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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 1 • Date Feb 2002

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Displaying Results 1 - 15 of 15
  • Vector wave function expansions of dyadic Green's functions for bianisotropic media

    Page(s): 57 - 63
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (725 KB)  

    An alternative set of Cartesian vector wave functions is presented to simplify the development of eigenfunction expansions of electromagnetic fields and dyadic Green's functions for bianisotropic media. With the eigenfields expanded using these functions, the determination of their expansion coefficients is facilitated via a concise 4×4 matrix method. Based on the complete dyadic discontinuity relations, the source consequents of the dyadic Green's functions are also explicitly expressed in terms of these functions. By incorporating the modified reciprocity theorem into the discontinuity relations, more compact source consequents are found to be related directly to the eigenfields in a complementary medium. These complementary eigenfields, in turn, can be deduced readily from their original counterparts by performing certain simple transformations. This manner of incorporating reciprocity provides a clear insight into the significance of each discontinuity relation and reveals the connections between the singularities, discontinuities and the complementary eigenfield components. For illustration, the vector wave functions expansions of the eigenfields for isotropic and uniaxial bianisotropic media are discussed View full abstract»

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  • Self-diplexing antenna using the square patch with a hole

    Page(s): 7 - 10
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (551 KB)  

    The paper proposes a double-layered circularly polarised self-diplexing antenna (SDA) using a square patch with a shorted hole, which is a new type antenna with improved diplexing characteristics. The equivalent relative permittivity can be adjusted by changing the size of hole. The E-plane radiation energy at ±90° is largely reduced when the relative permittivity is unity. To utilise this characteristic, a double-layered SDA is proposed which consists of the lower layer of a square patch with a hole and the upper layer of a 0.5 λ0 airgap square patch. Using this antenna, the isolation level was improved by a minimum of -54 dB View full abstract»

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  • Efficient hybrid discrete Fourier transform-moment method for fast analysis of large rectangular arrays

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (658 KB)  

    A novel approach combining the moment method (MoM) and the discrete Fourier transform (DFT) is developed for the fast analysis of electromagnetic (EM) radiation/scattering from electrically large, finite, planar rectangular arrays. In particular, the unknown array distribution to be solved is represented in terms of the DFT within the MoM for a given array excitation. The proposed DFT-MoM approach for large arrays has the advantage that it can overcome the inefficiency of the conventional MoM approach by drastically reducing the number of unknowns. The latter is possible because only a relatively few DFT terms are significant in this DFT-MoM. A useful criterion to select significant DFT terms is described. Numerical results are presented to indicate the efficiency and accuracy of the DFT-MoM analysis for determining the array distribution and the radiation pattern of large rectangular arrays with uniform excitation. It is found that the efficiency and accuracy of the DFT-MoM increases dramatically with an increase in array size. Furthermore, the DFT representation employed within the MoM can provide an asymptotic closed form solution for both the near and far fields of the array, which can be described in the ray format of the uniform geometrical theory of diffraction (UTD) View full abstract»

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  • Design method for antenna arrays employing ferrite printed transmission line phase shifters

    Page(s): 33 - 40
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (888 KB)  

    Ferromagnetic substrates are attractive for microstrip antenna array applications. An alternative method for using ferrites for beam steering with microstrip arrays is demonstrated. In addition, a method is presented to determine the optimum applied bias field values for maximising the array's beam steering angular span. The method relies on a knowledge of the propagation constant (βeff) behaviour within the ferrite substrate, and the finite element-boundary integral (FE-BI) method is employed for extracting βeff. Experimental and numerical data are included for validating the evaluation of βeff. To account for finite magnet dimensions, a static analysis is conducted to account for field spatial variations associated with the bias field. These spatial variations must be taken into account to properly model the ferrite propagation constant behaviour. Results are shown for this alternative array configuration, which achieves scan angles as large as 18° View full abstract»

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  • Mode characteristics in a circular chiral ferrite dielectric waveguide

    Page(s): 28 - 32
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (475 KB)  

    A circular dielectric waveguide with magnetically biased chiral ferrite materials in both the core and the cladding is introduced. The relations between the transverse electromagnetic field components and the longitudinal ones are derived in circular cylindrical coordinates. The coupled wave equations for the longitudinal field components are solved analytically and the eigenequation for general circular chiral ferrite dielectric waveguide is established. Mode characteristics including the cutoff, dispersion, and field distributions are investigated. The numerical results show that not only the cutoff frequencies but also the dispersion curves of HE and EH modes with the same mode number separate, and the ferrites and chiralities in the core and the cladding have different effects on the propagation characteristics View full abstract»

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  • Phase properties of single-layer patch arrays with applications to line-source-fed microstrip reflectarrays

    Page(s): 64 - 70
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (784 KB)  

    The analysis of scattering from an infinite periodic array of microstrip patches is employed for the numerical study of a line-source-fed, single-layer microstrip reflectarray. By utilising rectangular patch geometries in the modelling, reflection phase properties of the reflectarray are rigorously examined. Important parameters such as patch length, substrate permittivity and thickness are investigated. Also included is the effect of unattainable reflection phase on phase corrections and radiation characteristics View full abstract»

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  • Equivalent circuit parameters of coplanar stripline discontinuities

    Page(s): 11 - 16
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    The paper reports a study of equivalent capacitances and inductances of various coplanar stripline (CPS) discontinuities. To deal with equivalent capacitance, an integral equation for governing the distribution of excess charge near CPS discontinuity is derived and subsequently solved by the method of moments together with Galerkin's approach. The equivalent inductance is determined from the equivalent capacitance of its complementary structure, i.e. a coplanar waveguide discontinuity in free space by means of the duality concept. Numerical results for the open end, the symmetric step, the short end, and other extensive discontinuities are presented. In addition, simulated results in a quasistatic model are compared with data obtained by the FDTD method View full abstract»

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  • Dual band hybrid vehicular telephone antenna

    Page(s): 41 - 44
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    A dual band vehicular telephone antenna with a low profile and wide bandwidth is presented. Operating at the 900 MHz and 1800 MHz telephony bands, with a VSWR of better than 1.7, it is a hybrid construction combining a monopole with a top loading patch shorted to the ground-plane. Extra pins provide the upper frequency band resonance. The antenna has monopole radiation characteristics and can be hidden under a plastic panel or mounted on the vehicle roof View full abstract»

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  • Effects of walls on coupling between coupled combline resonators

    Page(s): 53 - 56
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    The effects of the open-side end-wall and ground walls (planes) on the coupling between two identical combline resonators coupled through slots are analysed. It is shown that the electric coupling, which is necessary to realise filters with transmission zeros, can be achieved only when the ground planes are sufficiently close to the resonator post while the open-side end-wall is sufficiently far from it. A criterion for choosing the wall distances from the post is presented. Also, it is shown that the tuning screw (which is mounted on the end-wall) significantly reduces the electric coupling only when it is very close to the post View full abstract»

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  • Quantifying numerical dispersion in non-orthogonal FDTD meshes

    Page(s): 23 - 27
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    Numerical electromagnetic models such as FDTD are widely used for the design and analysis of structures, including antennas. Numerical dispersion is one of the main sources of error that degrade the accuracy of the results-for each structure of interest, the users of the model must attempt to generate a mesh that will avoid introducing high levels of dispersion. This is, however, especially difficult for non-orthogonal meshes since little information is available on the dispersion properties of the non-orthogonal FDTD algorithm on complex meshes. For the first time, the dispersion in realistic non-orthogonal FDTD models of microstrip structures is quantified directly through numerical simulations. A test structure is considered, discretised using a number of nonorthogonal mesh configurations, including single and multiple skew angles. A numerical analysis of reflections generated at the transition between two mesh regions with different skew angles is also presented. These results give a practical guide to mesh generation for users of the algorithm View full abstract»

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  • Magnetic suspension for micro-actuators using microwave cavity resonators

    Page(s): 45 - 49
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    A new levitation technique which harnesses the Lorentz forces acting on the walls of a metallic electromagnetic cavity resonator is described. Both disc-shaped or cylindrical 'floats' which form part of the wall of the cavity are described. If the frequency of operation is high enough (>100 GHz) the dimensions of the system will be in the millimetre range. The technique requires that the cavity mode employed is relatively independent of the movement of the 'floating' wall. This basically means that the cavity wall currents must flow parallel to the edges of the floating wall, and that the wall is lifted from its contacting position by a distance of more than about 1% of the RF wavelength at the operating frequency. Experiments using a high-Q ring resonator, operating in a TM mode, show that substantial levitation forces are available at millimetre-wave frequencies, and that the system is intrinsically stable View full abstract»

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  • Electrostatic Green's functions for planar multilayered anisotropic media

    Page(s): 78 - 83
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (677 KB)  

    This paper presents a concise 2×2 matrix formulation of the electrostatic Green's functions for planar multilayered anisotropic media. The media may consist of any number of layers bounded by optional Dirichlet, Neumann or mixed walls. Both potential and normal-displacement Green's functions for arbitrary field and source locations are determined simultaneously in the spectral domain. The optional boundary wall and open conditions are incorporated universally through the reflection coefficients which relate the upward-bounded and downward-bounded partial eigenfields. These coefficients avoid the indeterminate calculations that may occur for open structures or large spectral variables. The resultant Green's function expressions are written in illuminating and explicit form ready to be utilised. For illustration., the grounded three-layered dielectric structure is considered analytically, along with simple extension to biaxial and symmetric anisotropic media. Numerical results are also demonstrated for the capacitance of microstrip on anisotropic substrates, including lithium niobate characterised by sets of permittivity at constant strain and constant stress View full abstract»

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  • Experimental characterisation and modelling of on-chip capacitors and resistors on GaAs substrates

    Page(s): 50 - 52
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    Experimental characterisation of various on-chip capacitors and resistors on GaAs substrates is performed, and these capacitor and resistor samples are tested up to 20 GHz using a Cascade 9000TM analytical RF probe station combined with a de-embedding technique. To accurately extract these passive device parameters, equivalent circuit models are presented for the capacitor and resistor. Excellent agreement is achieved between the measured and simulated data. The chosen circuit models depend on the layout and fabrication technology, and capacitor and resistor geometries View full abstract»

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  • Double-folded monopole antenna using parallel line or coaxial cable

    Page(s): 17 - 22
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (747 KB)  

    It has been shown that loading a certain reactance component at the feeding point of an antenna is useful in reducing antenna size. When a parallel transmission line with a short-circuited end is loaded onto a monopole antenna, we can obtain a small antenna called a parallel line loaded monopole antenna. However, a small antenna usually has low input resistance and low actual gain. The approach outlined is to increase the actual gain of the small loading antenna and utilise knowledge of a folded monopole antenna, which has a very high impedance value. A small folded monopole antenna called the double folded monopole antenna (DFMA) with high resistance and high actual gain can then be realised. An explanation of the operational principles of the DFMA is provided and the characteristics of small antenna design discussed. A coaxial cable is also used as the loading element for the loading antenna. It is proposed that a coaxial cable DFMA can be realised by replacing the parallel transmission line loading with coaxial cable transmission line loading. The advantage of the coaxial cable DFMA is that it has a small cross-sectional area, since the coaxial cable loading is embedded within the cylindrical antenna element. The results of actual testing of the coaxial cable DFMA are presented. All other results are provided by computer simulation using the method of moments, since the results are assumed to be similar to those recorded from practical experimentation View full abstract»

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  • Broadband and compact multi-pole microstrip bandpass filters using ground plane aperture technique

    Page(s): 71 - 77
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (891 KB)  

    A ground plane aperture technique is developed for effective enhancement of the capacitive coupling factor in a parallel-coupled microstrip line (PCML). By applying a so-called 'short-open calibration' (SOC) scheme in the fullwave method of moments (MoM) algorithm, this PCML with two external lines is characterised by an equivalent J-inverter network with its susceptance and two electrical line lengths. Extracted parameters indicate that the coupling factor appears to be frequency-dependent and its maximum value rises rapidly as the aperture is widened. With the introduction of a single microstrip line section between two identical PCMLs, a broadband and compact multi-pole microstrip bandpass filter is proposed for the first time, and its electrical behaviour is studied and optimised on the basis of its equivalent circuit network. The network-based optimised results are confirmed by an EM simulation of the entire filter layout, featuring ultra-broadband and four-pole bandpass behaviour. Further, a single capacitively loaded line section is utilised to formulate a multi-pole bandpass filter, and its electrical effects are also discussed for filter design. The predicted and measured results confirm attractive properties of the proposed multi-pole filter with BW=60%. |S11|<-16 dB and 220% wide upper stop-band View full abstract»

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