JPH06152236A - Shield base for plane antenna - Google Patents

Abstract

PURPOSE:To obtain the plane antenna shield base with high strength in which the water-proof function, the electromagnetic shield function of an amplifier section, the mount performance are improved and crack, damage or destruction hardly takes place. CONSTITUTION:The plane antenna incorporates a radiation electrode 35, a ground electrode 36, a ceramic dielectric body 33, and an amplifier 38. A conductive metallic film 39 is formed on one side of a shield base 50 applying electromagnetic shield to the amplifier 38 in a spatial recessed part 58 and the base 50 is fixed to the bottom 330b of a torus leg 330 of a ceramic 33. The shield base 50 is made of a ceramic made shield base having almost equal thermal expansion rate to that of a ceramic dielectric body. Thus, the shield base 50 and the ceramic dielectric body 33 are made of materials whose thermal expansion rates are close to each other, then a stress and a strain caused by a temperature change are minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar antenna, and more particularly to a shield substrate for a microstrip antenna used as a mobile communication antenna or the like.

[0002]

2. Description of the Related Art Planar antennas are used for moving bodies such as automobiles, aircrafts and ships because of their low air resistance, good mountability, simple structure, and inconspicuous appearance. Has been. As such a planar antenna, for example, a microstrip antenna as disclosed in JP-A-2-156708 is known.

Generally, a microstrip antenna for receiving radio waves in the microwave region has a structure as shown in FIG. 5, for example. In this antenna, a ground conductor 2 is formed on the bottom surface of a dielectric 1 such as Teflon or alumina made of a flat plate such as a disc or a square plate, and a radiation conductor 3 is formed on the top surface of the dielectric 1. The ground conductor 2 is grounded by a cable (not shown), and the radiating conductor 3 is a coaxial cable 4.

[0004]

In order to improve the directivity (antenna sensitivity) of the conventional microstrip antenna in the low elevation angle direction, the present applicant expands the ceramic dielectric in the centrifugal direction of the radiation electrode. We propose a planar antenna in which an annular leg is formed in this enlarged part. In this structure, for example, as shown in FIG. 4, the ceramic dielectric 33 between the radiation electrode 35 and the ground electrode 36 protrudes in the centrifugal direction, and the annular leg portion 330 is formed in this protruding portion.
The shield substrate 10 is fixed to the leg portions 330 b of the 30. The shield substrate 10 electromagnetically shields the amplifier 38 in the space recess 58 from the outside.

However, according to an experiment conducted by the present inventor, the shield substrate 10 is generally made of a conductive metal, and the ceramic dielectric 33 and the metal shield substrate 10 have large thermal expansion coefficients. As indicated by the arrow, it was found that cracks were generated in the ceramic dielectric 33 due to a large difference value between the expansion / contraction amount of the ceramic dielectric 33 and the expansion / contraction amount of the shield substrate 10 due to temperature change. .

Therefore, an important problem in using this type of microstrip antenna is to prevent the occurrence, breakage and destruction of the cracks as described above. This is because if cracks occur, water, air, etc. will enter from this part, disturbing the resonance frequency of the antenna and reducing the reliability of the antenna. The present invention has been made to solve such problems, and an object of the present invention is to provide a high-strength shield substrate for a flat antenna that is not easily damaged or destroyed.

Another object of the present invention is to provide a shield substrate for a flat antenna and a flat antenna, which are improved in waterproof function, electromagnetic shield function of an amplifying section, and mounting property.

[0008]

A shield substrate for a planar antenna according to the present invention for solving the above-mentioned problems is a radiation electrode,
A shield substrate used for a planar antenna incorporating a ground electrode, a ceramic dielectric, and an amplifier, which is a shield substrate having a coefficient of thermal expansion close to that of the ceramic dielectric. This shield substrate is preferably formed of a ceramic plate having a conductive film formed on its surface.

A planar antenna of the present invention for solving the above-mentioned problems is a flat plate-shaped radiating electrode, a flat central part provided in parallel with the radiating electrode, and a peripheral part of the central part in a centrifugal direction. Therefore, a ground electrode composed of an annular curved portion that is curved in the direction opposite to the radiation electrode and an extension portion that extends in the centrifugal direction from the curved portion; and a ground electrode that is sandwiched between the radiation electrode and the ground electrode and that is more centrifugal than the radiation electrode. A ceramic dielectric having annular legs that expand in a direction, an amplifier mounted in a recess formed by the central portion and the curved portion, and a shield that closes the recess to electromagnetically shield the inside of the recess from the outside. A shield substrate having a thermal expansion coefficient substantially equal to that of the ceramic dielectric is provided.

[0010]

According to the shield substrate for a planar antenna of the present invention, the ceramic dielectric and the shield substrate are made of materials having similar thermal expansion coefficients, so that the stress and strain generated due to temperature changes can be minimized. As a result, cracking, damage, and destruction of the antenna can be reliably prevented.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. An embodiment in which the present invention is applied to a communication microstrip antenna attached to a vehicle body will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic view of an antenna body, and FIG. 2 is a sectional view of a specific example thereof.

A microstrip antenna 30 according to this embodiment has a disc-shaped cover 31 made of an organic resin, and an antenna main body 32 housed in the disc-shaped cover 31 so that the antenna main body 32 can be attached to a vehicle body. The antenna body 32 includes a disk-shaped radiation electrode 35, a ground electrode 36, and a ceramic dielectric 33.
Consists of. In the antenna body 32, the radiation electrode 35 is formed on the top surface 33a of the disk-shaped ceramic dielectric 33, and the bottom electrode 33b of the ceramic dielectric 33, the concave bottom surface 33c, and the curved surface 33d, the ground electrode 36 in the space concave 58. Formed facing. The radiation electrode 35 and the ground electrode 36 are formed, for example, by applying a conductive paste or the like to predetermined positions on the surface of the ceramic dielectric 33 and baking the applied paste.

The flat plate-shaped radiation electrode 35 is formed only on the central portion of the top surface 33a of the ceramic dielectric 33 and not on the outer peripheral portion thereof. This is to improve the antenna directivity in the low elevation angle direction. The ground electrode 36 includes a flat central portion 36 a provided in parallel with the radiation electrode 35, and the central portion 3
It comprises an annular curved portion 36b curved in the direction opposite to the radiation electrode side from the outer peripheral portion of 6a in the centrifugal direction, and an extension portion 36c extending from the curved portion 36b in the centrifugal direction.

The ceramic dielectric 33 has an annular leg portion 330 which is sandwiched between the radiation electrode 35 and the ground electrode 36 and which is enlarged in the centrifugal direction from the radiation electrode 35. This enhances the antenna directivity in the low elevation direction. The amplifier 38 having an electronic circuit is arranged at the center of the space recess 58. The lead wire 40 is connected to the radiation electrode 35 and the amplifier 38. The lead wire 41 is connected to a coaxial cable that connects the electronic device in the vehicle interior to the antenna body 32.

The cover 31 has a first guide wall 31a having a size capable of accommodating the ceramic dielectric 33 and a second guide wall 31b having a size capable of accommodating the shield plate 50. Peripheral end 31d of the outer surface of the cover 31
Has a circular cross section. Shield board 50
A conductive first metal film 39 is formed on the upper surface of the. The schematic diagram shown in FIG. 1 is shown by distinguishing it so that the thickness t _{1 of} the first metal film 39 and the thickness t ₀ of the shield substrate 50 can be understood, but the thickness of the first metal film 39 is actually shown. it is a large thickness of the thickness t ₀ of the shield board 50 than t ₁ (t ₁
<< t ₀ ).

According to this embodiment, the ceramic dielectric 33
Since the shield substrate 50 and the shield substrate 50 are closely fixed to each other via the ground conductor 36 and the first metal film 39, the space recess 58 is formed.
Since the electromagnetic shield inside is completely completed and the difference in the coefficient of thermal expansion between the ceramic dielectric 33 and the shield substrate 50 is almost the same, the occurrence of overstress due to thermal expansion is prevented, so that cracking or breakage is prevented. To be done.

When assembling the antenna body 32 to the cover 31, first, the antenna body 32 is inserted into the first guide wall 31a via the O-ring 44, and then the shield plate 50 is attached via the O-ring 45. It is inserted into the second guide wall 31b, and then the shield plate 50 is fastened to the thick portion 31c of the cover 31 with the screws 48, 48. This allows the ceramic dielectric 33 and the shield plate 50 to cover the cover 31.
Fixed to. When the microstrip antenna 30 is attached to the body of a vehicle or the like, the arm 54 fixed to the shield plate 50 is tightened at a predetermined position with a screw or the like.

According to the microstrip antenna 30 of this embodiment, since the thickness of the ceramic dielectric 33 is relatively large, the antenna bandwidth becomes wide and the sensitivity at low elevation angle becomes good. Further, the antenna shape is relatively thin and has little air resistance. Furthermore, the cover 31
Since the peripheral end portion 31d of the is formed to have an arcuate cross section, after the antenna is mounted on the body of a vehicle or the like, the cover 31 is externally attached.
It is difficult to remove, and it also helps prevent theft.

The reception characteristic of the microstrip antenna 30 is shown in FIG. As shown by the solid line B in FIG. 3, the received signal strength is represented. In the conventional microstrip antenna, as shown by the dotted line C in FIG. 3, the sensitivity in the low elevation angle direction is particularly poor, and it is almost impossible to capture the radio waves of the artificial satellite at an elevation angle of 15 °, for example. On the other hand, according to the microstrip antenna 30 of the present embodiment, it can be understood that the sensitivity is excellent in the range of the low elevation angle direction and the range of the negative elevation angle direction as shown by the solid line B.

[0020]

According to the shield substrate for a planar antenna of the present invention, since the ceramic dielectric material forming the antenna and the shield substrate are made of materials having a coefficient of thermal expansion similar to each other, when the ambient temperature changes. The stress strain that occurs is minimized, and cracks and breakage are prevented. Therefore, invasion of water or the like is prevented, and the reliability of the antenna is significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a planar antenna of the present invention.

FIG. 2 is a cross-sectional view showing a specific example of the present invention.

FIG. 3 is a characteristic diagram showing a relationship of directivity of a microstrip antenna between an example of the present invention and a conventional comparative example.

FIG. 4 is a schematic view showing a microstrip antenna of a comparative example.

FIG. 5 is a schematic diagram showing a basic structure of a conventional microstrip antenna.

[Explanation of symbols]

 31 cover 32 antenna body 33 ceramic dielectric 35 radiation electrode 36 ground electrode 36a central part 36b curved part 36c extension part 38 amplifier 39 first metal film 48 screw (fastening means) 50 shield substrate 52 second metal film 58 space recess (Concave) 330 Ring leg

Claims (3)

[Claims] 1. A shield substrate used for a planar antenna incorporating a radiation electrode, a ground electrode, a ceramic dielectric and an amplifier, the shield substrate having a coefficient of thermal expansion close to that of the ceramic dielectric. A shield substrate for a flat antenna, which is characterized in that 2. The shield substrate for a planar antenna according to claim 1, wherein the shield substrate is a ceramic substrate having a conductive film formed on a surface thereof. 3. A flat plate-shaped radiation electrode, a flat center portion provided in parallel with the radiation electrode, and an annular shape curved toward the side opposite to the radiation electrode in a centrifugal direction from an outer peripheral portion of the center portion. A ceramic dielectric having a curved portion and a ground electrode formed of an extension portion extending from the curved portion in a centrifugal direction, and an annular leg portion held between the radiation electrode and the ground electrode and extending in the centrifugal direction more than the radiation electrode. A body, an amplifier attached to a concave portion formed by the central portion and the curved portion, and a shield substrate for closing the concave portion so as to electromagnetically shield the inside of the concave portion from the outside world, the thermal expansion of the ceramic dielectric body A planar antenna comprising a shield substrate having a coefficient of thermal expansion substantially equal to the coefficient.