JPS6340365B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rectangular waveguide type leaky antenna that is excited by connecting standard rectangular waveguides. This was done so as not to damage it.

Generally, a leaky antenna is a type of traveling wave antenna, which has a large number of holes or long slits provided in the wall of a waveguide along the tube axis. Traveling wave antennas generally have broadband characteristics, but this is because the electromagnetic wave radiation portion does not have resonance characteristics for electromagnetic waves. However, depending on the manner of connection between such a leaky antenna and a power feeding section that excites it, there has conventionally been a drawback in that desired broadband characteristics cannot always be obtained.

The first drawback of such conventional leaky antennas is
Taking the conventional rectangular waveguide type leaky antenna shown in the figure as an example, in the rectangular waveguide type leaky antenna shown in Figure 1a, as shown in the figure, a coaxial probe 3 is provided and a coaxial cable is connected. Since the width of the rectangular waveguide 1 constituting the leaky antenna is
That is, the dimensions of the H plane and the width of the slit 2 can be arbitrarily selected to achieve desired electromagnetic wave radiation characteristics as described later. As shown in the figure, a flange 4 is provided to connect a waveguide, and the waveguide excites the waveguide. The leaky antenna is constructed with a slitted rectangular waveguide having the same width as the rectangular waveguide, that is, the width of the H plane.

On the other hand, a leaky antenna with a structure in which a long slit is provided in the E plane of a rectangular waveguide parallel to the tube axis has an apparent phase propagation velocity in the tube as shown in Figure 2b, for example. The faster the phase propagation speed of the electromagnetic wave radiated from the slit of the leaky antenna, the larger the radiation angle α as shown in Figure 3. antenna gain increases. Therefore, when the width D of the H plane of the rectangular waveguide in this type of leaky antenna is changed, the amount of attenuation a of the electromagnetic waves inside the tube due to radiation has the characteristics shown in Figure 2a, and It is known that the apparent phase propagation velocity of electromagnetic waves in a tube has the characteristics shown in FIG. 2b. That is, according to the characteristics shown in Fig. 2b, the smaller the width W of the slot provided on the E-plane of the rectangular waveguide, and the smaller the width D of the H-plane, the smaller the apparent electromagnetic waves within the tube with respect to the speed of light C. The reciprocal C/v of the ratio of the phase propagation velocity v becomes smaller, the apparent phase propagation velocity of the in-tube electromagnetic waves becomes faster, and the gain of the leaky antenna can be increased as described above.

However, the width W of the slot provided in the E plane of the rectangular waveguide is the thickness of the rectangular waveguide, that is, E
There is a limit to increasing the antenna radiation loss by increasing the slot width W, which is limited by the width of the surface. Therefore, the width D of the H-plane of the rectangular waveguide must be reduced to increase the antenna gain, but according to the characteristics shown in Figure 2a, the width of the H-plane of the rectangular waveguide is The larger D is, the smaller the amount of attenuation of electromagnetic waves in the pipe per unit length of the waveguide due to leakage radiation from the slot becomes. This means that no radiation can be leaked from the slit. However, since the rectangular waveguide that can actually be used as a leaky antenna has a moderate finite length,
If the antenna length is limited, the electromagnetic waves within the pipe cannot be sufficiently radiated, and are wasted in the absorption resistance. Therefore, when the antenna length is actually limited, by making the width D of the H-plane smaller than in a standard rectangular waveguide and sufficiently increasing the radiation attenuation amount a per unit length, it is possible to It is necessary to effectively utilize the entire length of the antenna to increase the antenna gain.

However, when a leaky antenna consisting of a rectangular waveguide with a slit with a significantly narrower H-plane width is directly connected to a standard rectangular waveguide used for power feeding and excited, the width of the H-plane becomes significantly different. This means that the rectangular waveguides are directly connected, and a reactance is generated at the connection portion, deteriorating the propagation state of electromagnetic waves in the pipe or causing a cut-off state. Although it is possible to eliminate disturbances in the propagation state of electromagnetic waves within the pipe by compensating for the reactance generated at the connection, the band will naturally become narrower, and the wide band characteristic of leaky antennas will be significantly impaired. Become.

It is an object of the present invention to solve the above-mentioned conventional problems and eliminate their drawbacks, and to improve the standard rectangular waveguide used for power feeding without impairing the advantages of a traveling wave antenna made of a slitted rectangular waveguide or the like. It is an object of the present invention to provide a rectangular waveguide type leaky antenna with good characteristics that can be efficiently excited by directly connecting a wave tube.

In other words, the leaky antenna of the present invention transmits electromagnetic waves.
A leak port in the tube axis direction is provided in one of the tube walls of the first rectangular waveguide for propagation in the TE mode and the E-plane wall surface having approximately the same thickness as the E-plane wall surface of the first rectangular waveguide. a second rectangular waveguide, and the one E-plane wall surface provided with the leakage port of the second rectangular waveguide and the one E-plane wall surface of the first rectangular waveguide are connected to each other. the other E-plane wall surface facing the one E-plane wall surface with a taper therebetween and the leakage port of the second rectangular waveguide; and the one E-plane of the first rectangular waveguide. The wall surface and the other E-side wall surface facing each other are arranged on the same plane and connected to each other,
each of said other E disposed on the same plane including interconnections of said first and said second directional waveguides;
The second rectangular waveguide has a narrower H-plane wall width than the first rectangular waveguide by loading tapered dielectric plates at both ends in the tube axis direction along the H-plane wall surface. The electromagnetic wave propagated in the TE mode within the rectangular waveguide is radiated from the leakage port.

The invention will be explained in detail below by way of example embodiments with reference to the drawings.

As mentioned above, for example, a standard rectangular waveguide that is normally used for feeding electromagnetic waves and propagates the electromagnetic wave in TE mode, and a slit with a sufficiently reduced width of the H plane compared to the standard rectangular waveguide. An example of the configuration of the leaky antenna of the present invention in which a tapered dielectric plate is inserted and loaded in the connection part with the rectangular waveguide in parallel to the E plane is shown in FIG. 4a with the E plane parallel to the plane of the paper. Further, the H plane is shown in FIG. 4b parallel to the plane of the paper. In the illustrated configuration, the dielectric plate 7 loaded along the E plane is used for electromagnetic waves propagating in the rectangular waveguide 1 of the leaky antenna section provided with the slit 2 and the standard feeding waveguide section 6. By concentrating the field near the dielectric plate 7, it is possible to prevent the mismatch in the shape and dimensions of the E-plane loaded with the dielectric plate 7 and the opposite E-plane tube wall from disturbing the propagation state of electromagnetic waves in the tube. Therefore, the end of the loaded dielectric plate 7, especially the end in the slitted rectangular waveguide 1 where the width of the H plane is narrow and the opposing E planes are close to each other. In order not to disturb the propagation state of electromagnetic waves inside the pipe, the waveguide is tapered very gently so as not to disturb the propagation state of the electromagnetic waves inside the pipe. To prevent generation of undesired TM mode electromagnetic waves within the waveguide 1. That is, the effect of the loaded dielectric plate 7 is simply to lower the cutoff frequency of the slitted rectangular waveguide 1 with a narrowed H-plane width, and to propagate in the standard rectangular waveguide 6 in the TE mode. In addition to preventing electromagnetic waves coming from being cut off by the slitted rectangular waveguide 1,
The propagation state of the TE mode that continues from within the standard rectangular waveguide 6 is disturbed to prevent the TM mode from occurring, and the apparent phase propagation velocity of the electromagnetic wave inside the tube is large in both rectangular waveguides 1 and 6. The goal is to avoid making any differences.

Therefore, if the tip of the dielectric plate 7, especially the tip in the slitted square wave waveguide 1, is not gradually thinned, the propagation state of the TE mode will be disturbed and the TM mode will occur. Therefore, an electric field parallel to the tube axis is generated in the slit 2, and the electromagnetic waves radiated from the slit 2 contain both horizontal and vertical polarization. The performance of the horizontally polarized antenna used for transmitting and receiving television broadcast waves will deteriorate.

Furthermore, since the loading of the dielectric plate 7 extends to the inside of the rectangular waveguide 1 with slits, the apparent phase propagation velocity of the electromagnetic waves in the tube in that part is not affected by the loading of the dielectric plate 7. If there is too much difference from the inside of the rectangular waveguide 1, the directivity of the leaky antenna in the tube axis direction will be disturbed, making it impossible to obtain a single beam, resulting in an unnaturally shaped directivity pattern.

A preferred example of use of the leaky antenna of the present invention having the above-described configuration is for receiving and receiving horizontally polarized television broadcast waves in the 12 GHz band, as described above, but normal broadcast waves propagate almost horizontally. Therefore, to prevent rainwater from entering the pipe through slits etc. that act as antenna elements,
It is preferable that the E surface provided with slits or the like faces downward and is oriented in the direction in which the radio waves arrive in the longitudinal direction. Even in such an installation, in order to prevent rainwater from entering, it is possible to cover at least the slit with a thin, low-loss dielectric sheet such as a thin polyethylene film, so that some water droplets will be able to absorb the dielectric. Even if it adheres to the body sheet, there is little loss in the action of the slit, which does not create a resonance state, and large losses due to water droplets entering the waveguide can be sufficiently prevented.

Examples of the specifications of the leaky antenna of the present invention prototyped for 12 GHz microwave reception are as follows.

Dimensions Total length: 345 mm Slot length: 310 mm Characteristic gain: 20.2 dB Voltage standing wave ratio (VSWR): 1.4 or less (frequency 11.7 to 12.4 GHz) Polarization: Horizontal polarization (E side with slit facing downward, When the longitudinal direction is tilted and the state shown in Figure 3 is reversed and the direction of radio wave propagation is made horizontal) Dielectric plate material: Staircast (trade name) with a relative dielectric constant of 6 Note that the leaky antenna of the present invention has a rectangular shape. The material for the dielectric plate loaded in the waveguide is preferably one having a dielectric constant of about 4 to 6, and the required thickness of the dielectric plate is appropriately set depending on the dielectric constant.

Next, the frequency characteristics of the voltage standing wave ratio (VSWR) actually measured for the above-mentioned prototype example of the leaky antenna of the present invention are shown in Fig. 5, and the horizontal polarization when the prototype example is installed in the above-mentioned attitude with respect to the polarization is shown in Fig. 5. Figure 6 shows the horizontal directivity. As can be seen from the characteristics shown in Figure 5, the voltage standing wave ratio of the leaky antenna of the present invention is 0.7 in the frequency range of 11.7 to 12.4 GHz.
A relatively good value of about ~1.3 was obtained, and as for the horizontal directivity, as can be seen from FIG. 6, a relatively good unidirectivity was obtained.

As is clear from the above description, according to the present invention, even if a standard rectangular waveguide used for normal power supply is directly connected to a slitted rectangular waveguide, good matching can be achieved over a wide frequency band. A slitted rectangular waveguide leaky antenna with good directivity can be easily realized with a simple configuration.

[Brief explanation of the drawing]

Figures 1a and 1b are perspective views showing the structure of a conventional rectangular waveguide leaky antenna, Figures 2a and 2b are characteristic curve diagrams showing how the characteristics change due to changes in dimensions, respectively. Figure 3 is a side view showing the mode of electromagnetic radiation, and Figure 4 a and b.
5 is a top view and a side view showing the configuration of the leaky antenna of the present invention, FIG. 5 is a characteristic curve diagram showing an example of its voltage standing wave ratio characteristics, and FIG. 6 is a diagram showing an example of its directivity. It is a sexual pattern. 1... Rectangular waveguide, 2... Slit, 3... Coaxial probe, 4... Flange, 5... Wave front, 6...
...Standard rectangular waveguide, 7...Dielectric plate.

Claims (1)

[Claims] 1 A first rectangular waveguide that propagates electromagnetic waves in TE mode, and leakage in the tube axis direction on one of the tube walls of the E-plane wall that has almost the same thickness as the E-plane wall of the first rectangular waveguide. A second rectangular waveguide provided with an opening is connected to the one E surface wall surface of the second rectangular waveguide provided with the leakage port and one E side wall surface of the first rectangular waveguide.
The other E-plane wall surface of the first rectangular waveguide and the other E-plane wall surface facing the one E-plane wall surface, which is tapered between the two E-plane wall surfaces and the leakage port of the second rectangular waveguide is provided. The one E-plane wall surface and the other E-plane wall surface facing each other are arranged on the same plane, are connected to each other, and are the same including the interconnection portions of the first and second direction waveguides. By loading tapered dielectric plates at both ends in the tube axis direction along the other E-plane wall surface arranged on a plane, the H-plane is lower than that of the first rectangular waveguide. A leaky antenna characterized in that electromagnetic waves propagated in the TE mode in the second rectangular waveguide whose wall width is reduced are radiated from the leakage port.