JPH0476242B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a Rotman lens used as a phase shift element of an array antenna.

[Prior art]

FIG. 1 shows an external view of a conventional lens of this type. In FIG. 1, 1 is an insulating substrate, and 2 is a parallel flat plate portion printed on the insulating substrate 1, which is formed by a circular arc 3 and a lens curve 4. In FIG. 5(1) to 5(n) are beam terminals which are 50Ω lines, and these are connected to the parallel plate part 2 via tapered lines 6(1) to 6(n), respectively, and 7(1) to 7(n) is
These antenna terminals are 50Ω lines, and these are also connected to the parallel plate part 2 via tapered lines 8(1) to 8(n), respectively, and the tapered lines 8(1) to 8
Extension lines 9(1) to 9(n) at the center of (n) are concentrated at one point on the circular arc 3.

Next, the operation will be explained. A Rotman lens as a phase shift element of an array antenna adjusts the phase difference between each antenna terminal 7(1) to 7(n) corresponding to the required beam scanning angle θi by selecting a certain beam terminal 5(i). The shapes of the circular arc 3 and the lens curve 4 are determined so that . Assuming that the parallel plate portion 2 is a two-dimensional free space and the tapered lines 6(1) to (6)(n) and 8(1) to 8(n) are two-dimensional horn antennas, the beam terminal 5( The propagation loss between each terminal between i) and the antenna terminal 7(i) can be mainly divided into two factors: loss in the parallel plate portion 2 and gain due to the tapered lines 6 and 8. The loss in is the span loss, which is the propagation loss in two-dimensional free space, and the gain due to the tapered lines 6 and 8 is 2
It can be thought of as the antenna gain of a dimensional horn antenna.

In the lens shown in Fig. 1, when a large beam scanning angle θ is selected, for example, when beam terminal 5(1) is selected, this beam terminal and each antenna terminal 7(1) to
The trend of loss characteristics between (7) and (n) is roughly as shown in Figure 2. In the figure, fH is a high frequency and fL is a low frequency.

In this way, the loss characteristics of the beam terminal 5(1)
and antenna terminal 7(n), but this is because the propagation distance in parallel plate portion 2 is the longest, and 2
This is because the span loss in the dimensional free space becomes large.

Conventional Rottmann lenses are configured as described above, so when a beam terminal corresponding to a large scanning angle is selected, the difference in loss between the beam terminal and each antenna terminal is large, and there are problems such as asymmetry. There were flaws.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by directing each tapered line on the antenna terminal side not to a single point on the arc but to the vicinity of the center of the parallel plate part, the beam It is an object of the present invention to provide a Rotman lens that can reduce the asymmetry of loss between the terminal and each antenna terminal and reduce the difference in loss.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 shows a Rotman lens according to an embodiment of the present invention, and FIG. 4 shows losses between the beam terminal and each antenna terminal. In FIG. 3, the same symbols as in FIG. 1 indicate the same or corresponding parts, and the tapered line 8(1)
The central extension lines 10(1) to 10(n) of 8(n) are directed toward the center of the parallel plate portion 2.

The loss between each terminal of the Rottmann lens is the span loss of the secondary free space within the parallel plate portion 2 and the two-dimensional horn antenna due to the tapered lines 6(1) to 6(n) and 8(1) to 8(n). It is expressed by the gain of . In this embodiment, the tapered line 8(1) on the side of antenna terminals 7(1) to 7(n)
Since the direction of ~8(n) is directed toward the center of the parallel plate portion 2, there is a For a combination of both terminals that has a long two-dimensional free space length, that is, a large span loss, both two-dimensional horns are more likely to face each other, and the loss between them is corrected to be small. That is, for example, for the combination of the beam terminal 5(1) and the antenna terminal 7(n), the propagation distance in the parallel plate portion 2 is long, so the span loss in the two-dimensional free space becomes large, but in this embodiment, Since the tapered lines 6(1) and 8(n), which are two-dimensional horn antennas, face each other at an angle close to the front direction, the antenna gain of these two two-dimensional horn antennas becomes high, and the loss between the two terminals increases. can be made smaller. On the other hand, the loss between the beam terminal 5(1) and the antenna terminal 7(1) is due to the opposing angle of the tapered lines 6(1) and 8(1), which are two-dimensional horn antennas, compared to the conventional example. Therefore, the antenna gain of the two-dimensional horn antenna becomes low, and the loss between both terminals becomes large.

FIG. 4 shows trends in loss characteristics between the beam terminal 5(1) and each antenna terminal 7(1) to 7(n) in the case of this device. Although the average loss between each antenna terminal 7(1) to 7(n) increases slightly, the asymmetry of the loss characteristics is smaller than in FIG. ) is also becoming smaller.

〔Effect of the invention〕

As described above, according to the Rottman lens according to the present invention, since the tapered line on the antenna terminal side is oriented toward the center of the parallel plate portion, the loss characteristics from the beam terminal to each antenna terminal are asymmetric. This has the effect of reducing the loss and the difference in loss between each antenna terminal.

[Brief explanation of drawings]

FIG. 1 is an external view showing a conventional Rotman lens, FIG. 2 is a view showing an example of loss characteristics of a conventional Rotman lens, and FIG. 3 is an external view showing a Rotman lens according to an embodiment of the present invention. FIG. 4 is a diagram showing an example of loss characteristics of the Rotman lens of the above embodiment. In the figure, 2 is a parallel plate portion, 8 is a tapered line, and 7 is an antenna terminal. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A plurality of beam terminals for selecting the scanning direction of the array antenna, and a parallel plate portion that provides a two-dimensional free space for radio waves and constitutes a lens;
A stripline type rod in which an antenna terminal for connecting to an array antenna element, the beam terminal, the parallel plate portion, and a tapered line connecting between the antenna terminal are formed on the same insulating substrate with one side grounded. In the Mann lens, the opening direction of the tapered line on the antenna terminal side of the lens is directed near the center so as to reduce the asymmetry of loss between the beam terminal and each of the antenna terminals, and the taper line on the antenna terminal side A Rotman lens characterized in that the curvature of the lens curve on the antenna terminal side, which connects the opening of the line with a smooth curve, is smaller than the curvature of the lens curve on the beam terminal side.