JPS5921202B2 - Linear antenna device for circularly polarized waves - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a linear beam antenna with good circular polarization characteristics in the main beam direction.

Conventionally, among linear antennas, helical antennas, spiral antennas, cross dipole antennas, and the like are well known as typical beam antennas having circular polarization characteristics.

In particular, helical antennas have relatively high gain,
VHF as an antenna with good circular polarization characteristics.
It is widely used in the UHF band, both as a single antenna and as an element antenna in an array antenna.

However, if this antenna is also ideally fed and only a complete traveling wave current is induced on the antenna element, the radiation characteristic will be a complete circular polarization in the main beam direction (i.e. elliptical polarization - elliptical polarization). Long axis component of / Short axis component of elliptically polarized wave -
1) However, in reality, the antenna length is finite, there is a reflected wave from the end point, and the discontinuous structure of the feeding part also induces a current of the reflected wave component on the antenna element. be done.

Therefore, the electromagnetic waves generated by this current are reflected by a reflector (generally, a helical antenna is equipped with a reflector and is fed unbalanced power), and is radiated as a counter-rotating circularly polarized wave component superimposed on a normal-rotating component.

Therefore, the radiation characteristic in the main beam direction becomes elliptical polarization, and the elliptical polarization index usually takes a value larger than 1.

In this case, the structure of the feeding section has a large influence on the circular polarization characteristics, which is one problem when actually manufacturing this antenna.

Also, in the case of an array antenna that uses this antenna as an element antenna, the gain can be controlled by the number of antenna elements, element spacing, etc., but the elliptical polarization coefficient is determined by that of the element antenna. Improving the axial ratio of the array antenna ultimately results in improving the elliptical polarization factor of the element antenna.

Therefore, Kokichi provides an antenna with good circular polarization characteristics in the main beam direction by canceling the anti-rotation component that occurs due to the influence of the antenna structure etc. This case is also desired as a circularly polarized antenna.

The present invention has been made based on the above points of view, and the following is an axial mode helical antenna (helical 3λ 4
λ The diameter DH of the virtual cylinder will be explained in detail by taking -<DH<-5) as 4π as an example.

In general, the means to improve the circular polarization factor of a helical antenna are as follows: (1) Reflected wave component (It) generated at the antenna end point
It is necessary to suppress components generated due to the discontinuous structure of the power feeding section.

Regarding (I), it is known that as the number of helical turns increases, the elliptical polarization becomes better (Edwar
d, F. Harris.

Hel 1cal Antennas-antenna
engineeringhandbook, Ch.
apter 7. Mac GrawHill, 19
61), no specific method has been reported for (II) yet).

The present invention attempts to improve the elliptical polarization by mainly suppressing the (n) component, and two examples thereof are shown in FIGS. 1 and 2.

In FIG. 1, the diameter of the outside of the helical antenna 1 is approximately 1.
A metal cylinder 2 having a width of 4 to 1.7λ and a width of approximately 0.5 to 1.2λ is similarly arranged so as to have the same center axis as the helical antenna 1 and to be in close contact with a reflector plate 3. There is a diameter of approximately 1 on the outside of helical antenna 1 in Figure 2.
．． A metal ring 12 with a diameter of 4 to 1.7 λ is placed on the same center axis as the helical antenna 1 and approximately 0.5 to 1.
They are placed 2λ apart.

Note that 4 is a power supply cable, and 5 is a matching box.

In both, the metal cylinder 2 or the metal ring 12 is
Since they are arranged in a symmetrical structure with respect to the central axis of the helical antenna, discontinuities occur due to the action of the current on the metal cylinder or ring induced by the mutual coupling between this and the discontinuously structured feeding part. The continuous structure suppresses the components generated and operates as if it were close to an ideal power supply structure.

As a result, it has the effect of improving the elliptical polarization in the main beam direction.

FIGS. 3 and 4 show examples of experimental results showing the effect of improving the elliptical polarization index for the embodiment shown in FIG. 1.

The helical antenna used here has a helical diameter DH of λ/π, a number of turns of 20 turns, a pitch of 14 degrees, and a central feeding type, but the dimensions and shape of the antenna are based on the effects of the present invention. was found to have little effect on

FIG. 3 shows the change in the elliptic polarization index with respect to the change in the width of the metal cylinder when the diameter of the metal cylinder is selected to be 1.6λ.

Next, Figure 4 shows the elliptical shape of the metal cylinder with respect to the change in diameter, for the case of the cylinder width (L = 1.Oλ) where the elliptical polarization coefficient is improved the most, based on the results shown in Figure 3. This shows the polarization rate.

′°゛°″”°°゛”“〜afflicted.

According to the experimental results here, when L=o, 5~, the ellipse is 0.2
dB or less, and it can be seen that the elliptical polarization coefficient is improved by about 0.4 dB compared to about 0.6 dB in the case of only a helical antenna.

Note that, in this case, no decrease in gain occurred at all.

Furthermore, similar effects were obtained in the case of the metal ring shown in FIG.

It is clear that metal cylinders and metal rings are effective in improving the elliptical polarization of helical antennas.
Similar effects can be expected not only for helical antennas but also for other circularly polarized linear antennas such as crossed dipole arrays.

Although FIG. 1 shows an example in which the metal cylinder 2 is in contact with the reflector plate 3, the width of the cylinder is reduced while the front edge of the cylinder 2 is held in the same position, and the rear edge of the cylinder 2 is The same effect as described above can be expected even if the reflective plate 3 is made not to contact the reflecting plate 3 and a space is left between the two.

As described above, the antenna device of the present invention is a linear antenna to which a metal cylinder and a metal ring are added, which has the effect of improving the elliptically polarized wave ratio. It is promising as an element antenna for array antennas.

For example, it is expected to be used as antennas for maritime sanitary and aviation satellite communications where the effects of multiple reflections are a problem.

[Brief Description of the Drawings] Figures 1 and 2 are diagrams showing embodiments of the present invention, respectively.
is a side view, and B is a plan view. 3 and 4 are graphs showing the elliptical polarization characteristics of the antenna device of the present invention. DESCRIPTION OF SYMBOLS 1... Helical antenna, 2... Metal cylinder, 3... Reflection plate, 12... Metal ring.

Claims (1)

[Claims] 1. A metal cylinder or a metal ring having a common center axis is placed on the outside of the linear antenna for circularly polarized waves, and a reflector is placed on the feeding end side of the linear antenna for circularly polarized waves. Or the diameter of the metal ring is 1.4 to 1.7 of the wavelength used.
By selecting the distance between the front edge of the metal cylinder or the metal ring and the reflector to be 0.5 to 1.2 times the wavelength used, the radiation characteristics of the antenna are elliptically polarized in the main beam direction. A linear antenna device for circularly polarized waves, which is characterized by improved efficiency.