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Microwaves, Antennas & Propagation, IET

Issue 10 • Date July 14 2011

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Displaying Results 1 - 18 of 18
  • Technique for harmonic minimisation in high-power MMIC antenna switches using load-pull tuners

    Page(s): 1131 - 1135
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (570 KB)  

    Harmonic suppression in front-end monolithic microwave integrated circuit (MMIC) antenna switches for multi-band mobile phones is critical, and achieving sufficiently low values is challenging to meet. This study presents a novel technique for harmonic minimisation based on harmonically matching the input impedance of the relevant transmit port. It is shown how a load-pull system with an appropriate setup can be used for this purpose. This technique was successfully implemented on a single-pole-four-through switch, and harmonics were significantly reduced to values well below the specifications. Information extracted from the load-pull analysis was then used to design discrete matching networks as part of the application solution in commercial applications. View full abstract»

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  • Analysis, design and applications of the triple-mode conductor-loaded cavity filter

    Page(s): 1136 - 1142
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (925 KB)  

    This study presents the analysis and design of a new triple-mode filter that employs the recently proposed triple mode conductor-loaded cavity resonator. The resonator consists of a cubic-shaped metallic structure suspended in a metallic enclosure. The resonator is mounted in the cavity through a low-loss low-dielectric-constant support structure. The triple-mode conductor-loaded cavity resonator is considerably cheaper, easier to design and manufacture, and offers a significantly wider spurious-free response in comparison with the triple-mode dielectric resonator. A six-pole filter is designed using Ansoft HFSS employing the proposed triple mode conductor-loaded cavity resonator. The analysis shows that introducing asymmetry into the structure of the resonator in the form of chamfers or corner cuts creates the necessary perturbation to achieve the required coupling between the degenerate modes inside each block to realise the desired filter response. The six-pole triple-mode conductor-loaded cavity filter is fabricated and tested. Finally, two applications of the proposed concept are identified. The triple mode conductor-loaded cavity resonator is combined with higher Q-factor triple-mode ceramic resonators to realise a small size, high Q-factor filter with wide spurious-free response. Also, a direct-coupled band-stop filter is proposed employing the triple-mode conductor-loaded cavity filter. View full abstract»

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  • Very-low-sidelobe printed tapered arc-shaped wide-slot antenna array

    Page(s): 1143 - 1147
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (343 KB)  

    This study proposes two unique techniques to increase the impedance bandwidth and reduce the sidelobe level (SLL) of printed antenna arrays. In the first, a printed tapered wide-slot antenna array fed by an array of printed patch elements placed above a metal reflector is introduced. The impedance bandwidth of this antenna array is 10.3-23.1 GHz, that is, 76.6%. By tapering the width of each of the slot elements, a very low SLL of -33.5 dB is obtained. The proposed antenna has a stable radiation pattern over the range 14.7-17 GHz, that is, the 3 dB gain bandwidth is 14.5% and has a front-to-back ratio (F/B) level of 40 dB and a low cross-polar component <; -45 dB at broadside and <; -35 dB off-broadside direction. In the second technique, to achieve further improvement in the SLL of the antenna array the length of each of the slot array elements is tapered, in the form of an arc-shape, leading to an antenna array with very low SLL of - 35 dB at a centre frequency of 16.26 GHz, a wide bandwidth of 78.8%, 20 dB SLL bandwidth of 8.8%, and high F/B of 38 dB. A prototype of the antenna array is fabricated and the simulated and measured results are presented and discussed. View full abstract»

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  • One- and two-dimensional scattering analysis using a fast numerical method

    Page(s): 1148 - 1155
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (338 KB)  

    Most integral equations of the first kind are ill posed, and obtaining their numerical solution often requires solving a linear system of algebraic equations of large condition number. Solving this system may be difficult or impossible. Since many problems in one-dimensional (1D) and 2D scattering from perfectly conducting bodies can be modelled by linear Fredholm integral equations of the first kind, the main focus of this study is to present a fast numerical method for solving them. This method is based on vector forms for representation of triangular functions. By using this approach, solving the first kind integral equation reduces to solving a linear system of algebraic equations. To construct this system, the method uses sampling of functions. Hence, the calculations are performed very quickly. Its other advantages are the low cost of setting up the equations without applying any projection method such as collocation, Galerkin, etc; setting up a linear system of algebraic equations of appropriate condition number and good accuracy. To show the computational efficiency of this approach, some practical 1D and 2D scatterers are analysed by it. View full abstract»

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  • Constrained parameter extraction for microwave design optimisation using implicit space mapping

    Page(s): 1156 - 1163
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (655 KB)  

    To date, space mapping remains one of the most efficient design optimisation methodologies in microwave engineering. Still, its performance depends on the underlying surrogate model, in particular, its approximation and generalisation capabilities. By proper selection of the space mapping transformations and their parameters, a trade-off between these can be obtained. Often, this is done by trial and error that may lead to excessive computational overhead and poor quality of the optimisation outcome. In this study, an adaptively constrained parameter extraction is introduced. Based on convergence results for space mapping algorithms, it allows us to automatically find the approximation-generalisation trade-off through the adjustment of the surrogate model parameter space. Improved performance of the space mapping algorithm is obtained both in terms of convergence properties and the quality of the optimised design. Algorithm convergence is additionally improved by constraining the surrogate optimisation process. The authors' technique is validated using several microwave design problems. View full abstract»

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  • Design and full-wave analysis of conformal ultra-wideband radio direction finders

    Page(s): 1164 - 1174
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1025 KB)  

    The design and full-wave analysis of radio direction finders (RDFs) for ultra-wideband direction-of-arrival estimation is addressed. Conformal elliptically shaped dipoles are selected as antenna sensors by virtue of their good input impedance matching property, performance robustness and conformability. In order to achieve a full angular scanning coverage in the azimuthal direction, a uniform circular direction finding array topology is adopted. The parasitic coupling between the array elements is analysed rigorously, and a dedicated calibration method is used to compensate for non-idealities of the system. In particular, a computationally efficient design procedure for radio direction finding structures is proposed. This procedure, based on a suitable iterative approach, can be usefully adopted to determine the optimal array geometry in terms of number of antenna sensors and volume occupation, while providing a good insight into the physical limitations of the system. By using the developed optimisation technique, a novel RDF operating in the frequency range between 250 MHz and 3.3 GHz is designed, and the relevant performance is thoroughly investigated in realistic operative scenarios. It has been found that the proposed system is rank-1 ambiguity-free, and can be used for tracking both narrow and wideband radio signals. View full abstract»

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  • Compact metamaterial zeroth-order resonator bandpass filter for a UHF band and its stopband improvement by transmission zeros

    Page(s): 1175 - 1181
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (673 KB)  

    A microstrip bandpass filter for a UHF 900 MHz band is significantly miniaturised and its performance is enhanced using metamaterial (MTM) zeroth order resonator (ZOR) characteristics. Firstly, the authors propose that each of the resonators for a bandpass filter is implemented by a one-cell ZOR, and the coupling between neighbouring different ZORs is controlled to meet the primary goal on the bandpass filtering in the form of a sequential coupling mechanism. Secondly, this MTM ZOR filter is suggested to have transmission zeros (TZs) owing to source load coupling to improve the isolation from other wireless communication bands. The first and second proposed filters are less than one-sixth of the conventional filters in terms of size, and they present lower insertion loss and return loss in the passband and higher isolation in the stopband owing to the TZs, as verified by simulation and measurement. In addition, the MTM properties are verified with a dispersion diagram and the no-phase variation electric field distribution over the ZOR by a 3D EM simulation. View full abstract»

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  • Tunable electromagnetic band gap-embedded multimode resonators for ultra-wideband dual band, lower-ultra-wideband and upper-ultra-wideband applications

    Page(s): 1182 - 1187
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (627 KB)  

    Three ultra-wideband (UWB) microstrip band-pass filters (BPFs) are proposed using tunable electromagnetic band gap (EBG)-embedded multiple-mode resonator (MMR) and fork resonator. In the first case, a compact dual-band BPF is implemented using a cascade of a multimodal fork resonator with tunable EBG. The fork resonator forms the basic structure yielding multiple band-pass realisations and the EBG selects the desired bands. This yields a compact dual-band BPF with sharp cut-off characteristics, wide bandwidth and low insertion loss. In the second case, a lower UWB filter is proposed by tuning an EBG-embedded MMR with parallel coupled microstrip line. Open circuited coupling stubs are introduced within the EBG structure to suppress higher order pass bands. In the third case, an upper UWB BPF is proposed in a similar manner as the lower UWB filter. However, the EBG-embedded MMR structure and the coupling technique are different. It is shown that the measured results are well matched to the predicted ones in terms of insertion/return losses over the plotted frequency range of 0.1-20.0-GHz. All simulations were performed with advanced design system (ADS) momentum (2.5D method of moments). View full abstract»

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  • TE210 mode balanced oscillator using substrate integrated waveguide resonator

    Page(s): 1188 - 1194
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (609 KB)  

    A new balanced oscillator is proposed to generate anti-phase sources at Ku band. The proposed oscillator is stabilised with the TE210 differential mode of a single planar substrate integrated waveguide (SIW) rectangular cavity with mutually locked dual anti-phase outputs. The unloaded-Q of this resonator extracted through mixed mode S-parameters is 370 at 14 GHz. The differential coupling mechanism is presented and the coupling coefficient is parametrically studied. The proposed balanced oscillator provides 6.9 and 7.2 dBm output power for each balanced output with a phase noise of -101 dBc/Hz at 100 kHz offset measured at 14 GHz. The amplitude and phase balances of the two output signals are verified with measurement. The combined differential output power is 10.8 dBm and the phase noise is -109 dBc/Hz at 100 kHz offset. View full abstract»

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  • Amplitude-modulation characteristics of powercombining Class-E amplifier with finite choke

    Page(s): 1195 - 1202
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (765 KB)  

    Power back-off performances of a new variant power-combining Class-E amplifier under different amplitude-modulation schemes such as continuous wave (CW), envelope elimination and restoration (EER), envelope tracking (ET) and outphasing are for the first time investigated in this study. Finite DC-feed inductances rather than massive RF chokes as used in the classic single-ended Class-E power amplifier (PA) resulted from the approximate yet effective frequency-domain circuit analysis provide the wherewithal to increase modulation bandwidth up to 80% higher than the classic single-ended Class-E PA. This increased modulation bandwidth is required for the linearity improvement in the EER/ET transmitters. The modified output load network of the power-combining Class-E amplifier adopting three-harmonic terminations technique relaxes the design specifications for the additional filtering block typically required at the output stage of the transmitter chain. Qualitative agreements between simulation and measurement results for all four schemes were achieved where the ET technique was proven superior to the other schemes. When the PA is used within the ET scheme, an increase of average drain efficiency of as high as 40% with respect to the CW excitation was obtained for a multi-carrier input signal with 12%dB peak-to-average power ratio. View full abstract»

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  • Evanescent waveguide-based polarisation-agile antenna elements

    Page(s): 1203 - 1209
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (970 KB)  

    Polarisation-agile, evanescent waveguide-based antenna elements are proposed, which allow below waveguide cutoff operation from 1.07 to 1.49 GHz or below and above waveguide cutoff operation from 1.54 to 1.89 GHz for return loss 10 dB. Here square evanescent waveguide with 1.7 GHz cutoff is shunt loaded, respectively, with orthogonal pairs of coaxially excited cylindrical metal posts or flat metal strips positioned across the aperture of the waveguide. It is shown that linear or circular polarisation may be achieved depending on the excitations supplied to the input ports of the antenna. View full abstract»

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  • Pattern analysis of conformal array based on geometric algebra

    Page(s): 1210 - 1218
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (722 KB)  

    In this study, a general and systematic method for three-dimensional pattern analysis of arbitrary conformal arrays is presented; this analysis is based on the mathematical framework of geometric algebra and considers both directional and polarised element patterns. A compact representation of the conformal array pattern is presented. Aside from being simpler and more direct than other derivations in the literature, this derivation is also entirely general in that it expresses the transformations in terms of rotors that can easily be formulated for any arbitrary conformal array geometry. Analysing conformal arrays using geometric algebra is simpler than the traditional Euler rotation angles and matrix representations. As well as presenting the new derivation and comparing it with conventional methods, the authors also present simulation results on cylindrical and conical arrays to illustrate the practicality and conciseness of the proposed method. View full abstract»

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  • Tuning space mapping design framework exploiting reduced electromagnetic models

    Page(s): 1219 - 1226
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (761 KB)  

    Tuning space mapping (TSM) with embedded tuning elements is a recent development in space mapping technology. The process allows efficient design optimisation of microwave components by substituting sections in an electromagnetic model with corresponding sections of designable equivalent elements. Available parameters of these elements are subsequently tuned and their optimal values are `translated` into relevant changes in the original structure`s design variables. Although the TSM optimisation process typically requires only a few iterations to complete, the simulation of the structure with a number of co-calibrated ports (required for subsequent insertion of the tuning elements) can be substantially longer than that of the original structure. This results in substantial computational overhead of the design process. Here, the authors review a fast TSM algorithm that exploits a reduced structure with significantly fewer co-calibrated ports for creating the tuning model and allows us to obtain dramatic reduction of the computational cost of the optimisation process. In a design framework, the fast TSM as well as other TSM methods are implemented and automated in space mapping framework (SMF) software. Comprehensive verification and comparison with the standard TSM are provided through several examples of microstrip filters. View full abstract»

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  • Planar band-notched ultra-wideband antenna with square-looped and end-coupled resonator

    Page(s): 1227 - 1233
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (618 KB)  

    A square-looped and an end-coupled resonator used in a planar ultra-wideband (UWB) antenna to achieve band notched performance are presented here. To obtain notched performance in the wireless local area network band, both the square-looped and end-coupled resonator are designed and placed in a fork-shaped UWB antenna centre. The characteristics and schematic equivalent circuit of each resonator are also discussed. Parametric studies of a fork-shaped antenna with square-looped resonator are given as an example to explore the operating mechanism. Accordingly, the band-notched antenna can effectively select target bands by adjusting different resonator structures. The proposed antenna features flat gain frequency response and group delay as well as 10-25 dB gain suppression in the notched band. View full abstract»

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  • Tunable ferroelectric microwave bandpass filters optimised for system-level integration

    Page(s): 1234 - 1241
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (510 KB)  

    Tunable bandpass filters are critical components in emerging radio frequency front-ends. A system-aware design guideline and figure of merit (FOM) are developed for optimum system-level performance. The optimisation metric discussed here deviates from earlier guidelines as the filter bandwidth is allowed to vary in the tunable range, constrained only by the downstream system analogue to digital converter. The system-aware FOM uses worst-case filter design parameters and a tuning sensitivity term that captures the frequency tunability relative to material tunability. A 6.74-8.23-GHz tunable barium strontium titanate-based filter is presented as an example to illustrate the design methodology. View full abstract»

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  • Hybrid multiple-input multiple-output scheme combining precoded and non-precoded transmission

    Page(s): 1242 - 1249
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (395 KB)  

    A hybrid multiple-input multiple-output (MIMO) scheme capable of switching between non-precoded transmission and covariance-based precoded transmission is proposed. Such a hybrid scheme is desired as the covariance-based precoding gain is insignificant when transmission takes place in lowly correlated channels. Such a minor performance gain is not sufficient to justify the high-complexity precoding employed at the transmitter. The proposed scheme does not require a feedback channel or pilot symbols as knowledge of the downlink channel covariance and correlation is made available to the downlink transmitter through direct estimation from the uplink received signal energy. Performance studies carried out in both time division duplex and frequency division duplex systems reveal that the performance of the proposed scheme is on par with that of an existing MIMO precoding scheme with the added advantage of lower complexity and improved system efficiency. View full abstract»

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  • Dual-mode impulse radio ultra-wideband transmission for body area networks

    Page(s): 1250 - 1255
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (550 KB)  

    A dual-mode impulse radio ultra-wideband (IR-UWB) system, which combines body channel communication for wearable on-body transmission with conventional UWB communication for in-body to on-body transmission, is proposed. The basic system structure is presented, and the path loss characteristics are derived based on numerical analysis and measurement. Moreover, through a bit error rate performance analysis, the required transmit power against communication distance shows the feasibility for on-body and in-body transmissions at a data rate of at least 10 Mbps. View full abstract»

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  • Numerical dispersion improved three-dimensional locally one-dimensional finite-difference time-domain method

    Page(s): 1256 - 1263
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    A modified three-step three-dimensional (3-D) locally 1-D finite-difference time-domain (LOD-FDTD) method with reduction of numerical dispersion is introduced by virtue of parameter optimisation. Both theoretical and numerical studies of the unconditional stability of this proposed method are also presented. The numerical dispersion behaviour is investigated by comparison with the original LOD-FDTD method. The reduction of numerical dispersion error and the improved numerical accuracy can be observed from the numerical phase velocity computations under various time steps, spatial resolutions and frequencies. Numerical examples are included to illustrate the validity and improved accuracy of this proposed method. View full abstract»

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