JP2012068222A - Radar cross section (rcs) measurement system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure not only mono-static radar cross section (RCS) but also bi-static RCS in not a remote field but a neighboring field by solving the problem that conventional RCS measurement adopts only either measurement in a remote field or measurement in a compact range, and that a measurement method in the remote field is to include remote measurement while a measurement method in the compact range is limited to only mono-static measurement.SOLUTION: The radar cross section (RCS) measurement system is configured to measure the RCS by irradiating a sample which rotates with a plane wave, receiving a reflection wave from the sample by the probe antenna in a neighboring field, and converting this from the neighboring field into a remote field by using an array factor.

Description

  The present invention relates to a measurement method in which a radar cross section is measured in the near field and converted into a far field.

Currently, when measuring the radar cross section, there are two methods: a far field measurement method and a compact range measurement method. When measuring in the far field, there is a disadvantage that the measurement distance is long.
If λ is the wavelength, and L is the width of the sample, the measurement distance is 2L ² / λ or more. For example, if the width of the sample is 10 m at 10 GHz, measurement must be performed from 6.6 km or more. In the case of a compact range, the distance may be a short distance of about 20 m, but there is a drawback of only monostatic measurement.

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  As described in the background art, when measuring the radar cross section, the method of measuring in the far field must be measured in the far field. In addition, the method of measuring in the compact range is limited to monostatic measurement. It solves the desire to measure radar cross section (RCS) not from a distance, but also monostatic or bistatic.

  Rotate the sample. This sample is irradiated with a plane wave of electromagnetic waves. The electromagnetic wave reflected from the sample is received at one point, and the amplitude and phase for each angle are obtained. The radar cross section is calculated from the calculation formula using the idea of the array factor and ArrayFactor (AF) and the measured amplitude and phase.

  By rotating the sample once, the desired radar cross section such as monostatic or bistatic is obtained in the vicinity. Note that various radar cross sections can be obtained in one rotation by rotating the sample while moving a plurality of antennas whose angles from the plane wave to be irradiated are moved up and down, and changing the frequency.

An example of the whole structure of this invention. In addition, the lower figure of FIG. 1 is the figure which looked at the whole structure from the top. Sample for measuring radar cross section. The figure which shows the position of the probe antenna which receives a reflected wave, and the contents of the radar cross section, such as monostatic and bistatic. When the sample is rotated, the same element can be expressed as a circular ring array. This coordinate is shown. A radar cross section that is received by the probe antenna at various positions shown in FIG. 3 and converted to a far field. Note that an electromagnetic wave may be transmitted from the probe antenna instead of receiving the reflected wave by the probe antenna.

  1, 2, and 3, the sample is rotated by a command from a Windows computer containing a vector network analyzer and a program, and a radio wave is emitted from the primary radiator while moving the probe antenna up and down. The reflected wave is received by the probe, the amplitude and phase are recorded, and the near field far field conversion using the array factor is performed by the computer to obtain the radar cross section.

Based on the configuration shown in FIG. 1, the port 1 at the S parameter entrance / exit of the vector network analyzer is connected to the primary horn antenna 2. Port 2 is then connected to the probe antenna. On the other hand, a software that converts near-field and far-field using an array factor, a control program for a motor that rotates the sample 4, and a program that controls a linear motor that moves the probe antenna up and down. And connect to a linear motor. First, the probe antenna is placed at the position of 3b, that is, parallel to the plane wave coming out of the parabolic antenna 1, on the line passing through the center of the sample 4 and looking at the sample 4 and horizontally 45 ° to the right. Put. The vector network analyzer and _{S 21} mode, the frequency is fixed at 10 GHz, with a gate mode, so that 10cm, only 10cm behind the measurement before around the sample 4.
The radio wave transmitted from the port 1 at 10 GHz and transmitted from the primary radiator 2 is reflected by the parabolic antenna and becomes a plane wave to irradiate the sample 4. Then, radio waves reflected from all parts of the sample 4 are received by the probe antenna. At this time, the probe antenna cuts the waveguide WR90, and the thick part finishes the tip part thinly. Since the probe antenna has a wide -3 dB half-value angle, all reflections of the sample can be received. In this situation, the sample is rotated, and amplitude and phase information is obtained every 0.1 degrees.
Next, calculation formulas and comparison of actual measurement results when a simple array factor (AF) concept is applied to far-field conversion of near-field data acquired by cylindrical scanning will be described.
As shown in FIG. 4, the array factor (AF) of the cylindrical array when the same element rotates and moves 1, 2, 3... N is the same element N on the circumference of the xy plane. Is arranged in
Is obtained. Here, R = R _n is the radius of the circumference, and φ _n = 2πn / N is the array angle of the element antennas. The phase and amplitude of the measured as a complex number a _n, and inputs to the circular AF, it is possible to easily distant conversion. Note that equation (1) has already been displayed in a distant pattern.
The above is the antenna theory as a single-layer ring array, and it can be seen that a single ring array pattern can be obtained if the element coordinates and excitation phase are determined. When M ring arrays with a radius R _mn overlap in a cylindrical shape,
What should I do? Here, θ and φ are angles of the radiation pattern in space spherical coordinates. When the ring arrays of each layer are arranged in exactly the same way in the z direction, that is, when the element coordinates in the circumferential direction are the same, φ _mn = φ _n . Moreover, since the cylindrical shape is assumed, the radial distance is R _{m n} = R _n .
Transform of near field by cylindrical array factor Now, the procedure for evaluating the far field is shown. For this _purpose , it is considered that the phase and amplitude data acquired in the vicinity are input to the coefficient a _mn as complex numbers. At this time, all relative power supply phases incorporate information into a _mn as acquired data. Although the sampling position coordinates still have a degree of freedom at each point, since the radius of the cylinder is usually constant, R _mn = R can be set. The probe also performs probing scanning with the same antenna facing the z axis of the cylinder. The probe correction at this time may be considered as follows. That is, the probe pattern is set to f _p (θ _p , φ _p ). Here, θ _p and φ _p represent local coordinates at a sampling point at which data is acquired. When calculating the far-field radiation pattern using this probe pattern as a weight function, the array factor is multiplied. For simplicity, assuming f _p = cos (φ _p ) and considering a single-layer ring array only in the circumferential direction, this can be approximately converted to cos (φ−φ _n ) and scan coordinates, so the final Distant pattern after probe correction
Can be evaluated. For example, a type using an end portion of a waveguide is often used as an actual probe antenna, and this directivity pattern is measured in advance, digitized, and corrected. In addition, you may use the calculated value of a horn antenna approximately.
The results measured by the above procedure are shown in (1) of FIG. An angle of 0 degrees is a state in which the disk is facing the front, and this is a radar bisection value of 45 degrees in the horizontal direction bistatic, which is almost the same as the theoretical value. Prior to this experiment, a monostatic experiment was performed with 45 degrees set to 0 degrees, which almost agreed with the theoretical value. In the case of this experiment, it was transmitted from the primary radiator, but this may be radiated from the probe antenna and received by the parabolic antenna. Alternatively, the parabolic antenna may be an offset parabolic antenna, and the primary radiator may be shifted to a position off the plane wave path.

  In the case of the previous embodiment, the probe antenna is placed on 3b, but this is moved to 3c. At this position, the bistatic RCS is 45 ° horizontal and 20 ° vertical. The results are shown in (2) of [FIG. 5], which almost agrees with the theoretical values.

  Next, the probe antenna was placed in 3d. At this position, the probe antenna is a bistatic RCS of 45 ° horizontally and 40 ° vertically. The results are shown in (3) of [FIG. 5], which almost agrees with the theoretical values. The sample is rotated by 0.1 degree, the probe antenna is moved from the bottom to the top, and the sample is rotated by 0.1 degree, and the probe antenna is moved from the top to the bottom. In addition, although a probe does not stop still, it can move slowly and can acquire 10 points from 9.5 GHz to 10.4 GHz every 0.1 GHz. Once this is completed, if the probe antenna is moved 15 degrees horizontally, the RCS measurement of 45 degrees +15 degrees and the horizontal bistatic 60 degrees is started.

Various situations when measuring a sample with radar 1. 1. A reflected wave that returns to the place where the radar wave was transmitted in the monostatic mode. Bistatic mode (1) Reflected wave observed from a direction different from the transmitted wave of the radar transmitted wave on the horizontal plane (2) Reflected wave in the same or different direction as the transmitted wave of the radar transmitted wave on the horizontal plane Since the RCS of the reflected wave observed from below can be measured in the near field, there are many possibilities such as the development of a vehicle with a large reflected wave from the radar and the development of an aircraft with a small reflected wave from the radar.

1. 1. Parabolic antenna Primary radiator3. Probe antenna 3a. Probe antenna in monostatic mode position 3b. Bistatic mode with a 45 ° angle difference on the horizontal plane 3c. Probe antenna at a position of bistatic mode that differs by 45 ° on the horizontal plane and by 20 ° in the upward direction 3d. 3. Probe antenna at a position of bistatic mode that differs by 45 ° on the horizontal plane and by 40 ° in the upward direction sample

Claims (5)

  A rotating sample is irradiated with a plane wave, and the amplitude and phase of the reflected wave from each point of the sample are received by a wide-bandwidth antenna such as a waveguide opening, and near-field far-field conversion is performed using an array factor. A device that measures RCS.   The apparatus according to claim 1, wherein an angle of the receiving antenna can be taken on a horizontal plane and / or a vertical plane with respect to the sample as an axis from the line of the irradiating plane wave and the sample.   2. The apparatus according to claim 1, further comprising a receiving antenna capable of moving at an angle on a horizontal plane from the line of the irradiating plane wave and the sample with the sample as an axis and moving up and down.   4. The apparatus according to claim 1, wherein the receiving antenna is provided at a plurality of angular positions on a horizontal plane from the line of the irradiating plane wave and the sample with the sample as an axis.   Apparatus according to claim 1, 2, 3, 4 for producing plane waves using the compact range method.