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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 2 • Date Apr 2004

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Displaying Results 1 - 14 of 14
  • Three-dimensional monopole antenna for direction of arrival determination

    Page(s): 121 - 126
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (339 KB)  

    The design and realisation of a dodecahedral antenna is investigated. The three-dimensional design with pentagonally shaped faces is described. The simulation program NEC2 (numerical electromagnetics code, version 2) is used to simulate the proposed design. This dodecahedral antenna configuration is optimised for all pertinent parameters, according to the coupling constraints and the radiation pattern. The coupling values and the radiation pattern are measured and compared with the simulated values. View full abstract»

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  • Principle and results of microwave diversity imaging of conducting objects using multisource illumination

    Page(s): 149 - 155
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (330 KB)  

    The principle, measurement system, calibration and experimental results of microwave diversity imaging of conducting objects in a multisource illumination arrangement are presented. Theoretical analysis is developed under multiple plane wave illumination and physical optics approximation. The measurement system and calibration procedure are implemented based on plane wave spectrum analysis. Reconstructed images of four different types of conducting objects, including continuous shape and discrete line objects, measured in the frequency range 7.5-12.5 GHz, are shown in good agreement with the scattering object geometries. The experimental results demonstrate that the developed microwave imaging system is an effective approach to yield microwave images of scattering objects with a wide aspect angle. View full abstract»

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  • Two-pattern linear array antenna: synthesis and analysis of tolerance

    Page(s): 127 - 130
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (270 KB)  

    A 19-element linear array was synthesised that can be switched between narrow-beam and broad-beam patterns with stringent sidelobe level and roll-off requirements using only eight-bit phase shifters. The sensitivity of its performance to errors in element position, excitation phase or amplitude was analysed. Results obtained using simulated annealing and a genetic algorithm for optimisation were very similar, and consumed very similar amounts of computer time. View full abstract»

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  • Modelling of a microstrip antenna on a finite ground plane using the expansion wave concept and the aperture integral equation formulation

    Page(s): 109 - 114
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (383 KB)  

    A microstrip antenna located on a finite ground plane has been analysed. The calculation is split into several steps. In the first step, the microstrip antenna on an infinite ground plane is analysed using the moment method. In the next step, the radiation pattern is calculated using ray tracing techniques. The fields in the layered structure are expanded into a finite number of expansion waves. The expansion waves propagate up to the edges of the finite ground plane, where they diffract. Diffraction coefficients for these waves are calculated using a formulation based on the aperture integral equation. The experimental results are in good agreement with the proposed model. View full abstract»

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  • Tunable waveguide filter with bow-tie metallic posts

    Page(s): 156 - 160
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (776 KB)  

    A waveguide filter employing several conducting cylindrical posts that have a bow-tie shape is synthesised and investigated. The boundary problem of the bow-tie post that is used as a filter section is analysed using an iterative scattering procedure and the orthogonal expansion method. The procedure allows the fast calculation of the modal scattering matrix of the circuit. The shape of the investigated structure, its dimensions, rotation and location in the waveguide junction introduce additional degrees of freedom which can be used to tune the filter so as to obtain the required frequency response characteristic. The rotation of the posts enables the resonant frequency to be slightly changed, which helps to correct any inaccuracies created during fabrication. A good agreement is obtained between the results of this method and those obtained from FDTD simulations and measurements. View full abstract»

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  • Analysis and design of class-B dual fed distributed power amplifiers

    Page(s): 104 - 108
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    The analysis of, and derivation of design equations for, a class-B balanced single-ended dual-fed distributed amplifier is presented. This approach allows efficient combining of FET output power without multi-way power combiners, has a good port match, and is easy to design as the gate and drain transmission lines are uniform. The design method ensures that all FETs are optimally used and the efficiency is comparable to that of a conventional single-transistor class-B power amplifier using the same FET type. The design method was applied to a class-B four-FET balanced single-ended dual-fed distributed amplifier designed to operate at 1.8 GHz. Large-signal measurements revealed 8% downward shift of the centre frequency. The measured output power and drain efficiency was consistent with the simulations. The efficiency of the amplifier was comparable to a conventional single-transistor class-B power amplifier using the same type of FET. View full abstract»

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  • Simple satellite-tracking stacked patch array antenna for mobile communications experiments aiming at ETS-VIII applications

    Page(s): 173 - 179
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    The Japan Aerospace Exploration Agency (JAXA) plans to launch a geostationary satellite called Engineering Test Satellite-VIII (ETS-VIII) in 2004. In the paper, the feasibility of reaching a relatively high value of gain at low elevation angle by use of a simple left-handed circularly polarised four-element stacked patch array antenna for mobile satellite communications in the S-band frequency aiming at ETS-VIII applications is discussed. The characteristics of this antenna are confirmed by two numerical methods (the method of moments and the finite element method) and by measurements. Furthermore, the influence of the finite size of the ground plane was analysed using of the finite element method. Both numerical analyses and measurements are presented. In addition, the operation of beam-switching is experimentally confirmed. It is revealed that, by properly feeding the patches constituting the antenna, for an elevation El=48° (θ=42°) in Tokyo, four beams are created in the conical-cut direction at azimuth Az=6°, 96°, 190°, and 276°. The gain reached more than 6.5 dBic on the whole azimuthal range, with an axial ratio less than 3 dB. View full abstract»

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  • Z-domain formulations of equal-length coupled-serial-shunted lines and their applications to filters

    Page(s): 97 - 103
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (373 KB)  

    A new configuration consisting of parallel coupled lines (PCLs) and nonuniform transmission lines (NTLs) is employed to study lowpass and bandstop filters. In particular, each section of both PCLs and NTLs has the same electrical length. As a result, the transfer functions of such networks are formulated in the Z-domain. An optimisation algorithm is used to tune the characteristic impedances of coupled-serial-shunted lines so that the transfer functions of signal lines are close to the system functions of ideal prototype filters. A Butterworth bandstop filter and two equal-ripple lowpass filters are realised in the form of microstrip lines and their frequency responses are measured to validate this novel method. View full abstract»

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  • Effects of the ground and the human body on the performance of a handset antenna

    Page(s): 131 - 134
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (365 KB)  

    The effects of the whole human body and the ground on the performance of a handset antenna are studied through EM simulation. The complexity of the radiation pattern of a handset antenna is illustrated, and the specific absorption rate (SAR) level inside the head is increased using a more realistic model which includes the partial ground, the whole body and the hand. Four human models of different heights are compared, showing that the changing of model height has an effect on the SAR inside the human body and causes a slight variation of the far-field pattern. However, the different property of the ground plane has a more noticeable effect on the SAR and the far-field patterns. View full abstract»

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  • Stacked microstrip antenna for wideband and high gain

    Page(s): 143 - 148
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (459 KB)  

    The behaviour mechanism of the stacked antenna is synthetically clarified for the first time by investigating the results calculated using the FDTD method. The stacked microstrip antenna has particular characteristics, such as a high gain or a wide bandwidth. When the size of the parasitic patch, is nearly equal to the fed patch and the distance between the fed patch and the parasitic patch is approximately 0.1 wavelength, the bandwidth is increased. When that distance is approximately half a wavelength, the gain enhancement is obtained. The wide bandwidth and the gain enhancement are considered synthetically by the detailed investigation of calculated results including the near-field distributions. It is shown that the wide bandwidth and the gain enhancement are caused by a two-frequency resonance and leaky resonant cavity formation, respectively. The calculated input impedance and radiation patterns agree well with the experimental values. View full abstract»

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  • Design of an optimised 2.5 GHz CMOS differential LC oscillator

    Page(s): 167 - 172
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (295 KB)  

    An analytic method to predict the oscillation amplitude and supply current values of a differential CMOS oscillator. A simplified model to predict the phase noise performance for this type of oscillator is developed. Using this method, it becomes possible to design an optimised oscillator in terms of a minimum phase noise and low power consumption. The validity of the method has been verified by designing a LC CMOS oscillator using 0.25 μm CMOS technology. The predictions are in good agreement with simulation results over a wide range of the supply voltage. View full abstract»

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  • Impact of buildings on the performance of MEO satellite mobile communication systems for low bit rate applications

    Page(s): 161 - 166
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    Mobile communications for low bit rate applications via midearth orbit (MEO) satellites are considered. Owing to multipath interference, fading of the received signal appears in low bit rate applications. The received signal levels, at the mobile in the presence of buildings, are calculated using the uniform theory of diffraction (UTD) for horizontal and vertical polarisations. Buildings are considered in both residential and moderate urban environments. For easy reference, explicit mathematical representations with illustrations of all significant ray contributions are given. Furthermore, the signal levels data, extracted from the electromagnetics computations, are used to evaluate communication system performance in terms of bit error rate and depolarisation of the received signal. Moreover, computed results are in agreement with actual measured data. View full abstract»

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  • Modelling of finite size vane-loaded helical slow-wave structures

    Page(s): 135 - 142
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (317 KB)  

    The vane-loaded helical slow-wave structure is widely used in high power, broadband travelling wave tubes (TWTs). Taking the radial thickness of the helix into account, the finite size vane model is suggested for vane-loaded helical slow-wave structures (SWS). The expressions of the dispersion equations, interaction impedance and attenuation constant of this model are derived. Two vane-loaded helical slow-wave structures of the travelling wave tube (TWT) are calculated by the derived equations. The calculated results are compared with the results of measurement and the calculated results of the infinite number of vanes model (INV) that also considered the radial thickness of the helix. The influence on dispersion characteristics is analysed for the thickness of the helix and different centre angles of the vanes. It is interesting to find that the centre angle (2θ) of the vanes has a fixed value when the phase velocity is a minimum. View full abstract»

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  • A new wideband modelling technique for spiral inductors

    Page(s): 115 - 120
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (350 KB)  

    A new wideband modelling technique is presented, to exactly model the time-domain (TD) responses of microwave spiral inductors. This new method is suitable for modelling the spiral inductors used in switching-type microwave circuits, such as LC tank voltage-controlled oscillators (VCOs), or filters. The technique was developed based on applying an ultra-short impulse signal (30 ps) to the device. Furthermore, the layer-peeling technique (LPT) and hybrid equivalent circuits were used in the modelling process. Experiments were conducted to reveal the feasibility of the technique. Results show that the generated wideband models can be used to describe the TD responses of spiral inductors with a timescale down to picosecond order. View full abstract»

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