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Volume 138
Issue 5
IEE Proceedings H (Microwaves, Antennas and Propagation)
Volume 138, Issue 5, October 1991
Volumes & issues:
Volume 138, Issue 5
October 1991
New type of printed polygonal loop antenna
- Author(s): M. Cai and M. Ito
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 389 –396
- DOI: 10.1049/ip-h-2.1991.0066
- Type: Article
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p.
389
–396
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A new type of printed polygonal loop antenna (PPLA) has been devised by the authors. In the paper, analytical results of the new PPLA by the spectral domain method are shown, and two-dimensional current distribution on the printed circuit is obtained. The current distribution reveals that the new PPLA behaves like a slot antenna, unlike a conventional microstrip patch antenna. The radiation patterns and the input impedances are calculated from the current distribution. The results of numerical analysis agree very well with empirical results.
TM diffraction by a partly leaky halfplane
- Author(s): S.A. Bokhari ; M. Keer ; F.E. Gardiol
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 397 –406
- DOI: 10.1049/ip-h-2.1991.0067
- Type: Article
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p.
397
–406
(10)
The paper presents a hybrid method for the computation of scattered fields from a leaky halfplane illuminated by an electric line source. The structure consists of a large array of nonuniformly spaced, thin, perfectly conducting coplanar strips near the edge of a perfectly conducting halfplane. The analysis is carried out by a combination of the integral equation and physical optics methods. The solution for the current distribution on the strips is obtained by the use of the conjugate contrast source truncation iterative algorithm. Thus, matrix inversion is circumvented and the method is particularly well suited for large arrays of strips. An approximate procedure based on a physical optics derived resistive taper is given for the synthesis of strip spacings. Numerical results indicate that a moderate increase in diffraction loss in the halfplane shadow region is feasible by a judicious choice of strip spacing. Advantages and limitations of the method are also discussed.
Propagation and radiation characteristics of rectangular dielectric-loaded hybrid mode horn
- Author(s): E. Lier and C. Stoffels
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 407 –411
- DOI: 10.1049/ip-h-2.1991.0068
- Type: Article
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p.
407
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The propagation and radiation characteristics of a rectangular hybrid mode horn partially filled with a dielectric material are theoretically investigated. It is demonstrated that this horn, which belongs to a class called dielcore horns, exhibits high isolation between orthogonal modes over a substantial bandwidth. The mechanical simplicity and potentially low production cost, means that it constitutes an alternative to broadband horns with an elliptical beam and low cross-polarisation. The horn may find applications as a feed in radar and satellite antennas with elliptical reflectors, and as elements in array antennas.
Generalised field theory of irregular waveguide partially filled with longitudinally magnetised ferrite
- Author(s): Y. Rong ; W.-B. Dou ; S.-F. Li
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 412 –416
- DOI: 10.1049/ip-h-2.1991.0069
- Type: Article
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p.
412
–416
(5)
A numerical approach for solving the problem of an irregular waveguide partially filled with longitudinally magnetised ferrite is proposed. The approach is a combination of the mode expansion method and the boundary element method. Examples of this kind of waveguide are presented to show the validity and usefulness of this approach. Numerical results agree well with experimental results from the literature. Some useful curves and conclusions are given to make the design of Faraday rotation components easy.
Isolation of the travelling wave contribution to the backscatter pattern of conducting cylinders
- Author(s): M.C. De villiers and J.A.G. Malherbe
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 417 –420
- DOI: 10.1049/ip-h-2.1991.0070
- Type: Article
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p.
417
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The backscatter pattern of a long, perfectly conducting cylinder with flat endcaps exhibits a travelling wave lobe near end-on in the case of a θ-polarised incident electric field. The paper uses a method that combines the MOM and the UTD to isolate the travelling wave contribution, and approximate expressions are obtained empirically to correct the backscatter pattern calculated by means of the UTD, which does not include the travelling wave contribution. The travelling wave contribution is subsequently studied as a function of cylinder diameter and length.
Full wave analysis of arbitrarily shaped line-fed microstrip antennas using triangular finite-element method
- Author(s): K.-L. Wu ; J. Litva ; R. Fralich ; C. Wu
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 421 –428
- DOI: 10.1049/ip-h-2.1991.0071
- Type: Article
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p.
421
–428
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A numerical method is developed investigate arbitrarily-shaped line-fed microstrip antennas. The electric integral equation is by adopting the triangular shaped basis element and using the Galerkin procedure. In the integral equation, Sommerfeld-type full wave Green's functions are used. To enhance the computational efficiency, the full wave discrete image technique applied. To examine the method, comparison made between numerical and experimental which show excellent agreement. The experimental error is also discussed.
Rigorous analysis of the TM0n modes in a dielectric-post resonator with an annular slot in the upper plate
- Author(s): K.A. Michalski ; X. Di ; A.W. Glisson
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 429 –434
- DOI: 10.1049/ip-h-2.1991.0072
- Type: Article
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p.
429
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The problem of a cylindrical dielectricpost resonator with an annular slot in the upper plate is rigorously solved. The analysis is based on an integral equation for the electric field in the slot which in the absence of external excitation has nontrivial solutions only at the complex resonant frequencies of the structure. This integral equation is solved numerically by the method of moments, and the resonant frequencies are determined as the zeros of the associated matrix determinant in the complex frequency plane. Attention is limited to the axisymmetric TM0n modes. Sample numerical results are given, including the complex resonant frequencies, the associated modal fields, and the radiation patterns of the first few resonator modes, and show the dependence of these quantities on the width and location of the annular slot.
Two stage computation off apertures in finite screens
- Author(s): R. Kastner and N. Herscovici
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 435 –440
- DOI: 10.1049/ip-h-2.1991.0073
- Type: Article
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p.
435
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Large, finite screens containing smaller apertures with a variety of geometries are addressed. Owing to the large size of the finite screen it is assumed that matrix methods would not be applicable for the problem in its entirety. The use of the conjugate gradient (CG) algorithm may not provide the most efficient approach either, for the following reasons: each configuration requires a separate computation; a separate computation is needed for each excitation; it has been shown in the past that intricate geometries may inhibit convergence. The solution process separated into two distinct stages: (a) Green's function for the unperturbed, short circuited finite screen structure is evaluated numerically. At this stage the CG is applicable with good and predictable convergence characteristics and no large matrix needs to be stored, (b) This Green's function is subsequently used with a new magnetic field integral equation for the aperture region, solved by the moment method. Most of the matrix elements are useful for aperture configurations, hence computation time for each configuration greatly reduced. The scheme thus combines the two methods in a way that utilises their advantages where they are most applicable.
Applications of minimum redundancy arrays in adaptive beamforming
- Author(s): M. Fattouche ; M.B. Jorgenson ; S.T. Nichols
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 441 –447
- DOI: 10.1049/ip-h-2.1991.0074
- Type: Article
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p.
441
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It is shown, through analysis and simulation, that the use of a minimum redundancy array (MRA) in conjunction with an adaptive beamformer results in performance superior to that attained by a comparable system based on an array with uniformly spaced elements, or uniform array (UA) in terms of rejecting interferences located in close angular proximity to the look direction. Further, it is demonstrated that choosing the adaptive elements of a thinned adaptive array (TAA) based on a minimum spatial redundancy criterion, rather than spacing them uniformly, results in improved rejection of main lobe interferences, with negligible degradation in sidelobe interference rejection capabilities.
Influence of supporting dielectric layers on the transmission properties of frequency selective surfaces
- Author(s): P. Callaghan ; E.A. Parker ; R.J. Langley
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 448 –454
- DOI: 10.1049/ip-h-2.1991.0075
- Type: Article
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p.
448
–454
(7)
Single layer arrays of linear dipole slots and patches symmetrically embedded in a dielectric layer or bonded to its surface illustrate dielectric tuning effects in this mainly computer aided but partly experimental study. After its initial rapid decline as the layer thickness increases, the resonant frequency of the slots varies cyclically about the limiting value for the patches. Contours of transmission level on a frequency/thickness plot illustrate this frequency pulling effect and lead to a discussion of passband shaping and the sensitivity to angle of incidence. Equivalent circuit concepts account for the observed bandwidth and resonant frequency variations. The performance of two experimental surfaces is described, including the influence of trapped waves in the dielectric.
Electromagnetic interference of a plane wave incident on superstrate-loaded microstrip circuits
- Author(s): K.-L. Wong
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 455 –459
- DOI: 10.1049/ip-h-2.1991.0076
- Type: Article
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p.
455
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The exact analytical expressions for the plane wave reflection coefficient at the airsuperstrate interface of a four-layer model for superstrate-loaded microstrip circuit are given and the electromagnetic interference of a plane wave incident on such a model of the circuit is studied. Numerical results illustrating the power absorption by the model and the resultant electric and magnetic fields on the superstrate-substrate interface as a function of wave frequency, superstrate thickness, superstrate permittivity and incident angle are presented. The presence of the conducting strips on the surface of the circuit is also considered. Details of the numerical calculations are described.
Optical probing of millimetre waves in semiconductor waveguides
- Author(s): A. Alphones and M. Tsutsumi
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 460 –462
- DOI: 10.1049/ip-h-2.1991.0077
- Type: Article
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p.
460
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A noncontact optical probing technique for measuring the electromagnetic-field distribution on semiconductor waveguides is presented. Rib guide is considered for the experimental demonstration. Dispersion characteristics and the field distributions in the rib guide are calculated using the concept of effective dielectric constant and are compared with measured characteristics. The advantage of using this new measurement method at higher frequencies, beyond 100 GHz, is discussed.
Plane-polar near-field to far-field transformation with three kinds of fourier-bessel eigenvalue expansions
- Author(s): C. Cao ; E. Van lil ; A. Van de capelle ; K. Van't klooster
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 463 –468
- DOI: 10.1049/ip-h-2.1991.0078
- Type: Article
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p.
463
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An accurate way to compute near-field to far-field transformations by expanding the near-field into a Fourier-Bessel series is presented. All previous studies based on Fourier-Bessel expansions make use of a zero boundary eigenvalue condition. The other two boundary conditions (derivative, linear) are also studied and all the three boundary condition expansions are compared from a viewpoint of accuracy and efficiency in both the near-field and the far-field. The influence of the sampling density in the near-field measurement is also investigated.
Design of phase velocity tapers in coupled-cavity TWTs
- Author(s): V. Srivastava and R.G. Carter
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 469 –474
- DOI: 10.1049/ip-h-2.1991.0079
- Type: Article
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p.
469
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The efficiency of travelling-wave tubes (TWTs) operated under nonlinear conditions is usually enhanced by adjusting the phase velocity of the slow-wave circuit towards the output end of the tube. This technique, known as tapering, aims to maintain the optimum phase relationship between the electron bunches and the slow electromagnetic wave. The paper describes the results of a study of taper design carried out using a onedimensional large signal computer model of coupled-cavity TWTs. An improved taper design procedure for broad-band TWTs is suggested.
Analysis of a post with arbitrary cross-section and height in a rectangular waveguide
- Author(s): Y. Huang ; N. Yang ; S. Lin ; R.F. Harrington
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 475 –480
- DOI: 10.1049/ip-h-2.1991.0080
- Type: Article
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p.
475
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An analysis of a conducting post with arbitrary cross-section and height in a rectangular waveguide is given. The problem is solved by the method of moments in two ways. The first way is to solve the electric field integral equation (EFIE) for a thin post, for the current distribution along the post. The second way is to solve the magnetic field integral equation (MFIE) for a thick post. The equivalent circuits are evaluated, and the computed results show good agreement with experimental ones given by Marcuvitz [1].
Technical memorandum: microwave sensor for moisture measurements in solid materials
- Author(s): T. Lasri ; B. Dujardin ; Y. Leroy
- Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 138, Issue 5, p. 481 –483
- DOI: 10.1049/ip-h-2.1991.0081
- Type: Article
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p.
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A moisture sensor is described that consists of a microwave circuit working at 2.45 GHz. The system is an interferometer, a part of which is formed on a Duroïd substrate. The characteristics of the system are analysed and discussed. Preliminary experiments, made on different materials, for moisture contents smaller than 16%, show the accuracy of the sensor to be better than within ±0.1%.
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