By Topic

Microwaves, Antennas & Propagation, IET

Issue 6 • Date April 24 2012

Filter Results

Displaying Results 1 - 15 of 15
  • Miniaturised high-frequency and very-high-frequency antennas based on optimised non-uniform helical structures

    Page(s): 603 - 610
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    Helical windings are often used to shorten the length of a resonant low-frequency antenna, but this results in an antenna with narrow bandwidth for the normal mode. The windings are usually uniform, but in contrast the current study investigates the possible advantage of optimised non-uniform windings for improved bandwidth. Optimisation can involve a prohibitive number of variables when continuous variations along the antenna are described in terms of wire segment geometry. This study, however, reduces such requirements by describing the winding variations (pitch and radius) in terms of a limited number of parameters. These parameters are the coefficients of expansion of the variations in terms of radial basis functions. By this artifice, the optimisation problem is made tractable with limited computer resource. An evolutionary optimiser is used to achieve the optimal winding shape with respect to radius and pitch. Measured results from prototypes demonstrate the optimisation process to be effective. Further, simulations using non-ideal ground planes show the designs to be robust. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Miniaturised multi-band substrate integrated waveguide filters using complementary split-ring resonators

    Page(s): 611 - 620
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1289 KB)  

    A novel method for designing miniaturised multi-band filters using the complementary split-ring resonators (CSRRs) is proposed and demonstrated on the basis of substrate integrated waveguide (SIW) technology. By loading different types of CSRRs on the waveguide surface, multiple passbands propagating below the waveguide cutoff frequency can be generated separately. The proposed structures allow relatively independent control over the centre frequency and the coupling coefficient. The working principle is illustrated by the equivalent circuit and the filter coupling methodology is introduced for design purpose. Two types of dual-passband filters, a triple-band and a quadruple-band filter are designed and fabricated to validate the proposed concept. These filters are showing advantages in terms of compact size, good selectivity and stopband rejection, as well as the easy integration capability with other circuits. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Conformal array pattern synthesis using the weighted alternating reverse projection method considering mutual coupling and embedded-element pattern effects

    Page(s): 621 - 626
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (515 KB)  

    This article generalises a pattern synthesis technique to conformal arrays. An iterative method is used for optimisation of element excitations in an array of rectangular patch elements that are conformed to a hemispheric surface. The embedded-element co-polarisation and cross-polarisation patterns are evaluated using a full-wave method. These patterns are used in a newly introduced iterative synthesis algorithm to obtain the minimum sidelobe level (SLL) and cross-polarisation level (XPL). The mutual coupling effects on the synthesis results are investigated in this procedure. The synthesised patterns show adequate XPL and SLL comprised to other methods. The weighted alternating reverse projection (WARP) method is modified and it is shown that the WARP method can synthesise lower XPL and SLL than those of other methods. Compared with other synthesis method, the WARP improves SLL by 2 dB and XPL by about 1.5 dB in 19 element array. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Design of the current driver for inducing radiating ground edge current in a printed circuit board

    Page(s): 627 - 635
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (920 KB)  

    A new current driver is proposed to effectively excite ground edge current for radiation without additional space reserved for antenna design. Since the current driver functions as a feeding structure as opposed to a radiator, it can be designed as small as possible without deteriorating the antenna radiation properties. A circuit model of the miniaturised balun (balanced to unbalanced transformer) is introduced to explain the current-inducing mechanism and to provide some valuable physical insights into the characteristics of the current driver. The effect of a shielding metal box for the proximity circuitry near the current driver is also investigated. And it is shown that the nearby shielding box has minor effect on the performance of the driver, which demonstrates the feasibility of the current driver as an effective antenna structure in a compact wireless terminal. The current driver operating at 2.45 GHz is printed on an FR4 substrate of 0.4 mm and occupies only a small area of about 4 mm by 4 mm. The simulated and measured results come to a great agreement. Nearly omni-directional radiation patterns with a peak gain of about 1 dBi are obtained. Owing to the design flexibilities and the compactness, the current driver is feasible for wireless applications. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On-body channel statistical analysis based on measurements in an indoor environment at 2.45 GHz

    Page(s): 636 - 645
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (845 KB)  

    This study investigates the propagation phenomena and the fading experienced by on-body channels at 2.45 GHz, focusing on the effect of the human body in an indoor office environment. This investigation is based on signal measurements conducted for both stationary and mobile user cases using bodyworn antennas placed at various positions on the human body. The effect of the antenna location and the human body movement on the fading characteristics of the on-body channels is extensively studied through statistical analysis of the measurement data. First- and second-order statistics are also presented. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optimisation method on conformal array element positions for low sidelobe pattern synthesis

    Page(s): 646 - 652
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    An optimisation method for antenna element positions in conformal arrays is proposed in this study. Owing to the platform effect, the element pattern in a conformal array varies with its location. It is usually very time consuming to simulate the element patterns at all possible locations. In this proposed method, the patterns of an element located at an arbitrary position on the platform are obtained by interpolating the element patterns at several sampled locations using the model-based parameter estimation (MBPE) method. This interpolation strategy consists of two steps. Firstly, it interpolates the Fourier coefficients of the given element patterns at the sampled locations to acquire the Fourier coefficients of the element patterns at the desired location. Then the inverse discrete Fourier transform (IDFT) or the inverse fast Fourier transform (IFFT) algorithm is applied to obtain the element pattern. Compared with the conventional interpolation methods, this interpolation needs much fewer samples in the spatial domain and a smaller number of interpolation parameters. The element layout is optimised by the particle swarm optimisation (PSO) method. For each layout, the array excitations are obtained by the robust convex optimisation method. This proposed method is demonstrated through an optimisation on a cylindrical-parabolic conformal array. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Low phase noise V-band push-push voltage controlled oscillator using 0.15 μm GaAs pseudomorphic high electron-mobility transistor technology

    Page(s): 653 - 657
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    A low phase noise, low dissipated power and small-size V-band voltage-controlled oscillator (VCO) using dual cross-coupled pair configuration, capacitance-splitting technique and push-push topology is presented. The V-band VCO circuit uses 0.15 μm GaAs pseudomorphic high electron-mobility transistor technology. The VCO has low phase noise, of -108.43-dBc/Hz, at a 1-MHz offset from a 62-GHz carrier and can be tuned from 61.11 to 62.66-GHz. The figure of merit is -190.45-dBc/Hz. The power consumption of the VCO with 1.04-mm2 chip area is 24 mW, from a 1 V power supply. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ultra-wideband (UWB) coaxial-waveguide power divider using end-coupling structures

    Page(s): 658 - 662
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (371 KB)  

    Based on end open-circuited electrical coupling structure, a novel ultra-wideband (UWB) coaxial-waveguide power divider is presented in this study. The simple equivalent circuit for the presented UWB coaxial-waveguide power divider is developed and the maximum power handling capability of the presented coaxial power divider is evaluated. A UWB four-way coaxial-waveguide power divider is designed, optimised and fabricated. The simulated and measured results of the fabricated power divider show reasonable agreement. The measured input return loss is greater than 10 dB over the entire UWB band and also greater than 17 dB from 2.7 to 9 GHz. The measured average insertion loss, amplitude imbalance, group delay and group delay imbalance are about 0.4 dB (not including the 6 dB power-dividing insertion loss), 0.45 dB, about 0.41 ns and 0.5 ns, respectively, across the UWB band. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dual-polarised dielectric-loaded monopole antenna for wideband communication applications

    Page(s): 663 - 669
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1012 KB)  

    A dual-polarised dielectric-loaded monopole antenna for wideband communication applications is presented. The antenna is constructed by using two antenna elements orthogonal to each other. The antenna element consists of a microstrip-line-fed printed monopole with a finite truncated ground loaded with a dielectric resonator (DR). First, the antenna element is designed, fabricated and experimentally tested. Then the proposed design was extended to develop a dual-polarised antenna. The antenna impedance match is better than 10 dB over 91.3 from 4.4 to 11.8 GHz for both polarisations and the measured isolation between the two polarisation ports is better than 20 dB within the frequency band of interest whereas the maximum isolation achieved is 27 dB. The cross-polarisation levels in both planes are better than 20 dB. Both theoretical and experimental results in terms of return loss, isolation and radiation pattern are presented and discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Radar cross-section reduction for a microstrip patch antenna using PIN diodes

    Page(s): 670 - 679
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1035 KB)  

    The authors investigate in this study using PIN attenuator diodes to reduce the radar cross-section (RCS) of a microstrip patch antenna. A simple design guideline and a useful loading scheme are developed. In the investigation, PIN diodes are equivalent to capacitances and resistances when diodes are reverse-biased and forward-biased, respectively. According to the magnitude distribution of the induced electric field under the patch for a specific incidence angle, the loading positions of PIN diodes are selected near to where the maximum electric field appears. First, three typical incident angles are separately considered. As a result, RCS reduction for the microstrip patch antenna is realised by utilising the variable resistance characteristic (energy dissipation) of PIN attenuator diodes. Secondly, the loading positions for that three incident angles are combined to realise RCS reduction over a large angular spatial region and within a wideband frequency range, and thus an electronically controllable low RCS status can be successfully realised. The proposed design guideline is demonstrated. It is worth mentioning that, by real-time adjusting the bias status of each PIN diode, the antenna realised gain as well as the relative bandwidth is well maintained when the antenna is at work. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Printed internal antenna for mobile broadcasting (DVB-H/T-DMB) and communications (GSM900)

    Page(s): 680 - 684
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (738 KB)  

    This study proposes a printed internal antenna operating in the digital video broadcasting-handheld (DVB-H) band and the terrestrial digital multimedia broadcasting (T-DMB) L-band for mobile broadcasting and the GSM900 band for mobile communications. Owing to the limited physical size of the mobile terminal, the miniature antenna technique is very important for a low-band application. The proposed antenna consists of a printed rectangular monopole with a U-shaped slot, an extended ground stub and a folder-type chassis, which are easily printed on an FR4 substrate. The antenna occupies an area of only 50×27×mm2, which makes it attractive for use with modern multiband and multifunctional slim handsets. The combined behaviour of the antenna resonant mode and the chassis resonant mode is utilised without any matching circuits or magneto-dielectric materials. In addition, the proposed antenna uses a second higher-order resonance of the extended ground stub and the U-shaped slot. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Four-shaped 2 3 2 multi-standard compact multiple-input-multiple-output antenna system for long-term evolution mobile handsets

    Page(s): 685 - 696
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2029 KB)  

    The use of multiple-input-multiple-output (MIMO) antenna systems will be required by next generation wireless systems to achieve their high throughput data transmissions. In this work, the authors present the design and fabrication of a 2 - 2 MIMO antenna system for the 700-MHz band of the long-term evolution (LTE) wireless standard. The MIMO antenna system is based on a novel 4-shaped antenna geometry that is compact in size and covers two bands of operation. The dual-band 2 - 2 MIMO antenna system covers the 734-790-MHz and the 2307-2475-MHz LTE and industrial, scientific and medical (ISM) bands. It occupies an FR-4 material substrate size of 58-110-1.56-mm3. The antenna has frequency tuning capabilities without changing the over all size of the MIMO system substrate. Several isolation enhancements methods were investigated, and the values of the correlation coefficient (|ρ|max) were within the LTE requirements. The maximum obtained gain for a single operating antenna at 770 and 2380 MHz was 5 and 4.5 dBi, respectively. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Quasi-static and hybrid-mode analysis of asymmetric coupled cylindrical striplines

    Page(s): 697 - 704
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (310 KB)  

    Quasi-static and the frequency-dependent hybrid-mode analyses are presented for the general structure of coupled cylindrical striplines. Stationary expressions are derived for all elements of capacitance and inductance matrices which describe the quasi-static characteristics of the dominant C- and π-modes of asymmetric coupled cylindrical striplines. The hybrid-mode analysis is also developed to afford the frequency dependency of the phase constants as well as characteristic impedances. The characteristic impedances of asymmetric coupled striplines are evaluated first by using the appropriate definition based on the variational scheme. A very accurate numerical method is presented in incorporating the tight coupling between strip conductors and the edge singularities of the fields near the conductor edge properly. The frequency-dependent characteristics ensure consistency with the corresponding quasi-static solutions in lower frequencies, and the numerical results reveal the notable characteristics of the asymmetric coupled cylindrical striplines for the tight-coupling as well as the extremely weak-coupling cases. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Design of a printed dual-band coupled-line coupler with generalised negative-refractive index transmission lines

    Page(s): 705 - 712
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (831 KB)  

    A dual-band printed metamaterial coupler made of a microstrip line and a generalised negative-refractive-index (NRI) line is presented. Owing to the presence of two left-handed bands in the generalised negative-refractive-index transmission line (NRI-TL) unit cell, backward coupling occurs over two frequency ranges centred on 2.7 and 4.7-GHz. Measured results for an edge-coupled device are reported; peak coupling levels of -3.5 and -4.4-dB are observed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Precise frequency and bandwidth control of switchable microstrip bandpass filters using diode and microelectro-mechanical system technologies

    Page(s): 713 - 719
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (594 KB)  

    In this study, two reconfigurable bandpass filters are presented. The first filter is able to switch between WiFi and universal mobile telecommunications (UMTS) transmit band standards. Centre frequency, bandwidth and power specifications are precisely met by a switchable filter topology that includes two folded resonator extensions switched by only two PIN diodes. Design specifications require two filter states, one at 2.440 GHz with a 80 MHz bandwidth and a second state at 1.955 GHz with a 140 MHz bandwidth for the WiFi and UMTS transmit bands, respectively. The filter should handle a maximum power of 16 and 21 dBm for the WiFi and UMTS states, respectively. Measured results show very good agreement with the simulations. The filter topology meets power requirements of both standards. The second filter was designed using ohmic-contact cantilever-type MEMS able to switch between two different states with a centre frequency tunable range of 24 in C band. This design includes two additional switches to provide precise input and output couplings for each state. The filter was designed to have centre frequencies of 5 and 6.2 GHz, with a fractional bandwidth of 7 and 3 , respectively. Filter specifications were successfully met with the proposed topologies. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

IET Microwaves, Antennas & Propagation covers all aspects of microwave and antenna engineering and propagation.

Full Aims & Scope

Meet Our Editors

IET Research Journals
iet_map@theiet.org