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High Frequency Postgraduate Student Colloquium, 2001. 6th IEEE

Date 9-10 Sept. 2001

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Displaying Results 1 - 25 of 32
  • 6th IEEE High Frequency Postgraduate Colloquium (Cat. No.01TH8574)

    Publication Year: 2001
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  • Proximity coupled stepped T-feed wideband linearly polarised patch antenna

    Publication Year: 2001 , Page(s): 106 - 110
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (411 KB) |  | HTML iconHTML  

    A linearly polarised microstrip patch antenna fed by a novel stepped T-feed is presented. The antenna exhibits more than octave band impedance bandwidth for VSWR<2. The antenna operates over 1.05 to 2.4 GHz. Symmetrical far-field patterns are obtained over 46% of frequency band of operation and the cross polarisation level of the antenna is of the order of -18 to -25 dB over this band. Measured characteristics are compared with simulated predictions View full abstract»

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  • Cross-channel interference due to mode partition noise in WDM systems

    Publication Year: 2001 , Page(s): 142 - 146
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    The side mode suppression ratio of self-seeded, gain-switched optical pulses is shown to be a vital parameter in wavelength division multiplexed communications systems. Experiments carried out on a 2-channel wavelength multiplexed set-up using tunable self-seeded gain-switched pulse sources at 2.5 GHz, have demonstrated the cross-channel interference effects which may be encountered if the side mode suppression ratio of one of the sources becomes degraded View full abstract»

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  • A method for calculating the radiation pattern of a non-planar conformal array

    Publication Year: 2001 , Page(s): 111 - 118
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (471 KB) |  | HTML iconHTML  

    This paper describes the development of a mathematical algorithm to determine the volumetric array factor of a nonplanar conformal array. It shows the vector translation required to collimate the beam of each element to a common point. Following this, an illustration shows the mathematical rotations required to represent each element with respect to a common set of axes. A set of equations describes these rotations in Cartesian mathematical form. These are incorporated into a MATLAB(R) program to calculate the array factor. The program was tested and validated by comparing its output against that of the commercial method of moments wire antenna simulation tool NEC-WIN PRO (R) for a number of array variants. The results were found to be consistent View full abstract»

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  • The bandwidth benefits of close-to-chip lumped element matching of microwave high power amplifiers

    Publication Year: 2001 , Page(s): 147 - 151
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    The bandwidth benefits of Close-to-Chip matching using lumped elements within the transistor encapsulation compared with Off-Chip matching using distributed elements outside the transistor encapsulation for high power microwave transistors have been simulated at 2 GHz. Simulation results indicate that Close-to-Chip matching using lumped elements gives a wider bandwidth compared with conventional Off-Chip matching using distributed elements View full abstract»

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  • A balanced vector modulator for LMDS applications

    Publication Year: 2001 , Page(s): 152 - 157
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (418 KB) |  | HTML iconHTML  

    The design and performance of a monolithic microwave I-Q type vector modulator operating at 26 GHz is presented. The MMIC chip which measures 1.75 mm × 2.1 mm, employs direct carrier modulation to reduce hardware complexity and cost. The static constellation was obtained with swept bias voltage control, with this, modulation of 16-quadrature amplitude modulation (QAM) is demonstrated. Baseband input levels were applied at 2.5 MSample/s, by an arbitrary waveform generator to demonstrate a 10 Mbits/s data rate transmitter operating at 26 GHz View full abstract»

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  • Investigations into the use of SU-8 in the fabrication of a micro-optical bench for hybrid optoelectronic integration and packaging

    Publication Year: 2001 , Page(s): 164 - 167
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    The ultrathick negative photoresist SU-8 has been investigated for use in the fabrication of a passively aligning micro-optical suite including elements such as fibre alignment grooves, lens holders and device alignment features. The possibility for the fabrication of mirrors is also considered. The excellent micromachining properties of SU-8 using common low-cost, fast photolithographical techniques with processing temperatures of below 100°C make it an ideal material for the rapid, cost-effective prototyping of the above structures. A fibre-lens alignment structure has been fabricated and its accuracy evaluated View full abstract»

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  • Antenna array beam-steering by the integration of a series phase shifter

    Publication Year: 2001 , Page(s): 25 - 29
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (830 KB) |  | HTML iconHTML  

    Beam steering is defined as the ability to electronically steer the beam maximum of an antenna electric field pattern to some predefined point in space. Leaky wave antennas can be used for such a purpose but include inherent problems such as large size, difficulty in impedance matching and a large number of sidelobes in the resultant electric field pattern. This paper concentrates on a method for mimicking the operation of a typical leaky wave antenna array by the simple integration of a phase shifter into the array structure. Up to 12° beam steer is demonstrated using the integrated array whose structure is short and compact compared to the typical leaky wave arrays. The bias voltage of the phase shifter is used to control the impedance match of the array reducing the VSWR to below 1.5 where the 12° beam steer is experienced. The phase shift between the elements of the array, used to provide beam steering, is provided by scanning the frequency through a range of frequencies from 1.17 GHz to 1.23 GHz. This range is greatly reduced from typical leaky wave antenna arrays because the phase shifter also acts to provide an additional phase shift between the elements. The resultant radiation patterns also show improved characteristics as the number of sidelobes has been decreased View full abstract»

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  • A radio coverage and planning tool

    Publication Year: 2001 , Page(s): 35 - 40
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (523 KB) |  | HTML iconHTML  

    With the increased utilisation of mobile communications, and the speed necessary to keep radio systems efficient, a 'RAdioWave Coverage And Planning Tool', RAWCAPT, is proposed. This tool could prove not only cost efficient, but also time efficient for users needing to ascertain the optimal position for a transmitter-receiver radio systems for any urban terrain. The tool utilises a Lidar dataset as the input, due to fact that Lidar data is reasonably cheap compared to other forms of data. On completion of the tool, the full process of radio path planning will be contained within a solitary software application View full abstract»

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  • Hybrid radio/fibre distribution system based on a directly modulated laser transmitter with external injection

    Publication Year: 2001 , Page(s): 77 - 81
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (403 KB) |  | HTML iconHTML  

    The authors present the idea of using direct modulation of the laser for generating microwave signals for hybrid radio/fiber systems. The external light injection is used in order to increase the modulation bandwidth of the laser and at the same time to improve the overall system operation. The experiments show a 14 dB enhancement in performance of the system used for distributing a 155 Mb/s data signal on an 18 GHz carrier View full abstract»

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  • Gyroelectric properties of indium antimonide at terahertz frequencies

    Publication Year: 2001 , Page(s): 65 - 70
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (397 KB) |  | HTML iconHTML  

    The behaviour of a magnetised semiconductor can be characterised by a permittivity tensor, which combines the ohmic and displacement currents. The frequency dependence of the permittivity tensor elements is described. A semiconductor that is magnetised transverse to the direction of propagation such that the microwave electric field is perpendicular to applied static magnetic field (i.e. a TM mode) is described by an effective permittivity, εeff. The variation of εeff of indium antimonide (εr =17.7) as a function of frequency up to the terahertz region is described. The reflection and transmission coefficients for oblique incidence on a simple dielectric and semiconductor interface have been derived and it can be shown that a reflectionless condition is achievable only at normal incidence. The frequency dependence of the complex reflection coefficient for normal incidence is presented and discussed View full abstract»

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  • An automated active source and load pull measurement system

    Publication Year: 2001 , Page(s): 7 - 12
    Cited by:  Papers (13)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (439 KB)  

    A fully automated electronic load and source pull measurement system has been developed using standard Agilent ESG Frequency sources. Combined with a vector corrected time-domain waveform measurement system based on the HP-MTA (Microwave Transition Analyser) enabling real time waveform measurements of the current and voltages to be obtained. The system has been validated using measurements performed on a Heterojunction Bipolar Transistor operating in Class B with constant harmonic terminations on the load and source over variations in drive level View full abstract»

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  • Photoparametric amplifier for optical wireless communication system

    Publication Year: 2001 , Page(s): 168 - 173
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (530 KB) |  | HTML iconHTML  

    In this article a novel receiver based on Photoparametric Amplifier (PPA), which one of the alternative for receiver detection and amplification techniques is fully described. The PPA mode of operation involves optical detection and amplification within a single device. The amplifier operation is based on nonlinear characteristics of the photodiode and therefore, the mechanism constituting gain is highly nonlinear and different to that in conventional amplifier/mixer chain. It is able to provide selectivity and sensitivity at the same time, as required for wireless optical communications. In the proposed approach, the detector, front-end amplifier and mixer chain, are replaced by a single device, which reduced component count and therefore cost directly. Under optimum test conditions, the research group has demonstrated a power gain of 17 dB over a baseband detector (BW of 25 MHz), with improved noise performance View full abstract»

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  • Fabrication of dielectric-filled rectangular waveguide using thick-film processing

    Publication Year: 2001 , Page(s): 82 - 87
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (774 KB) |  | HTML iconHTML  

    This paper describes the use of photoimageable thick-film technology for the fabrication of rectangular waveguides. Thick-film technology is attractive for volume manufacture and recent materials developments, such as photoimageable dielectric and conductor pastes, have led to improved edge definition and smaller feature sizes, so that thick-film circuits can equal the performance of thin-film processing. A dielectric-filled rectangular waveguide fabricated using photoimageable thick-film materials is presented. The waveguide incorporates a new transition from RFOW probe to rectangular waveguide. Results show low attenuation across the 60-90 GHz frequency range View full abstract»

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  • Feedforward linearizer with reduced output auxiliary amplifier

    Publication Year: 2001 , Page(s): 13 - 18
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (469 KB)  

    Effective feedforward linearization of a power amplifier can be achieved without compromising performance, using an auxiliary amplifier of lower power than the main amplifier overcoming the inefficiency of the classic feedforward configuration, which employs two amplifiers of the same power rating. Reduction of the power rating of the auxiliary amplifier will lead to improved system efficiency. It is shown that the operating output power level and consequential intermodulation distortion level of the main amplifier are critical in determining the minimum saturation power level of the required auxiliary amplifier. Results of theoretical calculations and CAD simulations for the required minimum saturation power level of the auxiliary amplifier are presented and indicate close agreement View full abstract»

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  • Extraction of state function behaviour from large signal waveform measurements [pHEMTs]

    Publication Year: 2001 , Page(s): 88 - 93
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (527 KB) |  | HTML iconHTML  

    The nonlinear state functions of the pHEMT (pseudomorphic high electron mobility transistor) are fully extracted using dynamic measurements only. A systematic reverse waveform measurement technique combined with forward waveform measurements yield the intrinsic current and charge surface state functions. The reverse extraction results have been verified to be bias and power level independent and the resultant state functions obtained are confirmed to be unique. The technique shown is able to completely characterise state function behaviour and hence minimizes the extrapolation problems associated with existing state function extraction techniques View full abstract»

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  • Low noise integrated active antenna as image reject mixer (IRM)

    Publication Year: 2001 , Page(s): 125 - 129
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB) |  | HTML iconHTML  

    A patch antenna integrated with two Low Noise Amplifiers (LNA) is implemented to act as an Image Reject Mixer (IRM). The low noise active antenna system transforms a received radio frequency signal into two signals, which are out-of phase to each other. The image signals can be cancelled by the IRM. The antenna, LNA's, mixers and local oscillator (LO) are integrated into a single Active Integrated Antenna (AIA) module. An external IF 90° hybrid coupler is required in the IRM. The advantages of the LNA active antenna mixer system are low noise, image signal rejection, low cost and simple circuitry of front-end, and improved receiver sensitivity View full abstract»

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  • Performance analysis of switched-sector antennas for indoor wireless LANs

    Publication Year: 2001 , Page(s): 30 - 34
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (621 KB) |  | HTML iconHTML  

    Given the potential market for wireless LAN (WLAN) technology, capacity within the available 2 and 5 GHz frequency bands is likely to fall short of market demands. Multiple-sector antenna arrays are known to be able to provide capacity enhancement by means of interference reduction through spatial filtering. In this paper, the performance of an eight-element circular array acting as an Access Point (AP) in indoor wireless LAN environments is analysed. Spatial-temporal channel data used within the analysis were obtained from physical measurements within numerous indoor environments using a state-of-the-art wideband vector signal analyser. Performance analysis of the array employing a switched-sector controller within the Hiperlan/2 standard is appraised in terms of carrier-to-interference (C/I) ratios. Results show that an isolation of up to 15dB can be achieved between the two polarisations, by means of using an antenna array at the AP. It is shown that 54% of the time, 2 users per timeslot can be supported by the system View full abstract»

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  • Harmonic power generation from the non-linear output capacitance of silicon LDMOS devices

    Publication Year: 2001 , Page(s): 1 - 6
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (406 KB)  

    Compression and harmonic generation mechanisms coupled to the non-linear output drift-region capacitance of Silicon LDMOS FET transistors are thoroughly investigated. Large-signal time-domain analysis is performed on the device operated as a class AB amplifier. Observations confirm significant real power being shifted from the fundamental to the even order harmonics by the capacitive element acting effectively as a varactor diode multiplier View full abstract»

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  • Optimum network topologies for high power microwave filters

    Publication Year: 2001 , Page(s): 53 - 58
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (457 KB) |  | HTML iconHTML  

    A demand for high power filters is met by a theoretical procedure to produce prototype networks designed for high peak voltages. This is in contrast to previous techniques which look at physical design methods to minimise breakdown in the various technologies used for realisation. Limitations are placed on the optimisations to ensure practical topologies are generated View full abstract»

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  • A millimetre-wave detector for short range applications

    Publication Year: 2001 , Page(s): 71 - 76
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB) |  | HTML iconHTML  

    In this paper, a GaAs millimetre-wave detector for positive bias is presented. The circuit uses a 0.20 μm GM Schottky diode and achieves a state of the art sensitivity of approximately 1100 mV/mW under optimum conditions in the 65.5 GHz range. The bias is applied through a voltage divider, allowing for signals with very low frequencies to be detected. The detector has been integrated together with a patch antenna onto a single chip of 1.0×1.5 mm2, exhibiting similar sensitivities to the stand alone version. The integration resulted in a very small, mass producible detector circuit for broadband broadcasting, millimetre-wave propagation measurements, and motion detection applications View full abstract»

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  • High data rate pulse regeneration using non-linear transmission line technology (NLTL)

    Publication Year: 2001 , Page(s): 136 - 141
    Cited by:  Papers (1)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB) |  | HTML iconHTML  

    The application of Non-Linear Transmission Line (NLTL) technology to the restoration of signal integrity in electro-optic back-planes technology is reported. The non-linear transmission line synthesized uses coplanar wave-guide because it has better performance than the micro-strip line View full abstract»

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  • Fifteen pole superconducting filter for radio astronomy

    Publication Year: 2001 , Page(s): 47 - 52
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (350 KB) |  | HTML iconHTML  

    Application of high temperature superconducting (HTS) materials in the communication industry has become attractive in recent years. Mobile communications, radar, radio telescopes and satellite communication links are some of the many applications which use microwave filters made from HTS materials. Most HTS microwave filters reported in the literature were designed for narrow band applications; this is due to recent commercial requirements. However, some astronomy laboratories need to employ a fairly wide band filter for their radio telescope receivers. An HTS filter is ideal for this application because of the low intrinsic insertion loss and steep filter skirts. A fifteenth order Chebyshev HTS band pass filter, designed for Jodrell Bank Observatory, is presented for astronomy applications. Sonnet EM simulation results are provided for this 15-order filter with fractional bandwidth of 26.4%. Good agreement between theoretical results and simulations is obtained. Size miniaturization has also been carried out. Comparisons of simulation results between original and minimized design are also provided View full abstract»

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  • Adaptive Volterra-based predistorter design for RF high power amplifiers

    Publication Year: 2001 , Page(s): 100 - 105
    Cited by:  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB) |  | HTML iconHTML  

    This paper presents an efficient digital baseband predistortion linearizer to compensate for the nonlinear distortions induced by RF high power amplifiers in wireless communication systems. The proposed approach utilize a fast RLS filtering algorithm based on V-vector algebra and an indirect learning architecture to update the coefficients of a Volterra-based-predistorter. No preliminary identification of the nonlinear characteristics of the HPA, as required by the conventional pth-order inverse methods, is needed with this approach. Simulation results show that high performance and low computational complexity are achieved in nonlinear systems with a TWT-type power amplifier View full abstract»

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  • Composite materials for planar frequency agile microwave devices

    Publication Year: 2001 , Page(s): 59 - 64
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (510 KB) |  | HTML iconHTML  

    A strategy leading to development of tunable microwave planar devices is described. The characterisation of composite material systems is outlined and initial results are reported. Material systems based on SU-8 epoxy resist offer a viable route to ferrite loaded elements suitable for planar device fabrication View full abstract»

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