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Microwaves, Antennas & Propagation, IET

Issue 3 • Date Feb. 21 2011

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Displaying Results 1 - 16 of 16
  • Microwave modelling of radio frequency microelectromechanical rotary switches

    Page(s): 255 - 261
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (925 KB)  

    In this study, both full 3D electromagnetic and equivalent circuit modelling of a radio frequency microelectromechanical systems (RF MEMS) single-pole eight-throw rotary switch are reported for the first time. Excellent agreement has been achieved between measurements and modelled performance for frequencies up to 12 GHz. In order to validate the effectiveness of the modelling, a 2-bit true time delay phase shifter having a centre frequency of 2 GHz has been demonstrated. The traditional topology of the switched delay line was adopted with two rotary switches employed for signal routing. This phase shifter represents the first ever application of any RF MEMS rotary switch. It is shown that the switch model can accurately predict the measured performance of the phase shifter, without the need for adding new circuit elements or tweaking of model parameters. The low measured root mean square deviations of insertion phase from the predicted responses increase as 1.3 , 1.9 , 2.5 and 3.4 when the phase states are stepped through 0 , 90 , 180 and 270 , respectively. View full abstract»

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  • Design and experimental verification of ridge gap waveguide in bed of nails for parallel-plate mode suppression

    Page(s): 262 - 270
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (899 KB)  

    This study describes the design and experimental verification of the ridge gap waveguide, appearing in the gap between parallel metal plates. One of the plates has a texture in the form of a wave-guiding metal ridge surrounded by metal posts. The latter posts, referred to as a pin surface or bed of nails, are designed to give a stopband for the normal parallel-plate modes between 10 and 23 GHz. The hardware demonstrator includes two 90 bends and two capacitive coupled coaxial transitions enabling measurements with a vector network analyser (VNA). The measured results verify the large bandwidth and low losses of the quasi-transverse electromagnetic (TEM) mode propagating along the guiding ridge, and that 90 bends can be designed in the same way as for microstrip lines. The demonstrator is designed for use around 15 GHz. Still, the ridge gap waveguide is more advantageous for frequencies above 30 GHz, because it can be realised entirely from metal using milling or moulding, and there are no requirements for conducting joints between the two plates that otherwise is a problem when realising conventional hollow waveguides. View full abstract»

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  • Optimisation of MEMS-controlled reflectarray phase shifter cell

    Page(s): 271 - 276
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (337 KB)  

    An optimised design of an MEMS-based phase-shifter cell (reflectarray unit cell) based on an equivalent circuit model is presented. The optimisation is performed by controlling five key design parameters of the unit cell which are: the number of MEMS switches, their state (ON/OFF), their appropriate location inside the slot, their ON/OFF capacitances and whether they should be used singly or in a pair. By controlling and regulating these parameters through the equivalent electrical circuit, the design of the phase-shifter cell can be optimised. This optimisation process results in phase-shifter configurations that permit a 360° phase range along with the required number of linearly distributed phase states. Minimisation of power losses within the unit cell is also an issue addressed by the optimisation process. View full abstract»

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  • Tunable coplanar waveguide band-stop and band-pass filters based on open split ring resonators and open complementary split ring resonators

    Page(s): 277 - 281
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (502 KB)  

    In this study, the authors show that open split ring resonators (OSRRs) and open complementary split ring resonators (OCSRRs) can be loaded with varactor diodes in order to implement tunable filters in coplanar waveguide (CPW) technology. By loading a CPW with shunt-connected varactor-loaded OSRRs, a band-stop filter with tunable central frequency results. The electronically tunable band stop can be switched to a pass band by replacing the shunt resonators with varactor-loaded OCSRRs. To illustrate the possibilities of the approach, a tunable band-stop filter and a tunable band-pass filter have been designed and fabricated. The measured characteristics are in good agreement with the co-simulations (electric and electromagnetic) and with the circuit simulations of the electric model. The measured tuning range is roughly 120% for the stop-band structure (for varying voltages between 0 and 28%V) and over 30% for the band-pass filter (for varying voltages between 5 and 25%V). View full abstract»

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  • Numerical studies of bandwidth of parallel-plate cut-off realised by a bed of nails, corrugations and mushroom-type electromagnetic bandgap for use in gap waveguides

    Page(s): 282 - 289
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (995 KB)  

    Recently it has been shown that so-called gap waveguides can be generated in the gap between parallel metal plates. The gap waveguides are formed by metal ridges or strips along which local waves propagate, and parallel plate modes are prohibited from propagating by providing one of the surfaces with a texture that generates an artificial magnetic conductor (AMC) or an electromagnetic bandgap (EBG) surface on both sides of the ridges or strips. The bandwidth of the gap waveguide is determined by the cut-off bandwidth of a parallel-plate waveguide where one surface has such a texture (and no ridges or strips). This paper studies the bandwidths (or stop bands) of such parallel-plate cut-offs when the AMC or EBG is realised by a metal pin surface, corrugations or a mushroom surface. It is shown that cut-off bandwidths of up to 4:1 are potentially available, and thereby similar bandwidths should be achievable also for gap waveguides. View full abstract»

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  • Analysis and characterisation of coupled transmission lines loaded with complementary spiral resonators

    Page(s): 290 - 297
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (909 KB)  

    In this study, the behaviour of coupled microstrip transmission lines loaded with complementary spiral resonators (CSRs) is analysed in depth. CSRs are constitutive elements for the synthesis of metamaterials with negative effective permittivity which allows the suppression of undesired signals at a given frequency band. Several test prototypes have been characterised and modelled for transmission, crosstalk interference, isolation and signal integrity (SI). Experimental results reveal that CSRs provide a good solution to reduce crosstalk between parallel transmission lines in the radio frequency band with a low impact in terms of the SI. A design methodology based on the equivalent circuit model for the description of the proposed structures, including transmission lines and coupling parameters, is provided. View full abstract»

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  • Model for spatial-correlated clutter and its application to temporal-spatial correlated clutter

    Page(s): 298 - 304
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (645 KB)  

    Time-correlated clutter simulation based on the zero memory non-linearity transformation (ZMNL) and spherically invariant process (SIRP) suffers from spectrum expansion, and spatial-correlated clutter simulations may suffer from calculation complexity. To overcome these drawbacks, a new method of modelling and simulation of temporal-spatial-correlated clutter is proposed, based on the weighted norm in discrete complex linear space and a simple matrix transformation. Time-correlated clutter sequences with exact spectra can be generated by this algorithm through solving the minimum discrete weighted norm; whereas the spatial-correlated clutter can be generated by simple linear matrix transformations without complex calculations. It is shown that temporal-spatial-correlated clutter can be exactly and simply generated by the proposed method. Numerical simulation results show the feasibility and accuracy of this method. View full abstract»

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  • Genetic algorithm (GA)-enhanced almost difference set (ADS)-based approach for array thinning

    Page(s): 305 - 315
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1103 KB)  

    This study proposes a genetic algorithm (GA)-enhanced almost difference set (ADS)-based methodology to design thinned linear arrays with low-peak sidelobe levels (PSLs). The method allows one to overcome the limitations of the standard ADS approach in terms of flexibility and performances. The numerical validation, carried out in the far-field and for narrow-band signals, points out that with affordable computational efforts it is possible to design array arrangements that outperform standard ADS-based designs as well as standard GA approaches. View full abstract»

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  • Tunable sub-wavelength resonators based on barium-strontium-titanate thick-film technology

    Page(s): 316 - 323
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (503 KB)  

    This study shows recent results in the implementation of electrically reconfigurable structures based on sub-wavelength resonators implemented by means of ferroelectric materials. Barium-Strontium-Titanate thick films are employed as part of the substrate to implement electrically tunable split-ring resonators and open complementary split-ring resonators. Different structures have been fabricated proving the viability of this strategy for the implementation of reconfigurable structures. The achieved frequency shift reaches 12.6%. A parameter extraction method has been applied to study the effects of the modification of the dielectric permittivity of the ferroelectric material on the structure properties and its frequency response. View full abstract»

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  • Space-mapping modelling of microwave devices using multi-fidelity electromagnetic simulations

    Page(s): 324 - 333
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (897 KB)  

    The authors present efficient space mapping (SM) modelling of microwave devices where they assume a tight limit on the number of high-fidelity electromagnetic (EM) simulations available to set up a suitable model. The authors' method exploits a two-stage procedure. In the first stage, the standard SM surrogate is enhanced by a functional approximation layer using coarse-mesh EM simulation data. In the second stage, this surrogate is updated through space-mapping-based matching to high-fidelity EM simulation responses at a limited number of base locations (designs). The first stage normally uses a physically based coarse model, but in some cases direct approximation of the coarse-mesh EM simulation data is sufficient. The authors demonstrate that their proposed approach improves modelling accuracy in comparison with standard SM, and no extra fine model evaluations are required to set up the model. Applications to parametric design optimisation are discussed. View full abstract»

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  • Micromachined W-band waveguide and filter with two embedded H-plane bends

    Page(s): 334 - 339
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (599 KB)  

    A micromachined W-band through waveguide together with a passband filter embedded with a pair of H-plane bends is presented here. The novel design of the bend enabled direct and accurate connection between the micromachined circuit and standard waveguide flanges. The devices were fabricated using thick SU-8 photoresist technology. They were constructed with six gold- or silver-coated SU-8 layers, each of a thickness of 0.635 mm. These layers were then bonded on top of each other to form the waveguide and filter. A measured average insertion loss of 0.5 dB or 0.0278 dB/mm has been achieved by the 18 mm long through waveguide, and the return loss is better than 18.8 dB in the whole W-band. The asymmetrical capacitive irises coupled filter shows a 3 dB bandwidth of 8.61 GHz at a central frequency of 88.47 GHz. The passband insertion loss was measured to be between 0.97 and 1.1 dB and reflection loss is better than 15 dB. This performance demonstrates the potential of employing this micromachining and multi-layered technique to fabricate millimetre and submillimetre waveguide components. View full abstract»

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  • Hybrid ray-tracing model for radio wave propagation through periodic building structures

    Page(s): 340 - 348
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    A hybrid model is presented to study the radio wave propagation through periodic building structures for site-specific outdoor-to-indoor propagation. This hybrid model is based on combining ray-tracing and rigorous coupled wave analysis (RCWA) method, which is used to obtain the transmission properties of periodic building structures in the case of plane wave incidence. Numerical results of the hybrid model have been compared with those of finite-difference time-domain (FDTD) analysis. Good agreement has been achieved with substantially increased computation efficiency which validates the recommended hybrid method. View full abstract»

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  • Analytical approaches for nano-plasmonic and micro-millimetric antennas

    Page(s): 349 - 356
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    Antenna modelling approaches, based on suitable spherical harmonic expansions of the radiated electromagnetic field, are addressed and thoroughly investigated. Particular emphasis is put on the simultaneous transverse resonance diffraction (STRD) technique for plasmonic antennas. This method efficiently allows evaluation of the near-field distribution because of the interaction of optical sources, such as surface plasmon waves, with perfectly conducting wedges. The STRD technique based on the multipole expansion of Green's function (MEG) is particularly suitable for the design and rigorous analysis of wireless nano-systems. On the other hand, the characterisation of electromagnetic radiation processes in millimetric/micrometric short-pulse electrical antennas can be conveniently carried out by means of the dedicated singularity-expansion-method(SEM)-based methodology detailed in the second part of this study. Together, the proposed new analytical approaches provide a powerful and complete tool for small antenna design GHz and THz frequency ranges. View full abstract»

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  • Leaky-wave antenna based on microelectromechanical systems-loaded microstrip line

    Page(s): 357 - 363
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (661 KB)  

    The authors suggest and theoretically study an efficient leaky-wave antenna (LWA) with beam scanning governed by micro-electromechanical systems (MEMS) capacitors. The use of MEMS instead of varactors or magnetised ferrite substrate allows one to significantly decrease losses. The LWA is implemented as a periodically loaded transmission line (PLTL). In order to obtain maximal possible dispersion of a PLTL, resonant loads combining variable capacitors and stub strap inductors are applied. Analysis of dispersion properties and design of a unit cell of the PLTL are based on the analytical model with further numerical optimisation. Full-wave simulations are carried out for a realistic beam-scanning LWA, where the radiated beam can transit from forward to backward directions for a practical MEMS design. View full abstract»

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  • Multivariate gamma-gamma distribution with exponential correlation and its applications in radio frequency and optical wireless communications

    Page(s): 364 - 371
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (394 KB)  

    In this study, the multivariate gamma-gamma (G-G) distribution with exponential correlation is introduced and studied. Rapidly convergent infinite series representations are derived for the joint G-G probability density, cumulative distribution and moment generating functions. Based on these formulas, the performance of radio frequency wireless systems with diversity reception in the presence of composite multipath and shadow fading is analysed. Furthermore, the performance of single-input-multiple-output free space optical communication systems impaired by atmospheric turbulence is investigated. The correctness of the proposed analysis is demonstrated through various numerically evaluated results compared with equivalent computer simulation ones. View full abstract»

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  • Antipodal vivaldi antenna with tuneable band rejection capability

    Page(s): 372 - 378
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1252 KB)  

    An antipodal Vivaldi antenna with tuneable band reject capability is presented. The antenna presented has the capability to operate over the bandwidth 1.5-4.3 GHz at return loss <; -10 dB, but with a tuneable rejection band, the centre frequency of which may be varied in the range 1.8-2.8 GHz enabling rejection of cellular and ISM bands. Within this frequency range the return loss at the centre frequency of the rejected band varies from -2.7 to -4.1 dB. Farfield measurements show that radiation patterns are disrupted only within the rejected band and remain largely unaltered outside the rejected band. View full abstract»

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IET Microwaves, Antennas & Propagation covers all aspects of microwave and antenna engineering and propagation.

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