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Microwaves, Antennas & Propagation, IET

Issue 7 • Date May 16 2012

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Displaying Results 1 - 17 of 17
  • Design of novel microstrip directional coupler for differential signal decoupling

    Page(s): 721 - 728
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (835 KB)  

    This study describes a concept of a novel microstrip directional coupler for differential signal decoupling, which can be used to digital signal overhearing on printed-circuit-boards. The complete design method is proposed with rules given analytically. Considered methodology is suitable for synthesis of couplers with low coupling factors, which have negligible influence on the transmission in main line. Theoretical considerations are confirmed by numerical tests performed using full-wave simulator for the practical case of the coupler project and measurement results. The authors demonstrate that the accuracy of the design method is sufficient for practical system design both in terms of required coupling factor and influence on the main transmission line. View full abstract»

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  • Multi-arm cylindrical folded dipole antenna for collinear arrays

    Page(s): 729 - 734
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (781 KB)  

    A radiating element suitable for electrically long VHF/UHF collinear arrays is presented. Collinear arrays with an isotropic radiation pattern in the horizontal plane and vertical polarisation are usually made of stacked cylindrical dipoles. The proposed array element consists of a slotted cylindrical dipole and belongs to the class of transmission-line folded antennas. The structure of the proposed array element allows an easy and firm mechanical attachment to the metallic antenna mast, and at the same time it ensures a satisfactory isolation performance. Two prototypes operating at 300 MHz have been manufactured and characterised. The design procedure is described and measurements of the reflection coefficient and the isolation between adjacent elements are shown. View full abstract»

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  • Electrically small huygens source antenna for linear polarisation

    Page(s): 735 - 739
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (301 KB)  

    We study the possibility of creating a Huygens source antenna for linear polarisation with good matching to a 50 Ω feeding cable. For this purpose, we design two identical radiating elements, both comprising one electric and one magnetic dipole. The dimensions of these radiating elements are optimised numerically to obtain equally strong radiation from the electric and magnetic dipoles. The optimised prototype is then manufactured and its radiation properties are measured. View full abstract»

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  • Synthesis and microwave characterisation of (Zr0.8Sn0.2)TiO4-epoxy composite and its application in wideband stacked rectangular dielectric resonator antenna

    Page(s): 740 - 746
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (651 KB)  

    In this study, (Zr0.8Sn0.2)TiO4-epoxy composites are synthesised, characterised and used in dielectric resonator antenna applications. (Zr0.8Sn0.2)TiO4 and epoxy are mixed in five different ratios, that is, 50:50, 60:40, 70:30, 80:20 and 90:10 with small amount of hardner (HY 951). The crystal structure and cell parameters of (Zr0.8Sn0.2)TiO4 are confined by Rietveld analysis. The complex permittivity of the composite is measured at different microwave frequencies in X-band (8.2-12.4-GHz). It has been found that the permittivity is reduced by increasing the percentage of epoxy in composite system. The optimised weight percentage ratio of (Zr0.8Sn0.2)TiO4 and epoxy composite material are used in a two-layer rectangular dielectric resonator antenna using coaxial excitation for obtaining wideband performance. The effects of the antenna parameters like length, width and probe length are investigated using Ansoft's high-frequency structure simulator (HFSS) software. The agreement between simulated and experimental data is very good. The proposed design provides the measured impedance bandwidth of 58.7' (at resonance frequency 8.40'GHz) from 6.45 to 11.38'GHz for reflection coefficient (S11) of less than -10-dB with a measured average gain of 6.99-dB in the frequency range of 6.0-11.5-GHz. The radiation patterns are consistent throughout the operational bandwidth. View full abstract»

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  • Design of a wideband rasorber with a polarisationsensitive transparent window

    Page(s): 747 - 755
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (477 KB)  

    In this study, the authors present a thin wideband electromagnetic planar absorber for X- and Ku-band, which also has a polarisation-sensitive transparent window at frequencies lower than L-band. The design is based on a two-layer capacitive circuit absorber with the back-metal layer replaced with a polarisation-sensitive frequency-selective surface. The structure is studied for normal incident waves with two orthogonal linear polarisations. The authors optimised the structure to gain high transparency at low frequencies for one of the polarisations and at the same time good absorption efficiency for both polarisations at the high-frequency band. For one of the polarisation a -1.9 dB transmission with the transmission loss of less than 10% at 1 GHz as well as a 2.25:1 (75%) bandwidth of -20 dB reflection reduction are achieved. For the other polarisation, the authors obtained more than 3:1 (100%) bandwidth of -19 dB absorption. The transmission loss is significantly reduced compared to the authors- earlier design based on Jaumann absorber. Furthermore, the module of absorption quality is extensively improved. The improvements are based on using periodic arrangements of resistive patches in the structure design. The investigation of the structure for oblique angles of incidence and non-ideal materials shows that the design is robust. View full abstract»

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  • Wireless power transmission using dipole rectennas made on flexible cellulose membrane

    Page(s): 756 - 760
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (442 KB)  

    This study reports a wireless power transmission technology using dipole rectenna arrays made on a flexible cellulose membrane. Three flexible dipole rectenna arrays are designed, fabricated and characterised. A rectenna array with nine rectenna elements generates a maximum power of 75 mW with a conversion efficiency of 56%. Detailed fabrication and characterisation of the flexible dipole rectenna arrays are described. This flexible dipole rectenna can be used for biomedical applications. View full abstract»

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  • Modelling of aperiodic array antennas using infinitesimal dipoles

    Page(s): 761 - 767
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (503 KB)  

    An infinitesimal dipole model (IDM) for an antenna including mutual coupling is used to model the radiation patterns of aperiodic arrays. Each radiating element is modelled by a set of infinitesimal dipoles. The mutual coupling between the elements is calculated and the far field radiation pattern of the antenna is computed in a fast and efficient manner. An invasive weed optimisation algorithm is employed to find both the IDMs and the aperiodic array. The simulation results using IDM are verified with a full-wave analysis. View full abstract»

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  • X-band, high performance, SiGe-heterojunction bipolar transistors-low noise amplifier for phased array radar applications

    Page(s): 768 - 772
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    This study presents an X-band low noise amplifier (LNA) implemented in 0.25 μm SiGe BiCMOS process aiming for phased array radar applications. The LNA is composed of two cascode stages using SiGe heterojunction bipolar transistors to achieve low noise figure, high gain and a better matching to 50 Ω at the input and output, simultaneously. The first stage is designed for low noise performance whereas the second stage is optimised to improve the input third-order intercept point (IIP3). The LNA resulted in a measured gain of 21 dB, a noise figure of 1.52 dB and an IIP3 of -8 dBm at 10 GHz. The active chip area without pads is 620 × 820 μm2 and the power dissipation is 22 mW from a 2.2 V power supply. These performance parameters collectively constitute the best figure-of-merit value of 101, reported in similar technologies. View full abstract»

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  • A constructive smart antenna beam-forming technique with spatial diversity

    Page(s): 773 - 780
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (586 KB)  

    One of the most important processes in smart antennas, is beam forming. The major function of beam forming is to change the beam pattern of the antenna for a given angle. If the antenna does not change its direction based on the receiving signal, the signal losses will be high. So, in order to increase the efficiency and to reduce the signal losses in the system, here a new method is proposed for beam forming in smart antenna along with spatial diversity using fuzzy interference system and neural network (NN). In order to provide training for NN and fuzzy logic, a huge personalised training dataset is generated using Genetic Algorithm. Given a desired angle as input, the proposed method gives the corresponding antenna parameters and phase angle as output. The length of the beam, interference, phase angle, number of patterns and spatial diversity are the smart antenna parameters that are considered in the proposed method. In addition, the proposed method increases the efficiency in determining the smart antenna parameters. The proposed method is implemented and the results are analysed. The comparative and analytical results prove the performance of the proposed method over other existing methods. View full abstract»

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  • Radiation and circuit model of a planar resonator element with shorting via

    Page(s): 781 - 787
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (413 KB)  

    We propose the study of a planar quasi-lumped resonator element. It is composed of a shorting via, modelled as a parallel inductance and a very short open-ended microstrip line, modelled as a capacitance. We discuss the physical parameter influences of the resonator, which offer a path to control its radiation characteristic. A circuit model with closed-form expressions of the radiation resistance and the unloaded quality factor is presented. The discontinuity influences of the shorting via and the open-ended microstrip borders are discussed. The experimental and theoretical results verify the proposed circuit model. A radiation model based on the results of electromagnetic simulations has also been proposed. View full abstract»

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  • Low-power CMOS VCO with a low-current, high-Q active inductor

    Page(s): 788 - 792
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (434 KB)  

    This study describes an active inductor (AI) designed to reduce power consumption and to improve the quality factor. For these purposes, one of the transistors for the AI operates in the subthreshold region, and the AI uses the additive capacitor (AC) technique. The proposed AI was applied to a voltage controlled oscillator (VCO) to demonstrate the enhancement in power consumption and improvement in phase noise. The AI-VCOs with and without AC were fabricated using a 0.18 μm CMOS process and achieved frequency tuning ranges from 1.13 to 2.67 GHz and 1.3 to 3.24 GHz, respectively. The measured phase noise of the AI-VCO with AC is -92.2 dBc/Hz at 1 MHz offset, a 4 dB improvement compared to that of the AI-VCO without AC. The proposed VCO consumes 2.2-13 mW with a 1.8 V voltage supply and occupies 171 × 174 μm2 of core size without testing pads. View full abstract»

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  • Low-power UWB LNA with common-gate and current-reuse techniques

    Page(s): 793 - 799
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    A common-gate (CG) low-noise amplifier (LNA) that uses the current-reuse technique and is intended to achieve both ultra-wideband and low-power consumption is proposed. The CG amplifier enables wide-band input matching with low transconductance and low frequency-independent noise figure (NF) when employed at the input stage compared with the common-source amplifier. The current-reuse technique is adopted in order to reduce the power dissipation while achieving reasonable power gain. In addition, a shunt and series peaking technique is adopted to obtain wide bandwidth. The proposed LNA achieves a 3-dB bandwidth from 2.4 to 11.2 GHz, a maximum power gain of 14.8 dB, a minimum NF of 3.9 dB and a third-order input intercept point of -11.5 dBm while consuming 3.4 mW from a 1.5 V supply. A 0.18-μm CMOS process is utilised to fabricate the LNA. View full abstract»

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  • Open-loop tunable resonators and filters with constant bandwidth

    Page(s): 800 - 806
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (590 KB)  

    This study presents a compact novel design for achieving constant bandwidth tunable filters with wide tuning range. A method for linearising the Q-factor against frequency is proposed. A modified coupling structure is introduced to compensate for variations in filtering characteristic across the theoretical 50% tuning range of the filter. Filter design equations are provided for designing Butterworth or Chebyshev filters. An experimental second-order filter is demonstrated with 22.5% pass-band shift with only 3% bandwidth variation and insertion loss better than 3%dB. Furthermore, a third-order tunable bandpass filter with tuning range of 45% and less than 5% bandwidth variation is illustrated through simulation and modelling to show feasibility with higher filter orders. There is very good agreement between the theoretical and experimental results. View full abstract»

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  • Electrode impedance measurement in through-theearth communication applications

    Page(s): 807 - 812
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (447 KB)  

    Through-the-earth (TTE) communications are deployed in hostile environments with the rock as communication channel. The ground electrodes are one of the medium access solutions for this type of communications. Its operation is based on the injection of an electrical current into the earth and the detection of a potential difference between the receiver electrodes. The electrode impedance depends on many factors: the material (rock, earth ) where the communications take place, the wires used to connect the system to the electrodes, the type of electrodes etc. It is very important to know, in detail, this impedance in order to properly design the TTE communication transmitter. In this study, a measurement method developed to characterise the electrode impedance is presented. The method is applied in several terrains including three measurements as an example. Moreover, a circuit equivalent model for this impedance is proposed. The model parameters are adjusted to the measured data with a good fit. View full abstract»

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  • EVM measurements using orthogonal separation at the output of a non-linear amplifier

    Page(s): 813 - 821
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (699 KB)  

    A method is developed to obtain the error vector magnitude (EVM) of non-linear amplifiers by mean of orthogonalising the output of the amplifier to extract its uncorrelated non-linear terms. This method allows for extraction of in-band distortion power and spectral regrowth power from the measured RF waveforms which provides invaluable insight to the EVM behaviour of the device. From a frequency domain analysis, the EVM is attributed to the in-band distortion power and spectral regrowth power where it is determined that the in-band distortion power contributes more to the EVM degradation. The amplifier used for verification is modelled from Avago's MGA83563 measured amplitude distortion (AM-AM) and phase distortion characteristics (AM-PM). Finally, the relationship between EVM and gain compression characteristic is derived from the proposed orthogonal model. View full abstract»

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  • Synthesis of thinned planar concentric circular antenna arrays using biogeography-based optimisation

    Page(s): 822 - 829
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (601 KB)  

    This study presents a novel optimisation algorithm biogeography-based optimisation (BBO) for thinning large multiple concentric circular ring arrays. The objective is to achieve an array of uniformly excited isotropic antennas that will generate a narrow beam with minimum relative sidelobe level (SLL). BBO is a new comprehensive force based on the science of biogeography. Biogeography is the schoolwork of geographical allotment of biological organisms. BBO utilises migration operator to share information between the problem solutions. The problem solutions are known as habitats and sharing of features is called migration. In this study, the authors propose pattern synthesis method to reduce the SLLs with narrow beamwidth (BW) by making the ring array thinned using the BBO algorithm. The thinning percentage of the array is kept equal to or more than 50% and the BW is kept equal to or less than that of a fully populated, uniformly excited and 0.5%w, spaced concentric circular ring array of same number of elements and rings. The results obtained are compared with previous published results of modified particle swarm optimisation and differential evolution with global and local neighbourhoods. View full abstract»

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  • Experimental demonstration of antenna blockage reduction with a transmission-line cloak

    Page(s): 830 - 834
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    Transmission-line cloaking is a simple yet wideband technique for cloaking a mesh-like object. A novel transmission-line cloak design operating at microwave frequencies is presented with special emphasis in the design placed on ease of manufacture and practicality. The operation of the cloak is verified by studying the antenna blockage caused by the cloaked and uncloaked objects. It is shown both numerically and experimentally that the designed transmission-line cloak is capable of hiding a mesh-like metal object placed inside it from the incident wave in a variety of different scenarios and within a fairly wide frequency bandwidth. Also, the agreement between simulations and measurements is shown to be very good. View full abstract»

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