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Microwaves, Antennas & Propagation, IET

Issue 9 • Date June 19 2012

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Displaying Results 1 - 17 of 17
  • Design of compact branch-line couplers using π-equivalent artificial transmission lines

    Page(s): 969 - 974
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (642 KB)  

    Compact branch-line couplers (BLCs) are developed using π-equivalent shunt-stub-based artificial transmission lines (SSB ATLs). A conventional quarter-wave microstrip can be equivalent to a π-equivalent SSB ATL which is realised by a series high-impedance microstrip with two bilateral low-impedance shunt stubs. The SSB ATLs are then applied to implement a BLC. The low-impedance shunt stubs of the adjacent SSB ATLs are merged and replaced by the shunt branch-type structures. The folding technique is used to optimally miniaturise the coupler circuit size. Distributed-capacitor structures are employed to improve the operating bandwidth. At the design frequency 0.9πGHz, the developed 3- and 6-dB BLCs using shunt branch-type structures occupy about 8 and 8.2π of the circuit sizes of the conventional structures, respectively. In addition, the circuit size of the 3-dB BLC using shunt distributed-capacitor structures reduces to a 13.9π of the conventional one. View full abstract»

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  • Modelling and performance analysis of reverberation chamber using finite-difference time-domain method

    Page(s): 975 - 981
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (851 KB)  

    A reverberation chamber (RC) is modelled using a finite-difference time-domain (FDTD) method. To evaluate the performance, firstly, the electric field distribution and then the spatial correlation are computed inside the chamber using the FDTD method. In this work, dipole antennas operating at 750 MHz are used in transmitting and receiving mode. Empirical cumulative distribution functions obtained from FDTD simulations and measured S21 are compared with the Rayleigh distribution. The spatial correlation of the electric field inside the RC is computed from the FDTD-simulated and measured results and compared with published correlation functions. View full abstract»

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  • Electromagnetic compatibility of aperture antennas using electromagnetic band gap structure

    Page(s): 982 - 989
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (573 KB)  

    A rigorous solution to the problem of coupling reduction between the receiving and transmitting aperture antennas by using an electromagnetic band gap (EBG) structure is theoretically and experimentally investigated. The estimation of the decoupling level for the synthesised EBG structure is given. The radiation patterns of both the antennas are also presented. The moment method is used to solve the integral equations. Finally, the authors perform an experiment on the frequency dependence of the decoupling level and compare numerical and experimental results. Good agreement between simulation and measurement is achieved. View full abstract»

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  • Reconfigurable antenna design for mobile handsets including harmonic radiation measurements

    Page(s): 990 - 999
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1319 KB)  

    The design of a reconfigurable antenna with good load matching and covering a wide frequency range presents a practical challenge when the antenna size is tightly constrained. A procedure is presented for the design of a reconfigurable mobile antenna, which overcomes the antenna size limitations. Tuning is achieved by placing a varactor diode at a specific position across a slot in the radiator conducting surface. The fabricated antenna is designed to cover a wide band, between 1700 and 2040 MHz, at a return loss better than 10 dB. The radiation of harmonics generated because of the varactor non-linearities are simulated and measured. The experimental set-up ensures that the low levels of radiated harmonics are reliably validated. The experimental results show good agreement with that computed using the Friis equation. View full abstract»

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  • Compact substrate-integrated waveguide bandpass rat-race coupler and its microwave applications

    Page(s): 1000 - 1006
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (941 KB)  

    A reduced size rat-race coupler incorporating a bandpass frequency response characteristic is presented and designed based on substrate-integrated waveguide (SIW) technology. By use of electric- and magnetic-coupling structures between adjacent SIW cavity resonators, a conventional rat-race coupler and a bandpass filter with a 200-MHz bandwidth at a centre frequency of 7.75 GHz can be integrated as one component resulting in miniaturisation. A design process based on the coupled-resonator network is introduced to synthesise such a bandpass coupler with desired bandwidth, return loss and coupling. A Butler matrix and a six-port junction with bandpass response are then developed based on the proposed rat-race coupler. They represent excellent candidates for miniaturised transceiver and direct conversion systems. The measured results are in good agreement with the simulated predictions. View full abstract»

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  • Coupled-fed planar printed shorted monopole antenna for LTE/WWAN mobile handset applications

    Page(s): 1007 - 1016
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1815 KB)  

    A coupled-fed monopole antenna for LTE/WWAN mobile handset applications is presented. The proposed antenna consists of a top radiator and a bottom radiator. For the top radiator, the basic resonance of the shorted monopole and the resonance formed by the coupled feed combine to cover the LTE700, GSM850 and GSM900 bands. The coupled feed structure operates with the shorting strip as a loop. The resonance of the loop and the harmonics of the monopole combine to cover the GSM1900, UMTS and LTE2300 bands. By covering the GSM1800 band through the bottom radiator, the proposed structure covers the LTE700, LTE2300, GSM850, GSM900, GSM1800, GSM1900 and UMTS bands. A stable and omni-directional radiation pattern with reasonable gain has been observed over the operating bandwidth. View full abstract»

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  • Composite right/left-handed transmission line based on complementary single-split ring resonator pair and compact power dividers application using fractal geometry

    Page(s): 1017 - 1025
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (719 KB)  

    A new resonant-type composite right/left-handed transmission line (CRLH TL) is proposed based on the combination of a complementary single-split ring resonator pair (CSSRRP) etched on the ground plane and a series gap embedded in the conductor strip of a microstrip line. The CSSRRP, which is composed of two identical complementary single-split ring resonators (CSSRR) with face-to-face splits, demonstrates negative permittivity. An equivalent circuit model is presented and studied in depth through the Bloch theory and finally validated by the simulated full-wave S-parameters. The balanced condition for novel CRLH TL is also derived. Moreover, the negative refractive index and backward wave propagation are confirmed by the effective constitutive parameters. It is proved that the zero-degree phase-shift CRLH TL exhibits a significantly lower resonant frequency by constructing the CSSRRP as Koch curves of different iteration order (K-CSSRRP). To demonstrate the applicability, two compact prototype device examples are provided, these being a three-way fork power divider and a four-way series power divider. The three-way divider achieves a 74.2% size reduction and displays comparable performance relative to its conventional counterpart, whereas the four-way divider obtains a 56% bandwidth enhancement and a 48% size reduction in comparison with a conventional one using a one-wavelength meandered transmission line. View full abstract»

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  • Amplitude modulated signal transmission through a phase conjugating lens

    Page(s): 1026 - 1033
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    Free space transmission of an on-off modulated sinusoidal signal through a phase conjugating lens (PCL) is theoretically examined using a combined time/frequency domain approach. The on-off keyed (OOK) signal is generated by a dipole antenna located in the far-field zone of the lens. The PCL consists of a dual layer of antenna elements interconnected via phase conjugating circuitry. We demonstrate that electromagnetic interference between antenna elements creates spatially localised areas of good-quality reception and zones where the signal is significantly denigrated by interference. Next, it is shown that destructive interference and packet desynchronisation effects critically depend on bit rate. It is also shown that a circular concave lens can be used to produce high-quality signal reception in a given direction while suppressing signal reception in all other directions. The effect that the bandwidth of the phase conjugating unit has on the transmitted signal properties for the cases of high and low bit rate OOK modulation are studied and a signal quality characterisation scheme is proposed which uses cross-correlation. The results of the study yields understanding of the performance of phase conjugating arrays under OOK modulation. The work suggests a novel approach for realising a secure communication wireless system. View full abstract»

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  • Variable coupler for Butler beam-forming matrix with low sidelobe level

    Page(s): 1034 - 1039
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (483 KB)  

    A Butler beam-forming network with low sidelobe level (SLL) is proposed and demonstrated on the basis of variable couplers. A set of couplers with 0.75, 1.26, 3, 6 and 8 dB coupling levels are required to achieve an SLL of 13.6, 20 and 30 dB. Such variable coupling is achieved by creating a movable mirror structure in the common region of perpendicularly or cross-coupled waveguide building blocks. This mirror is composed of a 5 7 cylindrical rod array. The coupling and directivity characteristics depend on the position of this proposed fringe structure. In this work, WR28 is used to demonstrate the capability of this type of coupler over 26 30 GHz bandwidth. Structure usefulness and design procedure are validated by electromagnetic simulation high frequency structural simulator (HFSS) and prototype experimentation. Very good results are observed, that have also demonstrated attractive performances of the coupler. Measured results of couplers are used to assess the properties of Butler matrix with excitation coefficients corresponding to 13.6, 20 and 30 dB of SLLs. Radiation patterns obtained by this investigation show a promising performance. This proposed technique allows flexibility in the choice of excitation coefficients without degradation on the efficiency. View full abstract»

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  • Design and analysis of Brewster's angle polariser using inhomogeneous planar layers and Hill's method

    Page(s): 1040 - 1047
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (235 KB)  

    This study presents a generalised and easy-to-use method based on Hill's equation to analyse the electromagnetic wave propagation in inhomogeneous planar layers with arbitrary permittivity profiles. We explore the effects of polarisation, incidence angle, layers thickness and permittivity profiles on reflection and transmission characteristics. Hill's method is as an efficient tool to obtain an analytical solution to the propagation equations and is applicable to all arbitrary profiles of permittivity and permeability. Using Hill's method and an arbitrary profile of permittivity, numerical simulations for both polarisations transverse electric (TE)- and transverse magnetic (TM)-polarised waves are performed to compute the reflection and transmission of Brewster's angle polarisers having optimised thicknesses. The proposed polariser is analysed and optimally designed in microwave domain systems. The results obtained agree well with other published data. View full abstract»

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  • Design and construction of an ultrawideband backward wave directional coupler

    Page(s): 1048 - 1055
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    In this study the design and construction of an ultrawideband backward wave directional coupler is presented. The symmetric, non-uniform coupler covers the frequency range from 2 to 50 GHz with an average coupling of 16.6 2.4 dB while establishing directivity values greater than 10 dB from 10 MHz to 33.8 GHz and 8 dB up to 48.4 GHz. The design is based on coupled microstrip lines suitable for integration into planar front end modules of modern measurement systems. To account for the dispersive behaviour of such waveguides, wiggly-line technique is utilised. Accurate extraction of the waveguide frequency-dependent distributed equivalent circuit parameters is done by 2D finite element electromagnetic field (EM) simulation. To balance out the remaining mistuning appropriate scaling parameters are introduced. The influence of common manufacturing and assembly tolerances on the device performance is analysed. Measurement results of the synthesised coupler with planar matched isolated port are presented. View full abstract»

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  • Local response surface approximations and variable-fidelity electromagnetic simulations for computationally efficient microwave design optimisation

    Page(s): 1056 - 1062
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (357 KB)  

    In this study, the authors propose a robust and computationally efficient algorithm for simulation-driven design optimisation of microwave structures. Our technique exploits variable-fidelity electromagnetic models of the structure under consideration. The low-fidelity model is optimised using its local response surface approximation surrogates. The high-fidelity model is refined by space mapping with polynomial interpolation of the low-fidelity model data used as an underlying coarse model. Our algorithm is carefully developed to minimise the number of evaluations of both the low- and high-fidelity model in the optimisation process. The operation and efficiency of the approach is demonstrated through design of a microstrip filter, a double-ring antenna and an ultra-wideband monopole antenna. A comparison with other design approaches, including the direct high-fidelity model optimisation, is also presented. View full abstract»

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  • Radiation and absorption of waves emitted by a radial dipole in the presence of a layered dielectric sphere with a spherical screen

    Page(s): 1063 - 1069
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (470 KB)  

    Considered is the problem of electromagnetic wave radiation and absorption in the presence of a two-layer lossy dielectric sphere partially covered with a metal screen and illuminated by an elementary electric dipole. To find the field, the authors expand it in terms of spherical functions and use the method of analytical regularisation to reduce the problem to a matrix equation with favourable features. This enables us to obtain the radiation and absorption characteristics in a wide range of parameter variations and compare the efficiencies of shielding by different screens of varying angular size. As the studied structure can be viewed as a model of a head phantom with a helmet, the presented analysis can be useful for a control of specific microwave absorption rate levels. View full abstract»

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  • Coverage and read range comparison of linearly and circularly polarised radio frequency identification ultra-high frequency tag antennas

    Page(s): 1070 - 1078
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (804 KB)  

    This study presents a comparison between two dipoles acting as representatives of ultra-high frequency radio frequency identification (RFID) circularly polarised (CP) and linearly polarised (LP) tag antennas, respectively. As the CP dipole is derived from the LP dipole, they have equivalent reflection coefficient and radiation efficiency values, allowing the comparison to be focused on polarisation and radiation pattern. Then, a comparison of RFID angular and read range is investigated. This is conducted by combining the interrogation of CP and LP tags emulators by CP and LP readers with regulated power. The emulators are made up of the CP and LP dipoles embedded onto RFID tags with analog front-ends. A methodology is described for measuring the maximum angular and read ranges, involving maximum power allowed by European regulation. A 17.9% extra range is achieved by the CP tag and the CP reader compared to the LP tag with any kind of reader. Furthermore, null cancellation is observed in the former case in the region of interest. View full abstract»

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  • Tunable transmittivity and effective permittivity of a smart surface loaded by varactor diodes

    Page(s): 1079 - 1083
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (354 KB)  

    Smart surface was developed from a thin flexible substrate of a periodic strip array loaded by varactor diodes. The tunable electromagnetic properties, such as transmittivity and effective permittivity, were investigated through free space measurement as well as numerical calculation. It was found that the proposed surfaces show significant tunable characteristics under bias voltage. Transmittivity could be adjusted continuously from -2 to -20-dB at 4-GHz. The phase angle of transmittivity could also be tuned between -40- and -75- by changing bias voltage. Good agreement was found between the measurement and the simulation results. The potential applications of such tunable properties include smart radome or modulation screens of controllable transmission or phase delay. View full abstract»

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  • Dielectric resonator-based multiple-input multipleoutput antennas and channel characteristic analysis

    Page(s): 1084 - 1089
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (427 KB)  

    The authors report in this study, the investigation of propagation channel characteristics for multiple-input multiple-output (MIMO) systems based on polarisation diversity realised using dual-port dielectric resonator antennas (DRAs). The channel matrix entries in terms of complex transmission scattering parameters are measured directly from compact single-structure DRAs with multiple polarised ports and low mutual coupling in indoor wireless environment to calculate the complementary cumulative distribution functions (CCDFs) for channel capacity. Characterisation using theoretical expressions for MIMO capacity is demonstrated by spectral efficiency and eigenanalysis CCDFs from simulation and measurements based on dual-polarised cylindrical DRAs for a 2×2 MIMO system. View full abstract»

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  • Design and implementation of a controllable phase shifter using substrate integrated waveguide

    Page(s): 1090 - 1094
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (506 KB)  

    In this study, a controllable phase shifter using substrate integrated waveguide (SIW) technique is designed and implemented. The proposed phase shifter consists of a SIW section with a number of PIN diodes buried within the substrate. The phase shifting is achieved by changing the loading of the waveguide and that loading is controlled by turning the buried diodes ON and OFF. As a proof of concept, a prototype has been fabricated where four NIP diodes were used. Simulation and experimental results were in good agreement and a maximum differential phase of 45° has been achieved with good performance regarding return loss and insertion loss. View full abstract»

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