JPH0328841B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a radio wave lens called an R-kR type.

[Technical background of the invention and its problems]

A multi-beam antenna with receiving beams arranged in all directions is used in a detection device that can always know the direction, frequency, etc. of incoming radio waves. Several multi-beam antennas suitable for such purposes have been proposed in the past, and among them is an antenna using a radio wave lens called an R-kR lens shown in FIG.

This has the advantage that the structure is simpler than the Butler matrix multi-beam antenna because the lens can be constructed from a printed board. Furthermore, although multi-beam antennas using R-kR lenses and Rottmann lenses have the advantage of being able to construct the feeding system using a printed circuit board, they are not omnidirectional and must be made omnidirectional by combining multiple antennas. Nakatsuta. In this way R-
Antenna using kR lens is said to be optimal as an omnidirectional multi-beam antenna.

Here, the operation of the R-kR lens will be explained using FIG.

In FIG. 2, it is assumed that radio waves arrive from direction 1. This radio wave is transmitted to antenna elements 21, 22, 2
3, 24, and 25, and are guided to the lens 5 through circulators 31, 32, 33, 34, and 35, respectively. Here, if l ₂ + l ₃ + l ₅ is equal for all antenna elements, the radio wave guided to the lens 5 is focused on the terminal 50 of the circulator 30, passes through the circulator 30, and is guided to the receiver 40. It will be destroyed. In this way, the radio waves incident from one direction are received by the receiver 40. Furthermore, as is clear from FIG. 2, this antenna has an axially symmetrical structure and can form multiple beams as many as the number of receivers over the entire circumference. l ₂
Although it is not possible to make all +l ₃ +l ₅ strictly equal, let the relative permittivity of the dielectric material forming the lens 5 be ε, the diameter of the lens 5 be d, and the diameter of the antenna array be D.
When √d/D≒2, it is known that l ₂ +l ₃ +l ₅ is practically constant.

As explained above, the R-kR lens is an antenna that can form multi-beams in all directions, but it has the disadvantage that the back lobe tends to be high. The reason for this is that the radio waves incident from direction 11 in FIG. 2 are received by the antenna 20, pass through the circulator 30,
This is because if there is misalignment at the terminal 50 when the wave is propagated from the wave to the lens 5, the reflected wave will be received by the receiver 40 via the circulator 30. That is,
Receiving paulownia 4 that receives only the radio waves that originally entered from 1
0 will receive the radio waves incident from the rear 11, and the back lobe will become higher. This drawback can be eliminated by reducing the mismatch at the terminal 50. For this reason, when the lens 5 is constructed of a printed board as shown in FIG. 1, the lens 5 and the circulator are connected by a triangular matching part to avoid mismatching as much as possible. However, inconsistency is still unavoidable, and according to experiments, it is the worst.
A reflection of about 10 dB has been observed.

[Purpose of the invention]

The present invention has been made in view of the above drawbacks, and
An object of the present invention is to provide an antenna that does not cause reflection due to mismatch.

[Summary of the invention]

The present invention focuses on the fact that the lens 5 has a relatively inexpensive printed board structure, and uses two lenses to eliminate the reflection caused by the misalignment.

[Embodiments of the invention]

FIG. 3 shows an example of the configuration of the present invention. However, some of the connections between the antenna array, the lens, and the antenna element are shown, and the others are omitted. As shown in the figure, the input radio waves from the antenna element 21 are transmitted to the circulator 3.
1 and is divided into two by a 3 dB coupler 61. 2
The separated radio waves pass through lenses 51 and 52, and are added together by a 3dB coupler 60 and sent to a receiver 40.
received by. In other words, the configuration of the present invention has a structure in which the conventional lens is made into two lenses, each of which is fed and coupled by a 3 dB coupler, and electrically has an axially symmetrical structure similar to the conventional example. Therefore, multi-beams can be constructed in all directions. An example of the conditions for this antenna system to have the desired characteristics is √ ₁ d ₁ +√ ₂ d ₂ ≒4D …() ｜√ ₁ d ₁ −√ ₂ d ₂ ｜≒λ/2 …() 3dB The coupler is a 90° coupler...() The electrical lengths of the lines from the coupler output end to the lens are all equal...().

ε ₁ , ε ₂ : Relative permittivity, λ: Usage wavelength d ₁ , d ₂ : Lens diameter.

The operation of this embodiment of the invention will be described with reference to FIG. FIG. 4 shows the main parts extracted from FIG. 3 in a simplified manner.

Radio waves incident from the antenna element 21 pass through the circulator 31 and are divided into two by the 3 dB coupler 61. It is assumed that the phase of the radio wave incident on the lens 51 is delayed by 90° from the phase of the radio wave incident on the lens 52 at the output of the lens 61 (condition). While the divided radio waves pass through lenses 51 and 52, the phase difference differs depending on the condition (), and at the output ends 501 and 502 of the lenses, the output of 501 has a phase lead of 90° compared to the output of 502. . Therefore, when the outputs of 501 and 502 are added together by the 3 dB coupler 60, the output appears toward the circulator 30 and does not appear at the terminal of the non-reflection termination 70. Therefore, the receiver 4 is transmitted through the circulator 30 without loss.
It will lead you to 0. On the other hand, antenna element 20
The radio waves incident from the terminals 501 and 502 of the lens
It is reflected at the output end of 3dB coupler 60 and 50
Since the electrical lengths up to 1,502 are equal (condition), the reflected wave appears at the non-reflection terminal 70 and is transmitted to the receiver 40.
It does not appear in

From the above explanation, it was found that it is possible to improve the antenna using the R-kR lens, which conventionally had a high cross-lobe, and to lower the cross-lobe.
If this continues, it will not be possible to form a sharp beam forward. In order to form a sharp forward beam, l ₂ +l ₃ +l ₅ had to be approximately constant for the front antenna element group in FIG. He said that for that purpose, it is necessary to have √d2D.
Consider how this relationship is modified in the configuration of FIG. 3 according to the present invention.

In FIG. 2, l ₃ is constant for all elements, so l ₂ +l ₅ should be constant. This thing is This means that the phase term of is constant. If θ is smaller than this, √d2D is obtained. If we apply the same idea to Figure 4, It is sufficient if the phase term of is kept constant. Therefore, if we set √ ₁ d ₁ +√ ₂ d ₂ = 2d′ and transform equation (1) by setting √ ₂ d ₂ −√ ₁ d ₁ = λ/2 (by condition), we get e ^jkD/2cos 〓・e ^-jkd ′ ^cos 〓 ・2cos(kλ/4cosθ). Since it is sufficient to keep the phase term in the above equation constant, the condition is obtained as d′2D, that is, √ ₁ d ₁ +√ ₂ d ₂ = 4D. In this way, the conditions are such that a sharp beam is formed in the front.

As mentioned above, if the antenna with the configuration shown in Figure 3 satisfies the conditions (), (), and (), a low-wavelength omnidirectional multi-beam antenna, which cannot be obtained with the conventional type shown in Figure 2, can be obtained. It will be done.

In the above embodiment, an example was explained in which a 90° coupler was used as the 3 dB coupler, but the same effect can be obtained by using a 180° coupler as shown in FIG. In this case, the electrical length between the coupler output end and the lens terminal must have a difference of 1/4 of the wavelength used.
Further, only the condition √ ₁ d ₁ +√ ₂ d ₂ 4D is required between the diameters d ₁ and d ₂ of the lenses 51 and 52.

〔Effect of the invention〕

According to the present invention, an omnidirectional multi-beam antenna with a low backlobe can be obtained.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of an omnidirectional multi-beam antenna using a conventional printed board type R-kR lens.
Figure 2 is a diagram for explaining the operation of the R-kR lens. Figure 3 is a diagram showing an example of the configuration of the present invention. Figure 4 is a diagram for explaining the operation of the present invention. Figure 5 is a diagram for explaining the operation of the present invention. It is a figure which shows another Example. 20, 21... antenna element, 30, 31...
Circulator, 40... Receiver, 51, 52...
...Lens, 60,61...3dB coupler, 70,7
1...Reflection-free termination.

Claims (1)

[Claims] 1. A circular antenna array with a diameter D, a circulator connected to antenna elements constituting this antenna array, a receiver connected to this circulator, and a receiver connected to the circulator.
3 dB coupler and a first R- of dielectric constant ε ₁ and diameter d ₁
kR lens and a second R- lens with dielectric constant ε ₂ and diameter d ₂
kR lens, and between one of the output ends of the 3dB coupler and the terminal of the first R-kR lens and the
If the coupler is a 90° coupler, use a line of equal length between the other output end of the 3dB coupler and the terminal of the second R-kR lens, and if the coupler is a 180° coupler, use a line of equal length to connect the terminal of the second R-kR lens. A non-reflective termination is connected to the terminal separated from the input end of the 3 dB coupler, and the constant of the lens is selected to have a dimension of √ ₁ d ₁ +√ ₂ d ₂ 4D, and When the coupler is a 90° coupler, an R-kR lens is used whose dimensions are selected such that |√ ₁ d ₁ −√ ₂ d ₂ | is approximately an odd multiple of half the wavelength used. antenna.