHz, made of thick film YBa2Cu3O7-x on yttria stabilised zirconia (YSZ) substrates are demonstrated. Their measured end-fire gains exceeded that of similar cryogenically cooled thick film Ag arrays by 3-6 dB View full abstract»

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  • Simplified analysis of coated wire antennas and scatterers

    Page(s): 14 - 18
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    A simple prescription due to Popovic enables any analytical or numerical formulation for scattering or radiation by arbitrary bare-wire antennas of circular cross-section to be used for antennas having an electrically-thin coating of dielectric and/or magnetic material. The prescription relies on transforming any coating to the equivalent magnetic one and treating it as an impedance per unit length. It is applied within an existing analytical treatment for scattering by a bare half-wave dipole to obtain predictions for the radar cross-section of dielectric-coated dipoles. It is also used with the bare-wire moment-method code NEC to derive the current distribution on a coated monopole antenna. Agreement with limits of the underlying theory are comparing the results of this prescription with those obtained by an explicit moment-method treatment of a dielectric coating View full abstract»

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  • Study of electromagnetically coupled stacked rectangular patch antennas

    Page(s): 7 - 13
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    A technique for the analysis of electromagnetically coupled multilayer stacked patch antennas fed by coaxial probes is presented. It is based on the electric field integral equation and exploits the Galerkin procedure in the spectral domain for the solution of the equation. The technique is used to investigate the characteristics of a two-layer stacked rectangular patch antenna. The effects of substrate material, patch size, patch displacement and radome on the input impedance or on radiation patterns are presented. The results shed light on the direction of changes in the antenna's characteristics the with above mentioned parameters and hence are useful, when designing to shift the resonant frequencies, equalise the input impedances at the resonances, broaden the bandwidth and estimate changes in the radiation patterns View full abstract»

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  • New polarimetric calibration technique using a single calibration dihedral

    Page(s): 19 - 25
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    A new polarimetric RCS calibration technique using a dihedral corner reflector as the single calibration target is presented. This scheme is valid for any monostatic or quasi-monostatic radar system and characterised by five aspects: (a) scattering matrix measurements of only a single calibration dihedral at two orientations are needed; (ii) the radiation polarisation effect and the four measurement channels are separated in this new model; (iii) the frequency responses of four measurement channels are modelled as mutually independent and thus, no special care has to be taken for signal paths and nonreciprocal properties in a measurement system; (iv) the calibration procedure is simplified by taking advantage of small cross-polarised terms and no complicated matrix algebra is involved; (v) the calibrated results are valid for wideband applications because no assumptions are made relative to the theoretical solution for the calibration dihedral. This technique has been verified by several 2-18 GHz wideband RCS measurements using various feeds in the compact range at the Ohio State University ElectroScience Laboratory. Based on these measurements, an effective polarisation isolation close to -60 dB has been demonstrated View full abstract»

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  • Comparison between MMIC matrix and distributed amplifiers

    Page(s): 75 - 77
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    A comparison between a matrix distributed amplifier and a dual-stage distributed amplifier in the 2-18 GHz frequency range is presented. Both circuits were realised using the same MMIC technology and the same design criteria. A relevant result for the two different topologies shows equivalent small signal performance. In this example no advantages of the matrix amplifier are noticed over the conventional distributed amplifier. This interesting result encourages a more accurate investigation of the comparison between matrix and distributed amplifiers, using different technologies and a different number of active devices View full abstract»

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  • Coplanar coupled lines: the effects of the presence of the lateral ground planes, upper and lower ground planes, and the V-shaped microshield ground walls

    Page(s): 63 - 66
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (200 KB)  

    New types of coplanar transmission lines, V-shaped microshield coplanar waveguide coupled lines [VMCWCLs], and coplanar waveguide V-shaped microshield coupled lines [CWVMCLs], are proposed. Analytical formulas are presented for calculating the quasistatic TEM parameters of these coupled lines by means of exact conformal mapping techniques. Numerical results are also presented to illustrate the properties of these new kinds of coplanar coupled lines View full abstract»

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  • Moment method analysis of a horizontally polarised omnidirectional slot array antenna

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    An entire domain moment method analysis of an omnidirectional linear array antenna, in which the radiating elements are slot doublets in a rectangular waveguide, has been developed. A particular feature of the analysis is that direct computation of internal mutual coupling between broadwall slots on opposing walls has been incorporated. Numerical solutions are presented for the scattering properties of the slot doublets in both air-filled and dielectric-filled waveguides. The results are shown to be in good agreement with network analyser measurements View full abstract»

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  • Multimode equivalent network representation of inductive and capacitive multiple posts

    Page(s): 41 - 46
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    Novel multimode equivalent network representations for multiple inductive and capacitive posts in rectangular waveguides are presented. The network representations art derived from a rigorous formulation that leads to frequency independent integral equations. The network representations developed are used to compute the response of several waveguide devices, and comparisons between measured and simulated performances are also included, showing very good agreement up to millimetre-wave frequencies View full abstract»

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  • Hybrid mode analysis of parallel coupled inset dielectric guides

    Page(s): 57 - 62
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    The inset dielectric guide has shown potential for circuit and antenna applications. An efficient hybrid mode method, based on integral equation formulation and Galerkin's procedure, is presented for a rigorous analysis of parallel coupled inset dielectric guides. In comparison to experimental data, this model is seen to give more accurate calculations of the propagation and coupling characteristics than achieved in previous publications. Numerical results are presented to illustrate the influence of various structural parameters on frequency dependent coupling characteristics. It is found that high and flat coupling coefficients can be obtained by using very small guide separation and by the appropriate choice of slot height. Therefore this structure appears to be very useful for broadband coupler applications View full abstract»

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  • On the surface impedance used to model the conductor losses of microstrip structures

    Page(s): 35 - 40
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    In the numerical analysis of microstrip structures their finite conductivity is often modelled by using an equivalent surface impedance to relate the nonzero tangential electric field on the conductor surface to an equivalent electric surface current. The fields on top and below the patch are not necessarily the same and to account for this discontinuous tangential electric field a strict equivalence formulation should include magnetic surface currents. However, it is common practice to neglect them, presumably because they considerably complicate the surface integral equation and its numerical solution. Here it is shown that this practice leads to the use of an incorrect, although conservative, surface impedance. A basic assumption is that δ≪Δ≪λ with δ the skin depth, Δ the conductor thickness, and λ the free space wavelength View full abstract»

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  • Temperature stability of quality factor of junction circulators

    Page(s): 67 - 70
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    An aspect of the design of any circulator is the temperature stability of its gyromagnetic resonator. The possibility of stabilising such devices by optimising the ratio between the direct magnetic field and the magnetisation has been previously proposed. The paper aims to verify this condition by examining that of the quality factor of one C-band waveguide circulator using a CVG resonator. It indicates that the rule introduced in connection with the intersection of the magnetisation curves at different temperatures against the direct magnetic is equally applicable to this situation View full abstract»

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