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Microwaves, Antennas & Propagation, IET

Issue 2 • Date April 2007

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Displaying Results 1 - 25 of 43
  • 2.4 GHz Class-E power amplifier with transmission-line harmonic terminations

    Page(s): 267 - 272
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (730 KB)  

    The design procedure, fabrication and measurement of a Class-E power amplifier with excellent second- and third-harmonic suppression levels are presented. A simplified design technique offering compact physical layout is proposed. With a 1.2 mm gate-width GaAs MESFET as a switching device, the amplifier is capable of delivering 19.2 dBm output power at 2.41 GHz, achieves peak PAE of 60% and drain efficiency of 69%, and exhibits 9 dB power gain when operated from a 3 V DC supply voltage. When compared to the classical Class-E two-harmonic termination amplifier, the Class-E amplifier employing three-harmonic terminations has more than 10% higher drain efficiency and 23 dB better third-harmonic suppression level. Experimental results are presented and good agreement with simulation is obtained. Further, to verify the practical implementation in communication systems, the Bluetooth-standard GFSK modulated signal is applied to both two- and three-harmonic amplifiers. The measured RMS FSK deviation error and RMS magnitude error were, for the three-harmonic case, 1.01 kHz and 0.122%, respectively, and, for the two-harmonic case, 1.09 kHz and 0.133% View full abstract»

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  • Application of dual-mode filter techniques to the broadband matching of microstrip patch antennas

    Page(s): 273 - 276
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (266 KB)  

    Structures such as square or circular microstrip patch antennas may support two orthogonal resonant modes. The paper presents a new method of utilising the dual-mode property to increase the bandwidth of microstrip antennas. The input impedance of such a dual-mode antenna may be represented as a second-order ladder network of coupled resonators, where each resonator is coupled to a load resistor. A theoretical method for evaluating the coupling values in the network is presented, enabling the bandwidth of a dual-mode antenna to be maximised. A theoretical bandwidth improvement of up to 3:1 is achieved when compared to a single-mode antenna. This is confirmed with an experimental dual-mode circular microstrip patch antenna View full abstract»

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  • Wideband microstrip patch antenna design for breast cancer tumour detection

    Page(s): 277 - 281
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (422 KB)  

    A patch antenna is presented which has been designed to radiate frequencies in the range 4-9.5 GHz into human breast tissue. The antenna is shown by means of previously unpublished simulation and practical measurements to possess a wide input bandwidth, radiation patterns that remain largely consistent over the band of interest and a good front-to-back ratio. Consideration is also given to the antenna's ability to radiate a pulse, and in this respect it is also found to be suitable for the proposed application View full abstract»

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  • Identification of melting snow using data from dual-frequency microwave links

    Page(s): 282 - 288
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (263 KB)  

    Using data from a dual-frequency microwave link it is possible to identify periods of transmission affected by melting snow. This is because, in melting snow, the relation between attenuation and the amount of precipitation is nonlinear and depends on the frequency in a way that differs from the dependence in rain. This implies that the ratio of the single-frequency estimates of apparent rainfall rates will be different in melting snow from those obtained in rain. This forms the basis of an algorithm that is shown to work well for a 23-km dual-frequency (12.8 GHz/17.6 GHz) link near Bolton in north west England and for a 29-km dual-frequency (10.5 GHz/17.5 GHz) link near Essen in Germany. The effectiveness of the algorithm is judged by noting the recorded temperatures in those minutes identified by the algorithm as being affected by melting snow View full abstract»

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  • 'Surrounded-element' approach for the simulation of reflectarray radiating cells

    Page(s): 289 - 293
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    A new approach to analyse reflectarray cells is presented, which allows mutual coupling effects to be realistically accounted for by simulating each radiating cell with its actual neighbouring cells, either identical or not. The proposed approach is compared to more conventional approaches that consider either an infinite periodic environment or that neglect coupling effects. A comparison between reflectarray measurements and simulations leads to good agreement using the proposed approach View full abstract»

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  • Low profile wideband embedded dielectric resonator

    Page(s): 294 - 298
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (466 KB)  

    A dielectric resonator antenna (DRA) made of high dielectric constant substrate is studied. Embedding a higher dielectric disk inside the substrate disk enhances the bandwidth. A narrow slot excites the DRA. Embedded DRAs of different shapes are considered for wideband applications. An eye-shaped DRA made with a circular dielectric resonator disk embedded in an elliptical-shaped `host' DRA is found to have an impedance bandwidth of 28% with stable broadside patterns View full abstract»

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  • Wideband stair-shaped dielectric resonator antennas

    Page(s): 299 - 305
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    Wideband stair-shaped dielectric resonator antenna (DRAs) are designed. Wide bandwidths are achieved with one-step or two-steps stair geometries. Cricular and square cross-sections are discussed with two different excitation methods: coaxial feed and aperture coupled. The DRAs are designed in the X-band. An impedance bandwidth (S11<-10 dB) of 54.3% is obtained with the two-steps stair-shaped DRA. The antennas have broadside radiation patterns in all cases across the matching band. In addition, embedding the base into another dielectric material reduces the size of the stair-shaped DRA. Simulation results are compared with measurements and reasonable agreement is obtained View full abstract»

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  • On the two dimension applications of high-order vector finite elements to the study of electromagnetic resonance

    Page(s): 306 - 313
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (763 KB)  

    A set of hybrid vector-scalar finite elements for curved-triangle meshes is developed. These elements are applied to the study of electromagnetic resonance problems in which the variation in the field components along one coordinate is known in advance. The field component along this coordinate is modelled with polynomials of degree q. The other two field components are modelled with two dimension vector edge elements containing all irrotational functions up to polynomial degree m. Spurious modes are avoided only when q=m+1. The performance of these elements to order 4 is explored by applying them to some waveguides and axisymmetric cavities containing sharp edges, curved boundaries and/or uniaxially anisotropic materials View full abstract»

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  • Frequency-selective surfaces for GPS and DCS1800 mobile communication. 1. Quad-layer and single-layer FSS design

    Page(s): 314 - 321
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (893 KB)  

    In the paper, frequency selective surfaces (FSS) composed of quad-layer FSS with staggered tuning are designed, to allow signals to pass through at the frequency range of the global positioning system (GPS) cum DCS1800 mobile communications operation, while rejecting signals at the higher frequencies. The FSS is analysed by visualising the transformation of the admittance locus on the Smith chart, on subsequent additions of material layers to the multilayer stack-up. In addition, a single-layer FSS with convoluted loop elements (with interelement spacing of 6.08 cm) is designed to yield a similar band-pass response at 1.575 GHz (wavelength lambda=19.05 cm). This relatively close spacing is achieved by convoluting the conventional 1lambda square-loop element at its four corners. The convoluted segment provides a short-circuit response when the segment length is lambda/4 long. This provides a reflection to the electromagnetic energy at the selected band-stop frequency range. The performance of the quad-layer and single-layer FSS are compared View full abstract»

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  • Frequency-selective surfaces for GPS and DCS1800 mobile communication. 2. Integration with antenna for scattering reduction

    Page(s): 322 - 327
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (618 KB)  

    The paper describes a novel attempt to integrate a quad-layer frequency selective surface (FSS) with a circularly polarised Maltese-cross antenna for the global positioning system and DCS 1800 mobile communications. The effect of integrating the FSS with the antenna is presented for both in-band (1.5-1.9 GHz) and out-of-band (8.5-9.7 GHz) operation. For out-of-band operation, a reduction of antenna scattering is observed with the integration of the FSS. A comparison of the total scattering of the antenna with that calculated for the finite ground plate is included. The seemingly contradictory two-fold impact of the FSS performance on the link budget equation is illustrated View full abstract»

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  • Accurate and efficient method for analysis of scattering from dielectric shell of rotation by least-squares algorithm

    Page(s): 328 - 334
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    A novel and robust method for analysis of scattering from dielectric shells of rotation is presented. The calculation was done by using an E-fieldH-field integral equation plus the method of least-squares rather than using the combined field integral equation. The use of the E-fieldH-field integral equation defined just inside or outside the surfaces makes the source points and the field points slightly separated to avoid the singularity met by PMCHW or the Muller formulation. The least-squares method ensures the r.m.s error minimum on the boundary independent of the permittivity to overcome the inaccuracy existing in the PMCHW or Muller formulation, when permittivity is too small or too large. The calculated results show that this method possesses the advantages of good accuracy and convergence View full abstract»

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  • Spectral domain analysis of frequency-selective surfaces on biaxially anisotropic substrate

    Page(s): 335 - 340
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (339 KB)  

    A full-wave analysis is presented of frequency-selective surfaces (FSSs) on a biaxially anisotropic substrate. The integral equations are first transformed into the spectral domain ones through the use of the Floquet theorem and then solved by the method of moments. Since the wave immittance of the biaxially anisotropic substrate is derived in a closed form, the resulting impedance matrix can be obtained conveniently by using the spectral domain immittance approach (SDI). The validity of theoretical formulations is verified by illustrative numerical results and their comparisons. The obtained results are compared with the existing data and other analyses and good agreements are observed. The effects of biaxially anisotropy on the FSS have been studied and discussed View full abstract»

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  • Nonreciprocal left-handed transmission characteristics of microstriplines on ferrite substrate

    Page(s): 349 - 354
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (187 KB)  

    In this paper, a nonreciprocal left-handed transmission line has been investigated. It is composed of a normally magnetised ferrite microstripline periodically loaded with lumped capacitances and inductive stubs. Based on the simple equivalent circuit model for a predominant edge guided mode, the dispersion relation of the ferrite left-handed transmission line has been estimated, providing the backward wave characteristic in the positive and negative permeability frequency regions. With the aid of the finite element method, it is confirmed that specific three-dimensional structures do show left-handed characteristics as well as the nonreciprocity. Nonreciprocal transmission characteristics with the isolation of more than 30 dB are obtained numerically and demonstrated experimentally in the positive and negative permeability frequency regions, for the edge guided modes. It is explained that the nonreciprocity of the ferrite left-handed transmission line is caused by the leaky wave phenomenon from the microstrip to the ferrite substrate View full abstract»

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  • Statistical modelling of building transmission in a cellular urban environment

    Page(s): 355 - 362
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (417 KB)  

    Channel sounding measurements have been reported which show that transmission through buildings can be important for microcellular coverage planning. A theoretical-statistical model for propagation through a building, or row of buildings, is proposed in the paper. Expressions for the mean and covariance of the channel transfer function are obtained and compared with measurements. The model exhibits good prediction accuracy for residential homes, while similar trends with the measurements for office blocks were obtained also View full abstract»

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  • Direct conversion receivers using multiport structures for software-defined radio systems

    Page(s): 363 - 372
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (770 KB)  

    An analytical assessment for multiport structures as direct conversion receivers is presented. A new direct-conversion receiver based on a novel five-port structure suitable for software-defined radio applications is proposed. The five-port architecture provides some advantages compared with previous architectures. Numerical and microwave simulations have been conducted to show its capabilities as a direct demodulator. The proposed five-port has been constructed and the measured results indicate that the five-port receiver introduced can be used effectively as a software-defined radio receiver View full abstract»

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  • Specific attenuation and depolarisation in rain from 2-dimensional video disdrometer data

    Page(s): 373 - 380
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (482 KB)  

    Data from 2-dimensional video disdrometers (2DVD) taken in different locations are used to derive the specific attenuation for horizontal and vertical polarisations at 20 GHz. The data include both drop-size distribution and their axis ratio distributions. T-matrix calculations using data over 1 min integration time show a power-law dependence on rain rate. The best-fit coefficients are compared with those given in the ITU-R Recommendation P. 838, both versions 2 and 3. Closest agreement is seen for vertical polarisation for version 2 and the largest discrepancies are seen for horizontal polarisation for version 3. The discrepancies are attributed to the different assumptions in the drop-size distributions, as well as the upper limit of integration for deriving the specific attenuation. The variation of the crosspolar discrimination (XPD) against copolar attenuation (CPA) is also examined. The 2DVD data are used to simulate a beacon experimental scenario at 20 GHz, the actual locations of the two instruments being different but climatically similar. Good agreement is seen with one year of beacon measurements, but the latter shows more spread in the variation, partly attributed to drop oscillations. Calculations also show that XPD-CPA variation is sensitive to the assumed drop shapes View full abstract»

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  • Treatment of arbitrarily-orientated multiwire bundles and terminated multiwire transmission lines in FDTD method

    Page(s): 381 - 387
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (764 KB)  

    The finite-difference time-domain (FDTD) method is extremely versatile and widely used but there still remain structures in which the method encounters serious difficulties. One such situation is the analysis of bundles of closely spaced wires which are not parallel to the FDTD mesh. Similar problems are encountered in the analysis of multiconductor transmission lines such as PCB tracks. Recent research has yielded methods for treating single wires, orientated at an angle to the FDTD mesh, and for treating multiwire bundles which are aligned with the mesh, but not for both situations at once. In the paper, an enhanced method is presented which allows the treatment of wire bundles, including those which are arbitrarily orientated with respect to the mesh and those which may also be terminated with lumped components. Results are provided that show the consistency and accuracy of the proposed technique View full abstract»

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  • A millimetre-wave bandpass filter-lens array

    Page(s): 388 - 395
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (663 KB)  

    A filter-lens array (FLA) is a planar array of bandpass integrated antenna-filter-antenna (AFA) elements which are stagger-tuned in the vicinity of a centre frequency, so as to provide the phase shift required for transforming spherical and planar wavefronts. Due to the filtering response of the AFA elements, FLA presents a bandpass gain and can act as a combination of a conventional lensarray and a filter. An FLA structure is demonstrated with f/D=1.25 and 8.2% bandwidth at 35 GHz. This FLA is composed of 137 AFA elements and fabricated on two three-inch glass wafers (epsir=4.45). A gain of 25.6 dBi and a total efficiency of 45% have been measured at 35 GHz. The Ka-band FLA shows a low-loss scanning performance for up to at least plusmn30deg in the H-plane and plusmn20deg in the E-plane View full abstract»

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  • Broadband low-profile antennas for wireless applications

    Page(s): 396 - 400
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (378 KB)  

    Two novel broadband low-profile antennas are developed for the mobile terminals of wireless applications. The first one is a quasiplanar antenna which has a height of 0.06lambda0, where lambda0 is the free-space wavelength at the centre frequency. The second one is a planar antenna which has a height of 0.056lambda0. It is demonstrated that the quasiplanar antenna can achieve a bandwidth for VSWR<2 of more than 45%, while the planar antenna realises a bandwidth of more than 40%. More importantly, over these bandwidths the broadband low-profile antennas have a quite constant omnidirectional radiation pattern with a peak gain of around 1 dBi. The antennas are designed on a commonly used RT/Duroid substrate; hence it is easy to integrate with RF front-end circuits. The antenna structures are described and the simulation and experimental results are presented View full abstract»

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  • Printed antennas with variable conductive ink layer thickness

    Page(s): 401 - 407
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (462 KB)  

    One of the complex tasks in mass production of RF electronics is printing the communication antenna using electrically conductive ink. For example, this is very common for radio- frequency identification (RFID) tags. Electrical properties of the ink are mostly determined by conductive (e.g. silver) particles mixed into the ink solution and the way they `connect' in the cured ink. It is also desirable to minimise the amount of ink used per antenna, because high-conducting metals like silver used in the ink are rather expensive. Metal-based inks have limited conductivity, so the thicker the cured ink layer will be the better the antenna radiation efficiency can be achieved, but also the higher will be the costs. In the paper, the authors report on the investigations of the possibility of minimising the amount of ink used per antenna. This can be achieved by printing thicker ink layers, where antenna structures are known to have high current density. Two common antenna structures and a dedicated antenna for passive RFID are used in the investigation. The main result of the paper is that radiation efficiency depends primarily on the total amount of ink used for printing the antenna, rather than on the variations of the layer thickness within the antenna structure View full abstract»

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  • Dualband frequency-selective surfaces using substrate-integrated waveguide technology

    Page(s): 408 - 413
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (363 KB)  

    This paper proposes a dualband frequency-selective surface (FSS) based on substrate-integrated waveguide (SIW) technology. This novel dualband FSS is constructed using double square loop slots (DSLSs) and an SIW cavity. Its frequency performance is investigated by numerical simulation using the finite difference frequency domain (FDFD) method. Another dualband FSS, constructed using convoluted double square loop slots (CDSLSs) and an SIW cavity is also investigated in order to get close passband spacing. Simulation results show that these dualband FSSs have the advantages of higher selectivity and passband insensitivity to the incident angles and polarisations, compared with conventional multiband FSSs. Experiments are carried out to verify the simulated results, and the measured results show a promising performance of the proposed FSS View full abstract»

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  • Reconfigurable patch-antenna design for wideband wireless communication systems

    Page(s): 414 - 419
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (463 KB)  

    An effective design of a reconfigurable patch antenna, with a wide operational bandwidth for wireless communication and radar systems, is presented in this paper. The reconfigurable patch possesses an E-shaped structure and its operation frequency can be changed by integrated switches. The operational frequency of the antenna can cover an octave frequency range by utilising only two switch states. In state 1, the antenna operates from 9.2 GHz to 15.0 GHz and, in state 2, from 7.5 GHz to 10.7 GHz. Relative bandwidths of 48% and 35% are obtained in the two states, respectively View full abstract»

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  • Broadband-configurable bandstop-filter design employing a composite tuning mechanism

    Page(s): 420 - 426
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (355 KB)  

    A microwave bandstop-filter design is reported, which combines both continuous and discrete tuning using varactor and PIN diodes to achieve a two-octave tuning range. The useable passband for any given tuning point is limited, however, the composite tuning mechanism in the topology facilitates the separate tuning of the centre frequency and stopband to minimum-loss passband separation. A suitable and novel filter-synthesis procedure is developed, and the filter performance is verified through experimental results View full abstract»

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  • Improvement of performance of optically controlled microstrip phase shifters

    Page(s): 427 - 432
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (495 KB)  

    Two optically controlled phase shifters are proposed. The first structure is based on the microstrip ring resonator inserted between two gaps. Phase-shifting is performed by optically controlling the gaps capacitance. The structure has shown excellent characteristics, however the rejection rate is high. To minimise the reflected power, the second phase shifter, which is based on the rat race coupler, is proposed. In this case, the phase-shifting is performed by adding extra lengths to two gaps, judiciously placed along the microwave ports. The gaps act as short-circuits under sufficient illumination conditions. At 10 GHz, the structure provides a continuous variation of Deltaphi(S21) between 0 and 90deg, with Delta|S21| less than 5dB. On a 500 MHz band around 10 GHz, the phase variation is less than 5%. |S11| keeps <-20 dB within the experimental bandwidth 8.9-10.7 GHz. Both structures were fabricated on high-resistivity silicon substrate and the experimental results confirm the three-dimensional electromagnetic simulations View full abstract»

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