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Microwaves, Antennas & Propagation, IET

Issue 2 • Date March 2008

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Displaying Results 1 - 15 of 15
  • Patch-fed planar dielectric slab waveguide Luneburg lens

    Page(s): 109 - 114
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    The design of a patch-fed planar dielectric slab waveguide Luneburg lens weighing only 45 g and operated at 27 GHz in TM0 mode is described. The measured half-power beamwidth (HPBW) for a 10.8 lambda, 12-cm diameter lens fed by a microstrip patch placed in intimate contact with the lens rim is 6.9deg with 16.8 dB gain and 10% bandwidth for -10 dB feed return loss, lens cross-polar levels were below -20 dB. The lens is also capable of operating in the TE0 mode with similar radiation performance to that of the TM0 mode. Here, measured HPBW and gain is 8 and 15.5 dB at 27 GHz. Unlike other planar lens arrangements, because of its ability to handle both TM0 and TE0 modes the lens has the potential to deal with the circularly polarised signals, this aspect is also explored. View full abstract»

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  • Microwave reflection amplifier for detection and tagging applications

    Page(s): 115 - 119
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (314 KB)  

    A reflection amplifier module with up to 14 dB gain at 21 GHz is described, which is capable of direct detection of amplitude modulated incident signals at K band. The module consists of a single pseudomorphic high electron mobility transistor (pHEMT) transistor gallium arsenide integrated circuit attached to a microstrip patch antenna. Experimental sensitivity characteristics for the module are given for several bias conditions. These results show that the module is capable of direct detection of signals as low as -75 dBm. In addition, reflection gain control through d.c. bias modification is used to directly encode amplitude modulated backscattered information onto the amplified signal returned by the reflection amplifier tag. The authors also show how the incorporation of an ultra- thin absorber with the tag can be used to increase its re-transmitted signal performance characteristics. View full abstract»

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  • Sub-wavelength resonators: on the use of metafilms to overcome the λ size limit

    Page(s): 120 - 129
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (249 KB)  

    Metamaterials - in particular, double negative materials - have been used in the design of electromagnetic resonators as a means to overcome the classical lambda/2 size limitation. The surface equivalent of a metamaterial is a so-called metafilm - a surface distribution of suitably chosen electrically small scatterers. In this paper we illustrate how metafilms can be used to overcome the lambda/2 size limit in order to design resonators of very small dimension. We present expressions that relate the polarisability densities of the scatterers of the metafilm needed to achieve in principle any desired resonator size. To validate the analytical results, comparisons to full-wave simulations of resonators containing various metafilms are shown. The effect of loss is investigated, and it is shown that smaller resonator size is achieved at the expense of lower Q (quality factor). The results can be scaled; that is, the dimensions of the scatterers can range from relatively large to relatively small, depending on the frequencies of interest. View full abstract»

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  • Correlation between antenna radiation pattern and field performance for global positioning systems in telematics as a function of antenna placement

    Page(s): 130 - 140
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (639 KB)  

    The effect of antenna placement on the global positioning system (GPS) performance in telematics is investigated. Two sets of measurements were conducted. The first set consisted of measuring the vehicle-level antenna radiation pattern at three distinct antenna locations on a sedan vehicle. The second set consisted of a series of drive tests in three distinct driving environments. The field data were collected in parallel for each antenna location in all driving environments. GPS availability and accuracy results from the field testing are correlated to the vehicle-level antenna radiation pattern measurements. Results are presented to show the impact of the antenna placement on the GPS system performance and to demonstrate the good correlation between the vehicle-level radiation pattern measurements and the performance in the field. View full abstract»

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  • Green's theorem modelling of overmoded coaxial waveguides

    Page(s): 141 - 146
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (477 KB)  

    Electromagnetic boundary-value problems supported by closed-form solutions provide a framework for efficient and optimised design methods. Closed-form Green's theorem models are used when a well-defined source is coupled to a well-defined space or structure. Here the Green's theorem is applied to describe the relationship between the current in a coaxial probe and the electromagnetic fields inside an overmoded coaxial airspace. Several single-port boundary- value problems are illustrated before extending this to two-port problems with an application to a cavity filter. Each single and multi-port example is supported by experimental data that is in close agreement with the closed-form models in all cases. View full abstract»

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  • Rainfall measurements at Ku-band satellite link in Penang, Malaysia

    Page(s): 147 - 151
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (213 KB)  

    The rainfall path attenuation at 12.255 GHz measured at Universiti Sains Malaysia for 5 years (2002-2006) is presented. The data obtained are useful to investigate the impairment because of rainfall attenuation in satellite links operating in tropical and equatorial climates. The path attenuation increases significantly with the rainfall rate measured on the ground, with rain fades exceeding 20 dB being measured at rainfall rates of 130 mm/h. Maximum exceeded time for rain rate and attenuation were observed during the wet months. The cumulative distributions of attenuation derived from the measured data are presented and compared with those obtained with existing prediction methods. View full abstract»

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  • Physically based expansion on conformal Gaussian beams for the radiation of curved aperture in dimension 2

    Page(s): 152 - 157
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (151 KB)  

    A Gabor-based Gaussian beam expansion to describe the radiation of electric and magnetic currents on a regular curved interface in dimension 2 has previously been proposed. This expansion represents the radiated fields as a superposition of elementary beams, the conformal Gaussian beams, for which an analytical formulation has been developed. In the context of industrial design and optimisation of radomes, computation time is of primary importance. Therefore a new pragmatic approach to represent the radiated fields on a smaller set of conformal Gaussian beams is proposed. This new expansion does not use Gabor frames but is based on the physical properties of the configuration. Few numerical experiments are presented to evaluate its performances. View full abstract»

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  • Scattering of a plane wave by an anisotropic ferrite-coated conducting sphere

    Page(s): 158 - 162
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (104 KB)  

    On the basis of the three-dimensional spherical vector wave functions in ferrite anisotropic media, and the fact that the first and second spherical vector wave functions in ferrite anisotropic media satisfy the same differential equations, the electromagnetic fields in homogeneous ferrite anisotropic media can be expressed as the addition of the first and second spherical vector wave functions in ferrite anisotropic media. Applying the continue boundary condition of the tangential component of electromagnetic fields in the interface between the ferrite anisotropic medium and free space, and the tangential electric field vanishing in the interface of the conducting sphere, the expansion coefficients of electromagnetic fields in terms of spherical vector wave function in ferrite medium and the scattering fields in free space can be derived. The theoretical analysis and numerical result show that when the radius of a conducting sphere approaches zero, the present method can be reduced to that of the homogeneous ferrite anisotropic sphere. The present method can be applied to the analyses of related microwave devices, antennas and the character of radar targets. View full abstract»

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  • Microstrip delay line phase shifter by actuating integrated ground plane membranes

    Page(s): 163 - 170
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (618 KB)  

    The design, simulation, fabrication, measurement and performance of a V-band micro- strip delay line phase shifter using electrostatically actuated integrated micro-machined ground plane membranes are presented. The microstrip line is etched on an RFIC-friendly silicon substrate. The membrane is made of aluminium micro-ribbons and is fabricated on the ground plane side of the silicon substrate. The actuation of the ribbons away from the transmission line introduces an air gap between the radio-frequency (RF) substrate and the ground plane. By controlling the air gap thickness, a controllable phase shift in the transmission line is obtained. Each micro-ribbon measures 3.20 mm in length, 20 mum in width and 1 mum in thickness. A measured phase shift of 41deg at 50 GHz was achieved with an actuation voltage of 120 V. The fabrication process added a 20 mum initial air gap between the micro-ribbons and RF substrate, increasing the required actuation voltage for a given phase shift. The simulated phase shift results agree well with the measurements. View full abstract»

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  • Analysis of inductive multiport microwave devices employing a novel double parallel plate approach

    Page(s): 171 - 179
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (570 KB)  

    The authors present a novel surface integral equation approach to analyse inductive microwave devices with several parallel input-output ports containing inductive metallic and dielectric obstacles. The technique decomposes the main problem into three subproblems, employing different kinds of Green's functions. One of the subproblems uses the classical Green's functions of an infinite unbounded medium with the constitutive parameters of the dielectric obstacles. A novel point of the technique is the formulation of the two other subproblems with two different, 90deg rotated parallel plate regions. In these regions the parallel plate waveguide Green's functions are used to simplify the modelling of the excitation problem. The second novel aspect of the work is in the treatment of these Green's functions, to smooth their behaviour, and to improve their convergence. Several numerical results are presented to demonstrate the usefulness of the algorithms proposed. Also, several results for inductive microwave devices are presented to show the practical value of the approach. View full abstract»

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  • Size reduction and bandwidth enhancement of snowflake fractal antenna

    Page(s): 180 - 187
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    A new small-size and wideband fractal antenna in the shape of a snowflake is proposed. Various iterations of this fractal antenna with probe feed and capacitively coupled feed are compared and an optimised design is presented. It is shown that, with an air-filled substrate and capacitive feed, an impedance bandwidth >49% and, with a slot-loading technique, a reduction of about 70% in patch surface size compared with an ordinary wideband Koch fractal antenna are achievable. The simulation via a finite-element programme, and measured results on the return loss and the E and H-plane radiation patterns of the proposed antennas are presented and shown to be in good agreement. View full abstract»

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  • Efficient and accurate design of substrate-integrated waveguide circuits synthesised with metallic via-slot arrays

    Page(s): 188 - 193
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (303 KB)  

    A new class of substrate-integrated waveguides (SIWs) is proposed, which highlights a novel synthesis of waveguide circuits using metallic via-slot arrays instead of via-hole arrays. When the gaps between the slots are small enough, the broadside dimension of equivalent rectangular waveguide is approximately equal to the spacing between the inner walls of slots. Therefore the size of the SIW can directly be used to calculate propagation constants almost without phase bias. This new design is of critical importance in the design of substrate-integrated circuits (SICs) with fine and sensitive geometrical details with respect to circuit response such as filters and resonators. In this way, the design of SICs based on the new SIW structures can greatly be simplified. A finite difference frequency-domain method accelerated by an implicitly restarted Arnoldi method is developed to model the substrate-integrated resonant cavities with leakage. Simulated and measured results have confirmed the fact that conventional waveguide components are very similar to the SIW counterparts of the same structure. View full abstract»

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  • Design and implementation of a substrate integrated waveguide phase shifter

    Page(s): 194 - 199
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (201 KB)  

    The design and implementation of a phase shifter based on the substrate integrated waveguide (SIW) technique operating at 10 GHz are presented. The proposed phase shifter consists of a SIW section with two inserted metallic posts. The phase shifting in this configuration is achieved by changing the diameter and the position of these posts. Numerical simulations have been carried out for different diameters and positions, which have shown good agreement with the theory. A parametric study was also conducted to assess the impact of errors made on the diameter and position of the two metallic posts. To prove the concept, prototypes were fabricated and measured. Experimental results agree well with simulations and SII was better than -14 dB, S21 better than -1.08 dB and the phase error was less than 1.5deg. View full abstract»

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  • Fast and accurate radar cross-section computation over a broad frequency band using the best uniform rational approximation

    Page(s): 200 - 204
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (125 KB)  

    The method of moments (MOM) in conjugation with the best uniform rational approximation is applied to predict the broad-band radar cross-section of arbitrarily shaped three-dimensional (3D) bodies. The surface integral equations are solved using MOM to obtain the equivalent surface currents at the frequency points corresponding to the Chebyshev nodes, and then the surface current within the given frequency band is represented by the Chebyshev series. To improve the accuracy, the Chebyshev series is matched via the Maehly approximation to a rational function, which can be as good as the best uniform rational approximation. Using the rational function, the surface current is obtained at any frequency point within the frequency band. Numerical results for 3D arbitrarily shaped perfectly electric conducting objects and homogenous dielectric bodies are considered. Compared with the asymptotic waveform evaluation technique and the model-based parameter estimation, the proposed technique is accurate in much broader frequency band with lower memory required. View full abstract»

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  • Dual-broadband multistandard printed slot antenna with a composite back-patch

    Page(s): 205 - 209
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (309 KB)  

    A square slot antenna fed by a coplanar waveguide for dual-band multistandard applications is presented. Printed on the back of the square slot is a composite patch formed by an annular metal ring inscribed by a circular patch. Appropriate design of the composite back-patch resulted in five resonant bands, the first (last) two of which were combined to form a lower (upper) operating band. The ratio of the two operating band centre frequencies can be tuned larger than 2.5. A pair of notches was embedded in the annular metal ring to further broaden the lower (upper) operating band up to a fractional bandwidth of 37% (20%). The measured results indicate that the proposed antenna can cover the frequency bands of the following wireless communication standards: digital communication system, personal communication services, universal mobile telecommunications system and 2.4/5-GHz wireless local-area networks. View full abstract»

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