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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 2 • Date Apr 1996

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Displaying Results 1 - 18 of 18
  • Microwave measurement of the nonlinear refractive index of PZT

    Publication Year: 1996 , Page(s): 189 - 192
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    A new measurement system is presented and used for the determination of the nonlinear refractive index of lead zirconate titanate (PZT) at microwave frequencies. Cross-phase modulation has been used and nonlinear coefficients that are negative have been found. This implies that PZT is self-defocusing and that, in principle, soliton propagation in positive group velocity regimes is possible View full abstract»

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  • Wideband active microwave isolators using GaAs MMIC technology

    Publication Year: 1996 , Page(s): 179 - 183
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    The paper is concerned with circuit designs for wideband microwave isolators realised as monolithic microwave integrated circuits using depletion-mode GaAs MESFETs. An unbalanced version of a previously published balanced design is shown to have an interesting property of an approximately linear transmission function but the port impedances remain nonlinear. A previously published general circuit synthesis method is used to implement an isolator with transmission function and port impedances both of which are linearised. Measurements on a GaAs MMIC implementation are presented View full abstract»

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  • Convergence of the fictitious-current model

    Publication Year: 1996 , Page(s): 163 - 168
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    When the fictitious-current model is applied for an electromagnetic-scattering problem, the accuracy and convergence of numerical results are sensitive to the distance δt between the physical surface and the mathematical surface on which fictitious current sources are placed. In this model, δt must be neither too small nor too large, since a small δt degrades the accuracy of numerical solution, and a large δt makes the moment matrix unsuited to numerical computation. Thus, when iterative methods are used, there is a trade-off between the convergence rate and the accuracy of numerical solution. Also, it is found that there exist resonant peaks depending on sampling distance δs, and the geometry of the scatterer. Therefore, when this model is used for CNR frequencies, spurious frequencies can be obtained. It is found that there is a linear relationship between δt and δs which maintains a constant condition number. Using this relation, a useful modelling method for electromagnetic problems is introduced View full abstract»

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  • Transmission line analysis of symmetrical ring resonators

    Publication Year: 1996 , Page(s): 184 - 188
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    Symmetrical transmission line ring resonators are studied using the generalised reflection coefficient concept and the odd- and even-mode analysis method. The mode distributions for closed, tunable and selectively damped rings are derived. A normalised tuning characteristic is generated for a capacitively tunable ring, showing agreement with derivations based on current continuity in the limit of loose coupling. The perturbation of resonant frequencies by nonzero coupling is also calculated. An optimum value for an even-mode damping resistance is derived. A circuit simulator is used to demonstrate that the features derived analytically for lossless lines persist when realistic values of loss and dispersion are introduced View full abstract»

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  • Application of a source method for modelling step discontinuities in microstrip circuit

    Publication Year: 1996 , Page(s): 169 - 173
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    A source method is developed to determine the characteristics of a step discontinuity in microstrip circuits. Modelling of the circuit is proposed by a rigorous method including sources and using extended wavelet trial functions. The presence of a coupling two-port network, whose role is fundamental to the problem solution, is demonstrated. The numerical results obtained, giving the modulus of transmission and reflection coefficients for the STEP discontinuities, are compared with previously published data View full abstract»

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  • Analysis of TM scattering from open two-dimensional perfectly conducting shells using aggregated compactly-supported wavelet bases

    Publication Year: 1996 , Page(s): 152 - 156
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    A technique for the efficient analysis of electromagnetic scattering from open conducting structures is presented. The technique is based on the construction of a compactly supported aggregated wavelet basis that is used to transform vectors of arbitrary length. The use of this technique leads to a sparse method of moments (MoM) matrix, and speeds up matrix-vector products required in the iterative solution. The proposed algorithm can be appended to standard MoM codes and is capable of automatically handling an arbitrary number of unknowns and open-conductor configurations. For closed conducting structures, the method reduces to previously existing wavelet-based techniques View full abstract»

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  • Variational expression for propagation coefficient of an electromagnetic wave propagating along a closed rectangular chirowaveguide

    Publication Year: 1996 , Page(s): 174 - 178
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    A variational expression involving the transverse components of the electric field and their transverse derivatives is established for the propagation coefficient of an electromagnetic wave propagating along a lossless rectangular chirowaveguide with perfectly conducting walls. The solution providing the propagation coefficient of the dominant mode is given in terms of a very simple analytical expression enabling a tractable analysis of the device. The propagation coefficient of a second propagating mode is obtained simultaneously. The agreement between these variational results and those obtained by other methods is found to be very good View full abstract»

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  • Slot-coupled self-diplexing array antenna for mobile satellite communications

    Publication Year: 1996 , Page(s): 119 - 123
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    An experimental investigation of a novel two-layered slot-coupled self-diplexing antenna for mobile satellite communications is presented. A transmitting circular patch antenna is stacked on a receiving ring patch antenna. A modified symmetrical cross-slot is used to feed the circular patch antenna. Orthogonal two-point and four-point feeding methods for the ring patch antenna are compared. Characteristics of an isolated antenna element and a 16-element phased array antenna are presented. For the 16-element array, isolation between the transmitting and receiving ports was greater than 20 dB for a scanning angle of ±60 View full abstract»

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  • Radiation characteristics of rectangular patch antennas with a laminated ground plane

    Publication Year: 1996 , Page(s): 107 - 112
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    In modern aeronautical and automobile industries, composite materials are becoming increasingly popular for building the vehicular surface. The antenna engineer may face the situation of needing to design patch radiators above the composite material instead of a conductor ground plane. The input impedance and radiation patterns of a rectangular patch antenna attached to a laminated ground plane by using an integral equation approach is studied herein. The effects of composite lamina, substrate thickness and current probe location on the input impedance and radiation patterns are analysed. It is observed that the bandwidth of the patch antenna can be increased significantly when the substrate thickness is reduced. This observation is contrary to the conventional microstrip antenna concept and can be used to design a wideband microstrip radiator View full abstract»

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  • Volume-conformation method to study scattering by PEC objects with FDTD

    Publication Year: 1996 , Page(s): 131 - 136
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    The paper presents a volume-conformation technique to avoid the staircase approximation in the study of scattering by curved objects with the finite-difference time-domain (FDTD) method. This technique is based on a volume form of the Faraday and Ampere laws and it can easily be added to an existing FDTD code. Results for PEC sharply curved (ogive) and smoothly curved (sphere) objects are presented to show the efficiency of the method View full abstract»

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  • Balanced antipodal Vivaldi antenna for wide bandwidth phased arrays

    Publication Year: 1996 , Page(s): 97 - 102
    Cited by:  Papers (51)  |  Patents (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    The Vivaldi antenna, a form of tapered slot radiator, has been shown to produce good performance over a wide bandwidth, limited only by the traditionally used slotline to microstrip feed transition. The authors present a new antenna, the balanced antipodal Vivaldi, which incorporates an ultrawide bandwidth transition and overcomes the poor polarisation performance of the antipodal form. Good performance over a 1 to 40 GHz frequency range has been obtained. The use of the antenna in a linear phased array has also been investigated using elements constructed on high permittivity substrate. Wideband wide angle scanning with good cross-polarisation levels is obtained View full abstract»

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  • Fabry-Perot approach to the design of double layer FSS

    Publication Year: 1996 , Page(s): 157 - 162
    Cited by:  Papers (15)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    The analysis of the Fabry-Perot interferometer (FPI) is extended to cascaded surfaces with frequency dependent reflectivities, and provides a systematic procedure for the design of multilayer frequency selective structures (FSS). The FPI concept is also useful in diagnosing the origins of features in the transmission/frequency response curves. The approach eliminates much of the uncertainty in the initial design stages, where placing transmission and reflection bands at required frequency locations demands time and computing resources. The paper concentrates on double layer FSS and the application of the technique for design and diagnosis is illustrated by reference to the design of dichroic structures for microwave and submillimetre wavebands View full abstract»

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  • Electric field integral equation for cylindrical structures

    Publication Year: 1996 , Page(s): 147 - 151
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    An electric field integral equation for the induced current on a cylindrical perfect conductor with arbitrary cross-section is presented. The two-dimensional structure is excited by an arbitrary three-dimensional field. The integral equation is Fourier transformed along the cylindrical axis and decoupled in terms of the current components for computational efficiency. An example of an efficient moment method implementation using subsectional basis functions for solving the integral equation is given. The computed radiation patterns of dipoles in the presence of a conducting strip show good agreement with measurements and diffraction theory calculations View full abstract»

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  • Scattering parameters of arbitrarily oriented slot-coupled microstrip lines

    Publication Year: 1996 , Page(s): 141 - 146
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    The reciprocity method is extended to analyse arbitrarily oriented slot-coupled microstrip lines. The case of uniaxially anisotropic dielectric substrates is considered. The exact Green functions for these anisotropic substrates are used to solve for the unknown slot electric field, from which scattering parameters of a four-port network for this structure are obtained by using the reciprocity theorem. Comparison of numerical results for parallel microstrip lines with other available measured and computed data shows good agreement. It is found that for arbitrarily oriented microstrip lines, by varying slot inclination the angle coupling level can be widely controlled, and there exists maximum coupling for a certain value of slot inclination angle. Effects of other parameters such as slot length and dielectric anisotropy are also investigated View full abstract»

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  • Pattern synthesis with null constraints for circular arrays of equally spaced isotropic elements

    Publication Year: 1996 , Page(s): 103 - 106
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    In the paper we deal with the null synthesis of radiation pattern for single-ring circular arrays of equally spaced isotropic elements. The problem that we consider consists in finding the array pattern which minimises the mean-square distance from a given pattern, while being simultaneously null at assigned directions. We present a simple and efficient method of solution that uses a discrete Fourier transform (DFT) approach. At first, the unconstrained problem is solved in closed form, then the unconstrained optimum array pattern is modified in such a way as to produce the required nulls View full abstract»

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  • Radiation by axial slots on a dielectric-coated nonconfocal conducting elliptic cylinder

    Publication Year: 1996 , Page(s): 124 - 130
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    The radiation properties of axial slots on a conducting elliptic cylinder coated by a dielectric are investigated. The dielectric coating has an elliptical outer trajectory which is not confocal with the conducting slotted elliptic cylinder. A dual infinite-series solution based on the boundary-value method is obtained with the aid of the addition theorem of Mathieu functions. Both TM and TE cases are considered. The dual infinite series involved in the solution are then truncated to generate numerical results. The accuracy of the calculations is checked by comparison with published data. Other interesting results for different geometries are then illustrated View full abstract»

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  • Theoretical investigation of aperture-coupled rectangular dielectric resonator antenna

    Publication Year: 1996 , Page(s): 113 - 118
    Cited by:  Papers (21)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (588 KB)  

    Characteristics of an aperture-coupled rectangular dielectric resonator are investigated theoretically. A model based on the modal expansion method and the spectral domain approach is developed. Numerical results for Q factors, radiation efficiency and radiation patterns are presented for various values of material and structural parameters of the resonator, and it is found that by suitable choice of these parameters high efficiency, wide bandwidth and broadside radiation patterns can be achieved for the TE111y mode. Effects of aperture dimensions, aperture displacement and open-stub length on input impedances are also discussed. Results for return losses and radiation patterns are compared with available measured data, showing reasonable agreement. The results presented should be useful for the design of this type of new antenna View full abstract»

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  • Novel nine-port network analyser for measuring scattering coefficients of two-port devices

    Publication Year: 1996 , Page(s): 137 - 140
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    It is known that the dual six-port network analyser is able to derive the unknown scattering coefficients of a two-port device from the readings taken by eight power sensors. The paper outlines the development of a novel nine-port network analyser that requires only six power sensors for the same measurement function. Test results confirm that the prototype instrument is capable of yielding reasonably good measurement accuracies View full abstract»

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