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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 2 • Date 3 April 2006

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Displaying Results 1 - 15 of 15
  • Magneto-inductive waveguide devices

    Page(s): 111 - 121
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (322 KB)  

    Devices formed from magneto-inductive waveguides based on coupled loop resonators are considered using simple analytic theory, initially assuming lossless propagation and nearest-neighbour coupling. Two-port devices that were considered include mirrors, Fabry-Perot resonators, Bragg gratings and tapers, while more general N-port devices include power splitters and directional couplers. Conditions for multiple-beam resonance and Bragg reflection in two-port devices are identified, and it is shown that quasi-optical filters may be constructed by simple layout variations. Conditions for low reflection are identified in splitters, and it is shown that matched three-port splitters with arbitrary power division ratios may be achieved for a particular input port. However, matching is not possible for all ports simultaneously. Directional couplers are shown to operate well only at mid-band and with weak coupling. The effect of loss is then examined and it is shown that idealised performance is obtained using resonators with sufficiently high Q-factors. View full abstract»

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  • Design of periodically elevated groundplane SSS band-pass filter with suppressed second harmonic

    Page(s): 122 - 124
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1106 KB)  

    Using periodically elevated groundplane along the coupled line sections in the lower cavity of suspended substrate stripline (SSS), a parallel-coupled line band-pass filter having suppressed harmonic at 2f0 has been designed. Even and odd mode phase velocities in each coupled line section at 2f0 have been equalised by using the right number of periodic grounding cells with proper dimensions. Based on this equalisation technique, a filter at 2.4 GHz has been designed and fabricated to prove the concept. View full abstract»

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  • Improved heuristic diffraction coefficients for an impedance wedge at normal incidence

    Page(s): 125 - 132
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (661 KB)  

    A method to extend the range of validity of heuristic diffraction coefficients for an impedance wedge to all diffraction and incidence angles is suggested. The proposed diffraction coefficients enforce continuity of the total field, are reciprocal and symmetrical, and satisfy plausible boundary conditions on the wedge faces. Good agreement with Maliuzhinets' method is observed in all conditions, excluding those for which the first-order impedance boundary conditions are known to be inaccurate. View full abstract»

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  • Design and implementation of circularly polarised microstrip antenna array using a new serial feed sequentially rotated technique

    Page(s): 133 - 140
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    Investigation results on circularly polarised microstrip antenna arrays at 2.45 GHz are presented. Effects of the feed network in the sequentially rotated technique to improve the antenna performance are reported. A new serial feed sequentially rotated to construct coplanar-fed arrays of large size, that improves antenna performance, is proposed. The results achieved show that this technique not only leads to an improvement in bandwidth, but also results in a better radiation pattern with lower sidelobe levels in the E and H radiation planes. A new 2×2 antenna subarray that has been arranged using the serial-feed sequentially rotated technique was fabricated. The measurement results for resonant frequency, return loss, axial ratio, bandwidth and radiation pattern confirm the integrity of the simulation results. View full abstract»

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  • Three- and five-way low loss phase combiners for power amplifier sharing in cellular networks

    Page(s): 141 - 146
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1033 KB)  

    Novel low loss 3×3-way and 5×5-way phase combiners for power amplifier load balancing in wireless network cells are presented. Based on an air-filled coaxial multiring structure, the designs combine very low insertion loss with compact physical profile. The concept is studied for the PCS (personal communication service) transmit band in the range 1.91-1.99 GHz by simulation. Measurements validate the predicted very low insertion loss for the three-way combiner of 0.05 dB, while return loss and port isolation are both better than 25 dB. Simulations exhibit, with 0.15 dB insertion loss, a similar performance for the five-way device. Return loss and port isolation are better than 23 dB in this case. View full abstract»

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  • TLM modelling of reconfigurable antennas for multi-band operation

    Page(s): 147 - 151
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (303 KB)  

    Various TLM modellings of active devices embedded in antennas are presented. Two aspects are considered. The first aspect concerns a new 3-D modelling specifically developed for large device volumes compared to the cell size in a varactor-based tunable antenna. In the second aspect, simplified electrical models of PIN diodes are used to simulate switchable antennas. Results of measured data and TLM simulations for both reconfigurable antennas are compared and good agreement is reported. View full abstract»

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  • New approach for modelling distributed MEMS transmission lines

    Page(s): 152 - 162
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1092 KB)  

    The paper presents a new and more accurate model for the distributed MEMS transmission line (DMTL) structures. In this new model, the MEMS bridges that are used as the loading elements of the DMTL structures are represented as low-impedance transmission lines, rather than a lumped CLR circuit. The model also includes LC networks at the transition points from the MEMS bridges to the unloaded parts of the DMTL, which are simply high-impedance transmission lines. These LC networks are employed to model the effects of the impedance discontinuities. The accuracy of the model is verified with simulations and measurements in the range 1-20 GHz on various DMTL structures that are fabricated with an RF MEMS process based on electroforming on a glass substrate. The measurement results of the fabricated devices are in good agreement with the model with an error less than 5%. It is shown that this new model provides better agreement than the conventional method for the DMTL structures with a bridge width larger than 50 μm. View full abstract»

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  • Light-weight base station antenna with artificial wire medium lens

    Page(s): 163 - 170
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (674 KB)  

    The authors study the possibility of utilising a loaded wire medium as an artificial material for a beam shaping element in base station antenna applications. The wires in the lattice are loaded with a proper capacitive impedance to produce a structure effectively operating as a dielectric lens at the UMTS (Universal Mobile Telecommunications System) frequency range. It is proven with full-wave simulations that the interpretation of a finite-size wire lattice as a dielectric lens is physically sound, even with a moderate number of lattice periods. A prototype having a mechanically reconfigurable beamwidth is constructed and measured. It is shown that very promising performance can be achieved with a rather simple structure and a cheap manufacturing process. View full abstract»

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  • Effects of hardware imperfection on six-port direct digital receivers calibrated with three and four signal standards

    Page(s): 171 - 176
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    Online calibration is essential for the proper operation of six-port digital receivers in communication systems, as such calibration cancels out receiver ageing and manufacturing defects. Simple calibration methods, using only three or four signal standards (SS), were reported in a previous paper, where these methods were assessed using an ADS software simulation for an ideal six-port circuit. A unified and general theory is presented for examining the effects of hardware imperfection on the performance of a six-port receiver (SPR) calibrated using these simplified techniques. This can be used to establish permissible hardware tolerances for proper operation of SPRs in different digital modulations. View full abstract»

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  • Discussion and new proofs of the conditional stability criteria for multidevice microwave amplifiers

    Page(s): 177 - 181
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (201 KB)  

    In the design of microwave multidevice amplifiers, criteria ensuring conditional stability allow a better trade-off between performance and stability to be obtained with respect to unconditional stability criteria. Previous results concerning conditional stability of linear two-ports are discussed, and new proofs of the conditional stability criterion ensuring stability for all the values of input and output terminations located in circular regions of the Smith chart are provided. By following the proposed proofs, it is shown for the first time that necessary and sufficient conditions for conditional stability can be ascertained by means of a single parameter. The overall stability factors are directly obtained starting from Ohtomo's proviso on unconditional stability. Procedures to apply the conditional stability criterion to the synthesis of multidevice amplifiers are also outlined and illustrated by means of a case study concerning the design of a four-stage distributed amplifier in the 1-10 GHz frequency band. View full abstract»

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  • Adaptive plane-wave expansion algorithm for efficient computation of electromagnetic fields in low-frequency-problems

    Page(s): 182 - 190
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (246 KB)  

    An algorithm is presented for efficient computation of electromagnetic interactions between a large number of sources in electrically small problems. The algorithm is based on a plane-wave expansion of the free-space Green's function. The expansion consists of both propagating and evanescent plane waves, and is stable at low frequencies. The algorithm is used in the iterative solution procedure of the method of moments to reduce the computational complexity of solving the matrix equation. It reduces the complexity of the matrix-vector multiplication from O(N2) to O(N log N). The numerical results verify the validity and efficiency of the algorithm in solving large-scale and low-frequency problems. View full abstract»

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  • Surface-based broadband electromagnetic-circuit simulation of lossy conductors

    Page(s): 191 - 198
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1448 KB)  

    Surface-only boundary-element formulations are particularly efficient for electromagnetic modelling of microelectronic structures that consist of homogeneous sections, such as interconnects, packaged and on-chip microwave and analogue circuit components. However, broadband modelling, as necessitated in digital and ultrawideband systems, is not possible with standard surface-only formulations that rely on the surface impedance technique to model conductor loss. In existing methods, recourse is taken to volumetric solvers in such cases. A surface-only formulation is presented that is truly broadband, and solves the internal field problem exactly, utilising a newly developed lossy medium quadrature. The value of the proposed technique lies in its seamless behaviour over wide frequency ranges and its direct interconnectivity to circuit-level analyses. In particular, frequency-dependent parameters can be extracted via a surface-only approach, valid at all frequencies. The electromagnetic analysis is coupled to a lumped circuit formulation, via a recently developed contact model. View full abstract»

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  • BFGS quasi-Newton method for solving electromagnetic inverse problems

    Page(s): 199 - 204
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (714 KB)  

    Electromagnetic inverse problems have been found in numerous research areas, such as medical imaging, non-destructive testing, geophysical prospecting and microwave tomography. These inverse problems can be considered as a large-scale nonlinear programming problem. In the paper, a quasi-Newton algorithm based on Broyden-Fletcher-Goldfarb-Shanno (BFGS) Hessian matrix updating formula is introduced and applied to solve two-dimensional (2-D) electromagnetic inverse problems. Numerical results of image reconstruction from the simulation data for some dielectric cylinders are given, and the efficiency of the proposed method for image reconstruction is evaluated. View full abstract»

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  • Eighteen-pole superconducting CQ filter for future wireless applications

    Page(s): 205 - 211
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1912 KB)  

    A recent development of an eighteen-pole high-temperature-superconducting (HTS) bandpass filter with group delay self-equalisation for future wireless applications is reported. The filter is designed to have a 15 MHz pass-band at a centre frequency of 1967.5 MHz. The filter exhibits a quasi-elliptic function response implemented with a cascaded quadruplet (CQ) coupling structure. Two particular cross-coupled quadruplet realisations have been developed to implement either attenuation poles at finite frequencies or linear phase for group delay self-equalisation. The Monte-Carlo sensitivity analysis was performed and the results were used as guidelines for tuning the filter. The filter was fabricated on a 0.43 mm-thick sapphire wafer with double-sided YBCO films. Measured responses are presented to demonstrate the validity of the design as well as the potential of the filter. View full abstract»

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  • Erratum

    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (61 KB)  

    Presents an erratum to the paper by Pazin and Leviatan (IEE Proc. Microw. Antennas Propag., 2004, vol.151, no.4, p.363-9). View full abstract»

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