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Microwaves, Antennas & Propagation, IET

Issue 13 • Date October 23 2012

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Displaying Results 1 - 14 of 14
  • Triple stub circuit topology as simultaneous insertion phase, amplitude and impedance control circuit for phased array applications

    Page(s): 1399 - 1406
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (758 KB)  

    This study shows that the well-known triple stub circuit topology can also be used for controlling the insertion phase and amplitude of a given signal simultaneously, as well as preserving its impedance transformation ability. The triple stub circuit topology, which is nothing but an extension of the conventional double stub loaded-line phase shifter, results in one more degree of freedom to its solution when it is solved for its insertion phase. This additional degree of freedom not only brings the impedance transformation ability, but also allows tuning the circuit into a resonator at the frequency of interest whose quality factor can also be adjusted. This result is employed for controlling the amplitude of the output signal to any desired level, which is achieved using only low-loss transmission lines and shown to be true for any non-zero transmission line losses. The measurements of the fabricated sample circuits verify that it is possible to control simultaneously the insertion phase between 0 and 360° and the amplitude from -0.8 to <; -15 dB, whereas the input return loss is always kept better than -15 dB as an example of their impedance transformation capabilities. View full abstract»

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  • Design of coplanar waveguide-feed pentagonal-cut ultra-wide bandwidth fractal antenna and its backscattering

    Page(s): 1407 - 1414
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (837 KB)  

    A coplanar waveguide-feed pentagonal-cut fractal antenna and its backscattering are considered. The proposed antenna has been fabricated with optimised dimensions. The experimental results of this antenna exhibit ultra-wide bandwidth characteristics from 2.5 to 15 GHz. The proposed antenna has been simulated using a three-dimensional electromagnetic simulator. The experimental and simulated results are in good agreement. The effects of design parameters on impedance bandwidth have also been studied in detail. The experimental radiation patterns of this antenna are omni-directional in the H plane and bidirectional in the E plane. The measured group delay of the proposed antenna is almost constant throughout the band. The backscattering reduction of this proposed antenna is good throughout the band. This antenna can be useful for high data rate transmission in modern wireless communication, microwave imaging and vehicular radar. View full abstract»

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  • Modelling of composite right/left-handed transmission line based on fractal geometry with application to power divider

    Page(s): 1415 - 1421
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    A fully printed fractal-perturbed resonant-type composite right/left-handed transmission line (CRLH TL) is proposed with electrically smaller dimensions. The CRLH structure consists of Koch-curve-shaped complementary split ring resonators etched on the ground plane and capacitive gaps embedded in the Koch-curve-shaped conductor line. A generic modelling technique for a set of resonant-type circuits, demonstrated to be extremely useful in the accurate extraction of the circuit elements, has been developed for the first time based on the effective medium concept. With the help of this modelling method, a quarter-wavelength impedance transformer (QIT) made of the CRLH TL is readily synthesised. The full fractal perturbation gives rise to the large lumped circuit elements which predict a significantly lower resonance. To demonstrate possible applications of the CRLH QIT, a Wilkinson power divider is designed, fabricated and measured. A good agreement of S-parameters between simulation and measurement has confirmed not only the design, but also the modelling technique that is of a reference value for characterisation. The engineered divider obtains a 58.9% size reduction and exhibits moderate in-band and out-of-band (isolation) performances in comparison with its conventional counterparts, advancing a step in miniaturisation strategy. View full abstract»

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  • Compact wide-stopband microstrip bandpass filterbased on stub-loaded stepped-impedance resonators

    Page(s): 1422 - 1428
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (636 KB)  

    This study presents compact wide-stopband microstrip bandpass filters using stub-loaded stepped-impedance resonators. The resonators consist of three stepped-impedance sections. By adjusting the parameters of the resonators, one can control the frequencies of the resonant modes as well as the frequency of the transmission zero. When the transmission zero frequency is close to the spurious resonant mode frequencies, one can have a wide-stopband bandpass filter without external filtering circuits or increasing the resonator number for suppressing the spurious passbands. To validate the design concept, three dual-band bandpass filters and one wideband bandpass filter are designed, fabricated and tested. View full abstract»

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  • Design approach for return-loss optimisation of multi-stage millimetre-wave microelectromechanical systems dielectric-block phase shifters

    Page(s): 1429 - 1436
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (861 KB)  

    This study reports on the radiofrequency (RF) performance optimisation of a novel multi-stage microelectromechanical system (MEMS) dielectric-block phase-shifter concept. The objective is to minimise the average return loss for all possible operation states of a multi-stage phase shifter, without substantially compromising the overall insertion loss or in phase-shift performance. The optimisation method presented in this study is generally applicable to any type of multi-stage RF MEMS devices that are operated in all possible state combinations of the different stages. The return loss is optimized for a seven-stage MEMS dielectric-block phase shifter by adjusting the individual distances between the phase shifter stages, for the nominal frequency of 75 GHz as well as for 500 MHz and 1 GHz bandwidth. A total of seven different designs following different optimisation approaches are investigated by simulations and measurements of fabricated devices. The best concept was found for exponentially increasing distances between the stages that takes into account the proper actuation sequence for all possible phase-shift combinations. As compared with a non-optimised device previously published by the authors, the design offering the best compromise between return loss and insertion loss, achieved by this optimisation method, results in a significant return loss improvement of 11.8 dB (simulated) and 6.98 dB (measured), whereas compromising the insertion loss by only 0.75 dB (simulated) and 0.92 dB (measured). In contrast to that all other investigated concepts, including intuitive optimisation methods such as λ/4 distances or optimisation of equidistant concepts result in a much smaller or no return-loss improvement and some even in a drastic worsening of the insertion loss. View full abstract»

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  • Low-phase-noise 0.63-V, 1.7-mW, 11.55-GHz quadrature voltage controlled oscillator with intrinsic-tuned technique in 0.18-μm complimentary metal oxide semi-conductor

    Page(s): 1437 - 1442
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (593 KB)  

    A low-power and low-phase-noise 11.55-GHz quadrature voltage-controlled oscillator (QVCO) using intrinsic-tuned technique is demonstrated in a standard 0.18-μm complimentary metal oxide semi-conductor (CMOS) technology. Intrinsic-tuned technique means the intrinsic junction capacitances at the drain terminals of the cross-coupled transistors are regarded as varactors, so no extra low-Q accumulation-mode MOS varactors are needed. This in turn results in a reduction of power consumption, a minimisation of parasitic capacitance effect (i.e. an increase of the operation frequency) and an improvement of phase noise. The QVCO core draws 2.7μmA current from a 0.63μV power supply, that is, it only consumes 1.7μmW. The QVCO achieves a tuning range of 3.9μ (11.11μ11.55μGHz) and a low phase noise of μ114.7μdBc/Hz at 1μMHz offset from 11.55μGHz. The corresponding figure-of-merit is μ193.6μdBc/Hz, one of the best results ever reported for an X-band CMOS QVCO/VCO. The core circuit occupies a chip area of only 0.64μ0.58μmm2, that is, 0.37 mm2. View full abstract»

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  • Broadband dual-band stacked square microstrip antenna with shorting plates and slits

    Page(s): 1443 - 1450
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (851 KB)  

    A stacked microstrip antenna with shorting plates and slits is proposed as a broadband dual-band antenna. By shorting the upper patch to the lower patch at two apexes of the diagonal of the square patch, the bandwidths (for VSWR ≤2) at the two frequency bands are enhanced and the absolute gain at the high-elevation angles at the higher-frequency band is improved. Moreover, the cross polarisation in H plane at the higher-frequency band is reduced by inserting the slits on the lower patch conductor. The proposed antenna radiates to the high-elevation angles at the two frequency bands. The measured bandwidths (for VSWR ≤2) with an absolute gain at θ = 0° ≤ dBi are 19.1 and 18.7≤ at the lower and higher-frequency bands, respectively. View full abstract»

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  • Jamming recognition method based on the full polarisation scattering matrix of chaff clouds

    Page(s): 1451 - 1460
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (458 KB)  

    This article studies the probability density function (PDF) of the polarisation-radar cross-section (RCS) ratio based on the polarisation rotation transformation, of chaff cloud with all possible rotation angles. The PDF of this ratio is different between chaff cloud and a single dipole, even when the chaff cloud is sparse. The results indicate that the PDF of the chaff cloud polarisation-RCS ratio is different from that of other radar targets such as aircraft and missiles, which provides a key to discriminate chaff jamming among other targets. An analytical formula of the PDF of the polarisation-RCS ratio for chaff cloud with arbitrary orientation distribution is presented and validated by numerical electromagnetic simulation results for sparse and dense chaff clouds, respectively. In addition, three typical orientation distributions are analysed in detail. Based on this formula of the PDF, a pilot study is also carried out to compare the chaff cloud radar signature of this ratio with other targets, which confirms the feasibility of chaff-jamming recognition by computing the posterior probabilities. View full abstract»

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  • Miniature on-chip bandpass power divider with equalripple response and wide upper stopband

    Page(s): 1461 - 1467
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    In this study, a miniature bandpass power divider based on capacitive-loaded multicoupled line is proposed, which features equal-ripple insertion loss, return loss and isolation responses. Owing to the employment of capacitive-loaded transmission line resonators, it can achieve very compact size and wide upper stopband. The proposed bandpass power divider can be designed according to the conventional filter synthesis techniques, and is suitable for on-chip implementation. Specifically, a bandpass power divider with a centre frequency f0 of 5.5 GHz, 18.2% fractional bandwidth, and third-order equal-ripple response is designed and implemented using the commercial GaAs pseudomorphic high electron mobility transistor (pHEMT) process. The circuit size without pads is 0.87 mm × 0.95 mm, and the electrical size is only 0.057 λg × 0.062 λg at f0. The in-band insertion loss is less than 6 dB with a minimum insertion loss of 5.12 dB. The in-band return loss is better than 10 dB, and the isolation is better than 15 dB. In addition, a wide 30-dB upper stopband up to 57 GHz is achieved. View full abstract»

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  • Reverberating chamber profile identification

    Page(s): 1468 - 1472
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (179 KB)  

    This study proposes a model, based on the generalised K (GK) distribution, for identifying the reverberating chamber (RC) propagation channel profiles. Following this rationale, a parameter, given by a proper combination of GK parameters, is not only able to clearly distinguish between line-of-sight (LOS) and non-line-of-sight conditions, but it is also capable of providing a better granularity within these two macro groups (i.e. distinguishing the clear LOS condition from the near LOS one, that typically applies when an object partially shadows the link). Experiments undertaken over a large set of measurements accomplished by emulating different propagation channel conditions at the RC of the Università di Napoli Parthenope (formerly Istituto Universitario Navale, IUN) confirm the soundness of the model and the effectiveness of the proposed parameter. View full abstract»

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  • Expeditious diagnosis of linear array failure using support vector machine with low-degree polynomial kernel

    Page(s): 1473 - 1480
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (446 KB)  

    In modern electronic warfare, rapid failure detection of malfunctioning antenna elements followed by swift remedial action is crucial to the success of any military action in the battlefield. Driven by the need for more efficient detection techniques, a fast support vector machine classifier using low-degree polynomial kernel is developed to expeditiously detect and locate the failed elements of an analogue uniform linear array (ULA). This method will work on any analogue linear array configuration with digitally controlled phase-shifters and amplifiers. The results for a ULA sample are illustrated to demonstrate its effectiveness. View full abstract»

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  • Capacitive coupling of discrete micro-sized gaps for radiofrequency applications

    Page(s): 1481 - 1486
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (427 KB)  

    This study investigates the performance of a passive thin metallic object containing micro-sized gaps exposed to a plane wave excitation. This study has potential applications for emerging antenna fabrication techniques where the conducting sections are made from discrete metallic sections. This includes antennas composed of nanomaterials and conventional inkjet-printed antennas. Electromagnetic simulations showed metallic sections separated by a micro-sized gap were found to capacitively couple. The coupling can be enhanced by reducing the size of the gap, increasing the width of the metallic object or by filling the gap with a permittivity greater than unity. It should be noted that the DC value of parallel plate capacitor is not strictly valid at radiofrequencies - however, this study shows that the DC value of capacitance is a reasonable approximation and is useful to understand the behaviour. View full abstract»

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  • Effect of placing mushroom electromagnetic bandgap structures at the inset feedline of microstrip patches

    Page(s): 1487 - 1497
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (710 KB)  

    Placement of mushroom electromagnetic bandgap (EBG) structures at the inset feedline of patch antenna operating at 4.8 GHz is analysed in this study. Proposed design for (i) single patch and (ii) two-element patch array exhibits significant improvement in return loss, bandwidth and mutual coupling loss. Parametric analysis confirms that the optimal position of EBG structures is at a distance of 1.5 mm on both sides of the feedline. It is established that the return loss increases by 8 dB and bandwidth increases by 3.2 for single patch with EBG structures at the feedline. A 6 reduction in antenna size is realised when compared with conventional placing of EBG. Likewise in double patch, placing the EBG structures on either side of the corporate feedline improves the return loss by 2.5 dB and a 12 reduction in size is achieved when compared with customary positioning of EBG. Bandwidth improves by 4.82 . The superior reduction of mutual coupling of double patch with inset edge feed having EBG structures at feedline, in addition to single-column mushroom EBG structures placed between the patches is demonstrated. The mutual coupling loss increases by 3.5 dB and a size reduction of 20 is accomplished. In antenna arrays, EBG structures at the feedline considerably reduce side lobe level and back lobe level and improve directivity, because of optimal radiation patterns. Simulations are validated experimentally. View full abstract»

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  • Forward/backward spatial reconstruction method for directions of arrival estimation of uncorrelated and coherent signals

    Page(s): 1498 - 1505
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (549 KB)  

    An effective method to classify the directions of arrival (DOA) estimation of narrow-band signals in a coherent environment is proposed. The basic idea is to rearrange the correlation matrix. By combining the forward reconstructed correlation matrix with its conjugated backward form together, it is always possible to estimate any ⌊2(M+1)/3⌋ one-dimensional DOAs using an M-element uniform linear array (ULA) and any ⌊2(3⌊2⌊2)MN⌋ two-dimensional DOAs using an M×N-element uniform rectangular array. Other arrays that contain centrosymmetric sub-arrays can also be applied with our method. Simulation results demonstrate that the proposed method could both enlarge the effective aperture and reduce the computational complexity. View full abstract»

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