JPH0369208B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radar antenna device capable of wide-angle beam scanning over a wide frequency range.

First, a conventional antenna device of this type will be briefly explained. FIG. 1 is a plan view of a conventional antenna device. 1 is a parallel plate, 2a, 2b, 2c, 2d,...
... is an input element that supplies power to the parallel plate 1, 3
a, 3b, 3c, 3d, . . . are output elements for extracting electric power from the parallel plate 1, 4a, 4b, 4c, .
5 is an element antenna that radiates radio waves into space, 5 is an array antenna in which a plurality of element antennas 4a, 4b, 4c, .
c, . . . are transmission lines connecting the output element and the element antenna, 7 are transmission lines 6a of different lengths,
6b, 6c, . . . 8 is a center line, and this antenna device is vertically symmetrical with respect to the center line 8. 9a and 9b are input elements 2a,
2b, and the input elements 2a and 2b are at angles α and 2b from the center line 8, respectively.
It is in the θ direction. 10 is a straight line indicating the beam direction in space, and is oriented at an angle β from the center line 8.

Since this antenna device is configured as described above, the input elements 2a, 2b, 2c, 2d,...
When one of the input elements is excited, power is supplied into the parallel plate 1. The electric power within the parallel plate 1 is extracted by the output elements 3a, 3b, 3c, 3d, . . . and reaches the element antennas 4a, 4b, 4c, . The excitation amplitude and excitation phase of the array antenna 5 are determined depending on which input element among the input elements 2a, 2b, 2c, 2d, ... is excited, and the direction of the beam in space is determined according to the excitation phase of the array antenna 5. is decided. The positions of the input elements 2a, 2c, 2d are the points where the array antenna 5 fed by the entire feed system including the parallel plate 1 and the transmission lines 6a, 6b, 6c, . . . are excited in phase, that is, the focal point. When three focal points are given, the output elements 3a, 3b, 3
c, 3d, ... are arranged and the lengths of the transmission lines 6a, 6b, 6c, ... are determined, and when the input elements 2a, 2c, 2d at the three focal points are excited, the array antenna 5 It can be designed to eliminate the excitation phase error. Note that the focal point position depends on the size of this antenna device and the array antenna 5.
This is determined by the maximum beam scanning angle condition.
However, in this conventional antenna device, the plurality of input elements are input elements 2 at three focal positions.
Since it is assumed to be on a circular arc passing through points a, 2c, and 2d, it is in the direction of an angle θ measured from the center line 8, and when the input element 2b other than the input elements 2a, 2c, and 2d representing the three focal points is excited. An error occurs in the excitation phase at the array antenna 5. In order to reduce the excitation phase error in the array antenna 5, it is necessary to limit the size of the parallel plate 1. Further, when the input element 2a, which is one of the focal points, is excited, the angle β indicating the direction of the beam in space is limited to β=α. It is clear that the above-mentioned limitations reduce the number of design parameters, which is a disadvantage in optimal design. Furthermore, if the excitation phase error near both ends of the array antenna 5 becomes large, there is a drawback that the length of the array antenna 5 must be set within a range where the excitation phase error is small.

In order to eliminate these drawbacks, the present invention determines a curve for arranging input elements so as to minimize the excitation phase error over the entire array antenna, and
It is designed and constructed by increasing design parameters without limiting the size of the parallel plate and the size of the array antenna.The drawings will be described in detail below.

FIG. 2 is a plan view of a simplified antenna device for explaining the design method of the present invention. 1-10
is the same as that in Figure 1. 11 is a straight line indicating the aperture of the array antenna. Input element 2a, 2
The position c, 2d is the focal point, and the input element 2
By making the electrical length constant when each of a, 2c, and 2d is excited, the shape of the curve in which the output elements 3a, . . . are arranged and the transmission lines 6a, .
Determining the length of is the same as the conventional method. However, it is assumed that the parallel plate 1 is composed of a dielectric substrate having a relative dielectric constant ε _r and a pair of parallel conductor plates sandwiching the dielectric substrate from both sides. When the direction of the beam in space when the input element 2b is excited in the direction of angle θ as measured from the center line 8 is the direction of θ ₀ as measured from the center line 8, the position of the origin of the X, Y coordinate system Let ΔL be the difference between the electrical length of the optical path passing through the output element 3d located at 1 and the electrical length of the optical path passing through the other output elements, and
The length of is 2N max, the wave number in parallel plate 1 is k ₁ ,
The electrical length of only the transmission line connected to the output element 3d is W ₀ , the electrical length of only the transmission line connected to other output elements is W, the coordinate of the position of the output element is X,
Δl represents the excitation phase error of the array antenna 5, where Y is the distance between the input element 2b and the output element 3d, H is the position on the straight line 11 indicating the aperture of the array antenna with the center line 8 as a reference. =ΔL/
(√ _r N max) is given by the following equation.

Δl=n/√ε _r sin θ ₀ +S …(1) However It is. The following equation is defined using Δl in the first equation.

ε=∫ ¹ _-1 (Δl) ² dn …(3) When using the first equation as Δl in the third equation, ε is
This becomes a quadratic expression regarding sin θ ₀ . At this time, the minimum value εmin of ε and θ ₀ giving the minimum value are given by the following equation.

ε min＝∫ ¹ _-1 S ² dn−3/2 (∫ ¹ _-1 Sndn) ² …(4) sin θ ₀ = −3√ε _r /2∫ ¹ _-1 Sndn …(5) The fourth equation εmin is a function of θ, h, and θ, h
When the minimum value of εmin is further determined by varying independently, θ and h become the values that minimize ε in the third equation. By substituting θ and h at this time into the right side of Equation 5, θ ₀ can be found.

FIG. 3 is a plan view of a parallel plate portion as an embodiment of the present invention. 1, 2a-2d, 3d, 8,
9a and 9b are the same as those in FIG. 1, and the parallel plate 1 is symmetrical with respect to the X axis. Reference numeral 12 indicates an optimum curve obtained by determining θ and h that minimize εmin in equation (4), and reference numeral 13 indicates a partial circle obtained by the conventional method. In this embodiment, the parallel plate 1 is constructed by sandwiching a dielectric substrate with a relative dielectric constant ε _r of 15 between parallel conductor plates on both sides, and when the input element 2a is excited, the beam in space is measured from the center line 8. The center of the partial circle is located at the output element 3d, and the ratio F between the distance F between the input element 2a and the output element 3d and half the length Nmax of the array antenna 5 in FIG. /N
min is 1.4. As θ becomes larger (θ<22.5°), it can be seen that there is a large difference between the optimal curve 12 calculated using Equations 1 to 4 and the partial circle (arc) 13 calculated using the conventional method. Recognize. It has been confirmed that Δl in the first equation, which corresponds to the excitation phase error of the array antenna, is sufficiently small at 3×10 ⁻⁴ no matter which input element on the optimal curve 12 is excited. In addition, FIG. 4 shows the angle θ from the X axis of input element 2b, which represents the input element in FIG. 3, and the angle θ ₀ (second (shown in the figure)
This shows the relationship calculated using the fifth equation.

Note that, although the case has been described above in which a dielectric substrate having a dielectric constant ε _r of 15 is sandwiched between parallel conductive plates from both sides as a parallel plate, the dielectric constant may have any value. In addition, we have explained the case where the angle from the center line of the focal point on the curve where the input elements are arranged is 22.5 degrees, and the direction of the beam in space when the input elements at that position are excited is 45 degrees. There is no need to limit the value, and there is no need to limit the curve on which the input elements are arranged only between the focal points.
It is also possible to extend the curve in which the input elements are arranged beyond the position of the focal point. Furthermore, the sizes of the parallel plate and array antenna are design parameters, and the antenna device as a whole can be designed to have optimal characteristics.

As described above, according to the present invention, by determining the shape of the curve on which the input elements are arranged so as to minimize the excitation phase error of the array antenna, the position of the focal point on the curve on which the input elements are arranged is determined. The direction of the beam in space when exciting the input element is not uniquely limited, and the size of the parallel plate,
By leaving the size of the array antenna as a design parameter, there is an advantage that the antenna device as a whole can be designed and configured to have optimal characteristics, and when this antenna device is used as a radar antenna, etc., the effect can be significantly improved. big.

[Brief explanation of drawings]

Fig. 1 is a plan view of a conventional antenna device, Fig. 2 is a plan view of the antenna device simplified to explain the design method of the present invention, and Fig. 3 is a parallel plate portion as an embodiment of the present invention. FIG. 4 is a plan view showing the relationship between the position of the input element to be excited and the direction of the beam in space in the embodiment of the present invention. In the figure, 1 is a parallel plate, 2a, 2b, 2c, ... are input elements, 3a, 3b, 3c, ... are output elements, 4
a, 4b, 4c, . . . are element antennas, 5 is an array antenna, 6a, 6b, 6c, . In the drawings, the same or corresponding parts are denoted by the same reference numerals.

Claims (1)

[Claims] 1. Consists of a parallel plate that can be individually excited and has a plurality of input elements that supply power and a plurality of output elements that take out the power, and a plurality of element antennas, and transmits radio waves in space. an array antenna that radiates
It consists of a transmission line connecting the output element and the element antenna, and when three focal points are given at positions determined by the size of this device and the maximum beam scanning angle of the array antenna, the output element is arranged. The shape of the curve and the length of the transmission line are determined, and when the input elements at the three focal points are excited, the array antenna is excited in phase, and
In an antenna device in which a beam is emitted in an angular direction corresponding to the input element when a predetermined input element is excited, the beam passes from one input element to the output element located at the center of the curve in which the output elements are arranged. The difference between the distance between the transmission line connected to the output element and the element antenna, and the distance from the input element through another output element and the transmission line and element antenna connected to the other output element is calculated as the length of the array antenna. Let S be the value normalized by half the value Nmax, let S be the position of one element antenna of the array antenna, let N be the distance from the center of the array antenna, and let the coordinates of the other output elements be the coordinates of the other output elements where the output elements are arranged. The origin is the center of the curved line, and the orthogonal coordinates with the central axis as the θ, the length W of the transmission line connecting the above one element antenna and the output element that feeds it, and the length W of the transmission line that connects the element antenna at the center of the array antenna and the output element that feeds it _{. 0}
The value obtained by converting the difference between
Find S using the following formula, S=√(-) ² +(-) ²
+-
h Here, x=X/N max y=Y/N max h=H/M max w=W−W ₀ /〓ε _r・Nmax (However, ε _r is the dielectric constant of a parallel plate) Calculated above Regarding S ∫ ¹ _-1 S ² dn-3/2 [∫ ¹ _-1 S・n dn] ^2Here , n=N/N max (n; the aperture length of the array antenna is normalized to -1 to 1 The position of the input element is determined by determining h and θ so as to minimize the continuous position on the array antenna aperture when An antenna device characterized in that the arrangement of all input elements is determined by determining the arrangement of all input elements.