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Microwaves, Antennas & Propagation, IET

Issue 4 • Date June 2009

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Displaying Results 1 - 21 of 21
  • Multi-passband bandpass filters with low-temperature co-fired ceramic technology

    Page(s): 547 - 556
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (861 KB)  

    The bandpass filters with multiple passbands have been proposed. To achieve multiple passbands, transmission lines shunted with short-circuit transmission lines are adopted. Moreover, the bandwidth of each passband can be controlled by properly choosing impedances and electrical lengths of the transmission lines and short-circuit transmission lines shunted. The design procedures of the proposed multi-passband filter are also described here. Finally, the agreement between the measured results and theoretical predictions sufficiently validates the proposed design and filter configuration. View full abstract»

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  • Frequency selective characteristics of gratings with arbitrary profiles composed of left-handed materials

    Page(s): 557 - 563
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (439 KB)  

    The frequency selective surface (FSS) of gratings with arbitrary profiles composed of left-handed materials is systematically analysed by a method that combines the staircase approximation and the multimode network theory with the rigorous mode matching procedure. The effects of different periodic groove profiles, such as rectangle, ellipse and trapezoid on the reflection characteristics of the FSS are carefully studied and compared with each other. The variations of the frequency selective characteristics with dielectric loss and the comparisons between left-handed and right-handed gratings are also presented with the physical explanations of the related phenomena. View full abstract»

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  • Direct parameter extraction method for deep submicrometer metal oxide semiconductor field effect transistor small signal equivalent circuit

    Page(s): 564 - 571
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    A new direct parameter extraction method to determine the small signal equivalent circuit model for deep submicrometer metal oxide semiconductor field effect transistors (MOSFETs) is presented here. This method is a combination of the test structure and analytical methods without reference to numerical optimisation. The main advantage of this method is that the extrinsic resistances, inductances, as well as substrate parasitics can be obtained using a set of exact closed equations based on the cut-off mode S-parameter on wafer measurements. Good agreement is obtained between the simulated and measured results for a 90 nm MOSFET in the frequency range of 50-40 GHz over a wide range of bias points. View full abstract»

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  • Pareto optimal design of multilayer microwave absorbers for wide-angle incidence using genetic algorithms

    Page(s): 572 - 579
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (731 KB)  

    An application of the non-dominated sorting genetic algorithm II (NSGA-II) in designing high performance multilayer electromagnetic absorbers is discussed. Compared with traditional Pareto genetic algorithms, the NSGA-II can reduce the complex of calculation efficiently, as well as provide better optimisation results. Based on existing lossy materials, the Pareto fronts and corresponding optimisation schemes for different frequency bands and incident angles are presented. For instance, in the frequency band of 8-12-GHz with arbitrary incident angles and polarisations, a highest reflection of -17.02-dB can be obtained for the four-layer absorber with total thickness of 4.1933-mm. View full abstract»

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  • Wideband modelling of cascaded H-plane waveguide junctions using the generalised impedance matrix representation

    Page(s): 580 - 590
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    A strong interest in H-plane waveguide components composed of a large number of cascaded planar junctions is recently renewed. Therefore, the more efficient development of full-wave analysis tools of such devices is again receiving consideration, specially for its potential use within modern design tools. A novel technique for providing the wideband generalised impedance matrix representation of the inductive devices in the form of pole expansions, thus extracting the most expensive computations from the frequency loop is proposed. For such purpose, the whole device is first decomposed into simpler building blocks, i.e. planar junctions and uniform waveguides, which are modelled in terms of the proposed wideband matrices. Then, a novel iterative algorithm for the efficient combination of such matrices is followed. The complete technique has been successfully applied to the full-wave analysis of several inductive waveguide filters of great practical interest. View full abstract»

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  • In-depth analysis of reciprocal periodic structures of transmission lines

    Page(s): 591 - 600
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (621 KB)  

    An in-depth analysis of lossless reciprocal periodic structures of transmission lines (TLs) is presented. Interestingly, it is found that periodic structures can provide both non-negative (NNCR) and negative characteristic resistances (NCR). In addition, the magnitude of the voltage reflection coefficient associated with an equivalent model of periodic structures terminated with passive loads can be less than or equal to unity for the NNCR case, and can exceed unity and even approach infinity for the NCR case. However, associated powers are still conserved for both cases. Furthermore, an alternative derivation based on short- and open-circuited terminations for determining characteristic impedances and propagation constant of equivalent TLs is also introduced. An example of finite periodic TL structures, providing both NNCR and NCR cases, with varying the number of unit cells is also given. In addition, implementation and measurement are set up to verify theoretical and simulated results. It is found that these results are reasonably in good agreement. View full abstract»

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  • Analysis on the platform-tolerant radio-frequency identification tag antenna

    Page(s): 601 - 606
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (250 KB)  

    A new passive radio-frequency identification (RFID) tag antenna for the ultrahigh frequency band is proposed. It consists of a modified inductive feed and a radiating slotted copper trace (SCT). A ground plane is used in the design to make the tag antenna platform-tolerant. The radiating SCT is investigated first, and its return loss, antenna efficiency and radiation pattern characteristics are studied. The read range, differential radar cross section, input impedance and current distribution of the RFID tag that employs the SCT antenna are simulated, and reasonably a good agreement between the simulated and measured results is obtained. View full abstract»

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  • Broadband millimetre-wave passive spatial combiner based on coaxial waveguide

    Page(s): 607 - 613
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (429 KB)  

    A broadband millimetre-wave passive spatial combiner using a microstrip probe array and an oversized coaxial waveguide is successfully designed and tested. The equivalent circuit approach of transverse electromagnetic (TEM) lines is adopted to synthesise the coaxial stepped impedance transformer from a K connector with the oversized coaxial waveguide and to analyse the microstrip probe array. The equivalent susceptances of the step discontinuities for the power divider are calculated. A four-way coaxial waveguide passive power combining circuit operating at the entire Ka-band is designed, fabricated and measured. Experiments on the four-way passive combiner show that a minimum insertion loss of 0.7 dB has been achieved at about 29.5 GHz. The combiner has shown a bandwidth of 26.5-40 GHz with 10 dB return loss and less than 2.5 dB insertion loss. View full abstract»

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  • Edge-fed cavity backed patch antennas and arrays

    Page(s): 614 - 620
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (710 KB)  

    A new edge-fed patch antenna that mitigates spurious radiation issues when thick substrates are used to create the antenna is presented. The radiator can be classified as an edge-fed cavity backed patch. Here, a thin substrate is used to develop the microstrip feed line, thereby ensuring the track widths are small and subsequently decreasing spurious feed radiation. The patch radiator utilises the thick substrate employed in the cavity ensuring reasonable return loss bandwidth can be achieved. A single element and a 2 times 2 array have been designed, fabricated and tested using the proposed technique and it has been shown that significant reduction in pattern distortion and increase in gain can be achieved compared to conventional edge-fed microstrip patch configurations. Because of the thin tracks used to feed the radiators, the new technique is very applicable to large arrays of microstrip patches where the area consumed by the distribution network must be minimised to ensure good radiation performance. View full abstract»

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  • Sectorised antenna array and measurement methodology for indoor ultra-wideband applications

    Page(s): 621 - 629
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1090 KB)  

    A new sectorised antenna array (SAA) and measurement methodology are proposed for indoor ultra-wideband (UWB) applications. The proposed SAA comprises of one centre element and six side elements. The one centre element and six side elements are arranged in a semi-spherical antenna array configuration. The measurement system and methodology for the coverage of the SAA are developed. The measured bandwidth of the SAA for voltage standing wave ratio (VSWR) les2 is 37.5%, ranging from 3.06 to 4.47 GHz. The boresight gain is more than 5.2 dBi across the impedance bandwidth. The proposed SAA is able to provide omni-directional pattern with an average gain of 5.2 dBi over the angles (0-360deg). The discone reference antenna is used to measure the coverage of the proposed SAA. The proposed measurement study shows that the proposed SAA offers omni-directional coverage desirable in UWB indoor location and short-range communication systems. View full abstract»

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  • Simple calibration plane-invariant method for complex permittivity determination of dispersive and non-dispersive low-loss materials

    Page(s): 630 - 637
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (429 KB)  

    Complex scattering parameter measurements generally require meticulous measurements of materials since (a) the measured phase generally differs from the actual value, (b) a shift in calibration (reference) plane results in large errors and (c) the phase uncertainty of the reflection scattering parameters of low-loss materials greatly increases when the material thickness is of integer multiples of one-half guided wavelength. To overcome all these drawbacks, the authors propose an amplitude-only method for complex permittivity determination of dispersive and non-dispersive medium- and low-loss materials. The method utilises amplitude-only measurements of two identical samples where the length of the second sample is twice as long as that of the first. There are three main advantages of this method. First, it eliminates multi-valued terms that produce multiple solutions in the process of extracting the complex permittivity and, thus, allows one to measure unique complex permittivity. Secondly, it removes the dependency of the calibration plane on measurements and phase uncertainty in the measurements of the reflection scattering parameters. Thirdly, it uses an objective function, which depends on only one variable for its goal. This is very important since fast, dynamic and accurate computations could be achieved by using this objective function. The method is verified by amplitude-only and complex scattering parameter measurements of two low-loss samples fitted into a waveguide section in the X-band (8.2-12.4-GHz). View full abstract»

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  • Compact dielectric resonator antenna for microwave breast cancer detection

    Page(s): 638 - 644
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (703 KB)  

    A compact stair-shaped dielectric resonator antenna (DRA) is designed and fabricated for microwave breast cancer detection. A quarter-wavelength choke was incorporated to reduce the finite ground plane size. A more than 40% return loss of 10 dB centred at 6.5 GHz is achieved with a 50 Omega coaxial port. Parametric studies are carried out to provide practical insights into sensor design. The design is performed numerically and confirmed experimentally. A simple model for the tissue is considered and the interaction of the sensor with the tissue is investigated. Good matching is retained without adding any matching medium or lumped loads when the sensor is in contact with the tissue. A two-element sensor array is investigated numerically. A dipole antenna and a circular ultra-wideband dipole antenna are compared with the stair-shaped DRA with a choked ground plane. Preliminary results are obtained for the cases with different tumour locations. The DRA type of sensor reveals good potential for frequency-domain detection. View full abstract»

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  • Matching radio frequency identification tag compact dipole antennas to an arbitrary chip impedance

    Page(s): 645 - 653
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (395 KB)  

    A method for matching dipole antennas to capacitive or inductive arbitrary complex impedances is proposed for ultra high frequency radio frequency identification (RFID) tag antenna designs. It can be applied to straight, capacitive-loaded, meander or any small high-Q dipole topology. For this purpose, design stages are provided with the corresponding formulas. The reflection coefficient simulations and measurements of four implemented prototypes show the expected output when the RFID frequency band, bandwidth, chip impedance and maximum tag size are required as inputs for the method. The eventual S 11les10 dB bandwidth depends on the chip impedance Q factor and the antenna size. How this bandwidth is manifested in terms of the read range is also discussed. A length ratio of up to 31.1% regarding the standard lambda/2 dipole at resonance is obtained. View full abstract»

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  • Direct synthesis of transmission line low-/high-pass filters with series stubs

    Page(s): 654 - 662
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (574 KB)  

    A direct synthesis procedure is presented for the design of transmission line low-/high-pass filters with series stubs. The proposed prototype consists of a cascade of series stubs of electrical length thetasc alternating with uniform transmission lines of electrical length 2thetasc. An exact network synthesis technique is applied on the fully frequency-distributed transmission line filter structures. By short-circuiting these series stubs, a low-pass prototype can be established to synthesise the filters with both predictable in-band and out-of-band behaviours. Instead, if the series stubs are open-circuited, a quasi-high-pass or wide band-pass filter can be designed with specified frequency bandwidth and centre frequency. Based on the formulation of a transfer function, a set of closed-form design formula is derived so that the synthesis design can be carried out for the proposed filters with Chebyshev equal-ripple frequency responses in the concerned low- and high-pass bands. As design examples, two five-pole planar filters based on the low- and high-pass topologies are implemented by using hybrid slotline and coplanar-waveguide structures. After final optimisation is executed via full-wave electromagnetic software to take all the discontinuities into accounts, two designed filters are fabricated and measured to verify the proposed synthesis approach and confirm the theoretical predictions. View full abstract»

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  • Optimised small-size tapered monopole antenna for pulsed ultra-wideband applications designed by a genetic algorithm

    Page(s): 663 - 672
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (844 KB)  

    An optimised small-size printed tapered monopole antenna, PTMA, is designed for ultra-wideband applications. Optimisation is based on a real-coded version of Harik's compact genetic algorithm, RCCGA. The optimisation algorithm, RCCGA has lowered the antenna area by more than 48% compared with the previous work for 3.1 to 11.7 GHz bandwidth operation. The time- and frequency-domain performance of the antenna are also described in simulations and measurements. View full abstract»

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  • A printed CPW-fed slot-loop antenna with narrowband omnidirectional features

    Page(s): 673 - 680
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (202 KB)  

    The design of a novel CPW-fed printed slot-loop antenna with narrowband omnidirectional attributes is proposed. The antenna geometry is selected to reduce slot coupling, thus achieving both a narrow bandwidth and an omnidirectional radiation pattern simultaneously. A gain of 2.1 dBi is accomplished with high radiation efficiency. Very narrow fractional impedance bandwidths as low as 2.9 are realised with good omnidirectional radiation characteristics. A technique providing unconstrained control of the bandwidth in the range of 1.7 - 6.9% is described. View full abstract»

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  • CPW-fed ultra wideband slot antenna with arc-shaped stub

    Page(s): 681 - 686
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (510 KB)  

    An ultra wideband coplanar waveguide (CPW) fed slot antenna is presented. A rectangular slot antenna is excited by a 50-CPW with an arc-shaped tuning stub. For the proposed antenna, the -10 dB return loss bandwidth could reach 15.6 GHz (3.7-19.3 GHz), which is about 135% with respect to the centre frequency of 11.5 GHz. Details of the antenna design, simulation and measured results on the return loss and the E-and H-plane radiation patterns of the proposed antenna are presented. View full abstract»

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  • A simple dual-band microstrip-fed printed antenna for WLAN applications

    Page(s): 687 - 694
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (660 KB)  

    A novel microstrip-fed dual-band printed antenna for wireless local area network (WLAN) is presented. The antenna comprises a rectangular and a circular radiating element, which generate two resonant modes to cover 2.4/5.2/5.8 GHz WLAN bands. The design was experimentally verified by constructing the antenna on a FR4 (epsivr = 4.4) dielectric substrate (47 mm times26 mm times0.76 mm) and measuring its impedance and radiation characteristics at both the bands. The measured 10 dB return loss (VSWR 2:1) bandwidth in the 2.4 GHz band is 550 MHz (2.1-2.65 GHz) and it covers the bandwidth required for 2.4 GHz WLAN. The 5.2/5.8 GHz resonant mode has a bandwidth of 950 MHz (5.15-6.1 GHz) covering 5.2/5.8 GHz WLAN bands. A rigorous experimental evaluation confirmed that the dual-band printed antenna maintained good radiation characteristics with minimum cross-polarisation levels. View full abstract»

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  • Compact tuneable single and dual mode ferrite left-handed coplanar waveguide coupled line couplers

    Page(s): 695 - 702
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (651 KB)  

    For the first time, single and dual mode novel left-handed coupled line couplers implemented on ferrite substrates are reported. Both of the proposed couplers demonstrate novel characteristics of coupler operation with properties of tunability and non-reciprocity, which have not been demonstrated before. The proposed couplers are realised in a left-handed coplanar waveguide configuration, constructed using interdigital capacitors and various types of planar shunt inductors. The performance of the couplers has been studied theoretically and verified numerically. The single mode tuneable coupler demonstrates a coupling level as high as 4 dB with a maximum isolation level better than 25 dB. The dual mode tuneable coupler exhibits non-reciprocal operations with a near-zero dB coupling level and a maximum non-reciprocal isolation level of more than 30 dB. Moreover, both the couplers have very compact sizes: 10.32 mm times 19.8 mm for the single mode coupler and 10.2 mm times 19.8 mm for the dual mode tuneable coupler, respectively. View full abstract»

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  • Effect of urban-site and vegetation on channel capacity in higher altitude platform communication system

    Page(s): 703 - 713
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (996 KB)  

    Communication services using higher altitude platforms have highlighted a need for estimating the effect of local obstructions on radio wave link. Vegetation and buildings are the major factors responsible for attenuation. The authors have calculated the radio wave attenuation because of vegetation and buildings. Here, the authors have used the fitted radio international telecommunication union model to calculate the vegetation attenuation. The attenuation because of buildings is calculated for an urban-site (residential area of Netaji Subhas Institute of Technology, NSIT, New Delhi, India) using geometrical optics and a uniform theory of diffraction. Further, channel capacity is calculated for vegetation and urban-site environment using Shannon's channel capacity theorem. View full abstract»

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  • Investigations on metallic sphere-inserted conical horn

    Page(s): 714 - 721
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1329 KB)  

    Much research is recently being made in improving the performance of smooth wall conical horns as an alternative to the corrugated horns. This study investigates the performance of a metallic sphere-inserted conical horn in the Ku-band by using simulations and experiments. While the proposed horn displays improved performance in respect of gain, aperture efficiency and return loss, it is also more compact in comparison with the recently proposed disc(s)-inserted conical horn. View full abstract»

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