Browsing by Subject "Range resolution"

Now showing 1 - 7 of 7

Open Access
Pasif bistatik radarlarda seyreklik temellli ters evrişim kullanılarak hedef tespiti
(IEEE, 2015-05) Arslan, Musa Tunç; Tofighi, Mohammad; Çetin, A. Enis
Bu bildiride pasif radar (PR) sistemlerinin menzil çözünürlüğünü artırmak için seyreklik tabanlı bir ters evrişim yöntemi sunulmaktadır. PR sistemlerinin iki boyutlu uyumlu süzgeç çıktısı bir ters evrişim problemli gibi düşünülerek incelenmektedir. Ters evrişim algoritması, hedeflerin zaman kaymaları ve l1 norm benzeri dışbükey maliyet fonksiyonlarının epigraf kümelerini temsil eden hiperdüzlemler üzerine izdüşümü temellidir. Bütün kısıt kümeleri kapalı ve dışbükey olduklarından dolayı yinelemeli algoritma yakınsamaktadır. FM tabanlı PR sistemleri üzerinde benzetim sonuçları sunulmuştur. Algoritma frekans uzayı tabanlı ters evrişim yöntemlerine göre daha yüksek performansa sahiptir.
Open Access
Range resolution improvement in FM-based passive radars using deconvolution
(Springer-Verlag London Ltd, 2016) Arslan, M. T.; Tofighi M.; Çetin, A. Enis
FM-based passive bistatic radar (PBR) systems suffer from low range resolution because of the low baseband bandwidth of commercial FM broadcasts. In this paper, we propose a range resolution improvement method using deconvolution. The output of the PBR matched filter is processed using a deconvolution algorithm which assumes that targets are isolated, i.e., sparse in the range domain. The deconvolution algorithm is iterative and was implemented by performing successive orthogonal projections onto supporting hyperplanes of the epigraph set of a convex cost function. Simulation examples are presented.
Open Access
Range resolution improvement in passive bistatic radars using deconvolution
(2015-11) Arslan, Musa Tunç
Passive radar (PR) systems attract interests in radar community due to its lower cost and power consumption over conventional radars. However, one of the main disadvantages of a PR system is its low range resolution. The reason for this is, the range resolution depends on the bandwidth of the transmitted waveform and in a PR scenario, it is impossible to change transmitted waveform properties of a commercial broadcast. In this thesis, a post processing scheme is proposed to improve the range resolution of an FM broadcast based PR system. In the post processing scheme, the output of the ambiguity function is re-expressed as convolution of the autocorrelation of the transmitted signal and a channel impulse response. Therefore, it is shown that it is possible to use deconvolution methods to compute the channel impulse response using the output of the ambiguity function and the autocorrelation of the transmitted signal. Thus, using deconvolution to solve the channel impulse response provides an increase in the range resolution of the PR system. The method successfully increases the target separation distance and range resolution of a PR system using single FM channel signal. The conventional ambiguity function is able to separate two targets when the targets have about 17 km between each other where as the deconvolution based post processing method can decrease this to about 10 km. The deconvolution based post processing methods also decreases the side lobes around the target when the system uses multi channel FM signals. For a scenario in which three FM channels are employed, the highest side lobe is 1.2 dB below the main target peak and after deconvolution, this highest side lobe decreases to about 10 dB below the main target peak.
Open Access
Range resolution improvement in passive bistatic radars using nested FM channels and least squares approach
(SPIE, 2015) Arslan, Musa Tunç; Tofighi, Muhammad; Sevimli, Rasim Akın; Çetin, A. Enis
One of the main disadvantages of using commercial broadcasts in a Passive Bistatic Radar (PBR) system is the range resolution. Using multiple broadcast channels to improve the radar performance is offered as a solution to this problem. However, it suffers from detection performance due to the side-lobes that matched filter creates for using multiple channels. In this article, we introduce a deconvolution algorithm to suppress the side-lobes. The two-dimensional matched filter output of a PBR is further analyzed as a deconvolution problem. The deconvolution algorithm is based on making successive projections onto the hyperplanes representing the time delay of a target. Resulting iterative deconvolution algorithm is globally convergent because all constraint sets are closed and convex. Simulation results in an FM based PBR system are presented.
Open Access
Range resolution improvement in passive coherent location radar systems using multiple FM radio channels
(IET, 2006) Taşdelen, Akif Sinan; Köymen, Hayrettin
Passive coherent location (PCL) radar systems that use single FM radio channel signal as illuminator of opportunity have limited range resolution due to low modulation bandwidth and high dependence on the content that is being broadcasted from the FM station. An improvement in range resolution is obtained by using multiple adjacent FM channels, emitted from co-sited transmitters, which is often the case in large towns in countries, where the FM channel allocations are relatively weakly regulated. The proposed scheme computes the autocorrelation function of the signal directly received from the FM co-located transmitter, and compares it to the cross-ambiguity function, obtained from direct and target scattered signals. The geometry of the problem is like in the case of monostatic radar. The range information is obtained by the delay between the cross-ambiguity function and the autocorrelation function. It is shown that down to -37dB signal to noise ratio (SNR) the autocorrelation function of 7 FM channels with different contents can be successfully extracted from the cross-ambiguity function. The detection of the time delays is a linear estimation problem. The issue of time-delay estimation is a known topic of research. A powerful estimator can be found.
Open Access
Range resolution improvement in passive coherent location radar systems using multiple FM radio channels
(2007) Taşdelen, Akif Sinan
Passive coherent location (PCL) radar systems that use single FM radio channel signal as illuminator of opportunity have reasonable Doppler resolution, but suffer from limited range resolution due to low modulation bandwidth and high dependence on the content that is being broadcasted from the FM station. An improvement in range resolution is obtained by using multiple adjacent FM channels, emitted from co-sited transmitters, which is often the case in large towns. The proposed scheme computes the autocorrelation function of the signal directly received from the co-located FM transmitter, and compares it to the cross-ambiguity function, obtained from direct and target scattered signals. The geometry of the problem is like in the case of monostatic radar. The range information is obtained by the delay between the cross-ambiguity function and the autocorrelation function. When a single FM channel that has a modulation bandwidth of 25 kHz is employed the range resolution is 6 km. It is shown that down to −33dB signal to noise ratio (SNR), which corresponds to a distance of 110 km from the receiver, targets that are 3 km separated from each other can be detected with 3 adjacent FM channels. It is possible to detect targets that are 100 m separated from each other with 7 FM channels. The detection of the time delays is a linear estimation problem.
Open Access
Ultrasonic array characterization in multiscattering and attenuating media using pin targets
(Cornell University, 2021-05-31) Kumru, Y.; Köymen, Hayrettin
This paper presents an approach to characterize ultrasonic imaging arrays using pin targets in commercial test phantoms. We used a 128-element phased array transducer operating at 7.5 MHz with a fractional bandwidth of %70. We also used a tissue-mimicking phantom in the measurements. This phantom consists of pin targets with a 50 𝝁𝒎 diameter. We excited the transducer with pulsed and coded signals. We used Complementary Golay Sequences to code the transmitted signal and Binary Phase Shift Keying for modulation. We characterized the transducer array by using the transfer function, line spread function, range resolution, and beam width in an attenuating and scattering medium. We showed that the pin targets, which are very thin compared to the diffractionlimited focus of the transducer array, are suitable for the transducer characterization under weak reflected signal conditions.