JPS6136404B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a slot antenna.

An example of a conventional slot antenna is shown in FIG. In this example, slots 2 are cut in the H-plane of the waveguide 1, and the interval between each slot is one guide wavelength at the design center frequency. Therefore, the power supply port 3
The radio waves radiated from each slot while propagating within the waveguide 1 are directed toward the antenna in the front direction 4.
They are in phase and radiate strongly in this direction. However, at frequencies other than the design center frequency, the slot spacing and the channel wavelength do not match, so the phases are not aligned.
There is a drawback that the antenna beam deviates from the antenna front direction 4. Figure 2 shows this situation, where 5 is the directivity characteristic at the design center frequency, and 6 is the directivity characteristic at the design center frequency.
7 shows the directional characteristic at a frequency higher than the design center frequency, and 7 shows the directional characteristic at a frequency lower than the design center frequency. As a result, there is a disadvantage that the bandwidth with high gain is narrow in the front direction of the antenna.
It could hardly be used for communications.
This drawback occurs not only in slot antennas using waveguides as waveguides, but also in antennas using other waveguides such as dielectric lines or coaxial lines.

In order to eliminate these drawbacks, the present invention provides a slot antenna that has wideband frequency characteristics by adding a compensation device that cancels out the frequency characteristics of the phase in each slot.

The present invention will be explained in detail below with reference to the drawings.

FIG. 3 shows one embodiment of the present invention, in which a is a perspective view and b is a sectional view, 8 is a metal plate, 9 is the direction of the electric field, 10 is the antenna opening, and 11 is the path of the radio wave. show. The slot spacing is selected so that the radio waves radiated from each slot are in phase at the aperture 10 at the center frequency. Now, considering a frequency higher than the center frequency, the channel wavelength becomes shorter, so the phase up to each slot 2 is delayed as the distance from the feed port 3 increases. On the other hand, if the spacing between the metal plates 8 is selected near the cutoff frequency, a large dispersion characteristic can be imparted to the speed of radio waves propagating through the metal plates 8. Therefore, the phase delay due to the higher frequency compared to that in the waveguide 1 can be increased. Therefore, as shown in Figure 3b,
From slot 2 near power feed port 3 to antenna opening 1
By increasing the length of the metal plate 8 to 0, the phase lag can be increased in this portion, and the phase lag in the waveguide 1 can be compensated for. As a result, the amount of beam shift due to frequency change can be reduced.

Calculating the above effect using a mathematical formula is as follows. At the center frequency, the antenna aperture 1
From the condition that the phases are aligned at 0, the slot interval Δ
l is defined by the following formula.

Here, λ ₀ is the free space wavelength at the center frequency, a ₁ is the distance between the E-plane walls of the waveguide 1, and a ₂ is the distance between the E-plane walls of the waveguide 1.
, and θ is the angle formed between the antenna aperture 10 and the waveguide 1. Phase distribution Pi at antenna aperture 10
is numbered i=0, 1, 2...n in order from slot 2 closest to the antenna feeder 3.
It can be found using the following formula for the number slot.

Here, λ indicates the free space wavelength for each frequency. Therefore, in order to reduce the beam shift, a ₁ , a ₂ , and θ should be selected so that the phase distribution obtained by equation (2) becomes nearly uniform with respect to changes in frequency. Here, a ₂ must be greater than or equal to 2/λ, as is clear from equations (1) and (2), and since a ₁ > a ₂ , a ₂
<λ.

Figure 4 shows an example of the calculation results. The horizontal axis shows the normalized frequency, and the vertical axis shows the beam shift amount. Here, a ₁ =0.8636 wavelength, a ₂ =0.55 wavelength, and θ=30° are selected. It can be seen that in the conventional antenna, whose characteristics are shown by the chain line, a beam shift of about 6 degrees occurs in a 10% band, but in the present antenna, shown by the solid line, the beam shift is within about 0.5 degrees.

FIG. 5 is a front view of another embodiment of the invention. In the embodiment shown in FIG. 3, the spacing between the metal plates 8 was kept constant, but here, by changing the spacing between the metal plates 8, the same effect as changing the length can be obtained. Note that this embodiment can also be used in conjunction with the embodiment in which the length of the metal plate 8 is changed as in the embodiment shown in FIG.

FIG. 6 is a sectional view of another embodiment of the present invention, in which the depth is shortened by feeding power from a power feeding port 3 provided at the center of the antenna.

FIG. 7 shows another embodiment of the present invention in which the waveguide 1 and the front direction of the antenna are arranged at right angles, and is a sectional view.

FIG. 8 shows a front view of an embodiment of the present invention in which the slot is cut in a manner different from that used in the explanation up to now. Since the direction 9 of the electric field is perpendicular to the waveguide 1, a pair of metal plates 8 is provided for each slot 2.

Although the case where a waveguide is used as the waveguide has been described above, the present invention can also be practiced when using other waveguides such as a dielectric line, a coaxial line, a stripline, a parallel plate line, etc. can.
In that case, the dielectric line can be used as a radio wave radiating element by providing a discontinuous portion instead of a slot.

As explained above, according to the present invention, the band of the slot antenna can be significantly widened by adding a phase compensation device made of a metal plate provided parallel to the direction of the electric field. If slot antennas can be used for communications due to this wide band, there is an advantage that communication devices can be made more economical because the slot antennas have a simple structure.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a conventional slot antenna, Figure 2 is a radiation characteristic diagram of a conventional slot antenna, Figures 3a and b are a perspective view and a sectional view of an embodiment of the present invention, and Figure 4. is a characteristic diagram of the antenna of the present invention, No. 5
The figure is a front view of one embodiment of the invention, FIGS. 6 and 7 are cross-sectional views of one embodiment of the invention, and FIG. 8 is a front view of one embodiment of the invention. 1... Waveguide, 2... Slot, 3... Feeding port, 4... Antenna front direction, 5... Radiation characteristics at center frequency, 6, 7... Radiation characteristics when shifted from center frequency, 8 . . . Metal plate, 9 . . . Direction of electric field, 10 . . . Antenna aperture, 11 . . . Path of radio waves, 12 .

Claims (1)

[Claims] 1. In an antenna having a structure in which a plurality of slots or radio wave radiating elements are provided in place of slots in the middle of a waveguide, the direction of the electric field radiated from each of the radio wave radiating elements or the direction of the electric field used as the main polarization component of the antenna. A metal plate is provided approximately parallel to both sides of the radio wave radiating element at an interval of not less than half a wavelength and not more than one wavelength from the wall surface of the waveguide toward the front of the antenna. The phase at the antenna opening of the radio waves radiated from each of the radio wave radiating elements from the feed port through the waveguide, propagating through the metal plate, and reaching the antenna opening is the same as the frequency of the radio waves that have passed through any radiating element. A slot antenna characterized in that the antenna is designed so that it remains almost the same over time.