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Microwaves, Antennas & Propagation, IET

Issue 6 • Date September 2009

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Displaying Results 1 - 14 of 14
  • An approximated closed-form solution for inhomogeneous planar layers

    Page(s): 899 - 905
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (437 KB)  

    An approximated closed-form analytic solution is introduced for arbitrary inhomogeneous planar layers (IPLs). First, the differential equations of IPLs are written as a suitable matrix differential equation. Then, the matrix differential equation is solved to obtain the chain parameter matrix of IPLs. Afterwards, the electric and magnetic fields at any point and also the reflection and transmission coefficients are obtained using the chain parameter matrix. The validation of the introduced solution is studied finally. View full abstract»

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  • Dual antenna selection algorithms and feedback strategies with reduced complexity for multiple-input multiple-output systems

    Page(s): 906 - 916
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (570 KB)  

    A simple antenna selection strategy for multiple-input multiple-output wireless systems with partial feedback is presented. In the proposed scheme, both transmit and receive antenna selection are done at the receiver, significantly reducing feedback information. In addition, this scheme uses row/column probability density function for antenna selection to reduce computational complexity without performance degradation. Unlike other schemes, two different antenna selection algorithms are used in high and low signal-to-noise ratio regimes, respectively, achieving additional performance gain in comparison to the single antenna selection algorithm. Simulation results show that the proposed scheme nearly approaches the optimal closed-loop capacity (known as water-filling capacity) as random selection round for antenna selection increases. View full abstract»

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  • Single- and dual-passband microwave planar filters with coupled double-transmission-line resonators

    Page(s): 917 - 928
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    A type of planar double-transmission-line resonator, consisting of two open-ended half-wavelength transmission-line segments edge inter-coupled along their entire length, is proposed. This microwave resonator, because of the generation of double resonances, allows coupled-line bandpass filters with reduced longitudinal length to be implemented. This is the main contribution of this work. Furthermore, as an added feature of the aforementioned resonator, its two-line geometry makes it suitable for dual-band bandpass filter design. To prove the concept experimentally, two different examples of single- and one dual-passband microstrip filter prototypes within the 1-1.5 GHz range are synthesised, constructed and tested. The major advantages of these filter solutions are emphasised. A complementary section dealing with the analysis of the split-type double-transmission-line resonator is also reported. Here, as a result of this study, formulas for its exact design are provided for the first time. View full abstract»

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  • Design of monofilar and bifilar Archimedean spiral resonators for metamaterial applications

    Page(s): 929 - 935
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (427 KB)  

    Archimedean spiral resonators as the unit inclusion for a metamaterial structure is studied. These inclusions are very compact, which make them a good candidate for practical metamaterial applications. Equivalent circuit models and analytical design formulas are derived for monofilar and bifilar spiral resonators. The circuit parameters and resonance frequencies are directly predicted by the geometry of the spiral and dielectric substrate/resonator configuration. Numerical simulations on both bulk and planar designs show that the predicted resonance frequencies are accurate enough for a preliminary design. Finally, complementary spiral structures, that is, spiral-shaped apertures in the ground plane, are considered. Loading two transmission lines with a complementary monofilar and a complementary bifilar spiral resonator, two planar band rejection structures are built. Measured results for two prototypes present a good accuracy. View full abstract»

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  • Two-step preconditioning technique for hierarchical time-domain finite-element method

    Page(s): 936 - 942
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (333 KB)  

    A two-step factorised sparse approximation inverse and symmetric successive over relaxation preconditioned conjugate gradient (CG) algorithm is proposed to solve the large system of linear equations resulted from the hierarchical implicit time-domain finite-element method (TDFEM). Convergence properties and CPU time of the proposed algorithm are compared with those of other preconditioned CG schemes. Numerical results demonstrate that the present approach is efficient for solving the large sparse system from hierarchical implicit TDFEM. View full abstract»

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  • Design of 60 GHz millimetre-wave bandpass filter on bulk CMOS

    Page(s): 943 - 949
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (425 KB)  

    A 60 GHz integrated second-order bandpass filter using rectangular open-loop resonators was designed and fabricated on a 0.13 mum standard CMOS process. The size of the filter is 415.5 times 502.8 mum2.The designed filter has a pair of transmission zeros at finite frequencies in the stopband, exhibiting good selectivity. The measured filter with the grid ground plane has a flat passband and its 1 dB bandwidth is 9 GHz (59.5-68.5 GHz).The insertion loss is about 2.6 dB and the return loss is better than 8.5 dB across the passband. The effects of various ground configurations have been studied. The design was optimised with a new slotted ground plane, and its measurement shows a 1 dB bandwidth of 9 GHz (57 - 66 GHz). The insertion loss is about 1.5 dB and the return loss is better than 9.2 dB across the passband. The new optimised slotted ground provides better than 1 dB and 0.7 dB improvement to insertion and return loss, respectively. A very good agreement between the simulation and measurement results has been achieved for frequencies up to 110 GHz. Compared with other 60 GHz CMOS bandpass filters recently reported in the literature, this 60 GHz CMOS bandpass filter has achieved all of low- insertion loss, compact size and good selectivity in one design. The ground optimised design was also implemented as part of fully integrated 0.13 mum CMOS direct-conversion transmitter. View full abstract»

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  • Coupling matrix synthesis of cross-coupled microwave filters using a hybrid optimisation algorithm

    Page(s): 950 - 958
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (310 KB)  

    A hybrid optimisation algorithm that synthesises coupling matrices for cross-coupled microwave filters is presented. A binary encoded genetic algorithm is combined at regular intervals with a sequential quadratic programming local search method to form a hybrid, exploiting the speed of the local search, while maintaining diversity with the genetic algorithm. The genetic algorithm uses the stochastic uniform selection technique and a multiple point crossover operator. A compact, efficient cost function requiring only the determinant and a cofactor of the coupling matrix is used as the basis of the optimisation algorithm. Optimisation algorithms simplify the process of synthesising coupling matrices, compared with analytical synthesis. However, algorithms that use only local search methods cannot be guaranteed to find a global minimum. This hybrid method aims to extend the range of coupling matrices that can be synthesised by optimisation, while maintaining the speed of search. A coupling matrix for a tenth order coupling matrix for a dual band symmetric filter and a seventh order asymmetric filter are synthesised to verify the method. View full abstract»

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  • Application of gain-bandwidth bounds on loaded dipoles

    Page(s): 959 - 966
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    Physical limitations based only on antenna volume, form factor and material parameters are applied to electrically small antennas in the form of single dipoles. The upper bound on the gain-bandwidth product is solely determined by the polarisability matrix that characterises the antenna when it is immersed in a uniform applied static field. The polarisability, and hence the bandwidth, is increased by loading the dipole arms close to their ends. The half-power impedance bandwidth is increased from 5 to 13% by moving the coils from the centre to the ends of the dipole arms. The introduction of a stub-matching further improves the bandwidth but the physical limit is not reached. Finally, a dual-resonance dipole antenna is analysed. It is observed that a second resonance hardly reduces the bandwidth of the first resonance if the resonances are separated more than 1.7 times in frequency. View full abstract»

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  • Group delay equalised monolithic microwave integrated circuit amplifier for ultra-wideband based on right/left-handed transmission line design approach

    Page(s): 967 - 973
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (297 KB)  

    A group delay equalised InGaP/GaAs HBT monolithic microwave integrated circuit (MMIC) amplifier with an active balun for ultra-wideband (UWB) application has been developed. The MMIC consists of a broadband amplifier with an active balun and a group delay equaliser. The group delay equaliser was designed based on a theory using a composite right/left-handed (CRLH) transmission line. Adding a right-handed (RH) transmission line to a CRLH transmission line in parallel, a convex group delay characteristic is realised. Since various UWB components have concave group delay characteristics, the group delay equaliser can compensate a concave group delay characteristic of the amplifier in an operation frequency band. In this paper, dispersion, group delay and impedance characteristics for the proposed CRLH/RH circuit have been theoretically analysed. Moreover, a minimised group delay equaliser circuit on an MMIC has been designed and fabricated based on the proposed CRLH/RH circuit. A fabricated group delay equalised InGaP/GaAs HBT MMIC amplifier with an active balun exhibited an improved group delay characteristic compared with the MMIC amplifier without the group delay equaliser. The standard deviations of group delays for a frequency variation in a gain band were decreased from 12.8 to 5.5 ps at S 21 and decreased from 10.3 to 7.3 ps at S 31. View full abstract»

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  • Miniaturised coplanar waveguide-fed antenna and band-notched design for ultra-wideband applications

    Page(s): 974 - 986
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1436 KB)  

    A miniaturised coplanar waveguide-fed ultra-wideband (UWB) antenna is presented here. The wideband operation is obtained through an optimised curvature of the radiating element. The input impedance of the antenna is matched using an elliptically tapered coplanar waveguide line. A high-band rejection characteristic at wireless local area network frequencies is achieved by inserting an omega-shaped slot on the antenna surface. The frequency domain dispersion characteristic is studied by means of the antenna transfer function both numerically and experimentally. Time domain characteristic of the antenna is investigated in detail for both UWB single-band and multiband schemes. In order to efficiently characterise the antenna system for an arbitrary pulse source excitation, the pole/residue model of the antenna system transfer function is presented using the matrix-pencil method. View full abstract»

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  • Mathematical formulation for zero reflection from multilayer metamaterial structures and their notable applications

    Page(s): 987 - 996
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (530 KB)  

    The behaviour of bilayer structures composed of common materials and metamaterials (MTMs) under oblique incidence of plane waves is investigated by exact analytical methods. The TE, TM and elliptical polarisations are analysed. There are several combinations of double positive (DPS), double negative (DNG), epsilon negative (ENG) and mu negative (MNG) media for the bilayer structures, but only DPS-DPS, DPS-DNG and ENG-MNG bilayers with TE, TM and circular polarisations are analysed in detail. For homogeneous and isotropic MTM media, exact mathematical relations are derived for the design of reflectionless bilayer structures as a function of their geometry (thickness) and electric and magnetic parameters. Frequency dispersion is included in the formulations. It is shown that bilayers composed of common materials are not effective for the construction of zero reflection bilayer surfaces, whereas the application of MTMs is required to realise reflectionless phenomena. For the design of zero reflection bilayer structures, their thicknesses and values of epsiv and mu are determined. Finally, the performance of forward and backward notch filters observed by MTM bilayer structures are studied in detail and their designs and applications are investigated. The bandwidth of lossy MTMs increases considerably. View full abstract»

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  • Enhanced architecture for microwave currentmode class-D amplifiers applied to the design of an S-band GaN-based power amplifier

    Page(s): 997 - 1006
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (753 KB)  

    An enhanced architecture for the design of current-mode class-D (CMCD) power amplifiers (PAs) at microwave frequencies is presented. In the proposed structure, the harmonic impedance loading conditions of CMCD amplifiers are realised by using multiharmonic output impedance transformation networks instead of a combination of balun and lumped element tanks, typically used in CMCD PA designs. The advantage of the proposed approach is to remove design complexity from the balun and lumped element tank. A 39 dBm GaN- based CMCD PA was designed at 2.35 GHz - to the best knowledge of the authors the highest frequency for a CMCD PA reported in open literature - to validate and to demonstrate the capabilities of this architecture. The fabricated PA achieves 68% DC-to-RF efficiency (eta) and 65% power added efficiency. A comparison between this S-band amplifier and a conventional wideband-balun-resonant-tank CMCD PA at 1 GHz using a similar commercial active device demonstrates the frequency coverage and performance improvement of the proposed topology. View full abstract»

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  • Multiple access coding interferometers in wave radio

    Page(s): 1007 - 1010
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (209 KB)  

    Wave radios in the past have used passive wide-band with no multiple access (MA) coded interferometer architectures in modulator and demodulator circuits for QPSK digital data transmission and reception. The authors provide information and design insight on the use of MA coded interferometers in modulator and demodulator for UWB wave radio. Wave radio fitted with hardware MA coded interferometers offers MA to users as does CDMA using data codes. Experimental and simulation analyses of coded interferometers show that it is possible to establish a one-to-one wave radio hardware link by means of hardware-based codes (addresses). The number of UWB hardware-coded interferometers investigated is limited to three codes (code 0, code 1 and code 2) for demonstration purposes only. View full abstract»

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  • Multiplexing technique for direction of departure and direction of arrival estimation

    Page(s): 1011 - 1017
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (222 KB)  

    A novel multiplexing technique for angular estimation that avoids the use of switches and multiple RF chains is presented. The principle of operation is as simple as connecting cables of different electrical lengths to the antennas. The advantages are simplicity and fast measurements, which enables the study of time-variant channels. If the duration of the excitation signal is less than a certain limit (which depends on the delays introduced by cables and on the delay spread of the propagation channel), the technique performs a time-domain multiplexing. However, the technique is especially interesting in the case that the excitation signal duration exceeds this limit. In that case, it requires the frequency of the signal to increase or to decrease linearly in time, regardless if the variation is discrete or continuous in time. The post-processing of the receiver output used to separate the signals corresponding to each antenna is detailed in this study. Once separated, the signals can be processed with a high-resolution algorithm to estimate the direction of departure and the direction of arrival. To validate the capability of this method, simulation results and measurements in an anechoic chamber are presented. View full abstract»

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