By Topic

Microwaves, Antennas and Propagation, IEE Proceedings

Issue 6 • Date Dec 2001

 This issue contains several parts.Go to:  Part Supplement 

Filter Results

Displaying Results 1 - 16 of 16
  • Satellite propagation channel modelling using photogrammetry and hidden Markov model approach

    Publication Year: 2001 , Page(s): 375 - 380
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    In a typical satellite-Earth propagation path, the field strength of the received signal level changes with respect to time and space according to the changing morphology of the environment. It has been shown that the switching between different attenuation levels can be represented as a Markov stochastic process using the assumption that the channel properties are quasi-stationary in small periods of time. A hidden Markov model is introduced to replace the often used channel fading models, such as Rice, Loo and Rayleigh distributions. Three sets of parameters are trained to simulate the state transition and observation conditional probability density function among three basic propagation states that are categorised according to the environmental images. The simulated data were compared to the real RF measurement of satellite signals in several propagation properties, such as the cumulative fading distribution, level cross rate and error probability performance, at typical user environments. With the help of observation sets and their conditional probability densities, the proposed propagation channel simulator can model the satellite propagation properties with better accuracy than three-state Markov transition models View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Integral-equation-based analysis of transient scattering and radiation from conducting bodies at very low frequencies

    Publication Year: 2001 , Page(s): 381 - 387
    Cited by:  Papers (13)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (739 KB)  

    An implicit marching-on-in-time (MOT) algorithm for solving a time domain electric field integral equation pertinent to the analysis of transient scattering and radiation from perfect electrically conducting bodies that are excited by very low frequency signals is presented. Spatial variations in electric current densities are described by loop-tree basis functions to ensure stability of the time marching scheme when geometric discretisation lengths are much smaller than a light time step. Such basis functions were previously employed within explicit MOT solvers. However, to our knowledge, this is the first study to demonstrate their usefulness in tackling time domain integral equation low-frequency breakdown and related stability problems. This is achieved by deploying loop-tree basis functions within an implicit MOT scheme. Numerical examples that demonstrate the proposed scheme's effectiveness in analysing electromagnetically small or mixed scale structures and its ability to operate with time steps determined by the Nyquist criterion as opposed to geometric discretisation rules are presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Classification of metallic waveguides with complex cross-sections

    Publication Year: 2001 , Page(s): 398 - 402
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (418 KB)  

    A new classification scheme of waveguides with complex cross-sections is described. Only hollow metallic structures with a single contour are considered. Two new geometrical parameters, the number of ridges and the number of degrees of freedom, are proposed for evaluation of some of these waveguides. Transmission line characterisation criteria such as the type of propagating mode, geometrical peculiarities and calculation methods are analysed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dual-polarised stripline fed slot antenna incorporating signal cancellation

    Publication Year: 2001 , Page(s): 357 - 362
    Cited by:  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (808 KB)  

    A stripline fed cavity backed 'quad-slot' antenna is described in which two parallel slot pairs are orthogonally located in the tri-plate ground plane to form the dual-polarised antenna. Two of the orthogonally placed slots are fed from a quadrature hybrid while the other two are parasitically excited by the cavity mode. The hybrid and the slot antenna are designed and constructed as an integrated unit to minimise the return loss into the 'receiver' port and hence maximise the antenna sensitivity in passive tagging applications. The results obtained from computational modelling of the arrangement based on the moment method analysis of planar structures is compared with measurement and shown to be substantially in agreement View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Novel unified mode matching analysis of concentric waveguide junctions

    Publication Year: 2001 , Page(s): 369 - 374
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (639 KB)  

    A novel unified mode matching technique is proposed for the calculation of the modal scattering matrix of concentric waveguide junctions. The TE and TM modal fields in both waveguides which are connected to form the junction are expressed in the Cartesian coordinate system, so that the coupling coefficients of all the modes can be evaluated effectively. All types of waveguide junction are dealt with in a similar manner and no special function is required. As examples, the scattering parameters of nine types of waveguide junction are calculated and compared with other methods or measurements in the literature. Very good agreement in all these cases demonstrates the efficiency, accuracy and flexibility of this technique View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Generalised frequency-domain analysis of microwave Class-E power amplifiers

    Publication Year: 2001 , Page(s): 403 - 409
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (633 KB)  

    A frequency-domain method is formulated for the analysis of arbitrarily loaded Class-E circuits based on the harmonic balance technique. General loading requirements for optimum Class-E mode of operation are derived. Essential design information such as effects of turn-on resistance, harmonic terminations and idealised load-pull contours are given. The theoretical findings are then transformed into a straightforward design procedure. A 1.8 GHz experimental amplifier was constructed, which shows a state-of-the-art drain efficiency of over 90% from a 0.5 to 4 V supply voltage View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • P-adaptive finite element analysis of unbounded electromagnetic wave problems

    Publication Year: 2001 , Page(s): 388 - 392
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    The boundary that artificially truncates an unbounded domain in the finite element analysis of an electromagnetic wave problem necessarily introduces a numerical error. The adaptive technique proposed reduces this boundary error, as well as the usual finite element discretisation error. The scattering or radiating object and its immediate surroundings are meshed with hierarchal finite elements. Outside, a thick layer of free space is meshed with relatively few hierarchal wave-envelope elements. During p-adaption, increasing the order of the wave-envelope elements reduces the boundary error. Moreover, this reduction in boundary error is selective: in directions of strong radiation, the error reduction is greater View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Uniform amplitude excitation of radiating elements in array antenna pin-fed from radial waveguide

    Publication Year: 2001 , Page(s): 413 - 417
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (465 KB)  

    A practical method is presented for determining the lengths of the coupling wires (pins) in circular antenna arrays excited by a wave travelling in a radial waveguide. The validity of the proposed method is confirmed by comparing the calculated results with data published in the literature View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Two-layer MM-wave FSS of linear slot elements with low insertion loss

    Publication Year: 2001 , Page(s): 410 - 412
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (429 KB)  

    The performance of a very low loss frequency selective surface (FSS) comprising two air spaced planar arrays of linear slot elements is reported. The beamsplitter generates a low loss passband response with a very sharp transmission roll-off with frequency. Simulated and measured results in the 30 GHz and 300 GHz wavebands are used to quantify the performance improvement compared to a conventional multilayer dielectrically backed conducting ring FSS. The paper also discusses the effect of the array dimensions on the passband width and filter roll-off rate View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • New precision wideband direction finding antenna

    Publication Year: 2001 , Page(s): 363 - 364
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (199 KB)  

    A new wideband precision direction finding antenna is introduced. A 7-element printed log-periodic dipole array antenna is modified to become a direction finding antenna by bending it into a cylindrical structure. This antenna is extremely simple and there is no need for a matching network for wideband operation. Cardioid radiation patterns are obtained and presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Line charge distributions arising in the integral equation treatment of bent scatterers in stratified media

    Publication Year: 2001 , Page(s): 365 - 368
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (473 KB)  

    Within the framework of a mixed potential integral equation (MPIE) formulation, a precise theoretical treatment of connected vertical and horizontal metallisations; embedded in multilayered media is proposed. In particular, it is shown that Sommerfeld's choice for the vector potential Green's function GA can still be applied, provided that additional line integrals are taken into account in the formulation of the method of moments (MoM). The latter are precisely evaluated to ascertain their relative relevance and to quantify their influence on the predictions of practical parameters, such as input impedances, of some useful antennas View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Microwave envelope solitons in YIG film under oblique magnetisation

    Publication Year: 2001 , Page(s): 423 - 431
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    A detailed study of die output pulse profiles and envelope soliton characteristics are studied in a YIG film under oblique magnetisation for different input pulse widths, operating frequencies and ferrimagnetic resonance line widths. Dispersion characteristics and nonlinear characteristics of the YIG film are predicted by the first order multiple scale method. The analysis of the soliton in the YIG film is carried out using a split step Fourier method for arbitrary orientation of magnetisation. The conditions for the bright and dark soliton are established using the Lighthill criterion. A switchable bright to dark soliton is theoretically predicted by varying the angle of DC magnetisation. Pulse compression is also estimated for different magnetisation angles View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Single-patch and single-layer square microstrip antenna with 67.5% bandwidth

    Publication Year: 2001 , Page(s): 418 - 422
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (515 KB)  

    A square microstrip patch antenna with broadband operation is demonstrated. With an air-filled substrate of thickness around 0.1λ0 and one patch edge shorted by three symmetrical shorting pins, the antenna achieves an impedance bandwidth (return loss ⩽-10 dB) of 67.5%. The broadband feature of the antenna is mainly realised by exciting three resonant modes in a single patch and making them sufficiently close to one another. Details of the antenna design, equivalent circuit, and typical characteristics are presented and discussed both theoretically and experimentally View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Uncertainty contributions from mismatch in microwave measurements

    Publication Year: 2001 , Page(s): 393 - 397
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (481 KB)  

    One of the important error contributions in measurements of microwave attenuation and power is caused by mismatch between the attenuator and neighbour components such as the microwave source and load. Unless vector measurements of the reflection coefficients involved are performed in the measurement process the mismatch will contribute to the uncertainty. Warner (1977) has derived a formula for the case where the magnitudes of the reflection coefficients involved are known, but the phases are unknown, i.e. are evenly distributed between 0 and 2π. This case results in the so-called U-distribution. New formulas have been derived for calculation of the uncertainty contribution from mismatch for cases where only maximum values of the reflection coefficient magnitudes are known (and the phases are unknown). In these latter cases the distribution functions for the mismatch errors, and thus the uncertainties, deviate significantly from the case treated by Warner. It is therefore important to use the appropriate distribution function for the actual case when estimating uncertainties due to mismatch. By doing so the estimated uncertainty is typically reduced by a factor of two View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Transmission and reflection charts for two-port single impedance networks

    Publication Year: 2001 , Page(s): 351 - 356
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (671 KB)  

    The transmission and reflection charts for two-port single series impedance or shunt admittance networks are described. The charts are shown to have a scaling property, which allows the same chart to be used for convenience when the scale of the chart is changed. They can be used as an alternative to the Smith chart for impedance or admittance measurements. If the charts are built into a test instrument, the transmission response can then be used for impedance or admittance measurements. Applications of the charts for the identification of pure resonance in dielectric or cavity resonators, quality factor measurements and the observation of the critical state of superconducting resonators are also presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High gain planar antenna using optimised partially reflective surfaces

    Publication Year: 2001 , Page(s): 345 - 350
    Cited by:  Papers (151)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (741 KB)  

    A high gain planar antenna has been investigated, using an optimised partially reflecting surface (PRS) placed in front of a waveguide aperture in a ground plane. The antenna performance is initially related to the reflection characteristics of the PRS array following an approximate analysis. The array geometry is optimised using an analytical formula. The optimisation results are verified using a full wave model taking into account the edge effects. The array size for maximum antenna efficiency has also been investigated View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.