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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 6 • Date Dec. 2000

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Displaying Results 1 - 21 of 21
  • Ideal boundary and generalised soft and hard conditions

    Page(s): 495 - 499
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (538 KB)  

    Ideal boundary conditions require vanishing of the normal component of the complex Poynting vector at the boundary surface. A novel set of ideal generalised soft-and-hard-surface (GSHS) conditions is introduced which depends on a complex vector. The GSHS conditions reduce to those of the SHS (soft-and-hard-surface) boundary when the complex vector becomes real valued. Basic properties for a plane wave reflecting from a GSHS plane are derived. It is shown that TE and TM components (with respect to the complex vector and its complex conjugate) of a plane wave are reflected from the GSHS plane as from respective perfect magnetic or electric conductor planes. Image theory for the GSHS plane is given with an example. Finally, realisation of the GSHS plane and its application in polarisation transformation are discussed. View full abstract»

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  • Theory and experiment on microstrip patch antennas with shorting walls

    Page(s): 521 - 525
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (414 KB)  

    Experimental and calculated results based on the finite-difference time-domain method are presented on the impedance and radiation characteristics of the classic shorted quarterwave patch. It is found that, for foam substrates with relative permittivity close to unity, the bandwidths of the quarterwave patches are significantly larger than the halfwave patches. On the other hand, for microwave substrates with relative permittivities equal to 2.32 and 4.0, the bandwidths of quarterwave patches are less than those of halfwave patches, owing to the excitation of surface waves. The maximum gain in the case of foam substrate is in the range of 2-3.5 dBi, occurring 0-45/spl deg/ from broadside, depending on the substrate thickness. The use of a partial short, while reducing the resonant frequency, also decreases the bandwidth. The paper also describes the application of the shorting-wall principle to realise a compact wideband L-probe patch antenna. View full abstract»

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  • Octave bandwidth printed bow-tie fed partial cavity slot antenna

    Page(s): 483 - 486
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    A partial cavity backed wide bandwidth slot antenna fed with a bow-tie feed line is proposed as a viable element for mobile communication base station applications. A novel feeding mechanism consisting of a printed bow-tie feed placed within the slot aperture and metal baffles between the slot ground plane and a grounded backplane allow this antenna to operate over more than an octave bandwidth (1.15 to 2.46 GHz) with a VSWR<2. Measured radiation patterns are presented for the frequency range of 1.7-2.2 GHz, selected to give total coverage over the entire PCN and UMTS frequency bands. The gain of the antenna was found to be 5.4 dBi at 1.7 GHz and 4.6 dBi at 2.2 GHz. In addition to its bandwidth, a special feature of the slot antenna design is the small slot ground plane (1λ0×1λ0 ) and small background plane (2λ0×2λ0) needed for consistent pattern formation over the entire frequency range of interest View full abstract»

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  • Efficient analysis of a cubic junction of rectangular waveguides using the admittance-matrix representation

    Page(s): 417 - 422
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    In the paper an efficient and accurate method, based on the multimode-admittance-matrix representation and the theory of cavities, is proposed for the analysis of a six-port `cubic' junction composed of the orthogonal intersection of three rectangular waveguides. Very simple closed-form analytical expressions are explicitly detailed for all matrix elements of this basic key building block. More general waveguide multiport junctions, composed of a central cubic junction with arbitrarily shaped waveguide access ports, are also studied using a segmentation procedure. To validate the theory, numerical results are first discussed for a standard rectangular waveguide six-port cross junction. Finally, the analysis method proposed is also successfully applied to H- and E-plane T-junctions whose side arms are waveguides with rounded corners View full abstract»

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  • Investigation of the projection iterative method in solving the MoM matrix equations in electromagnetic scattering

    Page(s): 445 - 450
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    The projection iterative method (PIM) is convergence guaranteed when applied to solve the MoM equations with nonsingular matrices. Its decomposition procedure divides the matrix into some small subregions to avoid large matrix inversions. It is found that the convergence rate can be accelerated by introducing the relaxation factor to the PIM formulation. Three 3D examples are investigated to show the performance and validation of the PIM on electromagnetic scattering problems. A 2D infinite circular cylinder with TE field illumination is also studied to show the convergence of the method. The relationship of various PIM related parameters, such as the normalised residual norm, the number of iterations, the number of divided subregions, and the relaxation factor, is studied and presented, It is concluded that the operation count of the accelerated PIM is usually comparable to the direct method and the PIM can predict the RCS faster than the direct method with a reasonable accuracy View full abstract»

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  • Directional diversity of HF signals received over high latitude paths, and the possibility of improved data throughput by means of spatial filtering

    Page(s): 487 - 494
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    The high latitude ionosphere is a dynamic propagation medium in which HF radio signals associated with each propagation mode may arrive at the receiver over a range of angles in both azimuth and in elevation. Furthermore, ionospheric movements at the reflection points impose Doppler shifts and Doppler spreads onto the signals. Large Doppler spreads and multipath propagation in which the delay spread is large are particularly prevalent at these northerly latitudes and can result in a significant degradation in the performance of digital communication systems. This investigation suggests that the application of spatial filtering from simple antenna arrays comprising pairs or triplets of antennas can significantly reduce the level of apparent Doppler spreading, frequently to levels at which modern, high speed modems are expected to operate satisfactorily. The investigation concentrated on Doppler spread since this was the most significant factor in the data employed in this study; however, it is noted that reductions in effective multipath delay spread are also possible View full abstract»

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  • Dual-band patch antenna for mobile satellite systems

    Page(s): 427 - 430
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    The launch of new mobile satellite communication links for telephone and data applications demands development of small, low-profile, low-cost antennas. A single-layer, multi-band microstrip patch antenna is described, which operates over the frequency ranges of the Iridium and Globalstar satellite communication systems, 1.6 and 2.5 GHz. The antenna excites the TM10 and TM30 resonant modes which can operate with either dual linear polarisation or either hand of circular polarisation. The unwanted TM20 mode is suppressed using a combination of slots cut into the patch and by shaping the corners of the patch. Frequency band separations can be varied significantly from 1.3 to 2.5×the lower frequency. Data for designing the patch dimensions is presented. The return loss, impedance characteristics and radiation patterns are presented for a practical design View full abstract»

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  • Shadow blockage effects on the aperture efficiency of dielectric Fresnel lenses

    Page(s): 451 - 454
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    The effects of shadow blockage on the efficiency of a dielectric Fresnel lens is investigated. Since shadow blockage is a strong function of the F/D value, it should be factored into the design, especially for compact lenses designed with a small F/D. Equations are derived, based on ray tracing, to determine the decrease in aperture efficiency due to shadow blockage. Design curves have been generated to plot shadow efficiency against lens diameter for various values of F/D. Good agreement with measured radiation patterns is also demonstrated View full abstract»

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  • 1-port topology of the degree-1 and -2 terminated circulator

    Page(s): 437 - 443
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    The equivalent circuit in the impedance plane at port-1 of a 3-port circulator with ports 2 and 3 terminated in ideal resistive loads is a classic result. The purpose of the paper is to synthesise 1-port topology in the admittance plane in the case for which ports 2 and 3 are terminated in real resistive loads and in that for which the ports are loaded by broadband matching networks. This is done in terms of the eigenvalues of the problem region under the assumption that the in-phase eigennetwork may be idealised by a short-circuited boundary condition and an ideal 2-port gyrator circuit. The real part circuit and those at the split frequencies of the counter-rotating eigenvalues are also deduced as a preamble to realising the general circuit. The properties displayed by these circuits are compatible with existing experimental procedures for this class of device View full abstract»

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  • Complementary frequency selective surfaces

    Page(s): 501 - 507
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    A concept in frequency selective surface (FSS) technology that stems from Babinet's principle, whereby a hybrid of two closely coupled FSS, a layer of conducting elements and a layer of aperture elements are etched either side of a dielectric substrate, acronymed as complementary FSS (CFSS) is introduced. There are two narrow passbands separated by a distinct null. The CFSS creates electrically large elements from physically small ones to such an extent that a conventional λ/2 resonator in free space at the lower passband resonant frequency would be over three times longer than the dipole length employed in the CFSS. This passband is highly stable for normal and oblique TE and TM incidences, with less than 2% frequency shift. A full wave modal analysis is developed and two integral equations (IEs), an electric field IE and a magnetic field IE, are derived. These IEs are coupled and this renders them suitable for the solution of the CFSS problem. The interlayer dielectric region is critical to the location of the passbands as well as the in-band loss. Results are presented for dipole and ring CFSS and compared with measured data up to 40 GHz View full abstract»

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  • Multiple scattering of an E-polarisation plane wave from multiple cylindrical strips

    Page(s): 423 - 426
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    Multiple scattering of an E-polarisation plane wave from multiple cylindrical strips is investigated using the technique of the direct integral equation. The induced surface currents on multiple perfectly conducting strips are expanded in the form of a series of Chebyshev polynomials of the first kind. By using Galerkin's procedure, all the unknown expanding coefficients are determined by a set of matrix equations of infinite order, and then numerical results are presented to show the characteristics of the copolarised far-zone field changing with the angular width and number of strips as well as their relative orientations View full abstract»

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  • Author Index

    Page(s): 529
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (60 KB)  

    First Page of the Article
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  • Plane wave transmission through a pair of capacitive gratings

    Page(s): 455 - 462
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    A frequency-selective structure is investigated that represents a pair of gratings with narrow gaps in a thin conductive screen separated by a dielectric slab. In particular, the gratings may be closely spaced. The calculations show that the parasitic windows of the transparency may be shifted far from the operational frequency to the high frequency region, so that the ratio of the frequencies of the parasitic and operational windows of the transparency will exceed four. Expressions for the reflection and transmission coefficients are obtained. The results of calculations are compared with experimental data in the cases of both normal and oblique incidence View full abstract»

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  • Double-ring active microstrip antenna and self-mixing oscillator in C-band

    Page(s): 479 - 482
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    An active microstrip antenna with self-mixing oscillator is introduced with double-ring geometry. It is simple to implement and presents a dual-frequency response in the operating range of C-band (3.7-4.2 GHz). The circuit with common-drain FET is used as an oscillator as well as a mixer. This active microstrip antenna can be applied in ROTV of satellite communication as the down converter View full abstract»

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  • Analysis of coupled coplanar waveguides with V-shaped conductor backing using conformal-mapping method

    Page(s): 509 - 513
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    The V-shaped microshield coupled parallel coplanar waveguides, a new type of the coupled parallel coplanar waveguide (CP CPW), is proposed. Closed-form expressions are presented for calculating the quasistatic parameters of this coupled structure by using conformal-mapping techniques. The effect of the V-shaped conductor backing on the coupling between CPWs is also discussed. Comparisons are made between the present numerical results and the spectral-domain method results available in the literature for a conventional CP CPW. In addition, the coupling coefficient of the present coupled CPW is shown to be significantly lower than that of a coupled parallel CPW View full abstract»

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  • 45° linearly polarised post-wall waveguide-fed parallel-plate slot arrays

    Page(s): 515 - 519
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    A new configuration of three slots is proposed to radiate a 45° linearly polarised wave in post-wall waveguide-fed parallel plate slot arrays. The configuration consists of one radiating slot tilted to give the desired polarisation and two parallel λ/2-spaced reflection-cancelling slots without radiation in the boresight. A uniform aperture field is designed in a 76 GHz antenna. A good cross-polarisation level below -28 dB is achieved in the boresight. A gain of 29.8 dBi is obtained with 46.4% efficiency in a 5 cm square antenna View full abstract»

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  • Rain models for the prediction of fade durations at millimetre wavelengths

    Page(s): 431 - 436
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    Current ITU-R recommendations provide algorithms for estimating the exceedance statistics of rain-induced attenuation on terrestrial links. Another factor of interest, not currently covered by ITU-R recommendations, is the distribution of the durations of rain fades. This paper presents two algorithms for estimating this distribution. The distribution of the durations of rain events at different intensities is more fundamental than distributions of link fades. An expression for the average number of events per year of rain intensity greater than a given threshold has been developed from rain duration data gathered in the South East UK over three years. A method is presented for converting the distribution of rain durations into the distribution of link rain fade durations. The predicted distribution of rain fades is compared to 3 years' attenuation data on a 38 GHz, 9 km, terrestrial link. The second algorithm exploits features of the spatial and temporal power spectrum of rain rate predicted by models of turbulence. A method is presented for simulating rain rate, sampled in time and space, with the predicted power spectrum and the desired rain rate exceedance distribution. Rain duration distributions are derived from simulated data and compared to experimental results View full abstract»

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  • Subject Index

    Page(s): 530 - 532
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    First Page of the Article
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  • Broadband planar monopole antenna

    Page(s): 526 - 528
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    A novel kind of planar monopole antenna is experimentally presented for broadband applications. A square planar radiator is electromagnetically coupled with a probe-fed strip. The medium between the radiator and the strip is a thin dielectric slab. The parametrical effects on the bandwidth have also been examined experimentally. The proposed antenna is demonstrated to have an impedance bandwidth of 60% for a VSWR=1.5 and stable radiation patterns across the passband View full abstract»

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  • Behaviour of superresolution direction finding algorithms for HF signals propagating through the high latitude ionosphere

    Page(s): 469 - 478
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (948 KB)  

    The performance of high frequency direction finding systems is known to be related to the frequency of operation and to the propagation mode content of the incoming signal, which is dependent upon the electron density distribution in the ionosphere. In addition to large scale tilts that cause gross deviations of the signal from the great circle direction, irregularities in the ionospheric electron density distribution may be considered as providing a rough reflecting surface for HF radio waves. As a result, signals associated with each propagation mode arrive at the receiver over a range of angles in both azimuth and elevation. Measurements are presented of HF radio signals received over a disturbed, high latitude path. Multiple, closely separated traces were apparent in the time history of the calculated bearings, the precise nature of which depends upon the array geometry and algorithm employed. The presence of these multiple traces is attributed to the behaviour of the DF algorithms when the signals arrive over a range of azimuth and elevation angles due to the rough reflector nature of this disturbed region of the ionosphere View full abstract»

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  • Time-domain simulation and characterisation of TEM horns using a normalised impulse response

    Page(s): 463 - 468
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    A common way of describing antennas in the time domain is by means of their impulse response. When the time-domain antenna equations are expressed in terms of the normalised impulse response (normalised IR), they become very simple to use, because all frequency-dependent antenna characteristics are included in the normalised IR. This paper describes a method for measuring the normalised IR experimentally, using a vector network analyser. The normalised IRs of different air and dielectric-filled TEM horn antennas are compared and discussed. The normalised IR is found to be a powerful tool for simulating antenna behaviour directly in the time domain. Thanks to the introduction of the virtual source, (i.e. an apparent point in the antenna from which the radiated field degrades by a factor 1/r), the time-domain antenna equations can also be used near the TEM horns, although still in the far field of the antenna. Some examples of time-domain simulations and system modelling using the normalised IR are presented. In each example, the simulations are compared with measured data View full abstract»

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