Rcs Measurements in Multipath Environments

A measurement method and system based on conventional radars has been proposed to address the problem of radar cross-section (RCS) measurement of ship targets in open seas. Calibration errors for RCS measurement on ground plane range (GPR) are analysed, and the error elimination method and accurate RCS calculation formula are given. An RCS measurement system is designed by improving conventional radars. These systems measure two Luneburg lens reflectors of different sizes on the lake. The average RCS of the big Luneburg lens reflector is obtained, and the error is calculated to be 2.73% compared with its actual value, which verifies the rationality of the proposed measurement method and system. The system measures the RCS of a ship in the open sea and obtains its circumferential RCS distribution. The effect of the error in the ship's position calculation on the RCS measurement results is analysed, and the uncertainty range of the error is obtained.

The far-field radar cross section (RCS) measurement of a large scatterer is generally difficult due to the limitation of available measurement range. One way to avoid this difficulty is to adopt a scale model by compact range measurement. However, there are some problems in this measurement: it is labour intensive and expensive to construct the scale model, and the frequency characteristics of the surface impedance of the scatterer may not be reproduced at shorter wavelength measurements, so real target measurement is necessary to obtain accurate data. There exists a near-field antenna measurement technique, however a direct application of this technique for RCS measurement fails because the RCS depends on the locations of both the source and the observation points. Falconer (1988) has overcome the above difficulty and successfully estimated the far-field RCS by the near-field RCS measurement. We have also proposed a far-field RCS prediction algorithm which uses cylindrical or planar near-field RCS data. However these algorithms are applicable only for the monostatic RCS. We report novel prediction algorithms of the far-field bistatic scattering cross section (SCS) by extending the proposed algorithms. These are presented in cases of spherical, cylindrical and planar scanning. We also show simulation results of the far-field SCS prediction in order to validate our methods.

Radar cross section (RCS) measurements are widely employed for the target identification of objects such as aircraft. The RCS of large, complex geometries is usually determined in a well defined, scaled experimental setup. In such a setup, the measuring frequency equates the frequency of interest multiplied by the scaling factor of the model. For high scaling factors, frequencies well above 100 GHz result so that conventional microwave equipment reaches its technological limits. In this paper, we discuss the use of a fiber coupled terahertz time domain spectroscopy system for angle dependent RCS measurements. Several measurements on simple objects like metal plates with corresponding simulations are performed. We also investigate how angular misalignment and displacement of the scatterer effects the measurement results. Moreover, we discuss the influence of non planar incident wavefronts and compare experimentally obtained data to simulations using an enhanced physical optics model.

This communication deals with radar cross section (RCS) measurement of a horn antenna within a reverberation chamber (RC). RCs recently became a viable alternative to anechoic chamber to perform RCS measurement. Indeed, one can benefit from the RC statistical properties to retrieve the line of sight wave among the multiple reflections that occur within the cavity. It is the first time that this RC setup is used to measure the RCS of an antenna. More specifically, it is shown that it is possible to distinguish the antenna RCS measured for two different load conditions (short and match). As a consequence, it enables retrieving the antenna gain from RCS measurement performed in RC.

It is challenging to perform the near-field to far-field transformation with a high precision for the multiple-scattering targets using the conventional monostatic radar cross section (RCS) measurement. In this paper, a novel near-field to far-field transformation method with bistatic RCS measurement is proposed. First, the RCS measurement is perceived as a double radiation model. Doing this, the relationship of near-field data and far-field data at different angles is derived, and the convolution function is given under the cylindrical wave. Second, the near-field scattering data are acquired using the proposed bistatic RCS measurement method that combines one transmission and multiple receptions with the rotation of a revolving table. The near-field data are then extrapolated twice with the convolution function, and the far-field RCS are obtained accordingly. Moreover, this paper also analyzes the truncation angular and sampling intervals for the measurement consideration. Finally, the effectiveness and the high precision of the proposed transformation approach for the multiple-scattering target are demonstrated using the numerical simulations and the experimental characterization with an example of dihedral structures.

We propose a target identification scheme exploiting the temporal dependency and spatial structure of radar cross-section (RCS) measurements in low-frequency, passive, or long-range surveillance radar systems. We employ target RCS modeling integrated into a hidden Markov model (HMM) with state-duration modeling. Assuming that the radar system ensures a sufficient sampling time, it is possible to use the spatial characteristics of airborne targets, because there is consistency between successively sampled RCS measurements. In addition, to exploit the whole temporal characteristic of the sequence of RCS measurements,which has rarely been considered in the literature, we adopt the HMM and target RCS modeling. To accomplish this task, we accurately develop target RCS models and establish the relationship between the target-sensor orientations, which are the hidden states of the HMM, and the correspondingRCSmeasurements. The proposed target identification scheme, which only uses the sequence of RCS measurements, is demonstrated with simulation results and an analysis for various signal-to-noise ratios and target-fluctuation models.

A linear-scan-based wideband near-field radar cross section (RCS) measurement technique for achieving wide effective-angle-coverage is proposed in this letter. Both the data preprocessing and linear near-field to far-field transformation (LNF2FFT) techniques are used to ensure the accurate measurement of wideband far-field RCS in a wide azimuthal angle range. With the linear-scan-based near-field sampling strategy, the object under test (OUT) keeps stationary during the measurement process, and the equipment of turntable is not required. Moreover, based on the 2D plane wave expansion, LNF2FFT is proposed to translate the linearly sampled near-field data into far-field RCS pattern. An adaptive time gating strategy is also proposed to deal with the varied background property in liner samplings. Serval important practical factors relating to the measurement accuracy, such as phase center calibration, background subtraction and calibration, are also discussed in detail. Two illustrative test examples are presented, in which RCS measurement with wide effective-angle-coverage of ±35° and the average wideband measurement errors less than 0.4 dB are achieved in 1 m limited measurement range.

The single parabolic cylindrical compact range based on a linear array feed achieves a high-quality quiet zone through optimization of the array excitation. Its capability for testing automotive antennas has been demonstrated. As a plane wave generation device, Radar Cross Section (RCS) measurement is considered an important potential application. Furthermore, the high aperture efficiency offered by the linear array excitation optimization provides cost advantages, particularly for RCS measurements of large equipment. However, to date, there are no reported RCS measurements s specifically using the single cylindrical compact range with a linear array feed. Therefore, this paper presents RCS scattering tests using the line array compact range with optimized amplitude and phase excitation. The scattering test method is detailed, employing MIMO technology for interleaved transmit and receive operations with the linear array. The measured RCS results demonstrate strong consistency with simulation results, thereby confirming the feasibility of this approach for RCS measurement.

A free-space measurement system at 220 GHz ∼ 300 GHz has been built with stepped frequency continuous wave (SFCW) for Radar cross section (RCS) measurements. The system consists of vector network analyzer, Millimeter-Wave Converters and target support structure. The measurement techniques such as background subtraction, synchronous calibration and range distance compensation are verified by RCS measurement data. The system measurement accuracy is control within about ±3 dB at −21 dBsm.

Spatial filtering is a useful method to suppress undesired reflection from unwanted scatters in Radar Cross Section (RCS) measurements. Actually, it is difficult to prepare an ideal field which satisfies the far-field criterion for RCS measurements of large targets. We applied the filtering method to a bistatic RCS measurement in a near field and investigated the validity of that method by varying the scanning angular span. Electromagnetic simulations show that predicted RCS profiles from near-field data with unwanted scatters closely matched far-field reference data of the test target. In conclusion, the results show that the method is effective for bistatic RCS measurements in practical field enviroments.

The paper considers the influence of the interaction of the object under test with the top part of the pylon on the results of radar cross-section (RCS) measurement. The computer simulation of an experimental RCS measurement of the object in the field of a plane wave is carried out. The computations are performed in the FEKO program by the method of moments. Zones of the pylon that most affect the single-position RCS values of the object have been identified. These zones must be covered with a radar absorbing material (RAM) when conducting experimental studies of the objects scattering properties. The errors of the RCS measurement for two types of objects - spheres and vertically located cylinders - depending on the levels of the measured values are revealed. Three sizes of objects by their RCS values are considered to evaluate the measurement error at levels of approximate 0.1 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 0.01 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and 0.001 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

RADAR Cross Section Measurement And Imaging RRelated To Ship Target In The Sea Environment

We perform angle- and frequency-resolved radar cross section (RCS) measurements on objects at terahertz frequencies. Our RCS measurements are performed on a scale model aircraft of size 5-10 cm in polar and azimuthal configurations, and correspond closely to RCS measurements with conventional radar on full-size objects. The measurements are performed in a terahertz time-domain system with freely propagating terahertz pulses generated by tilted pulse front excitation of lithium niobate crystals and measured with sub-picosecond time resolution. The application of a time domain system provides ranging information and also allows for identification of scattering points such as weaponry attached to the aircraft. The shapes of the models and positions of reflecting parts are retrieved by the filtered back projection algorithm.

This article discusses a post-processing method to achieve highly accurate radar cross section (RCS) measurements in challenging test environments. In the ideal RCS measurement setup, the only received signal is the reflection from the object under test (OUT). However, this scenario is often not realizable in practice as outside measurements suffer from a multitude of scattering objects beyond the OUT, and even anechoic chambers have nonnegligible multipath clutter. Time-gating has been shown to be a powerful post-processing clutter suppression tool by temporally filtering any undesired return signals. However, this technique is only sufficient when there is ample spacing between the OUT and undesired return signals or when the sidelobes of one scatterer do not mask the return of a smaller nearby scatterer in the time domain. In the latter scenario, traditional time-gating techniques cannot separate the sidelobes from a nearby dominant scatterer overlapping with the main lobe of the OUT, and the RCS of the OUT cannot be extracted accurately. By applying the proposed stepped frequency continuous wave (SFCW) adaptive pulse compression (APC) algorithm, a range-dependent filter is created to iteratively estimate the range profile and suppress sidelobes allowing for temporal separation of the scatterers and accurate RCS estimation. To validate the concept, the RCS of a 15.2 cm sphere is extracted in two measurement configurations (with and without a large nearby dominating scatterer). The traditional matched filter data processing accuracy is compared to the proposed APC technique. Implementation of APC in post-processing yields a 71.2% improvement in average RCS error compared to traditional processing in the sphere-only measurement and an 88.2% improvement in the presence of a metal plate.

The near field system can not only be used for measuring the performance of antennas, it can also be used for RCS (radar cross section area) measurement except for multipath and range power decay. Time gating can reduce the problem of multipath between radar and target. The range correction table can compensate the problem of near field range power decay. Far field RCS can be generated by the transformation of measured near field data. In this paper the concept of transformation is applied for obtaining the far field RCS of the radar target from the near field measurement data. The processing technique is be used to generate the far field RCS pattern. The results of the far field RCS by this proposed technique is in quite good agreement with that obtained by direct far field measurement.