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Microwaves, Antennas & Propagation, IET

Issue 1 • Date January 11 2012

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Displaying Results 1 - 16 of 16
  • Circular polarisation from dual-layer square-ring microstrip antennas

    Page(s): 1 - 9
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (899 KB)  

    Stacked microstrip square-ring antennas are investigated for circular polarisation (CP). Enhancement of axial ratio bandwidth is obtained using stacked square rings and applying corner perturbations to both parasitic and driven rings. Both negative and positive corner perturbations are used and wide axial ratio bandwidths are demonstrated. A novel approach is presented, where a combination of positive and negative perturbations is adopted in the driven and parasitic rings, respectively, which resembles a sequential rotation and offers broad axial ratio bandwidth, along with a wide axial ratio beamwidth. The effects of finite ground plane on the CP performance of this antenna are studied, and methods are presented to overcome the problems associated with the degradation of the CP performance because of the finite ground plane. The effect of positioning the antenna asymmetrically on the ground plane is also studied, which shows that the ground plane symmetry is important for the CP antenna. The measured 3 dB axial ratio bandwidth of approximately 5.15 is achieved for dual-layer square-ring antennas. The measured right-hand CP (RHCP) gain is in excess of 7 dBic for a wide frequency range. The simulation results are in good agreement with the measured data. View full abstract»

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  • Design of wide-single-/dual-passband bandpass filters with comb-loaded resonators

    Page(s): 10 - 16
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (631 KB)  

    Novel wide-single-/dual-passband bandpass filters with comb-loaded resonators are proposed. With the comb-loaded resonators, wide single/dual passbands appear. In particular, dual passbands show up around 2.45 and 5.75 GHz and their bandwidth is 780 MHz. Furthermore, because of the uniplanar structure, the proposed filters are compact and can be fabricated on a printed circuit board. Design equations are provided. The agreement between measurement and the theoretical prediction validates the proposed structure. View full abstract»

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  • Compact multi-band printed dipole antenna loaded with single-cell metamaterial

    Page(s): 17 - 23
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    A compact multi-band printed dipole antenna loaded with reactive elements is proposed. The reactive loading of the dipole is inspired by the Epsilon-negative (ENG) and double negative metamaterial inclusions, which enable the loaded dipole to operate in multi-band. The reactive loads are realised by two rake-shaped split ring resonators facing each other. Investigations reveal that the loaded dipole radiates at two or three separated bands depending on symmetrical or asymmetrical loading and load locations. The new resonance frequencies are lower than the natural resonance frequency of the conventional half-wavelength dipole. In this range of frequencies, the radiation efficiency of the composite antenna is high. In order to validate the simulation results, a prototype of the proposed printed dipole is fabricated and tested. The agreement between the simulated and measured results is quite good. View full abstract»

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  • Design of multiple-passband filters using coupling matrix optimisation

    Page(s): 24 - 30
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (383 KB)  

    This study presents the design of microwave filters based on the coupling matrix approach; determination of the matrix is based on a hybrid optimisation algorithm which may be applied to cross-coupled filters having diverse topologies. Various filter responses from dual-band to quad-band are given as examples of the approach. The optimisation is performed on the coupling matrix and a genetic algorithm (GA) is employed to generate initial values for the control variables for a subsequent local optimisation (sequential quadratic programming search). The novel cost function in this study measures the difference of the frequency locations of reflection and transmission zeros between the response produced by the coupling matrix and the ideal response. The ideal response in the form of characteristic polynomials is determined from the filter specifications and generated by a recently developed iterative technique which is capable of realising multi-band filters with different return loss levels. Convergence of the coupling matrix optimisation is fast, and no initial values for the control parameters are required by the GA. An eighth-order X-band dual-band waveguide filter with all-capacitive-coupling irises has been fabricated and measured to verify the design technique. Excellent agreement between simulation and experimental result has been achieved. View full abstract»

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  • Review of the microstrip/negative-refractive-index transmission-line coupled-line coupler

    Page(s): 31 - 45
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1773 KB)  

    The microstrip/negative-refractive-index transmission-line (MS/NRI-TL) coupler is constructed by edge coupling a regular microstrip line to a backward wave negative-refractive-index transmission line. This coupler is primarily operated in the complex-mode band in which the eigenmodes are characterised by simultaneous phase progression and attenuation (in a lossless structure) and is accompanied by contra-directional power flow on the two lines. The complex modes that are excited by the sources in this coupler can be controlled independently and by examining the multiple reflections of these modes between the two terminal planes, the scattering parameters of the corresponding four-port device can be derived. Under a first-order approximation, it is determined that the MS/NRI-TL coupler is capable of achieving arbitrary coupling levels (by increasing the length of the coupler) and very high directivity (by making the coupler length equal to an odd multiple of half a guided wavelength). Useful nomographs that enable the realisation of MS/NRI-TL couplers to meet arbitrary design specifications are included and several applications of the coupler are also presented. View full abstract»

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  • Numerically efficient method-of-moments formulation valid over a wide frequency band including very low frequencies

    Page(s): 46 - 51
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    A method of moments (MoM)-based procedure is developed for efficient treatment of scattering problems over a wide frequency band where many of the conventional algorithms often fail. The proposed method uses a type of basis function whose radiated field is expressible in a convenient closed-form. This, in turn, circumvents the need to either employ the Green's function to formulate the problem, or having to deal with the singularities of the same. Furthermore, since the formulation deals with the electric fields generated by the basis functions directly, without involving the vector and scalar potentials typically employed in the conventional MoM formulation, it is possible to use a uniform formulation over a much wider frequency range without having to resort to special basis functions, for example, the loop-stars. Numerical results validating the accuracy and the numerical efficiency of the proposed method both in the near- and in the far-field regions are included in this study. View full abstract»

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  • Characterisation and application of embedded lumped elements in multilayer advanced thick-film multichip-module technology

    Page(s): 52 - 59
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    This study presents the characterisation and modelling of embedded multilayer and miniaturised lumped element inductors and capacitors in thin-film microstrip (TFMS) configuration with remarkably high performance using cost-effective photoimageable thick film multichip-module (MCM) technology. The proposed miniaturised multi-turn spiral inductors are designed with circular geometry and removal of the ground plane underneath the coil structure to improve the self-resonance frequency (SRF) as well as the quality factor (Q). The circular 2.5 turn spiral inductor has inductance of 3.7 nH, a high SRF of 8.4 GHz, high-quality factor and measures only 0.6 × 0.7 mm2. Using the high-performance lumped elements, a fully embedded TFMS low-pass filter (LPF) is demonstrated with a remarkably low-passband insertion loss of 0.3 dB, return loss better than 25 dB, wide spurious free stop band attenuation >;45 dB and yet highly miniaturised, measuring only 5.4 × 1.1 × 0.3 mm3. The measured response characteristics are in excellent agreement with the predicted response. The miniaturised filter is highly suitable for use as a discrete component or as part of the intermediate frequency (IF) section of a compact integrated microwave or millimetre-wave MCM. This represents one of the highest passive component performances ever reported for ceramic-based MCM technology. View full abstract»

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  • Solution of wide band scattering problems using the characteristic basis function method

    Page(s): 60 - 66
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (799 KB)  

    A numerically efficient method for the evaluation of wide band scattering characteristics is presented. This approach, which is based on the characteristic basis function method (CBFM), utilises the characteristic basis functions (CBFs) that are derived for the highest frequency in the range of interest. These CBFs, once generated, also capture the electromagnetic behaviour of the lower frequencies as well. The use of these bases, which will be referred to as ultra-wide band characteristic basis functions (UCBFs), enables one to solve the scattering for any frequency sample in the band without going through the time-consuming process to generate the CBFs anew. Numerical results shown validate the accuracy and the time efficiency of this method. View full abstract»

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  • Polarisation insensitive in-situ resistive sensor for high-power microwave pulse measurement in TE11 mode circular waveguide

    Page(s): 67 - 71
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    A resistive sensor (RS) based on the electron heating effect in semiconductors is considered for high-power microwave pulse measurements in TE11 (H11) mode circular waveguide. A plate-shaped semiconductor sample with contacts on its top and bottom is used as the sensing element (SE). A three-dimensional finite-difference time-domain method was applied for the calculation of the electric field strength in the SE. The optimal dimensions and specific resistance of the SE have been found, providing a flat frequency response for the RS when the SE position in the waveguide coincides with a polarisation plane of the wave. A polarisation-insensitive layout of the RS consisting of two SEs placed at 90° from each other has been proposed. It is shown that the sum of their signals (within °7°) is independent of the position of the polarisation plane in the waveguide. View full abstract»

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  • Design of broadside-coupled parallel line millimetre wave filters by standard 0.18-μm complimentary metal oxide semiconductor technology

    Page(s): 72 - 78
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (681 KB)  

    An equivalent circuit technique is used to design a class of compacted millimetre-wave band-pass filters in the standard 0.18-μm complimentary metal oxide semiconductor (CMOS) process. Thin film microstrip is fabricated on a lossy silicon substrate to realise low insertion loss. Using a broadside-coupled scheme and floating metallic patch structure, thin film microstrip band-pass filters are designed and fabricated. An equivalent circuit model and microwave theoretical network analysis is given to explain the performance of the proposed filters. Meandering transmission lines are used to miniaturise the chip size. A class of compacted K-band band-pass filters including one-pole, two-pole and three-pole designs is implemented. The measured results are in good agreement with predicted results. View full abstract»

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  • Adaptive penta-band handset antenna with hand effect compensation

    Page(s): 79 - 86
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (895 KB)  

    The increase in the number of cellular operating bands and the ever-increasing criteria antenna size reduction has pushed the need to use switchable antenna structures. Further, the presence of a hand in the close vicinity of the antenna causes deterioration in performance. The authors present a switchable antenna technique, evaluate the effect of the human hand on it and discuss a novel method to compensate for the mismatch. A penta-band switchable planar inverted-F antenna covering 824-960 and 1710-2170-MHz has been used in this study. The presence of the hand was observed to cause 2.0-6.0-dB loss in efficiency for the low band. Using the proposed extra-ground antenna switching method and the dynamic antenna matching, technique the total efficiency of the antenna can be improved by 0.5-2.5-dB compared to the mismatched case. View full abstract»

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  • Field localisation using real-time phase conjugation within a reverberant environment

    Page(s): 87 - 93
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (650 KB)  

    In this study, the authors provide experimental characterisation of the field location effects that occur within a reverberant environment. This is achieved using a single active analogue phase conjugating unit positioned within a reverberant chamber. The authors demonstrate significant spatial focusing of ON-OFF-keyed 2.4-GHz signals. Furthermore, the effect of polarisation randomisation within such environments is discussed and it is shown that the system is highly tolerant of antenna orientation and does not require line of sight for its operation. View full abstract»

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  • Reduced-size circularly polarised square microstrip antenna for 2.45 GHz RFID applications

    Page(s): 94 - 99
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    This study proposes a new design of circular polarised (CP), microstrip (patch) antenna using a set of slits and slots to effectively reduce the area of patch by 67% compared with the conventional, corner truncated, circular polarised square patch. The antenna is designed to operate at 2.45%GHz in the Industrial-Scientific-Medical (ISM) band and has many applications in short-range data communications such as in wireless sensors, radio frequency identification and personal area networking. The proposed antenna has been simulated using HFSS. The design has been fabricated and an extensive measurement campaign has confirmed simulation results. The proposed antenna has a low bore-sight axial ratio of 0.77 dB and a 10 dB bandwidth of 70 MHz. The overall antenna size is 19.6 mm x 19.6 mm on a substrate of thickness 1.59 mm. A second design with a more complex network of slots and slits achieves similar performance in simulation with an overall side length of 13.2 mm, but at the cost of a much larger input impedance. View full abstract»

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  • Near-field microwave model of multilayered structures illuminated by open-ended rectangular waveguides

    Page(s): 100 - 107
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (594 KB)  

    Near-field microwave non-destructive evaluation and inspection of structures and materials is widely used in various applications. Single-frequency measurements were found to be effective in detecting defects and abrupt changes, such as cracks and air voids, within homogeneous structures. However, in some complex structures with many variables, multiple-frequency measurements were utilised to solve problems associated with more unknown parameters. Those problems involved layered structures with more diversity in terms of number of factors that define the structure, namely, the thicknesses and relative complex permittivities (εr) of the layers. Later on, more systematic broadband techniques, such as frequency-modulated continuous wave, proved to be effective in measuring thicknesses of layers in a multilayered structure. However, obtaining permittivity information was still a big challenge. This study presents a novel analytical near-field model that relates the radiation of a rectangular waveguide with the reflection when applied to a dielectric multilayered structure. The input-output relation is characterised by the frequency response of the structure which was analytically derived. As a side result the distribution of the reflection coefficient over the aperture was also analysed and the expression was derived. The main goal is to define the relationship between the structure layers, in terms of thicknesses and relative permittivities and the aperture-s complex reflection coefficient (Γ) for all frequencies of operation. This model can be used in developing new microwave non-destructive evaluation techniques for inspecting the integrity of layered structures with potentially high resolution. View full abstract»

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  • Ultra-wideband circular slot antenna with reconfigurable notch band function

    Page(s): 108 - 112
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    An ultra-wideband (UWB) antenna is presented whose frequency characteristics can be reconfigured electronically to have either a single- or dual-band notch function to block interfering signals from C-band satellite communications systems, IEEE802.11a and HIPERLAN/2 WLAN systems for example. The proposed antenna is excited using a circular ring resonator fabricated on one side of the dielectric substrate with a circular slot etched on the ground plane. To realise a single- or dual-band notch characteristic the antenna includes a semi-circular parasitic strip located above the circular ring, and a T-shaped stub is located near the inner edge of circular ring. The parasitic strip and T-shaped stub are connected to the circular ring via PIN diodes to give the antenna reconfigurable capability by configuring the PIN diodes in a prescribed combination of ON and OFF states. It is shown that there is virtually no change in the antenna's E-plane and H-plane radiation patterns for the various PIN diode switching conditions. The proposed antenna's performance has been verified by measurements. View full abstract»

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  • Miniature ultra-wideband antenna for wireless universal serial bus dongle applications

    Page(s): 113 - 119
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (760 KB)  

    A miniature ultra-wideband (UWB) antenna for wireless universal serial bus (USB) dongle applications is presented. The proposed antenna comprises a half-circular quasi-self-complementary structure together with a triangular cut on a bent microstrip feed line. As a result of its simple geometry and compact size, the antenna can be easily integrated and printed on wireless USB dongle printed circuit boards. The dimension of the proposed antenna is only 16 mm 16.1 mm whereas the footprint size of the dongle board is 16 mm 60 mm, similar to that of a conventional USB flash disc. The simulated and measured results show that the antenna can achieve a UWB 10 dB impedance bandwidth with reasonable radiation properties. It also exhibits a much-reduced ground plane effect compared to the stand-alone design. In addition, a parametric study is performed to provide insights into the antenna operating mechanism. View full abstract»

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