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Microwaves, Antennas & Propagation, IET

Issue 8 • Date December 2009

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Displaying Results 1 - 19 of 19
  • Input impedance of probe-fed rectangular microstrip antennas with variable air gap and varying aspect ratio

    Page(s): 1151 - 1156
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (447 KB)  

    The input impedance of a rectangular microstrip patch with a variable air gap has been studied theoretically and experimentally. Unlike earlier investigations, the influence of the air gap along with the varying patch width in changing the patch impedance is thoroughly examined. An efficient computer aided design formulation is developed and used for this study, and the computed results are experimentally verified. Superiority of the present theory compared to some earlier models is also indicated. View full abstract»

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  • Ultra-wideband power dividers with good isolation and improved sharp roll-off skirt

    Page(s): 1157 - 1163
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (665 KB)  

    A novel class of ultra-wideband power dividers with good isolation and sharp roll-off skirt is proposed, analysed and designed on microstrip topology. By introducing a pair of quarter-wavelength short-circuited stubs and/or parallel coupled lines to two symmetrical output ports, good performance in terms of equal power splitting is achieved over the ultra-wideband range, that is 3.1-10.6-GHz. A single resistor is then placed between two output ports such that good isolation is achieved between them. By virtue of direct-current chocked and half-wavelength transmission zeros of short-circuited stubs and coupled lines, out-of-band roll-off skirt near the cut-off frequencies is sharpened to a great extent. Two types of these power dividers are analysed and optimised using the simple transmission-line based even- and odd-mode approach. Based on comparative study of these two types, an ultra-wide band divider with coupled lines has been designed and fabricated. Measured results evidently confirm the predicted features of the divider in terms of return losses at all the three ports, input-to-output insertion losses and output-to-output isolation. View full abstract»

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  • Two-dimensional nonradiating currents for imaging systems: theoretical development and preliminary assessment

    Page(s): 1164 - 1171
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (295 KB)  

    An analytical orthonormal set of basis functions for 2D nonradiating current is derived. Preliminary numerical investigation shows the capabilities of this set of currents in enhancing the solution to an inverse scattering problem. View full abstract»

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  • Integrated sub-harmonically pumped up-converter antenna for spatial power combining

    Page(s): 1172 - 1178
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (609 KB)  

    A Ka-band sub-harmonically pumped up-converter antenna employing the substrate integrated waveguide (SIW) technique is proposed and used to realise a low-cost transmitter together with spatial power combining architecture in this paper. A single Ka-band sub-harmonically pumped up-converter using SIW band-pass filter is developed, exhibiting a conversion loss of about 7 dB. Based on the designed up-converter and SIW feeding antipodal linearly tapered slot antenna (SIW-ALTSA), the integrated up-converter antenna is designed and fabricated. Measured results of equivalent isotropic radiated power (EIRP) and radiation patterns are given. Finally, a 2 2 up-converter antenna array is designed and fabricated. Measured result shows the array has a power combining efficiency of above 90 and IM3 EIRP of 16 dBm. In close-range point-to-point communication and radar systems, the demonstrated millimetre-wave sub-harmonically pumped up-converter antenna array can be considered as a transmitter because of its low cost, high dynamic range and high linearity. View full abstract»

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  • Broadband radial waveguide power amplifier using a spatial power combining technique

    Page(s): 1179 - 1185
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (565 KB)  

    A broadband radial waveguide power amplifier has been designed and fabricated using a spatial power dividing/combining technique. A simple electromagnetic model of this power-dividing/combining structure has been developed. Analysis based on equivalent circuits gives the design formula for perfect power-dividing/combining circuits. The measured small-signal gain of the eight-device power amplifier is 12-16.5 dB over a broadband from 7 to 15 GHz. The measured maximum output power at 1-dB compression is 28.6 dBm at 10 GHz, with a power-combining efficiency of about 91-. Furthermore, the performance degradation of this power amplifier because of device failures has also been measured. View full abstract»

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  • Design of circular polarisation microstrip patch antennas with complementary split ring resonator

    Page(s): 1186 - 1190
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (263 KB)  

    A novel design of circular polarisation microstrip patch antennas based on the complementary split ring resonator is numerically evaluated and experimentally verified. The non-resonant property of complementary split ring resonator is used as an asymmetric perturbation to excite the square microstrip patch antenna for circular polarisation radiation. The detailed parameters of the complementary split ring resonator on the circular polarisation radiation are studied. View full abstract»

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  • Study of a microwave ferrite resonator antenna, based on a ferrimagnetic composite (Gd3Fe5O12)GdIGX-(Y3Fe5O12)YIG1-X

    Page(s): 1191 - 1198
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (507 KB)  

    The authors report a study on microwave properties of a ferrimagnetic ceramic composite (Gd3Fe5O12)GdIGx-(Y3Fe5O12)YIG1-x. The magnetic and dielectric measurements at microwave frequency were made through the Hakki-Coleman-s procedure and through the excitation of a cylindrical ferrite resonator antenna (FRA). The hysteresis loops of the GdIGxYIG1-x ferrimagnetic composite were obtained. The numerical simulation study was performed using Ansoft's High Frequency Structure Simulator (HFSS') software. The agreement between the experimental data and the simulated results is very good. These results demonstrated that, by varying the material composition of the resonator, ferrimagnetic composite GdIGxYIG1-xcould operate as a magneto-dielectric antenna with bandwidth in the range of 7.5-11- and in the frequency range of 4.4-5.3-GHz. Additionally, all FRAs presented a low negative value of tau f, which indicates suitability for microwave applications such as mobile communication systems or satellite broadcast systems. View full abstract»

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  • Tag identification enhancement by using a distributed antenna structure for radio frequency identification systems

    Page(s): 1199 - 1205
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    This study presents a distributed antenna structure operating at a frequency of 915 MHz to increase the tag identification sensitivity for passive radio frequency identification (RFID) systems. The distributed antennas are connected to a reader with a four-port power splitter/combiner which consists of Wilkinson power splitters (WPSs), band pass filters (BPFs) and power amplifiers (PAs). Due to the polarisation of the electromagnetic field, the antennas are positioned on opposite sides in both vertical and horizontal directions of the object. This positioning improves the performance of the system, and increases the sensitivity when identifying unclearly positioned tags. An experimental RFID system is also set up to demonstrate the proposed structure. Simulation and experimental results indicate that using four distributed patch antennae can improve tag identification in passive RFID systems. View full abstract»

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  • Compact quasi-elliptic microstrip bandpass filter using terminated anti-parallel coupled-line

    Page(s): 1206 - 1210
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    A compact quasi-elliptic microstrip bandpass filter with lower and upper stopband zeros is presented. The bandpass filter consists of terminated anti-parallel coupled-line and the stopband zero is generated and controlled by the reactive termination. In comparison to the traditional parallel coupled-line bandpass filter, the proposed filter achieves simultaneous size reduction and sharp filter skirt. The usefulness of the proposed filter is validated by a simultaneously miniature and selective quasi-elliptic bandpass filter centred at 2.4 GHz with 4.6 fractional bandwidth as well as two transmission zeros at 2 and 3.2 GHz. View full abstract»

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  • Short backfire antenna with microstrip Clavin feed

    Page(s): 1211 - 1217
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (722 KB)  

    A single short backfire antenna has an enclosed structure with no sharp projections and approximately 15 dBi gains, making it attractive for handheld radio monitoring and other man-portable applications. However, a microstrip patch fed short backfire antenna had a broad E-plane radiation pattern main lobe, leading to a loss of gain and low aperture efficiency. The antenna was studied using a commercially available method of moment's software. Adding eight parasitic wires inside the cavity of a short backfire was found to narrow the E-plane radiation pattern main lobe, making it more like the H-plane radiation pattern and increasing the peak gain by 1.5 dB. A single proof of concept antenna was built at 1.49 GHz, which had a bandwidth of 2.3%, aperture efficiency of 78% and was shown to have equalized principal plane main lobes. View full abstract»

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  • Analytic solution of non-uniform transmission lines at low frequencies

    Page(s): 1218 - 1223
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (462 KB)  

    A simple approximated analytical solution is introduced to analyse arbitrary non-uniform transmission lines (NTLs) at low frequencies. First, the differential equations of NTLs are written as a suitable matrix differential equation. Then, the matrix differential equation is solved to obtain the chain parameter matrix of NTLs. Later, the voltage and current of the line are obtained at any point using the obtained chain parameter matrix. Finally, the validation of the introduced solution is studied. View full abstract»

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  • A miniaturised monopole antenna for ultra-wide band applications with band-notch filter

    Page(s): 1224 - 1231
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (918 KB)  

    This study presents a new miniaturised printed monopole antenna. The size of the antenna is 18times18 mm2. First simple design rules are given to arrive at an initial design for the antenna, then the antenna parameters are optimised for utilisation in ultra wide band (UWB) applications. The performance parameters like voltage standing wave ratio (VSWR) of the single antenna as well as transmission function, group delay and the fidelity factor of a two-antenna system are calculated and measured. It is shown that the band-notched performance can be obtained from the designed antenna by introducing simple pi-shape or V-shape slots in its radiating element. Good agreements between simulated and measured results are observed. View full abstract»

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  • Band-notched ultra-wideband bandpass filter design using combined modified quarter-wavelength tri-section stepped-impedance resonator

    Page(s): 1232 - 1236
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (323 KB)  

    This study presents a new band-notched ultra-wideband (UWB) bandpass filter (BPF) that is designed using a new structure-shared multi-mode resonator (MMR). The MMR is formed by combining two quarter-wavelength (lambda/4) tri-section stepped-impedance resonators (TSSIRs) in a proper fashion to exhibit both lambda/4 and half-wavelength (lambda/2) types of resonance. With the first two resonant frequencies of the inherent lambda/4 TSSIR, the first two of the parasitic lambda/2 SIR and the coupling peaks of the input/output interdigital parallel-coupled lines properly located in the UWB passband, a six-transmission-pole UWB BPF can be realised. In this filter design, besides obtaining a uniform in-band transmission response, a notched band centred around 5.5 GHz is created by embedding L-shaped open-end slots in the TSSIR and loading the TSSIR with closely coupled winding-type resonators (WTRs) to filter out the 5-GHz wireless local-area network radio signal interferences. In addition, spur-lines are embedded in the TSSIR to sharpen the passband skirts for selectivity improvement. View full abstract»

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  • High-frequency surface wave radar based on a sea floating antenna concept

    Page(s): 1237 - 1244
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    The concept of sea floating antenna array is to replace a conventional coastal receive unit by a sea floating array, constituted of a set of receive buoys. Waves and wind introduce movements of buoys in the array which generate disturbances in the array radiation pattern. In this paper, compensation methods for vertical and horizontal displacements are presented. This paper introduces algorithms for both displacements which are tested following different sea states. Then, these algorithms can be combined in series, providing a simple method to optimise the radiation pattern of the deformed array. View full abstract»

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  • Synthesis of non-uniformly spaced arrays using the Fourier transform and window techniques

    Page(s): 1245 - 1253
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (257 KB)  

    Under the Fourier relation between the array factor and its corresponding source distribution, synthesis approaches of non-uniformly spaced arrays (NUSAs) are proposed. Using the Fourier transform and synthesis concepts of space-tapered arrays, the optimum patterns like Chebyshev are used to synthesise NUSAs with uniform amplitude, whose array factors have the performance approximated to the chosen patterns. The Fourier transform properties can be used to control the array factor so that the proposed approaches are applied in different synthesis specifications. Based on the synthesised NUSAs with uniform amplitude and window techniques, under the sampling theorem, NUSAs with non-uniform amplitude can be easily obtained to improve the performance of the array factor, mainly in the reduction of sidelobe level. Synthesis examples show the advantages of the presented methods. View full abstract»

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  • Three-dimensional hybrid implicit–explicit finite-difference time-domain method in the cylindrical coordinate system

    Page(s): 1254 - 1261
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (299 KB)  

    A novel hybrid implicit-explicit (HIE) finite-difference time-domain (FDTD) method, which is extremely useful for problems with very fine structures along the ϕ-direction in cylindrical coordinate system, is presented. This method has higher computation efficiency than conventional cylindrical FDTD methods, because the time step in this method is only determined by the space discretisations in the radial and vertical directions. The numerical stability of the proposed HIE-FDTD method is presented analytically. Compared with the cylindrical alternating-direction implicit (ADI)-FDTD method, this HIE-FDTD method has higher accuracy, especially for larger time step size. At each time step, the HIE-FDTD method requires the solution of two tridiagonal matrices and four explicit updates. While maintaining the same size of time step, the central processing unit (CPU) time for this weakly conditionally stable FDTD method can be reduced to about 3/5 of that for the ADI-FDTD scheme. The numerical performance of the proposed HIE-FDTD over the conventional cylindrical FDTD method and cylindrical ADI-FDTD method is demonstrated through numerical examples. View full abstract»

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  • Numerical and experimental studies of split ring resonators loaded on the sidewalls of rectangular waveguides

    Page(s): 1262 - 1270
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (720 KB)  

    This work investigates the use of a lattice comprising split ring resonators (SRRs) as a negative permeability medium to achieve backward travelling modes within a rectangular waveguide. The loadings of such SRR-type periodic structures into a waveguide can be tailored such that the backward mode exists in a passband below the ordinary basic modal cutoff frequency, thus affording filtering capabilities and miniaturisation. Theoretical studies by two approaches are performed here, a moment method spectral domain analysis, and a commercial simulation tool. Parametric studies that characterise the effects of various dimensional and electrical properties on the dispersion behaviour of the SRR-loaded waveguide shall also be conducted. The SRR parameters are then optimised using the ant colony optimisation (ACO) algorithm to achieve a low backward passband, for a high degree of miniaturisation and isolation. Experimental results of measurements performed on a manufactured prototype of the optimised SRR-loaded waveguide will also be presented. View full abstract»

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  • Effect of antenna dimensions on the antenna footprint in ground penetrating radar applications

    Page(s): 1271 - 1278
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (715 KB)  

    Ground penetrating radar (GPR) surveys show that antenna characteristic is strongly influenced by soil conditions. The footprint of the antenna is an important parameter for a good detection result. Various conditions of soil in which a target is buried may change the footprint of the antenna. An antenna with capability to control its footprint is needed in GPR applications. In this study, the authors investigate several ultra-wideband (UWB) antennas with different dimensions to study the effect of antenna dimension on their footprint. Simulation and experiments show that large (small) antenna dimensions result in a large (small) antenna footprint when the observation is located in the near-field region. When the observation is located in the far-field, the footprint of the antenna becomes large (small) if the dimensions of the antenna are small (large). Thus, the size of the antenna footprint can be adjusted by varying the antenna dimension. It is applied in this work to develop a new method for controlling the antenna footprint to deal with varying soil condition. Measurements have been carried out to validate this concept. View full abstract»

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  • In-flight experiment for combined planar antennas and solar cells (SOLANT)

    Page(s): 1279 - 1287
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1270 KB)  

    An in-flight experiment to validate advanced solar antenna structures (SOLANT) in space is presented. Two different antennas have been designed and manufactured, one for Global Positioning System (GPS) reception and one for S-band beacon transmission. Both units use slot aperture radiators embedded in identical mechanical structures. The GPS antenna has been designed to generate an omni-directional radiation pattern with right-handed circular polarisation thus fulfilling NavStar specifications. The S-band beacon antenna is based on a four-element circularly polarised array providing 6 dBic of gain. These antennas are integrated within two solar panels, which form the upper layer of the antenna structure. The two panels are identical, make use of gallium arsenide (GaAs) solar cells arranged in two strings and provide a peak power of 10 W each. The SOLANTs were launched, fixed to a Cosmos payload adapter and remained operative for 2 years, well beyond their expected lifetime. This study summarises the design and performance tests performed prior the launch and during the orbital operation. View full abstract»

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