JPH06224614A - Radome and its manufacture - Google Patents

Abstract

PURPOSE:To propagate radio waves in-phase by varying the relative dielectric constant of each part so that the product of the square root of the relative dielectric constant and the thickness in the radio wave passing direction in each part is made constant so as to give the thickness of the radome to be easily processed. CONSTITUTION:Let thickness in the normal direction at incident points 5a, 5b of radio waves 3a, 3b of a radome 10 be 11a, 11b, thickness of the radome 10 in the passing direction of the radio waves 3a, 3b be 12a, 12b, and relative dielectric constants of the radome at the thickness of 12a, 12b, be 13, 14 respectively. Then the electric length of the radome 10 when the radio waves 3a, 3b pass therethrough is proportional to lambda/sq. rt. epsilon, where epsilon is the relative dielectric constant of the material and lambda is the wavelength of the radio wave. Thus, when the thickness 11a, 11b of the radome 10 in the normal direction is the same and the thickness 12a, 12b in the passing direction of a radio of a wave differs, the electric length is made equal by selecting the relative dielectric constants 13, 14 to be the relation of thickness 12a X square root of the relative dielectric constant 13 = thickness 12b X square root of the relative dielectric constant 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radome made of ceramics, particularly a radome used for missiles flying at high speed, and a method for manufacturing the radome.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view showing a conventional radome. In the figure, reference numeral 1 denotes a ceramic radome, which is formed in a dome shape so as to cover the front surface of the antenna 2. 3a and 3b are radio waves having the same phase emitted from the antenna 2, 4a and 4b are incident angles of the radio waves 3a and 3b with respect to the normal direction in each part of the radome 1, and 5a and 5b are radio waves 3a and 3b which are associated with the radome 1. Incident point, 6a, 6b
Is the thickness of the radome 1 in the normal direction at the incident points 5a and 5b, 7a and 7b are the thicknesses of the radio waves 3a and 3b in the radome 1 in the passing direction, 8a and 8b are the radio waves emitted from the radome 1, and
Is the phase plane after leaving the radome 1, and 15 is the central axis.

Next, the operation will be described. The relative permittivity ε of the material (ceramic) of the radome 1 is constant, and the radio waves 3a, 3b, 8a, 8b proceed from left to right in FIG. 3 before and after passing through the radome 1. Generally radio wave 3
Since the phase when a and 3b pass through the radome material is proportional to the thickness of the radome 1 and is proportional to 1 / (square root of ε), in order to change the phase, either the thickness or the dielectric constant should be set. Need to control.

In FIG. 3, the radio wave 3 emitted from the antenna 2
When a and 3b pass through the radome 1, refraction occurs at the incident points 5a and 5b according to Snell's law. At this time, since the incident angles 4a and 4b of the radio waves 3a and 3b are different, the thicknesses 7a and 7b in the passage direction of the radio waves in the radome 1 and the angles thereof are also different. If the radome 1 has a thickness 6a in the normal direction,
If 6b is the same, the thickness of the radome 1 in the passing direction is 7
Since a and 7b are different and the dielectric constants are the same, a phase shift occurs in the radio waves 8a and 8b after passing through the radome 1, and the radio waves do not travel in the desired direction (left to right in this case). . For this reason, conventionally, as shown in FIG. 3, the radome 1 is machined such that the thicknesses 6a and 6b in the normal direction are changed so that the thicknesses 7a and 7b in the radio wave passing direction are the same. Giving, radio waves 3a, 3b and radio waves 8a, 8b
A surface having the same direction, that is, a phase surface 9 is obtained.

[0005]

Since the conventional radome is constructed as described above, in order to propagate the radio wave in the desired direction, the thickness of the radome in the normal direction should be changed in each part. However, there is a problem in that the machining for changing the thickness for each part requires advanced machining technology and expensive machining equipment, which makes the inspection difficult. The present invention has been made to solve the above problems, and provides a radome and a method for manufacturing the radome which have the same thickness in the normal direction of the radome and can be easily manufactured by machining or the like. The purpose is to get.

[0006]

The present invention is the following radome and method for manufacturing the same. (1) In a ceramic radome configured to cover the front surface of the antenna, the relative permittivity of each part is changed so that the product of the thickness in the radio wave passing direction of each part and the square root of the relative permittivity becomes constant. The radome that made me. (2) The radome according to (1), wherein the thickness of each part in the normal direction is substantially constant. (3) In the method for producing a radome described in (1) or (2) above, a radome in which the relative dielectric constant of each part is changed by changing the sintering temperature of each part of a molded body made of a ceramics raw material and sintering. Manufacturing method.

[0007]

In the radome according to claim 1 of the present invention, the product of the thickness of the radio wave passing direction and the square root of the relative permittivity in each part is constant, so that the electric length in each part is constant and the desired value is obtained. Radio waves travel in the same phase in the direction of.

In addition to the above, the radome according to the second aspect of the present invention has a substantially constant thickness in the direction of the normal line at each portion, so that the processing becomes easy. That is, in the radome according to the present invention, the thickness in the normal direction of the radome becomes the same by changing the sintering temperature and changing the distribution of the relative dielectric constant when manufacturing the ceramics.

In the method for manufacturing a radome according to claim 3 of the present invention, the relative dielectric constant of each part is changed by changing the sintering temperature, and the desired radome can be manufactured efficiently by a simple operation. . That is, the radome according to the present invention utilizes the characteristic that the relative permittivity changes depending on the temperature at which the ceramics are sintered to give a distribution of the relative permittivity, so that the mechanical dimensions of radio waves passing through the radome are apparently different. Also, the phase length (electrical length (thickness)) is the same.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a radome of an embodiment. In the figure, the same symbols as in FIG. 3 indicate the same or corresponding parts. 1
0 is a radome, 11a and 11b are thicknesses in the normal direction at the incident points 5a and 5b of the radio waves 3a and 3b, and 12a and 12b.
Is the thickness of the radio waves 3a and 3b in the passing direction, and 13 is the thickness 12a.
Is the relative permittivity of the portion including, and 14 is the relative permittivity of the portion including the thickness 12b.

The electrical length when the radio waves 3a and 3b pass through the radome 10 is proportional to λ / (square root of ε) where ε is the relative permittivity of the material and λ is the wavelength of the radio wave. Therefore, like the radome 10, the thickness 11a, 11
When b is the same and the thicknesses 12a and 12b in the radio wave passing direction are different, if the relative permittivity 13 and the relative permittivity 14 are set to values having a relationship as in the following expression [1], the electrical length is increased. Will be the same. Thickness 12a × square root of relative permittivity 13 = thickness 12b × square root of relative permittivity 14 ... [1]

In the formula [1], the thicknesses 12a and 12b in the passage direction of the radio waves 3a and 3b are known, and the relative permittivities 13 and 14 may be derived from them. With the above,
A plane in which the directions of the radio waves 3 and 8 are the same, that is, the phase plane 9 can be obtained. In order to make the relative permittivity have a distribution, when performing sintering, which is a step of baking and hardening ceramics, for example, in the case of fused silica (SiO ₂ ) ceramics, the sintering temperature is high as shown in FIG. This can be achieved by utilizing the characteristic that the relative dielectric constant increases and the relative dielectric constant decreases as the sintering temperature decreases.

FIG. 2 is an example of a graph showing the relationship between the sintering temperature and the relative permittivity for the fused silica ceramics, and shows that the higher the sintering temperature, the higher the relative permittivity. In FIG. 1, (thickness 12a)> (thickness 1
Since it is 2b), from the formula [1] (relative permittivity 13) <
(Relative permittivity 14), and the closer to the central axis 15 of the radome 10, it is necessary to increase the relative permittivity.

Therefore, the relative dielectric constant can be changed as described above by increasing the sintering temperature closer to the central axis 15 of the radome 10 and lowering the sintering temperature closer to the peripheral portion. . For example, when the ceramic of FIG. 2 is used for the radome 10 of FIG. 1, the sintering temperature near the central axis 15 is 1280 ° C., the sintering temperature of the peripheral portion is 1220 ° C., and the sintering temperature of the intermediate portion between them is 1250 ° C. , When the thicknesses 11a and 11b in the normal direction are the same, (the thicknesses 12a and 12b in the radio wave passing direction) × (the square root of the relative permittivity 13 and 14) are equal, and the electrical length in each part of the radome 10 is equal. It becomes the same, and the phase plane 9 is obtained.

The radome 10 as described above is formed by molding a ceramic powder raw material so that the thicknesses 11a and 11b in the normal direction are constant, and then the temperature distribution, that is, the central axis 1 is formed.
It is manufactured by sintering in a sintering furnace whose temperature distribution is controlled such that the temperature is high around 5 and decreases toward the periphery. To control the temperature distribution as described above, the central axis 15
It is possible to precisely control the sintering temperature by disposing the heating sources in the vicinity densely or by configuring the sintering furnace so that the high temperature gas flows from the central shaft 15 side toward the peripheral portion. .

The radome 10 thus manufactured is shown in FIG.
Are used in the same manner as in the case of FIG. At this time, the radio waves 3a and 3b emitted from the antenna 2 travel in the same phase from left to right through the route of FIG.

The radome 10 has a thickness 11 in the normal direction.
Since a and 11b are the same, machining is easy,
No advanced machining technology or expensive processing equipment is required, and inspection is easy. And even in this case,
With a simple operation, the electric lengths of the respective parts become the same, and the radio waves can travel in the same phase.

By the way, when the radome 10 is processed, it is very difficult to make each part to have the same thickness, and in practice, it is processed with a dimensional tolerance of, for example, about ± 0.5 mm. Therefore, in the processing of a curved surface such as the radome 10 in FIG. 1, the tolerance may vary depending on the normal processing position. For example, the tolerance changes to the plus side or the minus side depending on the size of the curvature. Therefore, this tolerance can be grasped in advance, and the relative permittivity can be changed according to the thickness by using the above formula [1], and the same effect as that of the above-mentioned embodiment can be obtained.

[0019]

In the radome according to claim 1 of the present invention, since the relative permittivity of each part is distributed, it is possible to make the thickness of the radome easy to process, and even in that case, the radio waves travel in the same phase. A radome capable of being obtained can be obtained.

In the radome according to the second aspect of the present invention, the thickness of each part in the direction of the normal line is substantially constant, so that the radome can be obtained particularly easily by processing and with an inexpensive device and a simple operation.

According to the radome manufacturing method of the third aspect of the present invention, the relative permittivity of each part is changed by changing the sintering temperature. A radome can be manufactured.

[Brief description of drawings]

FIG. 1 is a sectional view of a radome of an embodiment.

FIG. 2 is a graph showing the relationship between the sintering temperature of fused silica and the relative dielectric constant.

FIG. 3 is a sectional view of a conventional radome.

[Explanation of symbols]

 1, 10 Radome 2 Antennas 3a, 3b, 8a, 8b Radio waves 4a, 4b Incident angles 5a, 5b Incident points 6a, 6b, 11a, 11b Thickness in normal direction 7a, 7b, 12a, 12b Thickness in radio wave passage direction 9 Phase plane 13, 14 Relative permittivity 15 Central axis

Claims (3)

[Claims] 1. In a ceramic radome configured to cover the front surface of an antenna, the relative permittivity of each part is set so that the product of the thickness of the radio wave passing direction in each part and the square root of the relative permittivity is constant. A radome that is characterized by changing. 2. The radome according to claim 1, wherein the thickness of each part in the normal direction is substantially constant. 3. The method for manufacturing a radome according to claim 1 or 2, wherein the relative dielectric constant of each part is changed by changing the sintering temperature of each part of the molded body made of a ceramic raw material and sintering. Characteristic radome manufacturing method.