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Microwaves, Antennas & Propagation, IET

Issue 14 • Date November 18 2011

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Displaying Results 1 - 17 of 17
  • Study of broadband near-field antenna for ultra-highfrequency radio frequency identification applications

    Page(s): 1661 - 1669
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (835 KB)  

    A novel antenna for applications in an ultra-high-frequency (UHF) radio frequency identification (RFID) reader system is proposed and investigated. The antenna achieves a gain of lower than -10-dBi in all directions with strong magnetic field distribution over the entire UHF RFID band of 830-950-MHz as well as good performance in detecting tags when applied in UHF RFID systems. The antenna configuration is described and the principle of operation is explained. To investigate the effects of each parameter on the antenna performance, a comprehensive parametric study is carried out and the results are presented in detail and discussed. To prove the concept, a prototype is developed and fabricated. The measurement results demonstrate that the antenna can achieve a broad bandwidth and low gain, and produce a strong magnetic field with relatively concentrated field distribution in the near-field region of the antenna. Hence, this work is very promising for UHF near-field RFID reader applications. View full abstract»

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  • Design and optimisation of a novel dual-band circularly polarised microstrip antenna

    Page(s): 1670 - 1674
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    A novel dual-band circularly polarised patch feed antenna is presented. It is theoretically analysed and simulated. It is optimised with a genetic algorithm (GA) which is capable of producing an antenna design that has a low voltage standing wave ratio (VSWR), low cross-polarisation and large bandwidths but small dimensions. A hybrid finite-element method/method of moment model was used to simulate the proposed antenna in which 1.54% axial ratio bandwidth was obtained. Both the effectiveness of the optimisation methodology and the proposed antenna configuration have been scrutinised by simulation and theoretical analysis. View full abstract»

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  • Reconfigurable tri-band H-shaped antenna with frequency selectivity feature for compact wireless communication systems

    Page(s): 1675 - 1682
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (994 KB)  

    This study presents an H-shaped reconfigurable antenna for wireless applications. The antenna consists of an H-shape radiator and a CPW printed on a circuit board and a varactor diode connecting the upper and lower arms of the H-shape radiator for reconfigurability. The uniqueness of the antenna lies on the ability to select the operating mode and frequencies electronically using a varactor diode. By selecting the DC-bias voltages of 11.5, 10 and 8 V across the varactor diode, which in turn selects the corresponding varactor capacitances of 2, 4 and 6 pF, the antenna can be controlled to operate in three different modes, namely a single-band mode to cover the GSM1900, a dual-band mode at 1.88 and 2.4 GHz to cover the GSM1900 and Bluetooth/WLAN, respectively and a tri-band mode at 1.57, 1.88 and 2.4 GHz to cover the GSM1900, WLAN and GPS, respectively. Furthermore, by varying the varactor capacitance from 7 to 13 pF, the GPS and WLAN bands can be tuned by 11.44% (1.57-1.4 GHz) and 6.46% (2.4-2.25 GHz), respectively, yet keeping the 1.88-GHz band unchanged. Detailed studies on the antenna's performance are carried out to investigate the behaviour of the antenna at each resonant frequency in each operating mode. View full abstract»

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  • Miniature microstrip-fed ultra-wideband printed monopole antenna with a partial ground plane structure

    Page(s): 1683 - 1689
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (662 KB)  

    A new microstrip-fed planar monopole antenna is presented for ultra-wideband (UWB) communication systems. The antenna structure consists of a dome-topped, bowl-shaped patch with a truncated ground plane structure. The ground plane is predominately tapered and includes a notch below the feed-line in the vicinity of the patch. The effects of dimensional parameters on the performance of the antenna have been investigated through a parametric study. Current density distribution on the antenna was also computed to gain a better insight of its behaviour. The antenna performance is validated through measurement, including its radiation patterns. The measured impedance bandwidth of the proposed antenna for |S11||| |10|dB is 10.35|GHz (2.65|13.0|GHz), constituting 132| impedance bandwidth. The fabricated antenna has a compact size of 18|20|1.6|mm3. Additional features that make the antenna a suitable candidate for UWB systems are its simple configuration, compactness and low fabrication cost. View full abstract»

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  • Fast integral equation-fourier transformation algorithm with grid-robust higher-order vector basis

    Page(s): 1690 - 1696
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (506 KB)  

    An integral equation-fast Fourier transformation (IE-FFT) with grid-robust higher order vector basis functions (BFs) are presented. A conformal mesh is required for traditional BFs based on common edges between adjacent elements. This is a very rigorous requirement for large and complicated electrical geometries. Instead of a conformal mesh, grid-robust higher-order vector BFs are used here. It maintains the flexibility of geometry modelling and reduces the number of the unknowns owing to the property of point BFs. An IE-FFT algorithm based on a flexible floating stencil topology is proposed to accelerate the solution of the IE. Comparing the IE-FFT with traditional RWG BFs, the present method has a much lower error of interpolation, and the matrix is also simpler to implement. Numerical results are presented to demonstrate the accuracy and efficiency of this method. View full abstract»

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  • Reduced log-periodic dipole antenna using a cylindrical-hat cover

    Page(s): 1697 - 1702
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (710 KB)  

    A technique to decrease the size of log-periodic dipole array (LPDA) antennas employing inductive loads on its elements is introduced. This technique consists of adding a short-circuited cylindrical hat cover at the end of each arm of the antenna. Simulation and measurement results show that the total area, if considered as a trapezoid, of a fabricated LPDA antenna, based on the proposed technique, is approximately 50% smaller than the size area of a reference antenna using a conventional technique. The parameters of the reduced antenna are slightly modified, preserving the bandwidth, impedance, polarisation and radiation pattern shape. The drawback of this technique is the small reduction of gain, from 7.5%dB for the conventional antenna to 6.4%dB for the reduced prototype in the middle operation band. View full abstract»

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  • Computation of the scattered fields from a dielectric object buried in a medium with a periodic surface by a decomposition method

    Page(s): 1703 - 1709
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (534 KB)  

    The electromagnetic scattering from a cylindrical dielectric object of arbitrary cross-section buried in a lossy dielectric half-space having a periodic surface is investigated using a new numerical method. The method is outlined for TMz (horizontally) polarised incident wave. The surface equivalence principle and a decomposition method are employed to form a set of electric field integral equations (EFIEs) for the currents on the object and the portion of the surface most strongly interacting with the object. Then, the method of moment (MoM) is used to solve the EFIEs in the frequency domain to obtain the scattered electric field. View full abstract»

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  • Trends in the incidence of rain height and the effects on global satellite telecommunications

    Page(s): 1710 - 1713
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    Satellite communications using millimetre waves, in Ka band and above, experience significant fading by rain. Strong attenuation is experienced between the ground station and a level known as the rain height, in ITU-R recommendations assumed to be 360 m above the zero-degree isotherm (ZDI). This study examines National Oceanic and Atmospheric Administration National Centres for Environmental Prediction (NCEP)/National Centre for Atmospheric Research (NCAR) Reanalysis 1 data to identify changes in the ZDI height over the last 30 years. Near the equator and the poles the ZDI height has been approximately stable over this period. However, in mid-latitudes, different regions show trends of increasing or decreasing ZDI height. Over the economically important regions of North America, China and Western Europe, the ZDI height has shown an increasing trend with peak rates in the range of 8 10 m per year. Given a 20-year life-time of a satellite system, this could lead to a 10 20 increase in fade intensity from a similar rain event. The effect will be compounded by increasing trends in the incidence of heavy rain recently identified in UK data. These trends will need to be considered when designing new systems. View full abstract»

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  • Multi-layer quadrature hybrid coupler design composed of multiple circular sectors

    Page(s): 1714 - 1719
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (483 KB)  

    A hybrid coupler design composed of multiple circular sectors is presented. It is designed to cover wireless local-area network bands at 2.4, 5.25 and 5.8 GHz, ultra-wideband at 3.1 4.8 GHz, digital multimedia broadcasting at 2.6 GHz and WiMax at 3.5 GHz. The coupler achieves an amplitude imbalance of 1 dB and a phase error of 5 at the outputs within the design frequency range. The developed coupler was compared with other existing designs in literature. It demonstrated advantages in terms of wide operating bandwidth as well as small physical size. View full abstract»

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  • Dual-band matching technique based on dual-characteristic impedance transformers for dual-band power amplifiers design

    Page(s): 1720 - 1729
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (701 KB)  

    This study demonstrates a novel matching network synthesis technique that matches any arbitrary reflection coefficient seen by the active device at two uncorrelated frequencies to the standard 50 load. The proposed matching network is fully transmission line based and, hence, can be used in high-power applications at higher frequencies. Unlike previously reported dual-band matching techniques, this work proposes and discusses various ways to achieve realisable solutions for arbitrary frequency ratios that account for fabrication limitations. The proposed synthesis approach is validated with the design and fabrication of a 10 W gallium nitride (GaN)-based class-AB amplifier for code division multiple access and Worldwide Interoperability for Microwave Access applications at 1960 and 3500 MHz. The amplifier has 59.8 and 55.1 drain efficiencies at saturation in the first and second bands, respectively. View full abstract»

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  • Reconfigurable cascaded coupled line filter with four distinct bandwidth states

    Page(s): 1730 - 1737
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (751 KB)  

    This study presents a cascaded coupled line filtering structure for the development of high-order reconfigurable microwave filters. A reconfigurable bandpass filter of this type that is capable of switching between four distinct bandwidth states ranging from around 20 to 50% 3%dB fractional bandwidth centred at 2%GHz, is described. The filter exhibits insertion losses ranging from 0.47 to 5.5%dB. The circuit is designed from a filter building block proposed previously in earlier literature. The publication enhances the understanding of this building block and shows why such a filter topology is used in order to develop higher order filters. This is done through mathematical modelling of the filter building block and theoretical simulation. The modelling shows that the centre frequency is only dependent on the set of even- and odd-mode impedances, which makes tuning the bandwidth easy. It also shows that changing the characteristic impedance of short-circuit stubs changes the bandwidth. The fabricated filter shows good agreement with electromagnetic simulated results. View full abstract»

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  • Received signal strength in large-scale wireless relay sensor network: A stochastic ray approach

    Page(s): 1738 - 1743
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (299 KB)  

    The authors consider a point percolation lattice representation of a large-scale wireless relay sensor network (WRSN) deployed in a cluttered environment. Each relay sensor corresponds to a grid point in the random lattice and the signal sent by the source is modelled as an ensemble of photons that spread in the space, which may `hit` other sensors and are `scattered` around. At each hit, the relay node forwards the received signal to its nearest neighbour through direction-selective relaying. The authors first derive the distribution that a relay path reaches a prescribed location after undergoing certain number of hops. Subsequently, a closed-form expression of the average received signal strength (RSS) at the destination can be computed as the summation of all signal echoes` energy. Finally, the effect of the anomalous diffusion exponent ` on the mean RSS in a WRSN is studied, for which it is found that the RSS scaling exponent ` is given by (3``1)/`. The results would provide useful insight into the design and deployment of large-scale WRSNs in future. View full abstract»

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  • Tapered impedance loading for suppression of edge scattering

    Page(s): 1744 - 1749
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    Tapered impedance loading is studied to suppress edge scattering from a rectangular metallic plate. Associated with the pattern multiplication theorem, a simple approach to this scattering problem is proposed assuming the current distribution of the target is broken into an array of overlapping triangles. This tapered impedance is realised by geometric variations based on frequency-selective surfaces concepts. Electromagnetic back-scattering of the as-prepared target from a rectangular plate with edge tapered impedance loading is analysed for both horizontal polarisation and vertical polarisation, and compared with that from one of the same shape but loaded with constant or no impedance on the edge. It is found that the proposed tapered impedance loading advances the wide angular radar cross section reduction of the target further than the other designs, and works with the change of the azimuth angular of incidence wave, solving the problem met by the popular trailing-edge serration method. View full abstract»

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  • Enhanced performance of a patch antenna using spiral-shaped electromagnetic bandgap structures for high-speed wireless networks

    Page(s): 1750 - 1755
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (462 KB)  

    This study describes the improvement of gain and bandwidth of a microstrip patch antenna achieved using a spiral-like electromagnetic bandgap (EBG) structure for high-speed wireless local area networks. The size of the antenna is only 45 × 45 × 2.47 mm and resonates at a frequency of 2.4 GHz. The gain and bandwidth of this antenna is 3 dBi and 67.4% greater than a conventional patch antenna. The working frequency of the patch antenna falls inside the EBG bandgap, which leads to the suppression of surface waves. Simulations of the antenna are conducted using the finite-difference time-domain analysis technique. The electromagnetic (EM) simulated and measured return loss, gain, directivity, radiation pattern, antenna efficiency and voltage standing wave ratio are presented for the proposed antenna array. These results allow one to determine the structures giving the best focusing performance and to obtain the frequency band for directive radiation. View full abstract»

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  • Radiation field computation of leaky coaxial cables by finite-difference time domain in cylindrical coordinates and equivalent source integration

    Page(s): 1756 - 1762
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (834 KB)  

    A combined scheme involving a conventional perfectly matched layer and lossy material is proposed for absorbing both the radiating and evanescent waves of leaky coaxial cables (LCX) efficiently. After parameter optimisation and correctness verification, the combined absorbing boundary is used to calculate the near field of LCX with horizontal triangle slots. The radiation field is then obtained by integrating the near field on an equivalent surface surrounding the cable. The LCX with horizontal triangle slots is desired to have advantages in generating smoother field distribution around the cable, especially for the vertical component. View full abstract»

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  • Integrated closed-form model and circuit model of lossy slot line

    Page(s): 1763 - 1772
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (585 KB)  

    An integrated closed-form model and circuit model are used to compute the conductor thickness-dependent effective relative permittivity εeff(f, t), characteristic impedance Z0(f, t), dielectric loss αd(f, t) and conductor loss αc(f, t) of a slot line. The circuit model demonstrates dispersion at frequencies below 1 GHz. It also computes the imaginary part of Z0(f, t). The accuracy of the circuit model is tested against several full-wave methods in the frequency range 0.1-60-GHz for a conductor thickness 3-50--m. For -eff(f, t) and Z0(f, t) the average deviation is <;1.36<;, for <;c(f, t) it is 1.88% and for total loss %(f, t) it is 2.13% against the full-wave methods and EM-simulators. View full abstract»

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  • Wideband antenna using a multiple-mode slotline radiator: Proposal and implementation

    Page(s): 1773 - 1778
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1007 KB)  

    A novel wideband antenna with a multiple-mode radiator on slotline is proposed. This slotline resonator is asymmetrically fed at a right angle by a short-ended microstrip line on the opposite side of the substrate. First, parametric studies are executed on frequency-dependent input impedance with respect to feeding positions and slot/strip widths, aiming at simultaneously exciting its first and second resonant modes for radiation. By properly choosing the port impedance, our initial predicted return loss exhibits the emergence of a wide operating band with a fractional bandwidth of 41.7% at 3.98%GHz, where two reflection zeros are created under dual resonant modes. Second, by introducing a quarter-wavelength impedance transformer, two 50-% microstrip-fed slotline antennas with short- or open-ended stubs in the feeding line are proposed and then designed for practical implementation of such a class of dual-mode slotline antennas. The measurements for these two antennas show that the impedance bandwidths are successfully achieved 40.0%41.0% as expected and the radiation patterns retain stable in the operating wideband with an antenna gain of about 4.0%dBi. View full abstract»

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