Browsing by Author "Kocjancic, Leon"

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    Characterisation of sidelobes for multibeam radar based on quasi-orthogonal LFM waveforms
    (IEEE, 2020-06-11) Balleri, Alessio; Kocjancic, Leon; Merlet, Thomas
    Multibeam radars (MBRs) enable multiple independent channels by simultaneously exploiting spatial and waveform diversity. Orthogonal waveforms are employed to form multiple independent antenna beams, each one providing a different function and using different dedicated radar resources. This paper investigates sidelobe levels in MBRs and presents a comparison with those of an Electronic Steerable Array (ESA) that employs a single waveform in transmission to generate multiple simultaneous beams. Simulations are carried out for a 3-channel MBR transmitting quasi-orthogonal Linear Frequency Modulated (LFM) waveforms at Ku band. The response of the MBR to an ideal point target as a function of aspect angle as well as that to multiple targets in different locations has been investigated. Results corroborate the analytical findings and show that the sidelobe levels with respect to angle, at the target range, are attenuated by the cross-ambiguity function properties between the waveforms employed. The range response to a target in low channel isolation suffers from cross-channel interference that may alter the noise floor characteristics of the radar, hence stressing the importance of suitable waveform selection.
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    Multi-Function RF Seeker Based on 3D Phased Array
    (Cranfield University, 2017-01-11 14:33) Kocjancic, Leon
    3MT presentation at the 2016 Defence and Security Doctoral Symposium.Current RF seekers in use today have mechanical steerable antennas. In order to reduce the cost of the mechanical system and to significantly improve the performance of the missile seeker, the electrically controlled 3D antenna array is proposed. Given solution will result in a much more robust antenna which will be capable of steering much faster and more accurately than existing solutions. Furthermore, the proposed antenna will provide an increased coverage and dwell time as a result of flexible beam steering. Additional degrees of freedom will allow it to carry out multiple tasks.The main aim of proposed PhD is to investigate theoretical background and realization of multiple beams that will conduct different tasks, such as radio-altimetry, target seeking, proximity activation and radar imaging. By using 3D antenna as a co-located multiple-input multiple-output system and by using suitable orthogonal waveforms the novel seeker will be capable of generating multiple beams.
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    Multibeam radar based on linear frequency modulated waveform diversity
    (IET, 2018-08-09) Kocjancic, Leon; Balleri, Alessio; Merlet, Thomas
    Multibeam radar (MBR) systems based on waveform diversity require a set of orthogonal waveforms in order to generate multiple channels in transmission and extract them efficiently at the receiver with digital signal processing. Linear frequency modulated (LFM) signals are extensively used in radar systems due to their pulse compression properties, Doppler tolerance, and ease of generation. Here, the authors investigate the level of isolation between MBR channels based on LFM chirps with rectangular and Gaussian amplitude envelopes. The orthogonal properties and the mathematical expressions of the isolation are derived as a function of the chirp design diversity, and specifically for diverse frequency slopes and frequency offsets. The analytical expressions are validated with a set of simulations as well as with experiments at C-band using a rotating target.
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    Multibeam radar system based on waveform diversity for RF seeker applications
    (2019-10) Kocjancic, Leon; Balleri, Alessio; Richardson, Mark A.
    Existing radiofrequency (RF) seekers use mechanically steerable antennas. In order to improve the robustness and performance of the missile seeker, current research is investigating the replacement of mechanical 2D antennas with active electronically controlled 3D antenna arrays capable of steering much faster and more accurately than existing solutions. 3D antenna arrays provide increased radar coverage, as a result of the conformal shape and flexible beam steering in all directions. Therefore, additional degrees of freedom can be exploited to develop a multifunctional seeker, a very sophisticated sensor that can perform multiple simultaneous tasks and meet spectral allocation requirements. This thesis presents a novel radar configuration, named multibeam radar (MBR), to generate multiple beams in transmission by means of waveform diversity. MBR systems based on waveform diversity require a set of orthogonal waveforms in order to generate multiple channels in transmission and extract them efficiently at the receiver with digital signal processing. The advantage is that MBR transmit differently designed waveforms in arbitrary directions so that waveforms can be selected to provide multiple radar functions and better manage the available resources. An analytical model of an MBR is derived to analyse the relationship between individual channels and their performance in terms of isolation and phase steering effects. Combinations of linear frequency modulated (LFM) waveforms are investigated and the analytical expressions of the isolation between adjacent channels are presented for rectangular and Gaussian amplitude modulated LFM signals with different bandwidths, slopes and frequency offsets. The theoretical results have been tested experimentally to corroborate the isolation properties of the proposed waveforms. In addition, the practical feasibility of the MBR concept has been proved with a radar test bed with two orthogonal channels simultaneously detecting a moving target.
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    Numerical characterisation of quasi-orthogonal piecewise linear frequency modulated waveforms
    (IEEE, 2019-07-01) Kocjancic, Leon; Balleri, Alessio; Merlet, Thomas
    This paper presents an analysis of the Doppler tolerance and isolation properties of five different sets of piecewise linear frequency modulated (PLFM) waveform triplets consisting of a combination of LFM subchirps. Different combinations of PLFM signals are used to produce waveforms with the same time-bandwidth product and optimise them with respect to isolation. The performance of the proposed waveforms are numerically investigated and a comparison between sets is presented. Results confirm that the waveforms have quasi-orthogonal properties and exhibit a degree of Doppler tolerance.
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    Study of the Frequency Slope Effect on the Chirp Waveform Orthogonality
    (IET, 2017-10-26) Kocjancic, Leon; Balleri, Alessio; Merlet, T.
    Multiple-Beam Radar Systems (MBRS) based on waveform diversity require a set of orthogonal waveforms in order to generate multiple channels in transmission and extract them efficiently at the receiver using digital signal processing. Chirp signals are extensively used in radar systems due to their pulse compression properties, Doppler tolerance and ease of generation. In this paper, we investigate the level of isolation between two linear frequency modulated (LFM) chirps as a function of the frequency slope and of the chirp starting frequency. Results are derived analytically and verified with a set of measurements at S-band.