JPH02219304A - Plane antenna - Google Patents

Abstract

PURPOSE:To thin the thickness of a film, to reduce dielectric loss, and to improve efficiency by selecting the film with superior mechanical or physical characteristic as the film made of synthetic resin. CONSTITUTION:The film 4 made of synthetic resin is provided with the thickness 4-20mum, tensile elastic modulus >=200kg/mm<2>, beading elastic modulus >=300kg/mm<2> in a plane antenna, and also, it is stuck directly on a conductor foil for pattern circuit without using an adhesive. Also, a rate of change of dimension after applying an etching treatment is set less than 0.2%. And a substrate for flexible print circuit in which a metallic conductor foil represented by copper or aluminum and the film 4 are stuck with each other is generated, and the metallic conductor foil on an unrequired part is eliminated by protecting a circuit pattern part by a method such as a screen print method, etc., and applying etching. At such a case, the thickness of the film can be reduced by selecting the film with superior mechanical or physical characteristic, and also, the dielectric loss can be reduced since the substrate for circuit includes no adhesive.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a highly efficient planar antenna composed of a patterned circuit formed using a laminate of a synthetic resin film and a conductor foil. be.

[Conventional technology]

Planar antennas in the microwave range used for satellite broadcasting, satellite communications, etc. have recently been designed to feed power on dielectric films made from synthetic resins, from the viewpoints of freedom of processing fine patterns, light weight, and cost. Types in which pattern circuits are formed in the part and radiation part are being actively developed.

Figure 2 shows a typical configuration of this type of antenna.The feeder circuit pattern shown in Figure 3 is shown as an example on one side of each of the synthetic resin films (4) and (5). (1), a radiating circuit pattern (2) is formed, a support (6) is arranged to maintain a space between the two circuit patterns (1) and (2), and a support (7) is arranged. A ground conductor (3) is located at a position facing the power supply circuit pattern (1) through the
is located. These supports (6) and (7) are
A synthetic resin film (4) that usually holds a circuit pattern;
(5) may be an insulating spacer inserted at an optimal location where spatial flatness can be maintained, or a sheet with a low dielectric constant such as a foam sheet may be used. Generally, the basic structure shown in Part 2 is called the suspended triplate system.

It is a well-known fact that the efficiency of a planar antenna with such a structure largely depends on the transmission loss in the feeding section, and that the smaller the line loss, the smaller the loss, and the higher the efficiency of the antenna. On the other hand, if the conductive foil used for the pattern circuit is constant, the line loss of the power feeding section is mostly dominated by the dielectric loss due to the film holding the pattern circuit.

Therefore, in order to improve the efficiency of a planar antenna having such a basic structure, it is necessary to reduce the dielectric loss of the feed section as much as possible. Fig. 4 is a sectional view showing the structure of a conventional flexible printed circuit board for a planar antenna, and Fig. 5 shows a pattern of electric lines of force in the power feeding section.
The dielectric loss of the film layer is affected by the amount that the film penetrates through the holding synthetic resin film (4). In order to minimize this effect, conventional efforts have been made to use synthetic resin films with as small a dielectric constant and dielectric loss tangent as possible, or to reduce the thickness of the film as much as possible in order to eliminate the effect of the film as much as possible. Ta.

From this point of view, synthetic resin materials such as polyester, polyethylene, polypropylene, or modified or copolymers thereof (dielectric constant approximately 2.0 in the GHz band, dielectric loss 60 to 80 x 10-') have been considered as candidates. has been selected as a material.

However, at a thickness of 40 to 50 μm or more, all of these have sufficient stiffness and maintain the flatness of the film, but when the thickness is less than this, the film itself tends to lose its stiffness. Moreover, in the etching process that is commonly used when forming circuit patterns, the dimensional change of the film after processing is large and the flatness is poor.
As a result, the frequency characteristics of the antenna may deviate significantly from the design. This phenomenon becomes more noticeable when the thickness of the film is about 20 to 30 μm.

Due to these circumstances, the practical limit for the thickness of conventional films is 40 μm at most.
When the above-mentioned synthetic resin film is used, the dielectric loss of the line is as large as about 1.0 dB/m, and there is a limit to the improvement of antenna efficiency. In general, as the thickness of the film becomes thinner, the dielectric loss of the line also decreases, so the thickness of the film can be reduced to 2 without reducing the mechanical strength.
A flexible printed circuit board for a planar antenna with a thickness of 0 μm or less has been desired.

[Problem to be solved by the invention]

The present invention was invented as a result of various studies in view of the situation of conventional suspended triplate planar antennas. In contrast to the conventional method of selecting materials, the goal is to create an efficient planar antenna by using films selected from the viewpoint of mechanical strength and dimensional stability.

[Means to solve the problem]

In other words, the present invention provides a planar antenna basically consisting of a pattern circuit of a radiating part and a feeding part, which is formed by etching a conductive foil laminated to a synthetic resin film, which corresponds to at least the feeding part. The film holding the pattern circuit has a thickness of 4 to 20 μm, a tensile modulus of 200 kg/mm or more, and a flexural modulus of 300.
kg/mm 2 or more, is bonded directly to a patterned circuit conductor foil without using an adhesive, and has a dimensional change rate of 0.2% or less after etching treatment. It is.

The purpose of the present invention is to reduce dielectric loss among line losses, and by selecting a synthetic resin material for the film mainly from the viewpoint of mechanical and physical properties, compared to conventionally used films. This was done based on the knowledge that a significant reduction in dielectric loss could be achieved.

Although it is true that the film used in the present invention is a material with a low dielectric constant and low dielectric loss, it is not necessary to have properties within the range of conventional candidates, and G
In the Hz band, it is sufficient that the dielectric constant is 4 or less and the dielectric loss tangent is in the range of 50 to 200 x 10-'.In fact, in the present invention, even if the film is made thin, the film itself does not deform or sag. It is necessary to have sufficient stiffness to hold the circuit pattern formed thereon with good flatness. In order to meet this requirement, the film has an elastic modulus of 200 kg/mm or more and a flexural modulus of 3.
It is necessary that the synthetic resin material has a weight of 00 kg/mm2 or more. If the elastic modulus or flexural modulus is less than this value, the rigidity of the film itself will be significantly reduced when the thickness is 40 μm or less, resulting in spatial parallelism between the power supply circuit pattern and the ground conductor or radiation circuit pattern. This is not preferable because it not only lowers the accuracy but also significantly lowers the workability during processing and assembly for pattern formation.

Further, since the dielectric loss decreases almost in proportion to the thickness of the film, the thinner the film is in the present invention, the more preferable it is, and the more preferably 20 μm or less. However, if the film becomes too thin, it will be difficult to make the film and it will not be possible to ensure sufficient mechanical strength.
m is the lower limit. The realistic thickness of conventionally used films was about 40 μm at most, and the dielectric loss was about 1.0 dB/m at most, but when the film thickness was 20 μm or less, The dielectric loss of the feeding part of the antenna of the present invention is 0.2 to 0.4 dB.
/m, which makes it possible to achieve a significant improvement compared to the conventional one.

The circuit patterned film that makes up the planar antenna with the basic structure shown in Figure 2 is usually produced by first creating a flexible printed circuit board by gluing the film to metal conductor foil, typically copper or aluminum. After protecting the portion that will become the circuit pattern using methods such as screen printing or photosensitization, unnecessary portions of the metal conductor foil are removed by etching with a ferric chloride aqueous solution, phosphoric acid aqueous solution, etc., and the desired pattern is formed. We get a pattern of
It is important that the film used in the present invention has an extremely small dimensional change rate after etching. The deformation cannot be ignored, resulting in poor flatness, frequency characteristics, and workability, which is undesirable.

Furthermore, as shown in FIG. 1, the flexible printed circuit board used in the present invention has a dielectric layer that does not include the adhesive (8) layer, compared to the conventional board shown in FIG. Body damage can be reduced. The requirements that the synthetic resin material of the flexible printed circuit board according to the present invention should meet are as described above, and for example, linear polyimide resin via amic acid can be cited as a suitable material.

In addition, in the present invention, the metal conductor foil used for forming the circuit pattern is made by laminating a synthetic resin onto the metal conductor foil, in order to avoid the burden of load on the film as much as possible.
It goes without saying that it is desirable to select a material that is as thin as possible without interfering with workability in processes such as coating and winding.

The present invention will be specifically explained below based on examples.

(Example 1) 59.4 g of purified anhydrous bulk phenylenediamine (55% mole of amine component) was mixed with 90% by weight of anhydrous N-methyl-2-pyrrolidone and 10% by weight of toluene so that the solid content was 15% by weight. % mixed solution, then purified anhydrous 3.3', 4° was added little by little, and reacted at 20°C for 5 hours.

Furthermore, 90.0 g of purified anhydrous 44'-diaminophenyl ether (45 mol% of the amine component) and 96.1 g of purified pyromellitic anhydride dianhydride (45 mol% of the acid component)
% by mole) were added in this order with stirring, and the mixture was reacted at 20°C for 5 hours.

This polyamic acid solution was cast onto a copper foil with a thickness of 18 μm so that the solid content was 20 μm thick.
The temperature was raised from 350°C to 350°C over 2 hours.

The thus obtained flexible printed circuit board was etched with an aqueous ferric chloride solution at 40° C., and the dimensional change rate of the film after removing the copper foil was 0.18%. In addition, the tensile modulus of the film alone is 300 kg/m
m", the bending modulus is 400 kg/m+n",
The dielectric constant at 12GHz is 4.0, and the dielectric loss tangent is 170.
It was X 10-'.

On the other hand, when this flexible printed circuit board was patterned and placed on a plastic support stand with a width of 5 mm and arranged at 10 mm intervals, the flexible printed circuit could be held without losing its flatness.

Furthermore, using this flexible printed circuit board, a width of 1
．． A 5 mm straight line was formed by etching, and a copper foil
A foamed polyethylene sheet of 2mm thickness - a flexible printed circuit - a foamed polyethylene sheet of 2+++n+ thickness - copper foil were laminated in this order, and the dielectric loss of the line was measured using a suspended triplate system with a characteristic impedance of 100Ω. Its value was 0.46 dB/m.

Next, a flexible printed circuit for radiation and a flexible printed circuit for power feeding were fabricated by etching using the flexible printed circuit board of this example, and laminated in this order on the grounding conductor plate with an interval of 2 mm between each. held. The aperture efficiency of the planar antenna thus obtained was 61%.

(Example 2) A flexible printed circuit board having a film thickness of 8 μm was obtained in the same manner as in Example 1. After etching, the dimensional change rate of the film was 0.2%, the tensile modulus of the film alone was 350 kg/mm2, and the bending modulus was 4.
00kg/mm2. Moreover, even when the flexible printed circuit patterned by etching was placed on the plastic support base of Example 1, the flatness could be maintained without almost losing its flatness.

The dielectric constant and dielectric loss of the film are 4.0.170 respectively.
There was no difference between X 10-' and Example 1. In addition, the dielectric loss of the line measured using the same method as in Example 1 was 0.30d.
B/m, and the antenna aperture efficiency was 63%.

(Example 3) Purified anhydrous 4,4'-diaminophenyl ether and purified anhydrous pyromellitic dianhydride were mixed at a ratio of 1:0.975 mol, and heated at 20°C. The mixture was reacted with stirring for 5 hours.

Using this polyamic acid solution, a flexible printed circuit board was obtained in exactly the same manner as in Example 1. After etching, the dimensional change rate of the film was 0.17%, and the tensile modulus of the film was 320 kg/mm2.
The flexural modulus was 420 kg/mm''.Furthermore, even when the flexible printed circuit patterned by etching was placed on the plastic support base of Example 1, it could be held without losing its flatness.

The dielectric constant of the film is 3.8, and the dielectric loss tangent is 200 x 10-
It was 4. Further, the dielectric loss of the line measured by the same method as in Example 1 was 0.556 B/m, and the aperture efficiency as an antenna was 60%.

(Comparative Example 1) In the same manner as in Example 1, a flexible printed circuit board having a film thickness of 30 μm was obtained. The dimensional change rate of the film after etching was 0.16%, the tensile modulus of the film alone was 300 kg/mm2, and the bending modulus was 400 kg/mm2.

Further, even when the flexible printed circuit patterned by etching was placed on the support base of Example 1, it could be held without losing its flatness at all and was strong.

On the other hand, the dielectric constant of the film is 3.5, and the dielectric loss tangent is 180X.
Although values equivalent to 10-4 and Examples 1 and 2 were obtained, the dielectric loss of the line was large at 0.75 dB/m, and the aperture efficiency of the antenna was also small at 55%.

(Comparative Example 2) Tensile modulus: 350 kg/mm", bending modulus: 40
A polyester adhesive containing polyester urethane and ethylene glycol terephthalate base was applied to a thickness of 3 μm on a 20 μm thick polyethylene terephthalate film of 0 kg/mm”, and a copper foil was attached.This flexible printing After etching the circuit board,
The dimensional change rate of the film was 1.0%, the appearance was noticeably wrinkled, and the film was weak. Furthermore, even if a flexible printed circuit patterned by etching was placed on the same stand as in Example 1, the film would sag between the frames and could not maintain its planar shape. It was completely unsuitable as a substrate.

(Comparative Example 3) A flexible printed circuit board was obtained in the same manner as in Comparative Example 2 using a polyethylene terephthalate sheet having a thickness of 40 μm. The dimensional change rate of the film after etching was 0.4%, and there were some wrinkles in appearance.

When the flexible printed circuit patterned by etching was placed on the stand of Example 1, it maintained its shape and retained its handleability. However, the dielectric constant of the film is 3°0
, the dielectric loss tangent was relatively small at 50 x 10-', but the dielectric loss of the line measured using the same method as in Example 1 was 1.1 d.
B/m was large, and the aperture efficiency was small at 53%.

(Effects of the Invention) According to the present invention, the thickness of the film can be made extremely thin by selecting a film with excellent mechanical or physical properties, and the electrical properties can be reduced compared to conventional ones. Even if the film itself is not necessarily superior, it is possible to realize a planar antenna with low dielectric loss and high efficiency.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a flexible printed circuit board for a planar antenna according to the present invention, Fig. 2 is a diagram showing a typical configuration of a planar antenna, and Fig. 3 is a diagram of a pattern of a flexible printed circuit for a planar antenna. In the figure showing an example, (a) is a radiation circuit pattern, (bl is a feeding circuit pattern). Fig. 4 is a cross-sectional view of a flexible printed circuit board for a conventional planar antenna, and Fig. 5 is a sectional view of a conventional flexible printed circuit board. FIG. 3 is a diagram showing the distribution of electric lines of force in a power feeding section of a flexible printed circuit board for a planar antenna.

Claims (1)

[Claims] (1) In a planar antenna that basically consists of a pattern circuit of a radiation part and a power feeding part, which is formed by etching a conductive foil laminated to a synthetic resin film, the pattern circuit corresponds to at least the power feeding part. The film has a thickness of 4 to 20 μm and a tensile modulus of 20
0kg/mm^2 or more, bending elastic modulus 300kg/mm^
2 or more, the antenna is bonded directly to a conductor foil for a patterned circuit without using an adhesive, and has a dimensional change rate of 0.2% or less after etching treatment.