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Microwaves, Antennas & Propagation, IET

Issue 12 • Date September 16 2011

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Displaying Results 1 - 18 of 18
  • Novel-integrated patch antennas with multi-band characteristics

    Page(s): 1393 - 1398
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (823 KB)  

    In this study, two integrated multi-band microstrip patch antennas have been proposed for the next-generation wireless systems. The first design consists of a right isosceles triangular patch integrated with a pair of monopoles. The patch resonates at 3.5 GHz (WiMAX, worldwide interoperability for microwave access) and the monopoles at 2.45 GHz (WLAN, wireless local area network) and 1.96 GHz (PCS frequency), respectively. Furthermore, to improve the gain profile and to achieve directive radiation characteristics towards zenith, a reflector ground plane has been placed below the patch. The detailed analysis of the pattern synthesis technique has been explained. Similarly, the second proposed design consists of a semi-circular patch resonating at 3.5 GHz integrated with a slot and a monopole. The slot and monopole resonate at 5.5 GHz (WiMAX) and 2.45 GHz, respectively. Both the designs are realised on a 1.58 mm-thick FR4 substrate (dielectric constant 4.4) and have a return loss better than 10 dB with desired radiation characteristics at the specified resonant frequencies. Prototypes of the proposed designs have been fabricated and their radiation characteristics have been measured. A close agreement has been found between simulation and measurements. View full abstract»

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  • Leaky-wave characteristics from double periodic composite right-/left-handed transmission lines

    Page(s): 1399 - 1407
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (711 KB)  

    A double periodically loaded leaky-wave antenna (LWA) based on composite right-/left-handed transmission lines is proposed. Dispersion characteristics and the radiation efficiency are investigated with the help of a singular perturbation procedure, and the radiation efficiency is numerically estimated as a function of the antenna length. In addition to the left-handed (LH) characteristic of the structure, a novel leaky-wave radiation is obtained below the LH passband with narrow bandwidth, and this point is focused on the leaky-wave phenomenon because of space harmonics of the Bragg reflection from double periodically loaded inductances and/or series interdigital capacitances. Compact LWAs are designed using microstrip lines with double/single periodically loaded inductances and/or capacitances. Radiation characteristics are measured for the investigated compact antenna, and the results demonstrate the expected novel leaky-wave behaviour. View full abstract»

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  • In-silico hyperthermia performance of a near-field patch antenna at various positions on a human body model

    Page(s): 1408 - 1415
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (590 KB)  

    A compact patch applicator designed to enhance targeted energy coupling at 434 MHz is a key enabler for sensitising temperature increments in body regions containing superficial tumours. A detailed finite difference time domain (FDTD) body model is used to explore simulated radio-frequency (RF) coupling and temperature increments for typical clinical conditions. The antenna impedance matching, specific absorption rate and thermal distribution parameters are evaluated to identify applied performance outcomes. The analysis reveals physiological-RF coupling patterns for an optimised closely coupled single-element applicator. View full abstract»

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  • Design and implementation of a band-pass filter using dielectric resonators with a new excitation structure

    Page(s): 1416 - 1423
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (850 KB)  

    A Tchebychev band-pass filter is constructed by placing high-quality factor TE01δ mode dielectric ring resonators inside a cut-off rectangular waveguide. The focus is on the design process and practical realisation of the filter, which includes choosing optimum geometry of a dielectric resonator, enclosure dimensions and the excitation structure. A novel excitation structure is introduced, which provides high coupling. Also, a new orientation in mounting dielectric resonators in cavity is suggested, which helps in making the filter response more symmetric. The three-pole band-pass-fabricated filter exhibits a symmetrical response with small band-pass ripple. View full abstract»

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  • Application of fractal binary tree slot to design and construct a dual band-notch CPW-ground-fed ultra-wide band antenna

    Page(s): 1424 - 1430
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (955 KB)  

    A compact dual band-notch ultra-wide band (UWB) antenna with a co-planar waveguide (CPW)-ground-feed is presented. A desired band-notch antenna is achieved by etching a narrowband dual resonance fractal binary tree into the radiating element of an existing UWB antenna. The new antenna reduces interference from UWB in the wireless local area network (WLAN) bands by attenuation of the measured return. The built prototypes have a compact size of 16×22 mm2 including the ground plane. This miniature size also delivers advantageous radiation patterns with good mono-polar characteristics across the UWB band. For this design the gain is attenuated within the desired WLAN bands. The maximum suppression obtained for the stops at 5.65 and 9.9 GHz are -13.1 and 7.2 dB, respectively. View full abstract»

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  • Synthesis of microstrip lowpass filter using defected ground structures

    Page(s): 1431 - 1439
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    This study reports a systematic synthesis process to design higher-order defected ground structures (DGS)-based lowpass filters (LPF) with Chebyshev and Butterworth responses on any useful substrate in the range εr=2.2=12.9, h=0.6=2=mm. The existing circuit models are re-examined and closed-form expressions are presented to compute the area of the DGS slot-heads for the given inductance. The present design method improves the design of the existing DGS-based LPF reported by several investigators = both in terms of the electrical performances and reduction in length up to 57.8=. The improvement in sharpness of the transition is up to 16=dB/GHz. The improvement in the 20=dB rejection bandwidth is up to 4.5=GHz. The group delay response of Butterworth LPF is better than that of Chebyshev LPF. However, length of Chebyshev LPF is small when compared with that of Butterworth LPF. The study also presents the design results of the ultra-wideband DGS-type LPF = at the cut-off frequencies of 5, 7.5 and 12=GHz. View full abstract»

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  • Ultrawideband microwave imaging of cylindrical objects with inclusions

    Page(s): 1440 - 1446
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (362 KB)  

    This study describes the development of a new algorithm for use in a recently established technique for imaging based on ultrawideband (UWB) microwave signals rather than ionising radiations such as x-rays. The method is based on Huygens principle (HP), which removes the need to solve inverse problems and, consequently, the need for matrix generation/inversion. In addition to its simplicity, it is shown that HP enables the detection of the extent to which different tissues or differing conditions of tissues, can be discriminated and render contrast in the final image. Moreover, UWB allows all the information in the frequency domain to be utilised by combining the signals from the individual frequencies to construct a consistent image. It follows that the methodology can identify the presence and the location of significant scatterers inside a volume. Validation of the technique through simulations and measurements on cylinders with inclusions is presented. View full abstract»

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  • Optimum design of broadband n-way rectangular power dividers with arbitrary power division and impedance matching

    Page(s): 1447 - 1454
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (896 KB)  

    A novel n-way rectangular power divider is presented, which has the capability of design for arbitrary power division among its output ports and arbitrary specification of impedances at all its terminal ports. Consequently, the impedance matching is also realised by its configuration. An accurate equivalent circuit is derived for the power divider, which is used to develop a design procedure by the method of least squares. Two prototype models, namely a three-way and a four-way dividers are fabricated and measured for different terminal impedances and power division ratios. The agreement among the results from the proposed design procedure, full-wave computer simulation and measurement is noteworthy. View full abstract»

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  • Generalised formulation for electromagnetic scattering from finite arbitrarily shaped grooves in a perfect conducting plane

    Page(s): 1455 - 1462
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (627 KB)  

    This study presents an analytical-based solution of electromagnetic plane wave scattering from a finite number of general-shaped grooves in a perfectly conducting plane. The formulation, for the near as well as far-field, is based on Fourier-integral representation of the scattered field and stair-case approximation of the grooves' fields. An efficient formulation of the scattering matrix based on hierarchical and modular formulations, which combines the boundary conditions between fields in groove layers and upper half space is demonstrated. The scattering matrix construction consists of two levels of matrices. The first level of matrices is the individual grooves scattering matrices and the coupling matrices between grooves. The second level of the matrices contains all the geometrical and physical parameters of the grooves as well as the incident field. The near and far-field results of finite rectangular and isosceles right triangle (IRT) grooves are in excellent agreement with a solution from high frequency simulation software, a finite-element simulator and previously published results. The proposed method is able to optimise finite asymmetric gratings for optical and terahertz applications. View full abstract»

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  • Flexible ultra-wideband polarisation diversity antenna with band-notch function

    Page(s): 1463 - 1470
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1085 KB)  

    A CPW-fed polarisation diversity monopole antenna on a flexible PET film for ultra-wideband (UWB) systems is proposed. The antenna consists of two heptagonal monopoles that are orthogonally and symmetrically aligned to have extended ground planes. The antenna is able to cover the entire UWB bandwidth from 3.1 to 10.6 GHz and shows a good isolation of less than 20 dB at each port over the entire UWB bandwidth. Also, it has a band-notch function to avoid overlap with the 5 GHz wireless local area network band. It can be easily mounted on a conformal shape, because it is fabricated on a PET film that is flexible enough to be mounted on a curved surface. Both the time-domain and frequency-domain characteristics of the antenna have been investigated by using the normalised antenna transfer function. From the results, it is observed that the proposed antenna can support polarisation diversity for UWB communications. View full abstract»

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  • Frequency adjustable microstrip annular ring patch antenna with multi-band characteristics

    Page(s): 1471 - 1478
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (996 KB)  

    This study introduces a frequency-tunable dual-band microstrip annular ring patch antenna design for wireless local area network (2.45 GHz) and Worldwide Interoperability for Microwave Access (3.5 GHz) applications. The proposed antenna produces realisable gain higher than 5 dBi and return loss better than 10 dB for the stated applications. The antenna design consists of an annular ring patch loaded with a slot or gap. This loaded ring excites higher-order modes around the dominant mode (TM11) of the annular ring thus making this design capable of dual-band operation. This design is realised on a 1.57 mm thick polytetrafluoroethylene substrate using a coaxial probe feed. In this study, a novel technique for independent frequency tuning has also been introduced by cutting grooves on the periphery of the ring at the desired locations. Furthermore, the design capability of multi-band operation (2.45 GHz/3.5 GHz/5.5 GHz) has also been explained in the later part of the study. Antenna operation has been verified with the help of two commercially available EM solvers (CST Microwave Studio and Ansoft HFSS Designer) and measurements. A close agreement has been found between the simulated and the measured results. View full abstract»

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  • Unifying interpretation of reflection coefficient and smith chart definitions

    Page(s): 1479 - 1487
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (562 KB)  

    This study develops a unifying theory that defines a single transformation from the impedance Z to the reflection coefficient Γ plane independently of the impedance normalisation in use; and the real or complex nature of the characteristic impedance Z0. The study starts off from the Kurokawa's definition of reflection coefficient to discuss the required steps to map Z into Γ and highlights the differences that exist between Kurokawa's and the standard Γ definition. As a logical consequence of the previous discussion, a new definition of reflection coefficient is proposed and validated: the apparent differences stemming from either the standard or Kurokawa's definition of reflection coefficient Γ are easily interpreted as particular cases of the proposed transformation. In the process, the study's unifying definition of reflection coefficient allows and facilitates one consistent interpretation of the Smith chart among the possible Γ definitions, including Kurokawa's. Experimental data supporting the study's conclusions are also presented. View full abstract»

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  • Mutual coupling suppression in microstrip array using defected ground structure

    Page(s): 1488 - 1494
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (475 KB)  

    A defected ground structure (DGS) is used to suppress mutual coupling between elements in a microstrip array and eliminate the scan blindness in an infinite phased array. Two kinds of DGSs, namely back-to-back U-shaped and dumbbell-shaped DGSs, are analysed and compared. The analysis indicates that the back-to-back U-shaped DGS is better at suppressing propagation of surface waves in microstrip substrate. A two-element microstrip array with back-to-back U-shaped DGS is designed and the array characteristics against different element distances are studied. The results show that the degree of the mutual coupling suppression is increased when the element distance is reduced. However, compared with the traditional array, a higher gain and lower side lobes are obtained when a larger element spacing is selected. The scan blindness of an infinite microstrip phased array in E-plane is studied by simulation, and the calculation demonstrates that the scan blindness can be eliminated by applying a back-to-back U-shaped DGS to the infinite phased array. View full abstract»

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  • 21-dB gain ultra-wideband complementary metal-oxide semiconductor low-noise amplifier with current-reuse technique

    Page(s): 1495 - 1501
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    A high-gain and wideband low-noise amplifier (LNA) employing a current-reuse technique is proposed. The current-reuse technique adopted at the first stage yields an exceptionally high gain due to the summation of n-type metal-oxide semiconductor (MOS) and p-type MOS transconductances, showing wide input matching with the aid of source inductors and load effects. The proposed LNA achieves better than 10-dB input return loss from 3.0 to 9.2-GHz, a minimum noise figure of 2.9-dB, a maximum power gain of 21-dB, a gain-bandwidth product of 554-GHz and a figure of merit of 31.8-GHz/mW while consuming 12.8-mW from 7.1-mA and 1.8-V. The proposed LNA is fabricated using a 0.18-μm complementary MOS process. View full abstract»

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  • Dual-band antenna design using a dual-feed monopole slot

    Page(s): 1502 - 1507
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (660 KB)  

    A dual-band antenna design using a dual-feed monopole slot is proposed for wireless local area network (WLAN) applications. Unlike designs using multiple slots for multi-band radiation, the proposed single-slot configuration is less complex, and the multi-band response is excited by a specially designed antenna feed. At 2.4 GHz, the antenna is operated in the resonant mode of the quarter-wavelength slot. With the proper phase difference between the voltages at the feeding microstrips, a travelling-wave mode is excited at 5.5 GHz. The tuning mechanisms of the antenna centre frequencies and bandwidths are explained in detail, and the position and shape of the slot are adjusted for better radiation responses. Simulation and measurement regarding the reflection coefficients and radiation patterns of the antenna are conducted. View full abstract»

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  • Scaled boundary finite element approach for waveguide eigenvalue problem

    Page(s): 1508 - 1515
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    The scaled boundary finite element method (SBFEM) is developed for the solution of waveguide eigenvalue problems, which combines the advantages of the finite element method and the boundary element method. A new variational principle formulation to derive the SBFEM equations for waveguide is developed. An equation of the dynamic stiffness matrix for waveguide representing the relationship between the `flux` and the longitudinal field components at the discretised boundary is established. A continued fraction solution in terms of eigenvalue is obtained. By using the continued fraction solution and introducing auxiliary variables, the flux`longitudinal field relationship is formulated as a system of linear equations in eigenvalue then a generalised eigenvalue equation is obtained. The eigenvalues of rectangular, L-shaped, vaned rectangular and quadruple corner-cut ridged square waveguides are calculated and compared with analytical solution and other numerical methods. The results show that the present method yields excellent results, high precision and less computational time and rapid convergence is observed. View full abstract»

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  • Source-model technique analysis of transient electromagnetic scattering by dielectric cylinders

    Page(s): 1516 - 1523
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (467 KB)  

    This study considers the application of the source-model technique to the solution of the problem of electromagnetic scattering by an arbitrarily shaped dielectric cylinder illuminated by a transient plane wave. The technique is utilised to study the scattering from a dielectric cylinder of circular cross-section and from a cylindrical void of the same cross-section lying in a dielectric medium. The effect of numerical parameters on accuracy and stability is studied and guidelines as to the choice of source location and their number are given. The scattering from a dielectric circular cylinder is then compared with the scattering by a cylinder of a rectangle capped by semi-circles cross-section, and the results are interpreted from a physical point of view. View full abstract»

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  • Synthesis of linear aperiodic arrays using a self-adaptive hybrid differential evolution algorithm

    Page(s): 1524 - 1528
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (313 KB)  

    A self-adaptive hybrid differential evolution algorithm is proposed to optimise linear aperiodic arrays with a minimum peak sidelobe level. The proposed method incorporates a local search operation into a differential evolution (DE) algorithm to accelerate its convergence rate. Moreover, the self-adaptive parameter control approach is employed to avoid tuning the parameters of the DE algorithm. Synthesis examples are compared with the linear aperiodic array designs in the literature. Numerical results demonstrate that our approach is superior to existing algorithms in terms of the high-quality solutions and relatively small computational cost. View full abstract»

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