By Topic

Microwaves, Antennas and Propagation, IEE Proceedings

Issue 1 • Date Feb 1998

Filter Results

Displaying Results 1 - 23 of 23
  • Intermodulation distortion in active microwave filters

    Page(s): 7 - 12
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    Active microwave filters have potential application in high-volume consumer products such as cellular-radio handsets. Active negative-resistance circuits may be coupled into physically small low-Q-factor filter structures to cancel resonator losses and produce apparently ideal filter characteristics. However, at large input-signal levels, the nonlinear active devices cause distortion effects, particularly with multiple signal inputs. Results from an experimental and computer-simulation study of saturation and intermodulation distortion in active negative-resistance microwave bandpass and bandstop filters are presented. These results have been generalised into simple formulas to enable the designer to determine the level of distortion in any specific filter of this type View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • General entire-domain Galerkin method for analysis of wire antennas in the presence of dielectric bodies

    Page(s): 13 - 18
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    A novel, entire-domain moment-method is proposed for the analysis of wire antennas and scatterers in the presence of lossy inhomogeneous dielectric bodies of finite extent. The wire part of the structure is approximated by arbitrarily positioned and interconnected straight-wire segments of lengths which can exceed one wavelength. The dielectric bodies are approximated by a system of trilinear hexahedrons, which can be electrically large (can also exceed one wavelength inside the dielectric, in any direction). The current along wires and inside dielectric bodies is approximated by one- and three-dimensional polynomials, respectively. The unknown current-distribution coefficients are obtained by a Galerkin-type solution of the system of coupled two-potential integral equations. The method is accurate, efficient and reliable. Its fundamental advantage over the (only existing) subdomain methods for the analysis of the same type of structures is a significantly reduced number of unknowns and, consequently, greatly reduced computing time. The proposed method enables rapid analysis of wire/dielectric structures exceeding moderate electrical size with even standard personal computers View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hybrid finite element solution of a quadrupole gyromagnetic waveguide

    Page(s): 128 - 130
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    Quadrupole bias fields are applied to ferrite-loaded waveguides in the implementation of nonreciprocal microwave quarter-wave plates. Specifying the tensor values and demagnetising effects for the ferrite in this type of bias field is difficult owing to the nonuniformity of the field and the existence of nonsaturated regions. A two-stage finite element solver is described here which may be used to evaluate the propagation characteristics of this type of geometry. Propagation constants are presented here for a magnetised square ferrite waveguide. The differential phase shift as a function of applied field is found to be linear and a backward wave exists over a narrow frequency band for one of the dominant modes View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Experimental study of novel resonant circular arrays

    Page(s): 92 - 98
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (788 KB)  

    Previous studies have shown that large circular arrays of cylindrical dipoles possess very narrow resonances when the frequency is varied. Only one array element is driven, and the rest are parasitic. At each resonance, the driving-point conductance is large, and the driving-point susceptance is zero. An associated experimental study is described in the paper. The experimental circular array consists of 90 vertical, thin-walled brass monopoles over an aluminium ground plane. The monopoles are electrically short and thick. The single driven element is the extension of the inner conductor of a rigid coaxial transmission line. Narrow resonances are found when the frequency is close to 2.5 GHz. The measured values of driving-point admittance are compared to corresponding theoretical values. Differences between measurements and theory are discussed; the overall agreement is very good. The measured results thus demonstrate the existence of narrow resonances in a physically real array and provide a strong indication for the validity of the underlying theory. The theoretical radiation patterns of the resonant array are discussed, and a potential application as a microwave beacon is described View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Numerical analysis of honeycomb antennas with an electromagnetic coupling feed system

    Page(s): 99 - 103
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    The first- and zeroth-mode radiation characteristics of a honeycomb antenna are analysed using the method of moments. The honeycomb antenna is fed by an unbalanced feed system, where an inverted L-wire is electromagnetically coupled to the antenna. The number of radiation cells is chosen to be Nx=2 in the x-direction and N y=13 in the y-direction. The first-mode radiation shows that, as the interior angle a increases, the half-power beam widths (HPBWs) in the two principal planes become wider. The maximum gain is obtained at α=180°. The zeroth-mode radiation shows that, as α increases, the HPBW in the H-plane decreases, while the HPBW in the E-plane increases. A maximum gain of approximately 19 dB is obtained at α=80°. Evaluation of the area factor, defined by the concept similar to the aperture efficiency, reveals that the zeroth-mode radiation has a larger value than the first-mode radiation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • CPW-fed slot antenna with wide radiating apertures

    Page(s): 104 - 108
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    A new wide slot antenna with capacitively coupled CPW-feed and metallic strips in the apertures is presented. The numerical analysis is based on the Galerkin moment method in the spectral domain approach. A simplified formula to calculate the input impedance is proposed. Theoretical and experimental results demonstrate the significant performance improvement of this modified structure. The influence of various design parameters is investigated. A 50% impedance bandwidth (SWR<2.0) and cross-polarisation levels below -20 dB are demonstrated View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Square spiral antenna on dielectric half-space: analysis using an electric field equation formulated by a finite-difference technique

    Page(s): 70 - 74
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    A tangential electric field equation for a wire antenna on a dielectric half-space of relative permittivity εr is formulated using a finite-difference technique. This equation involves only single-integral calculations and is used to obtain the current distribution of a square spiral antenna. The validity of the current obtained is checked by FD-TD analysis. Based on the current distribution obtained, the radiation characteristics of the spiral are evaluated. It is found that the gain in the dielectric material is larger than that in free space, with a ratio of εr1.5 in the broadside directions. As εr increases, the circularly polarised radiation region bounded by the critical angles in the dielectric becomes narrower and the resistance value of the input impedance becomes lower View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Design of circular patch antennas on ferrite substrates

    Page(s): 49 - 55
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    The design and performance of circular microstrip patch antennas on biased ferrites are described. Fundamental and higher-order modes are discussed and measurements presented for two different ferrites. The high permittivity of the substrate reduces the dimensions of the patches. The cavity model is extended to include multilayer ferrite-dielectric substrates with electromagnetic feedline coupling to the patch. This provides an accurate and fast CAD tool for predicting the resonant frequency over a wide bias range. Applying a DC magnetic bias field normal to the ferrite allows tuning of the resonant frequency by about 15%. Two hands of circular polarisation are generated when the magnetic bias is applied. The resulting radiation performance of the patches, in terms of the gain and quality of circular polarisation, is presented. It is shown that the gain is not dependent on the applied bias field and that good axial ratios are measured over a wide range of bias fields, both above and below saturation magnetisation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Spectral Green's functions for multilayer media in a convenient computational form

    Page(s): 85 - 91
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    The derivation of a simple and numerically efficient spectral Green's-function formulation for multilayer media is presented. From this formulation, the complete set of spectral Green's functions of scalar and vector potentials for a multilayer medium for vertical and horizontal electric as well as magnetic dipoles is obtained. By this method, the spectral functions of multilayer media and their derivatives can be obtained numerically by using a closed-form formula. This will remove the necessity of obtaining complicated spectral functions analytically. A number of numerical results are given for verification View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • TE/TM decomposition of electromagnetic sources in a nonreciprocal anisotropic medium

    Page(s): 109 - 115
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    The principle of source decomposition for electromagnetic problems is considered in the most general homogeneous anisotropic medium in which electromagnetic fields can be decomposed in two partial fields characterised by either TE or TM polarisation with respect to two given complex vectors. It is shown that, for each of the decomposed fields, the original medium can be replaced by a simpler equivalent medium, allowing one to apply existing analytic Green functions corresponding to each of the equivalent media. The problem of decomposing a given electromagnetic source into two parts corresponding to the TE and TM fields is solved in the case when the two complex vectors are coplanar. As an example, an electric current dipole is decomposed into two current sheets in the plane of the complex vectors. The source decomposition principle can be applied for solving field problems involving a homogeneous anisotropic space of the present type, for which no known analytic form for the Green dyadic exists View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Power synthesis of reconfigurable conformal arrays with phase-only control

    Page(s): 131 - 136
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    A new technique for the power synthesis of reconfigurable conformal arrays with phase-only control in the full three-dimensional and vectorial case is presented. The synthesis problem is stated as an intersection finding problem and is solved by means of a generalised projection algorithm. Following previous results in reflector and conformal antenna array power synthesis, a particular choice of the functional space wherein the problem is stated is exploited to alleviate the problem of false solutions, i.e. the possibility for the iterative solution algorithm of being trapped by a local minimum of the objective functional. Numerical examples showing the effectiveness of the presented technique are discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance of shaped beam quadrifilar antennas on the METOP spacecraft

    Page(s): 19 - 24
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (844 KB)  

    The design and performance of two low gain shaped beam quadrifilar helix antennas on a large complex spacecraft are presented. Scattering from the strongly illuminated satellite degrades the antenna performance by distorting the copolar pattern and increasing the cross-polarisation. This paper describes the results of numerical simulations of the installed antenna radiation patterns using the MoM and GTD techniques in the VHF and UHF bands, respectively. In this frequency range the size of the structure makes it difficult to model the antenna performance using either method, and the results must be interpreted carefully. The accuracy of the predictions has been established by comparisons with measurements using a 1/8 scale mock-up of the quadrifilars and spacecraft View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Efficient technique for determining beam scanning characteristics of axisymmetric paraboloid reflectors

    Page(s): 25 - 32
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (736 KB)  

    An efficient technique for the determination of the beam scanning parameters (viz. the direction of maximum gain, the number of beamwidths scanned, the scan limits with gain loss etc.) for axisymmetric paraboloid reflectors with defocused feed is presented. This technique can be used regardless of the respective range of focal-length-to-diameter ratio (F/D), the depth of illumination taper and the size of reflector. Representative numerical results obtained by using this technique are presented and discussed. These results also indicate the following: the direction of maximum gain deviates from both the direction of minimum pathlength variation and the direction of feed-displacement squint angle for the low F/D value; the orientation of directional feed to achieve maximum gain is complicated for the low F/D value with the large lateral feed displacement but approaches the point towards the vertex of reflector for the large F/D value; and the scan limits are substantially inferior to those inferred from earlier analyses, especially for the case of large F/D value and large feed lateral displacement View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Asymptotic boundary condition for corrugated surfaces, and its application to scattering from circular cylinders with dielectric filled corrugations

    Page(s): 116 - 122
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    A simple asymptotic solution for periodic corrugated surfaces when the corrugation period approaches zero is presented. The authors enforce an asymptotic boundary condition between the region inside the corrugations and the outer region, after a simple expansion of the fields in the corrugated region. This expansion is obtained by considering the corrugated region as a homogeneous region inside which the fields have no derivatives in the direction normal to the walls of the corrugations. The asymptotic corrugation boundary condition (ACBC) replaces the use of Floquet mode expansions (FME) of the field in the outer region, and it overcomes the known limitations of the surface impedance approach. The authors show how to apply the method to calculate the plane wave scattering from a circular cylinder with dielectric-filled corrugations. The series solution is obtained and verified with a solution based on Floquet mode expansions. Excellent agreement is obtained between the two solutions after introducing the ratio of the corrugation width (w) and the period (p) into the ACBC and with λ/p is about 10 or more View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Simple formulas for the gain and far-field of open-ended rectangular waveguides

    Page(s): 80 - 84
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    Simple formulae are presented for estimating the on-axis gain and far-field of open-ended rectangular waveguides (OEG). The on-axis gain formula is derived by incorporating in an approximate way the contribution of fringe currents at the shorter edges of the OEG into Schelkunoff's classical gain formula. By comparing this formula with Yaghjian's (1984) fringe current-based gain formula for the OEG, an explicit factor is arrived at to represent the effects on the H-plane pattern of the fringe current and reflection coefficient. Subsequently, a simple formula results for the H-plane pattern, which in turn makes the far-field estimation easier. Neither of these formulas need measured values of the aperture reflection coefficient of the OEG, unlike the approximate formulas by Yaghjian, and are simpler than these. The two sets of formulae compare very well with each other View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Near-field-far-field transformation from nonredundant plane-polar data: effective modellings of the source

    Page(s): 33 - 38
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    The paper provides a fast and accurate technique for the far-field evaluation from a nonredundant number of plane-polar near-field samples. By introducing very flexible modellings of the source, which fit very well a lot of actual sources, a new sampling technique is developed to recover the plane-rectangular data from the knowledge of the plane-polar ones. It must be stressed that the amount of required plane-polar data remains finite also when the radius of the scanning zone approaches infinity and it can be significantly lower than the amount needed by using a spherical modelling of the source. This result is based on an appropriate choice of the phase function extracted from the field expression and of the coordinates used to describe the plane and on the reduced volumetrical redundancy of the proposed source modellings. The effectiveness of the proposed technique is proved by numerical examples and its stability is verified by adding randomly distributed errors to the ideal near-field samples View full abstract»

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

    Page(s): 45 - 48
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    A class of linear arrays is introduced which, like Chebyshev arrays, have equal sidelobes in their radiation patterns. These arrays, compared to the conventional Chebyshev arrays with the same number of elements, the same size, and the same sidelobe level, provide higher directivities when the number of elements exceeds a minimum value for specified sidelobe level and element spacing. It is established that, for an arbitrary sidelobe level, the proposed arrays always provide higher saturation directivities. These arrays are synthesised using the zeros of conventional Chebyshev arrays repeatedly, and are referred to as modified Chebyshev arrays. Radiation characteristics of the proposed arrays are investigated. The influence of element spacing on the directivity difference between conventional and modified Chebyshev arrays is studied. Variations of directivity and half-power beamwidth against number of elements are examined and compared with those of conventional Chebyshev arrays View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Time domain calculation of the parameters of thin wire antennas and scatterers in a half-space configuration

    Page(s): 57 - 63
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    The space-time dependent parameters of a thin wire in the presence of an inhomogeneous medium are calculated directly in the time domain. The mathematical model is based on a newly established time domain integral equation (IE) of the Hallen type. The presence of a lossy half-space is taken into account by means of the Fresnel space-time reflection coefficient appearing in the IE kernel. The resulting integral equation is solved by the space-time finite element procedure newly developed for this purpose. A new integral formula for the electric field has been derived, and the far-field is evaluated by the finite element technique View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Mode-matching analysis of a waveguide junction formed by a circular and a larger elliptic waveguide

    Page(s): 123 - 127
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    The paper presents the formulation of a waveguide junction formed by an elliptic and a circular waveguide using the mode-matching method. The junction studied is concentrically joined with the cross-section of the circular waveguide completely enclosed by the elliptic waveguide. By expressing the modal fields in both waveguides in terms of Bessel functions, exact closed-form expressions for evaluating the coupling integrals are obtained. Theoretical results compare well with measurements and published results View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Quasistatic capacitance and frequency-dependent effective permittivity of multilayer microstrip patch antennas

    Page(s): 75 - 79
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    A variational method in the spectral domain is used to determine the quasistatic capacitance of a patch antenna within a nonhomogeneous multilayer structure. The patch is modelled both by a one dimensional analysis using a segment of an infinite transmission line and by a full two-dimensional representation. A new technique is presented for determining the relative permittivity of an equivalent single-layer structure, from which the frequency-dependent effective permittivity is obtained. Results for a number of different antenna structures are given and show good agreement with measured values View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Mutual coupling compensation in small planar array antennas

    Page(s): 1 - 6
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    Far-field pattern synthesis of small antenna arrays is a nontrivial problem. Typically the radiation patterns are required to exhibit low sidelobe levels, whilst maintaining the ability to scan the main beam in space. Mutual coupling is a pertinent problem when the number of antenna elements is small, often precluding the use of conventional tapering algorithms. A technique previously employed to compensate for mutual coupling in linear arrays is extended to include small planar antenna arrays. The method consists of the calculation of the coupling coefficients between the array elements, which are then formed into a matrix and used to compensate for the effects of mutual coupling. It is then shown that this method is not suitable for all planar array configurations and a new technique is developed which allows the calculation of coupling matrices for these element configurations. Measured data from a small planar antenna array is presented, with the outlined methods employed to produce sidelobe sum and difference beams View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Line-of-sight EM propagation experiment at 10.25 GHz in the tropical ocean evaporation duct

    Page(s): 65 - 69
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    An experimental investigation into anomalous propagation of microwave emissions transmitted from a low altitude in a tropical maritime environment is described. The measured amplitude values are compared with predicted values which were obtained by solving the parabolic equation. Knowledge of the refractive index profile, necessary for the parabolic equation formulation is obtained simultaneously from measurements of pressure, temperature and humidity taken on board a spar buoy located along the propagation path. Results show large variations in signal strength depending on the atmospheric conditions. In the absence of strong turbulence or precipitation, general agreement between the measured and predicted readings are observed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Voltage-current definition of impedance of double ridge waveguide using the finite element method

    Page(s): 39 - 44
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    The impedance of a ridge waveguide may be calculated by recognising that its electric field distribution is the same at cut-off and at infinite frequency and that the ratio of the transverse fields is equal to the wave impedance at infinite frequency. This means that a knowledge of the electric field normal to the interior metalisation of the waveguide is sufficient for the evaluation of the voltage-current definition of the characteristic impedance in ridge and other homogeneous waveguides. This paper provides one numerical solution based on the finite element method. It also includes some additional calculations on the power-voltage and power-current definitions of impedance. It therefore embodies descriptions of all three classic definitions of impedance in this sort of waveguide View full abstract»

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