JPS6247002B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a beam scanning method that makes it possible to shorten the time required to update target information and improve angle measurement accuracy in an electronic scanning radar that obtains target direction information by interpolation between a plurality of pencil beams. First, this type of prior art will be explained using an example of an electronically scanned three-dimensional radar. FIG. 1 shows the general configuration of a phase scanning three-dimensional radar. In the figure, 10 is a radar antenna, which includes N radiating elements A ₁ , A ₂ ...An, phase shifters B ₁ , B ₂ ...Bn connected to each radiating element, and a power divider C. Consisted of. Further, 11 is a beam controller, 12 is a transmission/reception separation circuit, 13 is a transmitter, 14 is a receiver, 15 is a signal processing circuit, and 16 is a computer. Figure 2 shows an example of the formation of a radar vertical surface coverage area using phase scanning and three-dimensional radar as shown in Figure 1. forming a region. In order to obtain the three-dimensional position information of the target using the target information obtained from such a series of beams, in addition to the radar's normal planar two-dimensional position information, interpolation calculations between adjacent beams are required. Therefore, it is necessary to know the elevation angle direction. For example, in Figure 2, the interpolated elevation angles between the beams are in the directions θ _22-1 and θ _22-2
The distance between them is calculated from the ratio of the target reflected signal intensities obtained from each of the beams 22-1 and 22-2.
FIG. 5 is a functional block diagram of two-beam interpolation calculation, where 50 is an antenna radiator, 51 is a receiver for both channels, 52 is a logarithmic amplifier for both channels, and 53 is a signal between both channels. 54 is an angle signal generator, and 55 is an angle signal terminal. In order to obtain the maximum aperture efficiency and the minimum beam width for a given antenna aperture, the above-mentioned antenna is usually set such that the wavefront of the radiated radio waves is in phase with the excitation phase of the aperture within a field perpendicular to the beam direction direction. Set the amount of phase shift of each antenna element to . As an example, consider a linear array antenna with an element spacing of d. The radiation beam is θ ₀ from the front direction of the array.
When scanning by [radian], the excitation phase φn of the nth radiating element is based on the excitation phase of the first radiating element as follows: φn=-2π/λ(n-1)d sinθ ₀ (1) Just set it. (However, λ is the free space wavelength.) The state in which the phase distribution of the antenna aperture is excited so as to be in phase with the beam direction direction is called co-phase excitation. Beam shape (power pattern) in this case
is known to be proportional to [sin(Kθ)/(Kθ)] ² , where θ is the angle measured from the beam nose and K is a constant. Furthermore, this equation can be expressed as a Gaussian function type exp (with K′ as a constant). −K′θ ² ). Angle measurement processing using an antenna having such a Gaussian function type radiation pattern will be described below. When the direction of angle measurement is between θ _22-1 and θ _22-2 in Figure 2, the received signal by beam 22-1 is guided to the channel in Figure 5, and the received signal by beam 22-2 is guided to the channel in Figure 5. After passing through the receiver 51, a logarithmic amplifier 52 performs logarithmic conversion, and a subtracter 53 calculates the difference between the two received signals. Finally, if the differential signal voltage is passed through an angle signal generator 54 that converts it into an angle, the angle signal terminal 55
An interpolated angle signal is output. The signal calculations during this time are as follows. The antenna power pattern is expressed as a Gaussian function exp [-K (θ-θ ₀ ) ² ] where K is a constant, θ is the angle indicating the target direction, and θ ₀ is the main beam direction θ _22-1 or θ _22-2 Assuming that the angle represents the following equation, the differential output voltage ΔV after logarithmic calculation is expressed by the following equation. ΔV=R·Δθ/〓 Here, R is a constant, Δθ is the beam width, and Δθ is the target direction angle measured from the intersection point of the two beams. From this formula, Δθ can be easily calculated by measuring ΔV. Now, since the series of beams shown in FIG. 2 have a nearly constant antenna gain, their high elevation angle region,
For example, excessive antenna gain occurs in beams 23-1, 23-2, and 23-3. Furthermore, since the vertical surface coverage area is scanned with a pencil beam, a large number of beams are required, and there is a drawback that it takes time to update target information. To solve these shortcomings,
A method is used to reduce the number of beams required for coverage while maintaining an appropriate antenna gain for coverage by expanding the vertical plane beam width in a high elevation angle region. Conventionally, this beam width expansion was
This is achieved by controlling the phase shifter of the antenna and applying a relatively simple functional distortion, such as a sine distribution, to the phase distribution on the array antenna aperture. However, in such a beam scanning method, due to the radiation characteristics of the antenna,
30-3, a beam having a complicated shape with ripples as shown in FIG. An object of the present invention is to solve the above-mentioned drawbacks by improving the beam scanning method, and to provide a radar method characterized by beam scanning that reduces the time required to update target information while maintaining angle measurement accuracy. It is in. In order to achieve such an object, the present invention controls the amount of phase shift applied to a phase shifter provided corresponding to a plurality of radiating elements, and sequentially scans a radiation beam in space from a radiation aperture formed by the radiating elements. In the electronic scanning radar to be formed, at least one set of two adjacent radiation beams of the radiation beam group sequentially scanned and formed has a substantially Gaussian shape and a beam width that excites the radiation aperture in phase. An excitation phase corresponding to each of the radiating elements is determined in advance so as to minimize the error between the radiation power pattern from the radiating aperture and the expected pattern function. and means for setting a phase shifter corresponding to each of the radiating elements, and an angle measuring means for receiving signals from the two adjacent enlarged radiation beams as input signals. Next, an embodiment of the present invention will be described in detail with reference to FIG. FIG. 4 is a diagram showing one vertical surface coverage area of the pencil beam phase scanning radar, where 10 is the radar antenna, 21 is the vertical surface coverage area required by this radar, 40-1, 40-2... is a narrow pencil beam group determined by the aperture size, 41-1, 4
1-2... shows an enlarged pencil beam group. In this embodiment, the radar antenna 10 uses a combined electronic and mechanical scanning system that performs electronic scanning in the vertical plane and mechanically rotates in the horizontal plane to cover 360 degrees. In order to achieve the required coverage area 21 with this kind of pencil beam scanning radar,
In the low elevation angle region where the coverage distance is maximum, a beam with the narrowest possible beam width determined by the antenna aperture is formed to cover the required coverage area, and in the high elevation angle region where the coverage distance is short, the antenna gain is The beam width is expanded within a sufficient range to ensure the beam distance, and the beam spacing is also expanded in proportion to the beam width.
Furthermore, in the above beam formation, both the narrow beam and the expanded beam are formed into Gaussian function shapes.
In order to realize such beam forming and beam scanning, an appropriate phase shift amount may be set in the phase shifters B _{1 .} . . Bn by a command from the beam controller 11 when expanding the beam width. The setting of this phase shift amount will be described below. In this embodiment, a Gaussian expected pattern function having a beam width wider than the radiation beam during co-phase excitation given by equation (1) is set as a reference using the following equation. g(u)=exp[−(au) ² ] (3) where u=(2πd/λ)(sinθ−sinθ ₀ ) (4) where d is the element spacing of the array antenna, and λ is the free space wavelength. , θ is the spatial angle and θ ₀ is the main beam scan angle. Next, an evaluation function ε=1/2π∫〓 ₋ {(u)−g(u)} ² du (5) expressed by the following equation is set. Here (u) is the radiation power p in the main beam direction
This is the normalized radiation power pattern of the array antenna normalized by (o), and is expressed as (u)=|E(u)| ² /|E(o)| ² (6). In addition, E(u) is the radiation electric field pattern of the array antenna, where the excitation amplitude of each element antenna is an, and the excitation phase for beam width expansion is _αo . It is expressed as However, u is a variable given by equation (4). Next, the error ε expressed by the evaluation function of equation (5) is
It is minimized by a solution method such as the so-called conjugate gradient method, and the solution αn is set as the excitation phase for expanding the radiation beam width. Based on this result, the amount of phase shift φn that should be set for each phase shifter
is determined as φn=−(2πd/λ)n·sinθ ₀ +αn(8), and the radiation pattern has a shape approximated by the Gaussian function of equation (3). In radar systems using Gaussian shaped antenna beams,
As explained in the related art, the direction of the target can be easily calculated by interpolation calculation between beams. This calculation is performed on radars with expanded beam width and beam spacing.
In the system, the target direction is calculated in the same way by considering the changed parameters. The time it takes for the radar system described above to completely cover one vertical coverage area with the beam is determined by the number of narrow beams M
Assuming that the number of main and expanded beams is N, and the transmission and reception time required for the required coverage in each beam direction is tj for beam j (j = 1...), becomes. The second term in the above equation is a term that indicates the reduction in scanning time due to beam expansion, and is the required time when beam expansion is not performed.

This shows that time can be saved for [Formula]. As a result, it is possible to increase the number of times the beam is irradiated on average, improving the probability of target detection, and increasing the number of times beams are formed in the direction that should be focused on searching or tracking. Can be done. In the above embodiment, one beam is formed at a time, but the same applies to a system in which a plurality of beams are formed at one time. In addition, although the antenna beam scanning methods are horizontal plane mechanical scanning and vertical plane phased beam scanning, the same applies to omnidirectional phased beam scanning and to forming beam groups simultaneously or non-simultaneously by simple switching. It is favorable for Note that the beam-to-beam interpolation processing for angle measurement in this embodiment is equally effective in a system in which extrapolation processing is also used. As explained above, the present invention expands the beam shape while maintaining a substantially Gaussian function shape in the high elevation angle region where a short-range target is targeted within the radar system coverage area, and at the same time, the beam spacing is also increased. By enlarging the beam, the number of beams formed in one vertical plane is reduced. As a result, it is possible to reduce the time required to scan one vertical coverage area while maintaining the necessary target detection performance and simple target direction interpolation method.
By effectively using the resource of time, detection probability and target tracking ability can be improved.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the configuration of a phase scanning three-dimensional radar.
Figure 2 is a diagram showing the conventional vertical beam scanning method.
Figure 3 is a diagram showing a conventional vertical plane beam scanning system in which beam width is expanded in a high elevation angle region, Figure 4 is a diagram showing a vertical plane beam scanning system according to the present invention, and Figure 5 is a diagram showing an interpolation calculation function. It is a block diagram. 10: Radar antenna, 11: Beam controller,
12: Transmission/reception separation circuit, 13: Transmitter, 14: Receiver, 15: Signal processing circuit, 16: Computer, 50:
Antenna radiation section, 51: Receiver, 52: Logarithmic amplifier, 53: Subtractor, 54: Angle signal generator, 5
5: Angle signal terminal.

Claims (1)

[Claims] 1. Electrons that sequentially scan and form a radiation beam in space from a radiation aperture formed by the radiation elements by controlling the amount of phase shift applied to a phase shifter provided corresponding to a plurality of radiation elements. In the scanning radar, at least one set of two adjacent radiation beams in the group of radiation beams formed by sequential scanning has a substantially Gaussian shape and a beam width obtained by co-phase excitation of the radiation aperture. An expected pattern function expanded more than the beam width is predetermined, and the excitation phase corresponding to each of the radiating elements is determined to minimize the error between the radiated power pattern from the radiating aperture and the expected pattern function. An electronic scanning radar system comprising: means for setting a phase shifter corresponding to a radiating element; and an angle measuring means whose input signals are received signals from the two adjacent enlarged radiation beams.