The Effect of Pulse Compression Chirp Parameters on Profilometry Information and Resolution

2018 ◽  
Author(s):  
Zuwen Sun ◽  
Natalie Baddour
Keyword(s):  
Pulse Compression ◽  
Imaging System ◽  
Matched Filter ◽  
Signal To Noise Ratio ◽  
Imaging Systems ◽  
Center Frequency ◽  
Matched Filtering ◽  
Linear Frequency ◽  
Recent Developments ◽  
Correlation Process

Recent developments in imaging systems have seen the implementation of a radar matched-filtering approach. The goal of the imaging system is to obtain information about an unknown object embedded in the system, by controlling the parameters of the input and measuring the response to the known input. The main merit of using matched filtering in imaging systems is the improvement of Signal to Noise Ratio (SNR). However, the correlation process used in matched filtering may result in a loss of resolution. One way to compensate for lost resolution is via pulse compression. Linear frequency modulated sinusoidal waveforms (chirps) have the property of pulse compression after correlation. Hence, both SNR and resolution can be enhanced by matched-filtering and pulse compression with a chirp. However, the theory behind the effect of chirp parameters on resolution is still not clear. In this paper, a one-dimensional theory of matched-filter imaging with a pulse compressed linear frequency modulated sinusoidal chirp is developed. The effect of the chirp parameters on the corresponding signal is investigated, and guidelines for choosing the chirp parameters for resolution considerations are given based on the developed theory and simulations. The results showed that by manipulating the center frequency, bandwidth, and duration of the chirp, the resolution can be easily enhanced.

scholarly journals A Novel Channel Calibration Method for Bistatic ISAR Imaging System

2018 ◽  
Vol 8 (11) ◽  
pp. 2160 ◽  
Author(s):  
Lin Shi ◽  
Baofeng Guo ◽  
Juntao Ma ◽  
Chaoxuan Shang ◽  
Huiyan Zeng
Keyword(s):  
Time Domain ◽  
Pulse Compression ◽  
Imaging System ◽  
Signal To Noise Ratio ◽  
Calibration Method ◽  
Imaging Systems ◽  
Calibration Coefficient ◽  
Channel Characteristics ◽  
Isar Imaging ◽  
The Time Domain

In practical bistatic inverse synthetic aperture radar (ISAR) imaging systems, the echo signals are modulated by non-ideal amplitude and phase characteristics of the transmitting and receiving channels, which seriously distorts image quality. However, the conventional channel calibration method based on a transponder is not applicable to bistatic ISAR imaging systems, since the baseline of the system is up to hundreds of kilometers. A channel calibration method only using calibration satellite echo information is proposed for the system, with a linear frequency modulation (LFM) waveform. Firstly, echoes of the calibration satellite are collected by tracking the satellite and multi-period echoes are aligned in the time domain, according to the pulse compression result. Then, the signal to noise ratio (SNR) is improved by accumulating multi-period echoes coherently in the time domain and the calibration coefficient is constructed based on the accumulated signal. Finally, spectrum of the echo signal is multiplied with the calibration coefficient to compensate the influence of channel characteristics. The effectiveness of the proposed method is verified by the simulation experiment with real satellite echoes.

scholarly journals Design and Numerical Analysis of an Infrared Cassegrain Telescope Based on Reflective Metasurfaces

Nanomaterials ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 2904
Author(s):  
Song Yue ◽  
Zhe Zhang ◽  
Kunpeng Zhang ◽  
Huifang Guo ◽  
Ran Wang ◽  
...  
Keyword(s):  
Imaging System ◽  
Imaging Systems ◽  
Optical Systems ◽  
Infrared Wavelength ◽  
Fabrication Errors ◽  
Real World Applications ◽  
Recent Developments ◽  
Cassegrain Telescope ◽  
Meta Atom ◽  
High Reflectance

Reflective imaging systems such as Cassegrain-type telescopes are widely utilized in astronomical observations. However, curved mirrors in traditional Cassegrain telescopes unavoidably make the imaging system bulky and costly. Recent developments in the field of metasurfaces provide an alternative way to construct optical systems, possessing the potential to make the whole system flat, compact and lightweight. In this work, we propose a design for a miniaturized Cassegrain telescope by replacing the curved primary and secondary mirrors with flat and ultrathin metasurfaces. The meta-atoms, consisting of SiO2 stripes on an Al film, provide high reflectance (>95%) and a complete phase coverage of 0~2π at the operational wavelength of 4 μm. The optical functionality of the metasurface Cassegrain telescope built with these meta-atoms was confirmed and studied with numerical simulations. Moreover, fabrication errors were mimicked by introducing random width errors to each meta-atom; their influence on the optical performance of the metasurface device was studied numerically. The concept of the metasurface Cassegrain telescope operating in the infrared wavelength range can be extended to terahertz (THz), microwave and even radio frequencies for real-world applications, where metasurfaces with a large aperture size are more easily obtained.

scholarly journals A Novel Design of Matched Filter for Digital Receivers

2019 ◽  
Vol 8 (3) ◽  
pp. 6000-6003
Keyword(s):  
Pulse Compression ◽  
Filter Design ◽  
Matched Filter ◽  
Signal To Noise Ratio ◽  
Digital Signal ◽  
Receiver System ◽  
Digital Pulse ◽  
Pros And Cons ◽  
Processing Techniques ◽  
Digital Receivers

In this paper, a brief review regarding introduction to the digital signal processing techniques particularly Digital Pulse Compression and Linear Frequency Modulation involved in matched filtering and some designs being used is presented. Also, the matched filter being developed is discussed by highlighting its pros and cons. The introduction of matched filter in the communication receivers has simplified the design of the system. The matched filter has improved the signal to noise ratio of the receiver system and hence has become an important element in the communication system. This paper also presents the possible challenges; the matched filter design and simulation results in MATLAB have shown satisfactory outputs of the receiver.

scholarly journals Performance of an Ultrasonic Imaging System Based on a 45-MHz Linear PVDF Transducer Array: A Numerical Study

2011 ◽  
Vol 2011 ◽  
pp. 1-15 ◽  
Author(s):  
Eivind Brodal ◽  
Frank Melandsø ◽  
Svein Jacobsen
Keyword(s):  
Acoustic Waves ◽  
Imaging System ◽  
Numerical Study ◽  
Signal To Noise Ratio ◽  
Ultrasonic Imaging ◽  
Time Derivative ◽  
Center Frequency ◽  
Transducer Array ◽  
Transducer Design ◽  
Different Depths

New designs of high-resolution ultrasonic imaging systems that operate in the 30–100 MHz region, for example, those based on linear transducer systems, are currently being investigated for medical purposes. Acoustic waves with frequencies in this range can detect microscopic structures in human tissue but will typically only penetrate a few mm because of large attenuation. However, this is sufficient for a diagnostic ultrasound scan of human skin. The signal-to-noise ratio and the focusing properties of the scanner are critical factors in dermatology, which are determined by the transducer design. A linear pulsed PVDF transducer array with a center frequency around 45 MHz is studied by applying numerical simulations, based on the finite element method (FEM), of this electromechanical system. Tx-beamforming properties of linear arrays with one, three, five, and seven active elements are investigated at different depths. The image quality obtained from synthetic Rx-beamforming, using responses from five electrodes, is estimated from reconstructed images of 25–100 m thick objects. The axial and lateral resolutions of these images are found to be similar with the Tx-beamforming resolution parameters estimated from the time-derivative of the pressure beams.

scholarly journals Interferenceless Coded Aperture Correlation Holography with Point Spread Holograms of Isolated Chaotic Islands for 3D Imaging

2021 ◽  
Author(s):  
Nitin Dubey ◽  
Joseph Rosen
Keyword(s):  
3D Imaging ◽  
Imaging System ◽  
Signal To Noise Ratio ◽  
Three Dimensional ◽  
Image Sensor ◽  
Two Dimensions ◽  
Imaging Systems ◽  
Coded Aperture ◽  
Axial Resolution ◽  
Point Spread

Abstract Interferenceless coded aperture correlation holography (I-COACH) is an incoherent digital holographic technique with lateral and axial resolution similar to a regular lens-based imaging system. The properties of I-COACH are dictated by the shape of the system’s point response termed point spread hologram (PSH). As previously shown, chaotic PSHs which are continuous over some area on the image sensor enable the system to perform three-dimensional (3D) holographic imaging. We also showed that a PSH of an ensemble of sparse dots improves the system’s signal-to-noise ratio (SNR) but reduces the dimensionality of the imaging from three to two dimensions. In this study, we test the midway shape of PSH, an ensemble of sparse islands distributed over the sensor plane. A PSH of isolated chaotic islands improves the SNR of the system compared to continuous chaotic PSH without losing the capability to perform 3D imaging. Reconstructed images of this new system are compared with images of continuous PSH, dot-based PSH, and direct images of a lens-based system. Visibility, SNR, and the product of visibility with SNR are the parameters used in the study. We also demonstrate the imaging capability of a system with partial annular apertures. The reconstruction results have better SNR and visibility than lens-based imaging systems with the same annular apertures.

scholarly journals New Side Lobe Cancellation Method of Linear Frequency Modulated Radar Signals

2020 ◽  
Vol 9 (4) ◽  
pp. 1275-1279
Keyword(s):  
Pulse Compression ◽  
Matched Filter ◽  
Roc Curves ◽  
Side Lobe ◽  
Radar Detection ◽  
Operating Characteristics ◽  
Detection Capability ◽  
Linear Frequency ◽  
Optimum Filter ◽  
Long Pulse

Pulse Compression (PC) technique has many advantages in signal processing of radar systems which enhances the radar performance. For a long pulse, the range detection capability can be increased with PC while maintain the advantage of resolution in range for uncompressed pulse. There are many PC techniques such as Binary and Linear Frequency Modulation (LFM) Codes, which can be utilize in radar. The radar detection performance is affected by unwanted signals, which called side lobes that may mask the weaker useful signals, which are present near to strong signals. Pulse compression that uses LFM code is discussed and contrasted with matched filter keep tracked of Hamming windowing filter technique to eliminate the level effect of side lobes. In the present paper, a proposed optimum filter is introduced to enhance both the radar detection capability and resolution in range. The proposed optimum filter representation is evaluated and compared with the classical matched filter response associated with Hamming windowing filter according to the representation of radar detection through Receiver Operating Characteristics (ROC) curves and resolution performance.

scholarly journals Design and Implementation of an Enhanced Matched Filter for Sidelobe Reduction of Pulsed Linear Frequency Modulation Radar

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3835
Author(s):  
Ahmed Azouz ◽  
Ashraf Abosekeen ◽  
Sameh Nassar ◽  
Mohamed Hanafy
Keyword(s):  
Cross Sections ◽  
Software Defined Radio ◽  
Pulse Compression ◽  
Matched Filter ◽  
Linear Frequency ◽  
Radar Cross Sections ◽  
Operational Characteristics ◽  
Computational Speed ◽  
Iteration Methods ◽  
The Mathematical Model

Pulse compression techniques are commonly used in linear frequency modulated (LFM) waveforms to improve the signal-to-noise ratios (SNRs) and range resolutions of pulsed radars, whose detection capabilities are affected by the sidelobes. In this study, a sidelobe reduction filter (SRF) was designed and implemented using software defined radio (SDR). An enhanced matched filter (EMF) that combines a matched filter (MF) and an SRF is proposed and was implemented. In contrast to the current commonly used approaches, the mathematical model of the SRF frequency response is extracted without depending on any iteration methods or adaptive techniques, which results in increased efficiency and computational speed for the developed model. The performance of the proposed EMF was verified through the measurement of four metrics, including the peak sidelobe ratio (PSLR), the impulse response width (IRW), the mainlobe loss ratio (MLR), and the receiver operational characteristics (ROCs) at different SNRs. The ambiguity function was then used to characterize the Doppler effect on the designed EMF. In addition, the detection of single and multiple targets using the proposed EMF was performed, and the results showed that it overcame the masking problem due to its effective reduction of the sidelobes. Hence, the practical application of the EMF matches the performance analysis. Moreover, when implementing the EMF proposed in this paper, it outperformed the common MF, especially when detecting targets moving at low speeds and having small radar cross-sections (RCS), even under severe masking conditions.

scholarly journals Comparison of the performance of different radar pulse compression techniques in an incoherent scatter radar measurement

2009 ◽  
Vol 27 (2) ◽  
pp. 797-806 ◽  
Author(s):  
B. Damtie ◽  
M. S. Lehtinen
Keyword(s):  
Adaptive Filtering ◽  
Pulse Compression ◽  
Matched Filter ◽  
Signal To Noise Ratio ◽  
Minimum Mean Square Error ◽  
Radar Signal ◽  
Incoherent Scatter Radar ◽  
Low Snr ◽  
Incoherent Scatter ◽  
Scatter Radar

Abstract. Improving an estimate of an incoherent scatter radar signal is vital to provide reliable and unbiased information about the Earth's ionosphere. Thus optimizing the measurement spatial and temporal resolutions has attracted considerable attention. The optimization usually relies on employing different kinds of pulse compression filters in the analysis and a matched filter is perhaps the most widely used one. A mismatched filter has also been used in order to suppress the undesirable sidelobes that appear in the case of matched filtering. Moreover, recently an adaptive pulse compression method, which can be derived based on the minimum mean-square error estimate, has been proposed. In this paper we have investigated the performance of matched, mismatched and adaptive pulse compression methods in terms of the output signal-to-noise ratio (SNR) and the variance and bias of the estimator. This is done by using different types of optimal radar waveforms. It is shown that for the case of low SNR the signal degradation associated to an adaptive filtering is less than that of the mismatched filtering. The SNR loss of both matched and adaptive pulse compression techniques was found to be nearly the same for most of the investigated codes for the case of high SNR. We have shown that the adaptive filtering technique is a compromise between matched and mismatched filtering method when one evaluates its performance in terms of the variance and the bias of the estimator. All the three analysis methods were found to have the same performance when a sidelobe-free matched filter code is employed.

scholarly journals Simulation and Performance Analysis of Chaotic Sequences using Enhanced Cuckoo Search Optimization Method

2019 ◽  
Vol 8 (4) ◽  
pp. 10225-10231
Keyword(s):  
Adaptive Filters ◽  
Pulse Compression ◽  
Matched Filter ◽  
Search Algorithm ◽  
Signal To Noise Ratio ◽  
Cuckoo Search ◽  
Optimization Method ◽  
Chaotic Sequence ◽  
Radar Signal ◽  
Linear Filter

The mostdesirable property required for pulse compression is that the output should have low peak sidelobes that prevent weaker targets from being masked off in the nearby strong targets. Pulse compression can be obtained with matched filter. Matched filter is an optimal linear filter used in radar signal processing and various communication fields to increase the signal to noise ratio. The output of matched filter consists of unavoidable sidelobes which causes false alarm for multiple target detection in many radar system design.For this purpose, mismatched filter is used after matched filter. Inthis paper a new method of design of mismatched filter is discussed which reduces these sidelobes in the compressed waveform. Here new version of cuckoo search algorithm is used along with differential evolution techniquefor complete design of proposed filter to compare the performance of chaotic sequence. The performance of pulse compression is measured in terms of peak sidelobe ratio. The simulation results showthatdevelopmentin the performance of chaotic sequence is obtained at the output of cascaded filter. And further improved performance is achieved with adaptive filters

Some Quantification Problems in Parallel EELS Images

1990 ◽  
Vol 48 (2) ◽  
pp. 36-37
Author(s):  
G. Botton ◽  
G. L’Espérance ◽  
M.D. Ball ◽  
C.E. Gallerneault
Keyword(s):  
Electron Microscope ◽  
Imaging System ◽  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Acquisition Time ◽  
Thickness Variation ◽  
Transmission Electron ◽  
Distribution Of Elements ◽  
Scanning Transmission ◽  
Present Distribution

The recently developed parallel electron energy loss spectrometers (PEELS) have led to a significant reduction in spectrum acquisition time making EELS more useful in many applications in material science. Dwell times as short as 50 msec per spectrum with a PEELS coupled to a scanning transmission electron microscope (STEM), can make quantitative EEL images accessible. These images would present distribution of elements with the high spatial resolution inherent to EELS. The aim of this paper is to briefly investigate the effect of acquisition time per pixel on the signal to noise ratio (SNR), the effect of thickness variation and crystallography and finally the energy stability of spectra when acquired in the scanning mode during long periods of time.The configuration of the imaging system is the following: a Gatan PEELS is coupled to a CM30 (TEM/STEM) electron microscope, the control of the spectrometer and microscope is performed through a LINK AN10-85S MCA which is interfaced to a IBM RT 125 (running under AIX) via a DR11W line.

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