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Microwaves, Antennas & Propagation, IET

Issue 7 • Date October 2009

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Displaying Results 1 - 16 of 16
  • Non-line-of-sight on-body ultra wideband (1ߝ6 GHz) channel characterisation using different antenna polarisations

    Page(s): 1019 - 1027
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (822 KB)  

    Ultra wideband (UWB) is a promising technology for wireless body area networks (WBANs). The authors investigate the wave propagation in the frequency range of 1-6-GHz for non-line-of-sight (NLOS) channels from the front to back of a human body by considering different wave polarisations: perpendicular and tangential with respect to the body. Time domain electromagnetic (EM) simulation using the anatomical model of a human body assuming frequency-dependent tissue properties is conducted. Radiographs of the energy density and delay spread of the NLOS channels are provided. The energy fading of UWB signals for the on-body channel suggests that the optimisation of the receiving antenna position for efficient signal transmission can be useful. A significant enhancement of the on-body communication link is identified by exploiting the transceiver antennas at the perpendicular to body polarisations. The impacts of body environment reflections on the channel characteristics of different polarisations are studied. The results show that the perpendicular polarisation channel characteristics are less influenced by the body environment reflections and are more stable regarding energy density and delay spread than tangential polarisation. The frequency-dependent propagation loss of on-body UWB channels is derived, where the efficient communication bandwidths for both perpendicular and tangential wave polarisations are given. View full abstract»

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  • Omnidirectional ADE antenna with a GO-shaped main reflector for an arbitrary far-field pattern in the elevation plane

    Page(s): 1028 - 1035
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (483 KB)  

    This work presents a formulation for shaping the main reflector of a dual-reflector antenna designed to offer an omnidirectional coverage with an arbitrary radiation pattern in the vertical plane. The subreflector is generated by an axis-displaced ellipse and the main reflector is shaped to achieve a prescribed far-field radiation pattern. The shaping procedure is based on geometrical optics (GO) principles. Two distinct far-field ray structures are investigated. The GO-shaping results are validated by an analysis using the accurate method of moments technique. View full abstract»

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  • Improvement of open resonator technique for dielectric measurement at millimetre wavelengths

    Page(s): 1036 - 1043
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (270 KB)  

    An open resonator system is designed and constructed for the accurate measurement of complex permittivity at Ka band. It is solved successfully for the first time in how to achieve the consistency of cavity lengths corresponding to different resonant frequencies over a broad band and how to determine the proper permittivity from multiple transcendental equation roots of one sample. Many kinds of samples such as fused quartz, Teflon, quartz ceramic, MgF2 and MgAl2O4 are measured and the results are in good agreement with published data. The systematic error analysis shows that the relative standard deviation of the measurement system is less than 0.172% for permittivity and 18.35% for loss tangent. The software developed to control the system improves the measurement efficiency greatly. View full abstract»

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  • Time-constant control analysis of microwave differentiators

    Page(s): 1044 - 1050
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (490 KB)  

    A model describing the time constant of a wide-band microwave differentiator is presented. The time constant combined with the amplitude response dictates the circuit behaviour of a microwave differentiator. By representing the formulations of differentiators in the discrete-time (or Z) domain, the authors implement the differentiators with equal-length transmission lines. The approach method consists of discrete signal processing techniques, transfer functions in the Z domain and optimisation algorithms. Three differentiators with different time constants and frequency bands are built and tested. The experimental results are in good agreement with theoretical values. View full abstract»

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  • Design and implementation of planar ultra-wideband antennas with multiple notched bands based on stepped impedance resonators

    Page(s): 1051 - 1059
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1010 KB)  

    A new family of microstrip-fed ultra-wideband (UWB) antennas with multiple (triple/quadruple) notched bands is proposed. The notched bands are generated by a band notched filter composed of double stepped impedance resonators (SIRs). Through tuning the characteristic impedance and the electrical length of each section of the SIRs, multiple notched bands as well as the desired high attenuation can be created in desired frequencies. Frequency domain measurements have been conducted to examine the band notched characteristics of the proposed antennas. Based on the analysis of antenna transfer function (S21), group delay and gain of the proposed antenna, it is shown that the proposed antenna is suitable for UWB applications or for multi-band applications. View full abstract»

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  • Feed-forward linearisation technique for impulse radar ultra-wideband over fibre

    Page(s): 1060 - 1068
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (911 KB)  

    The authors present the linearisation of impulse radar ultra-wideband (IR-UWB) transmission system over fibre. The radio frequency signal of IR-UWB is transmitted over 50 km of the single mode fibre (SMF) using external Mach Zehnder modulator (MZM), amplified, linearised and detected by photodetector receiver. For improving the linearity and suppressing the four-wave mixing (FWM) caused by semiconductor optical amplifier (SOA) and 50 km SMF, the system uses feed-forward technique. Link performance was evaluated for two IR-UWB signals to suppress the FWM. The theoretical simulation results demonstrate a distortion cancellation that is produced by SOA of better than 25 dB over 1550 nm single mode optical fibre cable. In addition, the characteristic transmission of UWB pulse radio through 50 km single mode radio over fibre (RoF) system, such as BER measurements to evaluate the performance of the UWB with respect to different laser power output level, is investigated. This technique has been used to successfully transmit indirectly modulated data using laser diode at 10 GB/s light-wave transmission system. View full abstract»

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  • DOA estimation for non-Gaussian signals using fourth-order cumulants

    Page(s): 1069 - 1078
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (253 KB)  

    A novel method based on fourth-order cumulants (FOC) is proposed for direction of arrival (DOA) estimation with uniform linear array (ULA). The method can be applied in the situation that the non-Gaussian independent and coherent signals coexist with unknown coloured Gaussian noise. The method comprises two steps: the first step is to estimate the independent signals, and then they are eliminated; the second step is to resolve the coherent signals with the reconstructed FOC matrix of coherent signals. The proposed method can also be extended to the scenario when independent, partially correlated and coherent signals coexist, and the number of signals resolved by our method can exceed the number of array elements. Simulation results demonstrate the effectiveness and efficiency of our method. View full abstract»

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  • Unequal dual-frequency Wilkinson power divider including series resistor-inductor-capacitor isolation structure

    Page(s): 1079 - 1085
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    A novel Wilkinson power divider operating at arbitrary dual-frequency (namely dual band) with unequal power dividing ratio is proposed here. The asymmetric structure that consists of seven sections transmission lines with different characteristics impedances is given to satisfy the unequal and matching characteristic. To obtain the ideal isolation, a series resistor-inductor-capacitor (RLC) structure is applied. Furthermore, the closed-form design equations of the proposed dual-frequency power divider are derived based on circuit theory and ideal transmission line theory. Finally, calculation, simulation and measurement results of an example indicate that all the theoretical features of the unequal power divider can be fulfilled at the desired dual-frequency simultaneously. View full abstract»

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  • Rain attenuation statistics over a terrestrial link at 32.6 GHz at Malaysia

    Page(s): 1086 - 1093
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    Rain-induced attenuation in the vertically polarised signal propagating at 32.6 GHz over a terrestrial path link of 1.4 km was measured for a period of one year (i.e. from January to December 2006) at Cyberjaya (2 55 N 101 39 E). Different rain attenuation prediction models such as International Radio Communication Union (ITU-R), synthetic storm technique (SST), Moupfouma and Crane Global are compared with the annual statistics of rain attenuation that have been derived from the measured experimental data. It has been observed that the measured values differ from those predicted using ITU-R, and the Crane Global model but follow closely those predicted using SST, Moupfouma and Silva Mello et al. models, resulting in low percentage of RMS errors below 6%. The Moupfouma model was developed for prediction from 0.1 to 0.001% of the time when rain attenuation is exceeded compared to the other models. View full abstract»

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  • Parasitic-aware robust concurrent dual-band matching network for a packaged LNA

    Page(s): 1094 - 1101
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    A generalised form of a concurrent dual-band matching network has been proposed for a packaged CMOS low noise amplifier (LNA). To eliminate the detrimental effects of component non-idealities on matching performance, a modified set of design equations has been developed. The robustness of the proposed network has been demonstrated at the GSM900 and DCS1800 bands. Incorporating this network, an LNA designed in a 0.18 mum CMOS process provides S 11 of -33 and -30-dB, gain of 16.54 and 11.03-dB and noise figure of 1.35 and 2.37-dB, respectively, at 900-MHz and 1.7-GHz. The LNA draws a current of 2-mA from 1.8-V supply. View full abstract»

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  • Improvement of an ultra-wideband antenna for high-power transient applications

    Page(s): 1102 - 1109
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (785 KB)  

    Recently, LGE and XLIM Laboratories initiated collaboration on high-power microwave (HPM) transient radiation source conception. Ultra-wideband (UWB) antennas have been originally designed for UWB radar demonstrators. These prototypes have been built to support high-voltage (HV) short duration pulses with a 25 kV amplitude. Because of its high gain and its capability to radiate short pulses without dispersion within the 300 MHz-2.5 GHz frequency band, a type of these UWB antennas, the Valentine Antenna, has been chosen to be the radiating element of two new high-power HV UWB sources. This antenna, originally designed for low voltage, is made of two curved metallic strips and a copper coaxial-to-strip transition with a classical N connector. Some modifications were achieved in order to improve the dielectric strength of the antenna. Consequently, it is now able to radiate pulses delivered by HV (up to 300 kV), few hundreds hertz, subnanosecond transient sources. Initially, a 3-D model of the antenna was first computed with a time-domain electromagnetic software so as to study the influence of these modifications on the radiating element main characteristics. Then, frequency and transient domains studies were realised. Presented results demonstrate that the antenna S 11 parameter remains relatively unchanged and that in the entire frequency band, gain is 1 dB lower than the expected value with the original low-voltage design. This new HV antenna and its main radiation characteristics are described. View full abstract»

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  • Triple-frequency meandered monopole antenna with shorted parasitic strips for wireless application

    Page(s): 1110 - 1117
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (495 KB)  

    The performance of a triple-frequency meandered-strip monopole antenna for wireless application is presented. The proposed antenna comprises of a microstrip-fed monopole with an additional meandered strip and a ground plane with three protrudent strips on the opposite side of the substrate. By adding these shorted parasitic strips to this monopole, good impedance matching for multi-band application is obtained. Tuning effects of the additional shorted strips to the different resonant modes were examined and prototype of the proposed antenna had been constructed and experimentally studied. The measured results explore a broadband triple-frequency operation covering the required bandwidths of the PCS-1900/UMTS-2100 and the 2.4/5.2/5.8 GHz WLAN standards, a near-directive radiation pattern and a good antenna gain for this design. View full abstract»

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  • Dual frequency band antenna combined with a high impedance band gap surface

    Page(s): 1118 - 1126
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1003 KB)  

    A compact dual-band antenna structure for automotive and aerospace applications is discussed. A bow tie dual-band electromagnetic band gap (EBG) element geometry is presented that has a reduced cell dimension compared to the wavelength yet has sufficient bandwidth for mobile communication applications. The EBG was combined with a printed planar monopole to produce a structure 8 mm thick. The return loss and radiation patterns gave satisfactory performance at two frequency bands with bandwidths of 11% at 1700 MHz and 7% at 2600 MHz. There was suppression of the back radiation at both bands of 5 dB or better even for the small 3 times 3 element EBG used and the antenna was platform tolerant. View full abstract»

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  • Prediction of ground multipath parameters from range-gain measurements using Prony's technique

    Page(s): 1127 - 1132
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (370 KB)  

    Prony's technique is used to estimate multipath parameters from range-gain patterns produced by ground multipath interference in line-of-sight radio links. The field distribution at the transmitting antenna side is obtained by digital reconstruction from the range-gain pattern that is recorded, at constant height, along ground surface. The technique is presented as a competitive alternative to the Fourier transform, where much shorter data windows are sufficient for the proposed technique. The technique is validated by calculated and measured range-gain patterns, and the predicted values are in good agreement with the actual ones. Prony's technique produced predictions with comparable errors to the Fourier technique from much smaller data windows. View full abstract»

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  • Design of Sierpinski gasket fractal microstrip antenna using real coded genetic algorithm

    Page(s): 1133 - 1140
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (614 KB)  

    A novel technique for designing Sierpinski gasket fractal microstrip antenna is proposed. In the absence of any available closed-form formulae, this scheme uses an evolutionary method, based on real coded genetic algorithm (RCGA) in conjunction with electromagnetic simulations. This method determines the side-length and the fractal iteration number of the antenna, for operation at 4.56, 7.51 and 11.78 GHz. The design simulation of the antenna uses two different RCGA implementation strategies. The Adewuya mating with Gaussian mutation is the basis for the first one, whereas the second one uses heuristic crossover in conjunction with non-uniform mutation. Converging results, from these two strategies to those obtained from experiments on fabricated prototypes, validate the proposed method. View full abstract»

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  • Bi-dimensional bi-periodic centred-fed microstrip leaky-wave antenna analysis by a source modal decomposition in spectral domain

    Page(s): 1141 - 1149
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (533 KB)  

    A novel source modal decomposition in spectral domain is used to analyse the radiation from a finite bi-dimensional (2-D) omnidirectional centred-fed microstrip leaky-wave antenna (LWA). The driving element of the 2-D microstrip LWA induces the excitation of surface waves along (Ox) and (Oy) directions. Thus, the 2-D structure can be modelled as a phased array antenna. The electric integral equation in the spectral domain is reduced to simple expressions by using the admittance operator, based on a simple transverse equivalent network taking into account all the antenna characteristics and the central excitation. Several numerical results are given for a 2-D structure operating in a large frequency range. View full abstract»

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