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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 56 • Date Oct/Dec 2002

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Displaying Results 1 - 12 of 12
  • Characterisation and modelling of coplanar transmission lines on SiC substrates

    Page(s): 253 - 256
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (439 KB)  

    The paper investigates the characteristics of microwave transmission in coplanar waveguides (CPWs) fabricated on various silicon carbide substrates. Propagation constant and characteristic impedance measurements were performed at frequencies from 0.1 to 10 GHz. Different propagation modes are observed as a function of frequency and substrate resistivity. In the case of the low-loss structure, a quasi-TEM equivalent circuit model was developed from the available process parameters, taking into account the effects of electromagnetic fields in CPW structures. View full abstract»

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  • Electronic beam tilting using a single reactively loaded circular wire loop antenna

    Page(s): 271 - 274
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (499 KB)  

    The near-field current distribution along a circular loop wire antenna is modified by the inclusion of an electronically controllable reactive load, a varactor diode, into the antenna to provide beam pattern shaping. Modifications to a 4:1 balun are shown which permit varactor biasing while facilitating the impedance match of the circular loop, VSWR 1.3 to 1.9; this VSWR is superior to that previously reported for a reactively loaded wire antenna. In addition, it is shown that a reactively loaded dipole structure can provide only 10° beam tilt while the circular wire loop structure provides up to 27° beam tilt. View full abstract»

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  • Analysis of the dual-polarised patch antenna and two-element array by FDTD

    Page(s): 275 - 279
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (481 KB)  

    The effects of a dual-polarised patch antenna's structure parameters, such as the width of the feedline, the relative dielectric constant and the depth of the substrate, on the antenna resonant frequency, reflection coefficient and isolation are analysed by means of the FDTD method. The different effects of the structure parameters on the two-element array are compared with that of individual elements. The changes in the array's coupling with the antenna parameters are also studied by means of the FDTD method. View full abstract»

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  • Balance measurements in double-Y baluns

    Page(s): 257 - 260
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (634 KB)  

    Amplitude and phase balances in a double-Y balun, which transforms a coplanar waveguide with finite ground plane (CPWFGP) into a coplanar line (CPS), are investigated theoretically and experimentally. Measured results are presented for two baluns with different lengths of open- and short-circuited stubs. The balun with longer stubs demonstrated better amplitude balance. In the frequency range 3 to 14 GHz the measured amplitude balance is better than 1 dB and the phase balance is better than 8°. At the frequencies where resonances of the parasitic even mode appear, the balun has poor characteristics. View full abstract»

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  • Parallel- and cross-polarisation backscattering cross-sections of a conducting circular cylinder of finite length for a circularly polarised incident wave

    Page(s): 280 - 285
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    Expressions for the backscattering cross-section of a perfectly conducting circular cylinder of finite length when a circularly polarised plane electromagnetic wave is incident on the cylinder at an arbitrary angle to the axis are derived for parallel-polarisation and cross-polarisation returned waves. It is shown that as ka sin α (where k=2 π/free-space wavelength, a=cylinder radius, α=angle with cylinder axis) increases to infinity, the backscattering cross-section formed by a parallel-polarisation returned wave, σpa, diminishes to zero, while that formed by a crosspolarisation returned wave, σcr, approaches the backscattering cross-section for a linearly polarised incident wave. Also, it is demonstrated that the ratio σpacr becomes only a function of ka sin α, independent of the cylinder length, and therefore one can estimate a cylinder diameter by measuring the ratio σpacr. Results of experiments to verify the theoretical results and to demonstrate the possibility of estimating a cylinder diameter are shown. View full abstract»

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  • Isolator using a ferrite-coupled-lines gyrator

    Page(s): 291 - 294
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (386 KB)  

    The theory and design of an isolator based on a new concept using a section of axially magnetised ferrite coupled line (FCL) are presented. The isolator consists of a resistive four-port junction cascaded with an open- or short-circuited section of FCL representing a gyrator circuit. Design procedures for microstrip and slot-line configurations are described. The main feature of the isolator is its multiple reversing of operating direction with frequency. Application of the microstrip FCL section to the design of a gyrator is considered. The performance of the isolator is predicted by cascading S-matrices of the microstrip FCL gyrator and resistor circuit. The simulated scattering characteristics of the proposed isolator confirmed the correctness of the concept of the proposed novel nonreciprocal device. View full abstract»

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  • Printed backfire wideband circularly polarised tapered gap loop antenna

    Page(s): 261 - 264
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    A new type of broadband printed loop antenna is presented. The antenna produces backfire linearly polarised signals over a wide band of frequencies 1.2 to 2.2 GHz, with <3 VSWR. The front-to-back ratio of the antenna is 22 dB; its on-axis cross-polarisation level is around -25 dB at 1.5 GHz and is better than -16 dB; over the entire frequency band. Backfire radiation is achieved by using a novel wide printed rectangular loop radiating element with integral tapered gaps. These gaps provide the phasing necessary for the radiating elements of the antenna to enable backfire radiation in the plane of the loop. Two such printed tapered gap loops are arranged in an orthogonal configuration to produce broadband circularly polarised radiation. Here for a VSWR ≤3 the bandwidth is more than an octave (1.1 to 2.4 GHz) with an axial ratio of <4 dB. Simulated and measured results are presented for both configurations. View full abstract»

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  • Frequency selective surface as a polarisation transformer

    Page(s): 248 - 252
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (506 KB)  

    The polarisation transformation properties of frequency selective surfaces are reported. Examples of microstrip structures which transform polarisation from linear to circular are described. A relatively broadband polarisation transformer can be designed for a limited range of angles of incidence. Alternatively, a polariser for a wide range of angles of incidence can be designed to operate over a narrow frequency band. A polariser that can be electronically switched is also characterised. The finite-difference time-domain (FDTD) method and the waveguide simulator technique are used to analyse the reflection of a plane wave from these periodic structures. View full abstract»

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  • Scattering in a section of ferrite-coupled microstrip lines: theory and application in nonreciprocal devices

    Page(s): 286 - 290
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (554 KB)  

    A section of axially magnetised ferrite coupled microstrip lines (FCL) is analysed using the method of field expansion, which is based on the interaction of the dominant ferrite and isotropic modes in the ferrite-dielectric interfaces of an FCL. The scattering matrix of a four port microstrip FCL junction is obtained from matching of the fields at the ferrite-dielectric interface at both ends of the FCL. The performance of the microstrip FCL section is investigated numerically and the results of simulation are compared with available experimental data to demonstrate the efficiency of the approach. The configurations of the circulator and novel quasicyclic devices comprising the FCL section are reported and their scattering characteristics are calculated and discussed. View full abstract»

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  • Sixth-order elliptic function filter using triple-mode dielectric-loaded cylindrical cavities

    Page(s): 237 - 242
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (683 KB)  

    The realisation of a band-pass sixth-order elliptic filter using two triple-mode dielectric-loaded cylindrical cavities is described. In this filter the degenerate modes are two orthogonal hybrid (HE121) modes and one TM021 mode. Compared to a similar filter designed with empty cavities, the developed filter is approximately six times smaller in volume and three times lighter in weight. Data on degenerate modes and on coupling coefficients are generated by a computer program developed for the analysis of cylindrical cavities axisymmetrically loaded with dielectrics. View full abstract»

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  • Wideband bandpass filter design with three-line microstrip structures

    Page(s): 243 - 247
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (525 KB)  

    A systematic procedure is described for designing wideband bandpass filters based on parallel coupled three-line microstrip structures. It starts with modal analysis of a three-line coupled microstrip circuit. A database of modal eigenvoltage coefficients and modal characteristic impedances for a specified value of substrate εr is established. The relation between the circuit parameters of a three-line coupling section and an admittance inverter circuit is derived, so that the filters can be synthesised by a standard procedure. As compared with traditional parallel coupled lines, the proposed three-line design has the following two important features for the design of wideband filters: the tight line spacings of end stages can be greatly relaxed; and the stopband rejections are improved. Four filters with fractional bandwidths from 40% to 70% are fabricated on substrates with low and high dielectric constants. Prediction and measurement results are in good agreement. View full abstract»

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  • Hybrid dyadic-mixed potential integral equation analysis of 3-D planar circuits and antennas

    Page(s): 265 - 270
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (758 KB)  

    The electric field integral equation for planar circuits and antennas in multilayered media is usually solved with a spectral domain approach to compute the required Green's functions. The fact that these Green's functions are available in closed form in the spectral domain has not been exploited to the utmost up to now. Optimal use of the analytical expressions can be made when the structure is composed of horizontal and strictly vertical conducting surfaces. For such a geometry, a hybrid dyadic mixed potential field formulation is presented. The essential elements of the theory are worked out for a homogeneous medium above an infinite ground plane. The principle can, however, be extended to arbitrarily multilayered media. Numerical results for circuits and antennas are provided. View full abstract»

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