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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 1 • Date Feb 2004

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Displaying Results 1 - 16 of 16
  • High-frequency radio wave diffraction from singly curved, convex surfaces a heuristic approach

    Publication Year: 2004 , Page(s): 43 - 53
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (630 KB)  

    An alternate approach is presented for the prediction of induced surface currents on perfect electric conducting (PEC) circular cylinders of large radius by observation of the asymptotic behaviour of the Fock currents. The currents are separated in the fashion of the physical theory of diffraction in terms of a uniform or physical optics component and a nonuniform or diffraction component which is highly localised to the shadow boundary. The approach can be extended to that of a general convex surface by application of known methods such as incremental-length diffraction coefficients. The case of the 2D PEC circular cylinder at normal incidence is developed first and then extended to that of oblique incidence analytically. The resulting expressions for the induced current are algebraic and are shown to be highly accurate for cylinders having radii of curvature larger than a wavelength. Total near-fields generated by this macromodelled current are in good agreement with those of the exact solution everywhere. View full abstract»

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  • Compact dual concentric ring printed antennas

    Publication Year: 2004 , Page(s): 37 - 42
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (749 KB)  

    A novel small printed antenna structure is prepared that, depending on the excitation orientation, can yield low crosspolarised field generation or good quality circular polarisation (CP). The configuration consists of concentric shorted annular ring printed antennas. Each ring is loaded by a localised dielectric layer and can therefore be optimised to operate at a certain frequency, thereby enhancing the overall bandwidth of the antenna. Probe-fed configurations are investigated such that the appropriate feed network can be located below the radiating elements, thus minimising the footprint of the entire antenna. For a balanced feed configuration, the overall size of the antenna (including the ground plane and feed network) was 5×7×1.3 cm for operation centred at 2.1 GHz. The 10 dB return loss bandwidth was approximately 11.5% and the crosspolarisation levels were more than 15 dB below the co-polar patterns for both principle planes. The CP version was of similar size with an impedance bandwidth of 12.4% and a 3 dB axial ratio bandwidth of 16%. View full abstract»

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  • Micromachined 300 GHz high Q resonant slot frequency selective surface filter

    Publication Year: 2004 , Page(s): 31 - 36
    Cited by:  Papers (13)  |  Patents (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    The design of a low loss quasi-optical beam splitter which is required to provide efficient diplexing of the bands 316.5-325.5 GHz and 349.5-358.5 GHz is presented. To minimise the filter insertion loss, the chosen architecture is a three-layer freestanding array of dipole slot elements. Floquet modal analysis and finite element method computer models are used to establish the geometry of the periodic structure and to predict its spectral response. Two different micromachining approaches have been employed to fabricate close packed arrays of 460 μm long elements in the screens that form the basic building block of the 30 mm diameter multilayer frequency selective surface. Comparisons between simulated and measured transmission coefficients for the individual dichroic surfaces are used to determine the accuracy of the computer models and to confirm the suitability of the fabrication methods. View full abstract»

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  • Analysis of dielectric loaded cubical cavity for triple-mode filter design

    Publication Year: 2004 , Page(s): 61 - 66
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (329 KB)  

    Commercially available 3-D transmission-line matrix method (TLM) software is employed to analyse a cubical cavity resonator loaded concentrically with a cubical dielectric of dielectric constant 37. For the first time, a useful mode chart for seven degenerate modes of the resonator is generated from the computed results of the resonant frequencies. As an application of the mode chart, a triple-mode bandpass Cheb~yshev filter is designed and fabricated using the resonator operating in TM111 mode. The unexpected asymmetry and the transmission zero in the response of the filter are attributed to the coupling between the input and output. When the coupling is characterised, close agreement between the simulated and measured performance of the filter is obtained. View full abstract»

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  • Fields in an FSS screened enclosure

    Publication Year: 2004 , Page(s): 77 - 80
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (321 KB)  

    Efficient use of the radio spectrum demands frequency reuse in increasingly localised regions in the built environment. It may be possible to employ frequency selective screens (FSS) to provide electromagnetic separation of adjacent areas. To study the signal isolation capability of these structures, field distributions have been measured inside a small enclosure with one wall clad with FSS which had very broad reflection bands. The FSS arrays were densely packed linear dipoles, on rigid and on flexible film substrates. Measurements were made at 2.45, 5.0 and 8.1 GHz. The spatial isolation was very significant: the signal attenuation averaged over the enclosed volume was 20 to 30 dB, but the field amplitudes and insertion losses were position dependent. The variations were characterised by Rayleigh statistics, except for the highest field levels. There, the observed probability density functions (pdfs) often deviated from the Rayleigh form, possibly owing to signal leakage around the FSS edges, especially with thin film substrates, indicating problems in applying it satisfactorily to existing surfaces. In an existing building, it might therefore be acceptable to replace only part of a wall with frequency selective material, metallically screening the remainder. In new buildings, frequency selectivity would be built in, with electromagnetic performance addressed at the design stage. View full abstract»

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  • Insertion phase and phase slope parameter of microwave junction circulators

    Publication Year: 2004 , Page(s): 54 - 60
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (321 KB)  

    An important quantity in the description of any junction circulator is its insertion phase over the frequency response of the specification. This paper provides some experimental data on this quantity for a degree-1 stripline device using an irregular hexagonal resonator for a number of different shape angles. In addition, a phase slope parameter is defined and related to the susceptance slope parameter of the gyrator circuit. The group delay of the junction is also deduced. A relationship between the phase angles of the reflection and transmission scattering parameters is separately deduced and verified. View full abstract»

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  • Neural model for coplanar waveguide sandwiched between two dielectric substrates

    Publication Year: 2004 , Page(s): 7 - 12
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (295 KB)  

    A new approach based on artificial neural networks is successfully introduced to determine the characteristic parameters of a coplanar waveguide (CPW) sandwiched between two dielectric substrates. Neural models were trained with eight different learning algorithms to obtain better performance and faster convergence with a simpler structure. The best results were obtained from the models trained with Levenberg-Marquardt and Bayesian regulation learning algorithms. The results obtained from the neural model are in very good agreement with theoretical and experimental results available in the literature. The presented neural model is valid for both conventional and sandwiched CPWs. View full abstract»

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  • 5.5 GHz 802.11a 0.18 μm CMOS pre-power amplifier core with on-chip linearisation

    Publication Year: 2004 , Page(s): 26 - 30
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (275 KB)  

    This paper details the development of a 0.18 μm CMOS based amplifier core for the 802.11a standard. The amplifier core operates at 5.5 GHz and includes an adaptive biasing scheme to linearise the amplifier under high input power. Measurement results confirm that this linearisation scheme extends the 1 dB compression point by 4 dB over an unlinearised amplifier core. The supply voltage and bias current for the linearised amplifier are 1.8 V and 5.5 mA respectively, delivering 2 dBm into a 50 Ω load when operated at the 1 dB compression point of -3.3 dBm. All the components of the linearisation scheme are implemented on-chip enabling maintenance of a single chip transceiver solution. View full abstract»

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  • Low cost architecture of direct conversion digital receiver

    Publication Year: 2004 , Page(s): 71 - 76
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (303 KB)  

    The paper presents a low-cost architecture for a direct conversion digital receiver that uses six-port technology. An experimental prototype has been constructed and tested. Analogue carrier recovery and decision circuits are investigated as a means to provide future system integration and high data rate capacity. The designed receiver is operated at an ISM frequency of 2.45 GHz and uses a QPSK modulation format. Results on data rate limitations are given for QPSK signals up to 52 Mb/s. Test results related to adjacent channel, co-channel and CW interferences are presented for a data rate of 40 Mb/s. Phase offset between carrier and reference signals, along with carrier frequency deviation performances, are also presented for a rate of 40 Mb/s. A frequency hopping spread spectrum technique is discussed on the basis of the proposed architecture. View full abstract»

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  • Application of GPS phase delay measurements in radio science and atmospheric studies

    Publication Year: 2004 , Page(s): 1 - 6
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (393 KB)  

    Observation of phase delay from GPS satellites, combined with advanced software processing, allows the quantity of water vapour in the atmosphere to be continuously monitored. This paper reports on four years of measurements and analytical studies directed towards establishing the accuracy of the technique. It also examines the role of horizontal gradients of wet delay in determining accuracy, and evaluates the potential of extending the technique to measurement of radio refractivity gradients using a tomographic inversion technique. View full abstract»

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  • Fast Gaussian beam based synthesis of shaped reflector antennas for contoured beam applications

    Publication Year: 2004 , Page(s): 13 - 20
    Cited by:  Papers (15)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (413 KB)  

    A relatively efficient procedure is proposed, which combines a novel Gaussian beam (GB) approach for fast computation of reflector antenna radiation patterns with an iterative optimisation technique, to synthesise a shaped reflector surface for contoured beam applications. The GB approach employs relatively few Gaussian beams as electromagnetic basis functions to represent the field radiated by the feed; each of these GBs launched from the feed then reflects and diffracts from the reflector surface to yield the radiation field produced by the reflector antenna. Closed form expressions are used for calculating this GB reflection and diffraction; consequently, the reflector radiation pattern, which needs to be computed repeatedly in any iterative synthesis procedure, can be obtained in an extremely rapid fashion via the present GB method. In contrast, the conventional procedure, which requires a numerical integration of the currents induced by the feed over the large reflector surface to calculate the radiation field, is far less efficient and lacks physical insight. Furthermore, the GB approach is used in conjunction with a fast and convergent synthesis procedure which is developed via a modification of the usual steepest descent method (SDM) to ensure a more global reflector shaping optimisation and smooth contoured beam patterns. Numerical results are presented to validate the proposed approach. View full abstract»

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  • Application of the Z-transform technique to modelling linear lumped loads in the FDTD

    Publication Year: 2004 , Page(s): 67 - 70
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (266 KB)  

    A Z-transform technique derives an updating algorithm for the finite-difference time-domain equations dealing with a lumped load. Such a load can be used to simulate equivalent circuits of terminations for microstrip structures, including IC or digital devices. The advantages of the Z-transform technique are pointed out and numerical results validating the method included. View full abstract»

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  • Consistent and reliable MESFET parasitic capacitance extraction method

    Publication Year: 2004 , Page(s): 81 - 84
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (323 KB)  

    An improved model is proposed to evaluate the parasitic capacitances of GaAs MESFET transistors from the cold-FET S-parameter. Inherent in most conventional parasitic de-embedding methods, the extraction result for Cpd varies drastically with Vgs under cold-FET measurement, and this is in great contradiction with the normally adopted bias-independent Cpd assumption in active device modelling. An improved model is proposed to tackle this problem. Model parameters can thus be uniquely determined by using only two sets of cold-FET S-parameters under different Vgs biasing conditions. The resulting capacitance value, Cpd, is found to be independent of Vgs when Vgsp. View full abstract»

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  • Analysis of waveguide-fed dielectric resonator antenna using a hybrid finite element method/moment method

    Publication Year: 2004 , Page(s): 91 - 95
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (263 KB)  

    A hybrid finite-element method/moment method (FEM/MM) is used to analyse a waveguide-fed dielectric resonator antenna with a dielectric constant εra. Green's function for the dielectric hemisphere, rather than the free-space Green's function used in conventional hybrid FEM/MM, is employed to establish the integral equation. To simplify the analysis, two different kinds of basis function are used to discretise the slot field in the FEM and MM, respectively. The accuracy of the hybrid FEM/MM is confirmed by measured data for the special case of one waveguide-fed slot radiator, i.e., εra=1. The numerical results demonstrate that the energy coupling can be greatly improved by placing a dielectric resonator inside the waveguide. View full abstract»

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  • Frequency- and time-domain expressions for transfer functions and impulse responses related to the waveguide propagation

    Publication Year: 2004 , Page(s): 21 - 25
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (310 KB)  

    Analytic expressions for frequency dependent transfer functions and their time dependent inverse Fourier transforms, which represent the forward transmission and the multiple reflection in a waveguide section, are derived. Making use of these analytic expressions, the multiple reflection of a narrowband Gaussian pulse in a waveguide section with different load side and generator side terminations is graphically demonstrated. This shows that early reflections are in general less dispersed than later ones. For electrically long waveguide sections operating high enough above their cutoff frequency, the different reflections are temporally distinguishable. However, in both electrically short and evanescent waveguide sections, the temporal overlapping between the different reflections is so strong that their individual identification is not possible. It is also shown that recently reported superluminal propagation of pulse peaks can take place in electrically short evanescent waveguide sections only. Increasing the waveguide length beyond a certain limit destroys such a superluminality. View full abstract»

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  • Design and experimental investigation of a wideband polarisation filter

    Publication Year: 2004 , Page(s): 85 - 90
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (393 KB)  

    The design of a wideband polarisation filter composed of a two-dimensional perforated flat conducting plate is presented. The experimental procedure used to verify the validity of the design algorithm is explained. The filter is used to suppress the cross-polarisation of both a horn antenna and a large array of dielectric resonators. Effective suppression of the cross-polarisation (in the order of 15 dB) was observed for both cases. The insertion loss is in the order of 2 dB in the case of the horn, and 0.6 dB in the case of the array antenna. The 10 dB return loss bandwidth is measured to be 15%. It is demonstrated that the filter can be installed in close proximity to the antenna radiating aperture without any significant degradation in its insertion loss or polarisation isolation performance. View full abstract»

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