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Microwaves, Antennas & Propagation, IET

Issue 2 • Date March 2009

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Displaying Results 1 - 20 of 20
  • High-frequency method for scattering from coated targets with electrically large size in half space

    Publication Year: 2009 , Page(s): 181 - 186
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (359 KB)  

    The high-frequency method for solving the scattering from coated targets of electrically large size in half space is presented. In order to consider the scattering fields of the targets in half space, the half-space physical-optic (PO) method is deduced by introducing the half-space Green's function into the conventional PO method. Combined with the graphical-electromagnetic computing method to read the geometric information of all visible facets, the impedance boundary conditions are utilised to account for the targets-covered with radar-absorbing material in half space. The numerical results show that this method is efficient and accurate. View full abstract»

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  • Accurate analysis of printed reflectarrays considering the near field of the primary feed

    Publication Year: 2009 , Page(s): 187 - 194
    Cited by:  Papers (12)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    An analysis technique is proposed for the analysis of reflectarrays placed in the Fresnel zone of the primary feed. The technique is based on the classic analysis of reflectarrays considering local periodicity, improved by considering the near field radiated by the feed horn instead of ideal feed models. The incident field on each reflectarray cell is obtained by applying field transformation to the measured far field (FF) of the horn antenna. The stronger variation of the incident field is considered by increasing the number of samples per reflectarray cell for the incident and reflected waves. This enhanced analysis has been applied to the analysis of a multi-fed and multiple-shaped beam reflectarray placed in the Fresnel zone of the feed horns. The antenna was proposed as a central station antenna for a local multipoint distribution system in the 24.5-26.5-GHz band. The antenna was designed by considering an approximate FF feed model in the radiation pattern synthesis and the reflectarray design. The results obtained through the enhanced analysis are compared with those from measurements of a prototype, validating the proposed analysis procedure and providing a significant improvement with respect to conventional analysis. View full abstract»

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  • Defected ground and patch-loaded planar transmission lines

    Publication Year: 2009 , Page(s): 195 - 204
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (606 KB)  

    Two new structures, defected slotline and patch-loaded coplanar waveguide (CPW), are introduced and quasi-static geometrical models for them and for the defected ground structures in microstrip and in CPW configurations are developed, combining those structures with the patch-loaded slotline and the stepped impedance resonators (SIRs) in a microstrip; and thus, a unified approach for the realisation of series and parallel stubs in different planar transmission line configurations is presented. Complementarity between the different structures has been investigated. It has been found that an identical dumbbell-shaped defect and a SIR in a microstrip are complementary to each other. Consequently, a new technique is developed to compensate for the effect of a defect in the ground of a microstrip. All theoretical predictions have been confirmed with both EM simulations and measurements. View full abstract»

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  • Detailed characterisation of an indoor MIMO channel in the double directional spatial domain

    Publication Year: 2009 , Page(s): 205 - 213
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (518 KB)  

    The spatial domain characteristics of an indoor multiple-input multiple-output (MIMO) communication system are examined in detail. Using a high-resolution algorithm, the authors were able to effectively estimate multipath parameters on the joint azimuth of arrival/azimuth of departure (AoA/AoD) domain. The analysis showed dense clustering phenomena at the vast majority of considered locations and a strong correlation between the azimuth spreads of the two angular domains with the presence of line-of-sight (Los) specular components or when the distance between the transmitter (Tx) and the receiver (Rx) is low. The authors also noticed higher azimuth dispersions, compared with those reported in the literature, which can be attributed to low antenna heights and local scattering interactions in the vicinity of both the transmit and receive arrays. Finally, the impact of the spatial global parameters on the ergodic MIMO capacity was tested revealing a direct relation between them. View full abstract»

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  • Mean effective gain of antennas in a wireless channel

    Publication Year: 2009 , Page(s): 214 - 227
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (345 KB)  

    The mean effective gain (MEG) is one of the most important parameters for the characterisation of antennas in wireless channels. An analysis of some fundamental properties of the MEG is provided and corresponding physical interpretations are given. Three points are analysed in detail: (i) closed-form expressions for MEG in a mixed environment with both stochastic and deterministic components are provided, showing that the MEG can be written as a sum of gains for the deterministic and stochastic components, (ii) it is shown that under some assumptions, the propagation channel and the antenna are equivalent in the sense that the impact of the channel cross-polarisation ratio (XPR) and the antenna effective cross-polar discrimination on the MEG are symmetrical, (iii) based on the fact that MEG depends on random variables, such as the XPR and antenna rotations because of user's movements, the average, the minimum and maximum MEG of antennas are defined, respectively. Finally, the maximum effective gain of antennas is derived and shown that it is bounded by 4pietarad, where etarad is the radiation efficiency of the antenna. View full abstract»

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  • Characterisation of GaAs pseudomorphic high electron mobility transistors for Volterra-series circuit analysis

    Publication Year: 2009 , Page(s): 228 - 234
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    Explicit extracting procedures for nonlinear transconductances and capacitances of GaAs pseudomorphic high electron mobility transistors are presented for Volterra-series circuit analysis. Nonlinear transconductances are acquired by low-frequency harmonic measurements with the associated phase polarities at various attenuations. Biased-dependent scattering parameter (S-parameter) measurements are utilised with curve-fitting processes to deduce the nonlinear capacitances. The extracted data up to third-order nonlinearities are validated by the two-tone signal tests in a bias range of 180-250-mA and a power sweep of -9.3-6.7-dBm, respectively. This device characterisation is quite useful for intermodulation reduction of power amplifier designs in modern digital wireless communications. View full abstract»

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  • Diagnostic of phased arrays with faulty elements using the mutual coupling method

    Publication Year: 2009 , Page(s): 235 - 241
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (750 KB)  

    The ability to calibrate phased array antennas by utilising the mutual coupling method (MCM), which takes advantage of the mutual coupling effect between adjacent elements, is addressed. The basic assumption of the method is that the mutual coupling between adjacent elements is equal for all elements in the array and its major deficiency is its failure in the case of faulty elements. A parametric study to identify the effect of faulty elements in the array has been conducted. It has been shown that displacement of one element in the array may cause a significant error in the calibration, which affects its radiation characteristics (increase in the far side lobe level). The main contribution is the presentation of the effect of faulty elements in the calibration process and the proposal of a way to detect and bypass the faulty elements in a phased array calibrated by the MCM. View full abstract»

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  • Variable toroidal ferrite phase shifter

    Publication Year: 2009 , Page(s): 242 - 249
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (454 KB)  

    Careful design of the magnetic bias circuit used in ferrite phase shifters can help to reduce space, weight and energy consumption. Low reluctance circuits must avoid air-gaps and this can be achieved using toroidal-shaped ferrite inserts positioned inside a rectangular waveguide. Here, these ferrite inserts are fabricated using a viscous plastic processing method that avoids machining and produces a continuous magnetic circuit. Finite-element methods are used to initially model the magnetostatic solution for the bias circuit before being used to analyse the microwave performance of a double toroid phase shifter. A closed-form technique is introduced to model the dielectric slab waveguide impedance transformer. The final insertion loss was < 1 < dB over the 9.5 < 10.3 <GHz band and return loss of 20 < dB was achievable. The phase shift calculation agrees to within 10< of the measured values. View full abstract»

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  • Measurements and modelling of cellular interference in local point-to-multipoint distribution systems

    Publication Year: 2009 , Page(s): 250 - 259
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (965 KB)  

    Frequency and polarisation reuse for optimum spectral efficiency in local multipoint distribution system (LMDS) networks generate co- and adjacent-channel inter-and intra-cell interference because of the line-of-sight constraints among transmitting and receiving antennas. Such operational constraints limit the system capacity and affect link performance. Measurements at 40 GHz from a number of possible interference scenarios for two different LMDS reuse cellular plans of dual-frequency and dual-polarisation discriminations are presented. An electromagnetic-stochastic propagation model is employed. The model successfully predicts the interference parameters and takes into account the effects of multiple paths and depolarisation caused by reflection and scatter from building surfaces at millimetre-wave frequencies. The probability density function of the signal-to-interference ratio and the statistical channel parameters, such as the average signal strength and the Rician K-factor, are extracted from the measured data and compared with model predictions. View full abstract»

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  • Passive intermodulation in printed lines: effects of trace dimensions and substrate

    Publication Year: 2009 , Page(s): 260 - 268
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (414 KB)  

    A comprehensive experimental study was performed to identify and discriminate mechanisms contributing to passive intermodulation (PIM) in microstrip transmission lines. The effects of strip length and width, and substrate materials on PIM performance of printed lines were investigated in the GSM900, DCS1800 and UMTS frequency bands. The major features of the experiment design, sample preparation and test setup are discussed in detail. The measurement results have demonstrated that the PIM level cumulatively grows on the longer microstrip lines and decreases on wider strips and, thus, indicated that the distributed resistive nonlinearity of the printed traces represents the dominant mechanism of intermodulation generation in the printed lines on PTFE-based substrates. View full abstract»

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  • Elimination of scan blindness with compact defected ground structures in microstrip phased array

    Publication Year: 2009 , Page(s): 269 - 275
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (540 KB)  

    A compact H-shaped defected ground structure (DGS) is applied to reduce the mutual coupling between array elements and eliminate the scan blindness in a microstrip phased array design. The proposed DGS is inserted between the adjacent E-plane coupled elements in the array to suppress the pronounced surface waves. A two-element array is measured and the results show that a reduction in mutual coupling of 12 dB is obtained between elements at the operation frequency of the array. The scan properties of microstrip phased arrays with and without DGS are studied by the waveguide simulator method. The analysis indicates that the scan blindness of the microstrip phased array can be well eliminated because of the effect of the proposed DGS. Meanwhile, the active patterns of the array centre element in 7times3 element arrays with and without the H-shaped DGS are simulated, and the results agree with those obtained by the waveguide simulator method. View full abstract»

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  • Microstrip bandpass filters based on zeroth-order resonators with complementary split ring resonators

    Publication Year: 2009 , Page(s): 276 - 280
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (293 KB)  

    The zeroth-order resonant (ZOR) properties of the left-handed material (LHM) unit cells composed of complementary split ring resonators and series gaps are analysed. The method to determine the resonant frequency and susceptance slope parameter is proposed. A bandpass filter (BPF) is designed by connecting the ZORs with admittance inverters. Experimental verification is provided and a good agreement has been found between the simulation and measurement. Compared with the bandpass structure fabricated by simply cascading the same amount of LHM unit cells, the proposed BPF has much better selectivity, more symmetrical responses and controllable bandwidth. View full abstract»

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  • Complex gyrator circuit of a three-port circulator using a planar resonator composed of a gyromagnetic disk, a triplet of UEs and a triplet of single radial magnetic walls

    Publication Year: 2009 , Page(s): 281 - 287
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    A classic planar gyromagnetic resonator, encountered in the construction of three-port circulators, is one with top and bottom electric walls and a magnetic sidewall symmetrically loaded with a triplet of single magnetic walls. The main purpose is to experimentally characterise the complex gyrator circuit of a three-port junction using a resonator made up of a circular region, a triplet of single magnetic walls and a triplet of short 5deg long UEs. It is compatible with the design of degree-2 circulators with commercial specifications and one experimental example is included for completeness sake. The effect of the UE embodied in the resonator under consideration is to decouple the coupling angle of the resonator terminals from any external microwave circuits, thereby facilitating the practical design of degree-2 circulators. A similar magnetised resonator loaded with a triplet of triple magnetic walls instead of single ones is also dealt with. It has the effect of reducing the spacing between the first three cut-off numbers of the isotropic geometry. View full abstract»

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  • Performance analysis of multiple-input multiple-output orthogonal frequency division multiplexing systems under the influence of antenna mutual coupling effect

    Publication Year: 2009 , Page(s): 288 - 295
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (353 KB)  

    The effect of antenna mutual coupling on signal correlation and bit error rate (BER) of a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system has been modelled. A MIMO-OFDM model with correlated channels is presented. The correlation matrices are determined with the antenna mutual coupling taken into account. The effect of antenna mutual coupling is characterised using the receiving and transmitting mutual impedances. A rigorous expression for the BER of the system employing quadrature phase-shift keying digital modulation is derived. A 2times2 MIMO-OFDM system using the Alamouti space-time block code for OFDM symbol transmission over 64 sub-channels spanning a 20 MHz band centred at 5.2 GHz is simulated. The simulated results show that the antenna mutual coupling has a significant effect on the BER performance, especially when the spacing between the antenna elements is small. View full abstract»

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  • Modelling of soft and hard surfaces using ideal perfect electric conducting/perfect magnetic conducting strip grids

    Publication Year: 2009 , Page(s): 296 - 302
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (375 KB)  

    Strip-loaded surfaces and corrugated surfaces can be efficiently analysed using asymptotic boundary conditions that are valid in the limit of vanishing strip and corrugation period, respectively. An even simpler boundary condition is obtained by assuming that the surfaces are ideally soft or hard. This corresponds to a curvilinear grid of quasi-parallel perfect electric conducting (PEC) and perfect magnetic conducting (PMC) strips of incremental width and period, referred to as a PEC/PMC strip grid. Such a simple model for soft/hard surfaces speeds up the design process and provides the proper object parameters under the ideal soft or hard conditions. After reaching the designed characteristics, one can study the bandwidth of realisations of the surface using the asymptotic boundary conditions and finally make a complete and detailed study of all characteristics of the realisations by including even the finite period of the strips and corrugations. The ideal PEC/PMC strip model is used here as an example applied to bodies of revolution (BOR) such as soft horns with transverse corrugations and hard horns with longitudinal corrugations. The longitudinally corrugated horn is not a BOR, but both the asymptotic boundary condition and the ideal PEC/PMC strip model make it possible to analyse it as a BOR with an anisotropic wall and this reduces the computer time enormously compared to a full wave analysis for a finite corrugation period. It is shown that the PEC/PMC strip grid can predict the radiation patterns well at the centre frequency, but the bandwidth cannot be determined. View full abstract»

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  • Filter characterisation using one-port pulsed radio-frequency measurements

    Publication Year: 2009 , Page(s): 303 - 309
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (167 KB)  

    A method for extracting the loaded quality factor of the first resonator of a bandpass filter using one-port measurements is introduced. Properties of the quality factor are reviewed, and a time-domain approximation is used to estimate the loaded Q value from the decay rate of the filter's natural response. narrowband 900 MHz Chebyshev filters are characterised. View full abstract»

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  • Faster 3D finite element time domain - Floquet absorbing boundary condition modelling using recursive convolution and vector fitting

    Publication Year: 2009 , Page(s): 310 - 324
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    A recursive convolution (RC) based on the vector fitting (VF) method and triangular temporal basis functions is employed to compute the Floquet absorbing boundary condition (FABC) formulation in the vector 3D finite element time-domain (FETD) modelling of doubly periodic structures. This novel implementation (VF-RC-FETD-FABC) results in significantly lower computation time requirements than the standard convolution (SC) implementation. The numerical examples presented show a reduction in computation time requirements by a factor of at least 3.5. In addition, a time window in excess of 50 000 time steps is recorded over which practically stable results are obtained. This temporal window is sufficiently large to allow the modelling of many practical problems. The results from four such problems are presented, confirming the accuracy and speed of the VF-RC-FETD-FABC software. View full abstract»

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  • Broadband flexible comb-shaped monopole antenna

    Publication Year: 2009 , Page(s): 325 - 332
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1098 KB)  

    A broadband comb-shaped monopole antenna is proposed. The antenna has dimensions of 19 mm times 12 mm. The measured results show good agreement with the numerical prediction, and broadband operation with 10 dB impedance bandwidth of 44.75 (1.7 - 2.68 GHz). The antenna is built on one side of a flexible-printed circuit board (PCB) dielectric substrate. Folded and rolled antenna structures, which are transformed by the proposed planar antenna structure, are presented. Each antenna has a broadband impedance bandwidth that covers the PCS, UMTS, WiBro, WLAN and SDMB bands. Also, omni-directional radiation patterns over the operating bands have been obtained. The proposed antennas are suitable for mobile communication applications requiring a small antenna. View full abstract»

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  • Optimised design of multi-band cellular base station antenna array for GSM and UMTS deployment

    Publication Year: 2009 , Page(s): 333 - 347
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (817 KB)  

    A tri-band dual polarised printed patch array is designed for GSM and UMTS cellular deployment using an efficient moment method code driven by a marginal distribution optimisation algorithm. Novel techniques are introduced to expedite analysis while maintaining adequate accuracy, and two methods are used to aggregate elements into an array for pattern synthesis: unequal spacing and phasing. Optimisation criteria such as cross-polar isolation, return loss and radiation pattern characteristics are successfully achieved in simulation, and a measured prototype element supports the antenna concept. View full abstract»

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  • Design of compromise sum-difference patterns through the iterative contiguous partition method

    Publication Year: 2009 , Page(s): 348 - 361
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (678 KB)  

    An innovative approach for the synthesis of sub-arrayed monopulse linear arrays is presented. A compromise difference pattern is obtained through an optimal excitations matching method based on the contiguous partition technique integrated in an iterative procedure ensuring, at the same time, the optimisation of the sidelobe level (or other beam pattern features). The flexibility of such an approach allows one to synthesise various difference patterns characterised by different trade-off between angular resolution and noise/interferences rejection in order to match the user-defined requirements. On the other hand, owing to its computational efficiency, synthesis problems concerned with large arrays are easily managed, as well. An exhaustive numerical validation assesses the reliability and accuracy of the method pointing out the improvements upon state-of-the-art sub-arraying techniques. View full abstract»

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