Identification of Radar Targets in Resonance Zone: E-Pulse Techniques

A new method for systematic correlation of measurements in semi-anechoic and anechoic chambers is presented. A signal measured in a semi-anechoic chamber is first processed using the matrix-pencil method which is applied sequentially on small frequency intervals. On each interval the measured signal is decomposed into its propagating wave components. The component corresponding to the wave reflected from the ground is identified and removed to fully retrieve the signal measured in an anechoic chamber. Three examples using log-periodic and Vivaldi antennas in different anechoic and semi-anechoic chambers for varying frequency ranges illustrate the method. The proposed decomposition algorithm can be utilized to characterize measurement test site imperfections.

The E-pulse technique which typically uses transient scattering data from radar targets in free space is one of the most well known resonance based radar target recognition schemes on which target recognition is based. In this communication, the possibility of subsurface target recognition based on the E-pulse technique is investigated using numerical examples of a metallic hip prosthesis embedded in models of realistic human tissue.

Antenna measurements in anechoic chambers are increasingly carried out using special field strength probe (mainly for antenna measurements in the near field using the holographic method), the characteristics of which have a great influence on the accuracy of the measurement results. Therefore, in the case of using field strength probe in the measurement process, it is necessary to calibrate them and evaluate the extended error in order to increase the measurement accuracy and improve the measurement repeatability, which ultimately makes it possible to manufacture antenna devices with high characteristics. The article discusses methods for measuring the uncertainty sources that have the greatest impact on the accuracy of measurements in anechoic chambers, their numerical values and ways to deal with them. Also, the characteristics of the radar absorbing material and the configuration of the anechoic chamber itself have a significant impact on the value of the total uncertainty. A method for calculating the total uncertainty is shown.

The measurement of radiated emission (RE) in an anechoic chamber becomes very challenging at high frequencies, up to 60 GHz, because the scanning plane of the receiver is in measurement standard deviation from the actual wavefront. As a result, the RE intensity of the devices may be underestimated, resulting in electromagnetic interference. The deviation between the electric field at the far-field vertical scanning point and the actual wavefront is researched. Then, in an anechoic chamber, a hybrid deep learning amendment model of convolutional neural network (CNN) and transformer is proposed to correct the RE measurement at a 3 m distance. The results indicate that the correction is reliable, with an average error of 6.35% for a 3 m distance in a semianechoic chamber and less than 4.83% for other test scenarios. The proposed method provides a promising solution for RE measurement at a millimeter wave band in an anechoic chamber.

In the implementation of E-pulse technique based radar target recognition system, only one E-pulse is constructed for each target and it is considered to be aspect-independent, which is grounded in the knowledge that E-pulse synthesis is based on the poles of targets and they are aspect-independent. But our recent study suggests that the poles obtained by pole extraction algorithm are aspect-dependent although theoretically poles of targets are aspect-independent. This is because the residues of the poles are aspect-dependent. The residues represent the contributions of the poles to the late-time transient scattered field and they may be so small at some aspect angles that the corresponding poles can not be extracted by pole extraction algorithm. Consequently, different poles may be extracted at different aspect angles. If only one E-pulse is constructed using the poles extracted at one aspect angle, it may not work for the transient scattered fields at other aspect angles. In order to solve this problem, we propose a multi-directional E-pulse technique which constructs multiple E-pulses for different angle regions of a target. Numerical results show that the proposed method is very robust and can dramatically improve the recognition rate of E-pulse technique.

In this paper we look into a near-field measurement setup consisting of a cylindrical reflector and a linear array feed. The main application is Random Line-Of-Sight Over-The- Air measurements in anechoic or semi-anechoic chambers (i.e., anechoic chamber with reflecting floor). More specifically, the aim is testing the wireless communication systems on automotive vehicles. The aim is to generate the uniform field distribution of a plane wave over a pre-defined test zone containing the car or at least the part of the car containing the antenna(s). The field intensity variations over the testing zone have been investigated for reference measurements over the testing frequency bandwidth, i.e., 1.6–2.8 GHz.

The Transient Electromagnetic Scattering Laboratory (TESL) is described which employs a unique dual-channel ultra-wideband impulsive illuminating source. This is a free-field facility where targets are suspended within an anechoic chamber. A highly coherent primal step pulse is amplified by two GaAs wideband power amplifiers having complementary passbands which feed individual wideband horn antennas. This yields an effective 1 - 12 GHz impulse bandwidth. A high speed digital processing oscilloscope samples the output of a single receiving horn. The TESL has facilitated research into radar target identification using complex natural resonances. Theory and operational characteristics of the facility are discussed and technical improvements are described which have yielded significant improvement in both the effective bandwidth and the signal-to-noise ratio of transient scattering measurements. Experimental validations are shown which illustrate the level of fidelity attainable and consideration is given to recent enhancements, including an increase of measurement bandwidth to 50 GHz.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The extinction pulse (E-pulse) technique has been widely applied to the problem of free-space radar target identification. In this paper, the possibility of applying the same E-pulse technique to a subsurface target recognition scheme is investigated. In particular, the detection of depth changes of a metallic target is considered with numerical examples that determine the depth of a hip prosthesis model buried inside representative human tissue.

A novel dual-band textile hexagonal AMC design covering the entire 2.5/5.5 GHz WiFi bands for wearable applications is presented through FEM simulations and reflection coefficient phase measurements in anechoic chamber. The designed structure shows polarization-angle independence under normal incidence and its angular stability under oblique incidence is also analyzed.

This paper presents a theoretical model to extract the orientation of any scatterer under normal incidence. Analytical expressions are given for mono-static configuration in co-polarization and can easily be extended in crosspolarization. The proposed approach is particularly interesting to determine chipless tag orientation, i.e., to use a chipless tag as an orientation sensor. Since the method is valid for any scatterer, antenna mode do not have to be separated from the structural mode before estimation, thus the proposed approach can directly be applied on raw signal without time gating. Measurements in anechoic chamber are done to evaluate the performance of the proposed solution.

Methods to improve the results obtained by the E-pulse radar target discrimination technique are discussed. This is achieved by using a family of polynomials as subsectional pulse basis functions. The sensitivity of E-pulse performance to the presence of random noise disturbing the target impulse response for this family of pulse functions is investigated. Numerical examples of discrimination between differing targets are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

One-dimension range profile identification of radar targets based on a linear interpolation neural network

Ultra-wideband radar systems provide great potential for radar target detection, identification and imaging through their inherent high-resolution capabilities. This paper considers two applications of a stepped-frequency ultra- wideband radar--detection of targets close to a disturbed sea surface, and imaging of airborne targets. A new technique for target detection is presented, based on the E- pulse concept and designed to eradicate the sea clutter signal while enhancing the target response. A simulation of a missile travelling above an evolving sea-water model is considered, and results are compared to measurements made in an anechoic chamber. Finally, the effects of signal bandwidth and bistatic angle on image resolution are explored, using a time-domain imaging identity with measured, band-limited signals.

&lt;p&gt;This work presents the design and experimental validation of a dual-band fully reconfigurable circularly polarized (CP) reflectarray (RA) antenna for satellite communication applications in the Ku-band. The proposed structure operates with the downlink and uplink beams at frequency bands of [10.8-11.8] and [14-15.4] GHz, respectively. Simultaneous and independent beam control is provided over each of the two bands. The constituent unit cell is composed of two interleaved circular loops of different sizes to address the two frequency bands. Each loop is loaded using four varactor diodes. The loops are symmetrically loaded in the transverse plane to provide an isotropic response suitable for CP applications. A phase range of more than 300° is achieved in both bands as the capacitive loading varies, with an average of 2 dB loss in the lower frequency band and 3 dB loss in the higher band. In this article, the response of the unit cell is studied through full-wave simulations and verified through quasi-optical (QO) measurements, and the fully tunable performance of the reflectarray is validated through measurements in a near-field anechoic chamber.&lt;/p&gt;

The key problem in any decision-making system is to gather as much information as possible about the object or the phe-nomenon under study. In the case of the radar targets the frequency and angular information is integrated to form a radar image, which has high information content. A supper-resolution technique (MUSIC 2D) is used in the paper in order to reconstruct the target image. A supervised self-organizing neural network was developed to classify the images obtained in this way for ten different radar targets in an anechoic chamber. 1.