JPH0363241B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a circular microstrip structure in which a radiating element and a power feeding strip line are formed by a conductor film provided on a dielectric substrate. Regarding polarized antennas.

[Technical background of the invention and its problems]

A conventional microstrip circularly polarized antenna of this type is generally constructed as shown in FIGS. 1a and 1b. That is, a radiating element 2 made of a rectangular conductive film, a 90° hybrid coupler 4, and two strip lines 5 and 6 are formed on a dielectric substrate 1, and one terminal of the 90° hybrid coupler 4 has a A non-reflection terminator 8 is installed, and the output side of the 90° hybrid coupler 4 and the strip line 5,
A matching circuit 9 is inserted between 6 and 6. In addition,
A ground conductor film 7 is formed on the back surface of the dielectric substrate 1 .

In this antenna, when a signal is input from the feed end 3, two outputs from the 90° hybrid coupler 4 with equal amplitude and a phase shift of 90° are supplied via the matching circuit 9 to the strip lines 5 and 6. Since the strip lines 5 and 6 are connected to the center of adjacent sides of the radiating element 2, the current excited by the strip line 5 and the current excited by the strip line 6 are orthogonal to each other on the radiating element 2. As a result, circularly polarized waves are excited on the radiating element 2.

However, in such a circularly polarized antenna, in addition to the radiating element 2 and the strip lines 5 and 6, a 90° hybrid coupler 4, a non-reflection terminator 8,
A matching circuit 9 or the like is required, and the area required for one element becomes large. As a result, not only does the cost increase, but the loss also increases, making it difficult to obtain good characteristics. Furthermore, when constructing an array antenna, there were also manufacturing difficulties, such as the design position of the radiating element being subject to significant restrictions.

[Purpose of the invention]

An object of the present invention is to provide a microstrip circularly polarized antenna that is small, inexpensive, has good characteristics, and is suitable for array formation.

[Summary of the invention]

In the present invention, two strip lines are branched so that a current with a phase difference of 90 degrees flows from the feed end through a T-branch, and these strip lines are formed close to two opposing sides of a radiating element. If the wavelength considering the dielectric constant is λg, then the terminal ends of these strip lines should be opened with a length difference of λg/4, or
Alternatively, circularly polarized waves can be emitted by short-circuiting one end.

〔Effect of the invention〕

In the microstrip circularly polarized antenna according to the present invention, the elements provided on the dielectric substrate basically only need to be a radiating element, a strip line, and a simple T-branch, and there is no need for a non-reflective terminator, so it is small and It will be cheaper. Further, electrical loss is reduced accordingly, and characteristics can be improved.
Furthermore, since the improvement in the space factor reduces restrictions on the position of the radiating elements, it is advantageous in manufacturing when realizing an array antenna.

[Embodiments of the invention]

FIG. 2 shows an embodiment of the present invention, in which a radiating element 1 made of a rectangular conductive film is placed on a dielectric substrate 11.
2 and T branch 14 and microstrip line 1
5 and 16 are formed by adhesion. 13 is a power feeding end. Further, a ground conductor film 17 is formed on the back surface of the dielectric substrate 11 .

The strip lines 15 and 16 are formed close to opposite sides of the radiating element 12 and are distributed coupled to the radiating element 12. Here, the strip line 15,1
6 is connected to the dielectric substrate 11 at the operating frequency.
When λg is the wavelength in consideration of the dielectric constant of , that is, the wavelength in consideration of the wavelength shortening rate given by the dielectric constant, the opening is shifted by a length of λg/4. Also, the T branch 14 of the strip lines 15 and 16
The length from the line 1 to the radiating element 12 is determined by considering the dielectric constant of the dielectric substrate 11.
The phase difference between the currents flowing through the currents 5 and 16 is 90°. Further, the shape of the radiating element 12 is a square with a side length of λg/2.

The operation of this circularly polarized antenna will be explained. An input signal input from the feed end 13 is distributed by a T branch 14 to strip lines 15 and 16 with equal amplitude and in phase. Here, on the strip line 15 side,
If the interval between the radiating element 12 and the strip line 15 and the width of the strip line 15 are selected so that the impedance seen from point F on the radiating element 12 side matches the impedance seen on the T-branch 14 side, the strip line 15 The coupling between the strip line 15 and the radiating element 12 becomes inductive coupling,
The current is maximum at the center A of the connecting portion with 2. At this time, as shown in _FIG . Occurs between.

On the other hand, on the strip line 16 side, the strip line 16 is open at a point extended by λg/4 in the direction away from the radiating element 12 from point G corresponding to the open end of the strip line 15, so the open end of the strip line 15 is The current reaches its maximum at point G corresponding to . Therefore, the voltage is maximum at the center B of the portion of the strip line 16 that is coupled to the radiating element 12. At this time, since the coupling between the strip line 16 and the radiating element 12 becomes capacitive coupling, a current _I2 in a direction perpendicular to the strip line 16 is excited on the radiating element 12, as shown in FIG. 3b, and the electric field is radiated. This occurs between the side of the element 12 parallel to the strip line 16 and the ground conductor film 17. This electric field is applied to the strip line 1 by a distance corresponding to a phase of 90° from the T branch 14 of the strip line 16.
5, so its phase is shown in Figure 2 a.
It lags behind the electric field by 90°. In this way, the directions of the currents excited on the radiating element 12 by the strip lines 15 and 16 are perpendicular to each other, the amplitudes are equal, and the phases are shifted by 90 degrees, so that circularly polarized waves are radiated from the radiating element 12. will be done.

The present invention can be implemented with various modifications. For example, instead of providing a length difference of λg/4 between the strip lines 15 and 16, both lines may be made the same length, and the terminal end of one line may be short-circuited. Similar results are obtained.

Further, when the present invention is applied to an array antenna, for example, a radiating element may be arranged between two strip lines at an interval of λg of the dielectric substrate. Of course, three or more strip lines may be arranged in parallel and the radiating element may be arranged between them.

[Brief explanation of drawings]

Figures 1a and b are a plan view and a cross-sectional view taken along the line X-X' of a conventional microstrip circularly polarized antenna;
Figures 2a and 2b are a plan view and an X-
The X' arrow sectional view and FIGS. 3a and 3b are diagrams showing the current direction on the radiating element corresponding to each strip line for explaining the operation of the same embodiment. 11... Dielectric substrate, 12... Radiation element, 13
...Feeding end, 14...T branch, 15... Strip line, 16... Strip line, 17... Ground conductor film.

Claims (1)

[Claims] 1. A radiating element made of a rectangular conductive film is formed on a dielectric substrate, and two strip lines branched so that a current with a phase difference of 90° flows from the feeding end via a T-branch are connected to the radiating element. They are formed close to two opposing sides of the element and distributed coupled to the radiating element, and the ends of these strip lines have a length of λg/4, where λg is the wavelength considering the dielectric constant of the dielectric substrate. A microstrip circularly polarized antenna characterized by being either open with a difference or short-circuited at one end.