JPH0569323B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a wideband antenna that provides a wideband antenna element with unidirectional antenna radiation characteristics.

(Prior Art) Conventionally, as this type of wideband antenna, for example, the one shown in FIG. 4 is known.

In FIG. 4, reference numeral 1 denotes an antenna electrode of a broadband antenna, for example, an antenna electrode of a two-striped planar Archimedean spiral antenna.

In addition to the above shapes, the antenna electrode 1 may be a multi-strand log spiral antenna, a log periodic antenna, or a wideband antenna having a self-complementary structure.

Reference numeral 2 denotes a cavity, which is used to make the directional characteristics of the broadband antenna formed by the antenna electrode 1 unidirectional, and the inner wall surface of the cavity 1 is a good electrical conductor.

The function of this cavity 2 is that the radiation characteristic of the antenna electrode 1 itself is a bidirectional characteristic that radiates to both sides of the antenna electrode surface. , which makes the antenna directivity unidirectional.

For example, in Fig. 4, the wave traveling into cavity 1 is almost completely reflected because there is almost no loss within the cavity, giving the antenna directivity characteristics that are unidirectional in the direction shown by arrow 3. .

By the way, it is widely known that the radiation characteristics of a broadband antenna equipped with the cavity 2 are determined by the interference between the direct wave radiated directly into free space from the antenna electrode 1 and the indirect wave re-radiated from the cavity 2. Are known. That is, at frequencies where the depth of the cavity 2 is an odd multiple of λ/4 of the antenna excitation wavelength λ, direct waves and indirect waves constructively interfere with each other in the front direction of the antenna as shown by arrow 3. It generates a radiation pattern with a narrow beam width and a peak in the direction. Furthermore, at frequencies where the cavity depth is an even multiple of λ/4, direct waves and indirect waves interfere to cancel each other out, producing a so-called conical pattern with a gain peak in a direction other than the front direction of the antenna.

(Problems to be Solved by the Invention) However, in the case of a conventional broadband antenna equipped with such a cavity, especially a broadband antenna equipped with the cavity 2 which is a lossless reflector as shown in FIG. As mentioned above, since strong interference between direct waves and indirect waves occurs, the antenna radiation pattern exhibits strong frequency dependence, and is suitable for applications where the shape of the radiation pattern must be kept approximately constant over a wide band. There was a problem that I couldn't use it.

This problem is caused by the existence of the cavity itself, and therefore cannot be solved no matter how wide-band characteristics the antenna element exhibits. In reality, with the structure shown in FIG. 4, the limit for maintaining a substantially constant radiation pattern is one octave.

On the other hand, fill cavity 2 with a radio wave absorber,
Another possible method is to absorb all the energy traveling inside the cavity and eliminate indirect waves.

However, in this case, although the radiation pattern can be maintained approximately in the same shape over several octaves, another problem occurs in that the antenna gain is significantly reduced due to absorption.

The mechanism by which the antenna gain decreases when the cavity 2 is filled with a radio wave absorber is thought to be due to the following three points.

(A) The impedance of the cavity becomes smaller compared to the impedance of free space, and the impedance of the cavity becomes lower in proportion to the direct wave and the wave into the cavity, and the wave into the cavity is absorbed, reducing efficiency. .

(B) When the radio wave absorber approaches the antenna electrode 1, the current flowing on the antenna electrode 1 is attenuated. This is because the electromagnetic field accompanying the antenna current spreads around the antenna electrode and propagates.

This situation is shown in Fig. 5. 4 is a radio wave absorber filled in the cavity 2, and in the case of the broadband antenna electrode 1, the position where radio wave radiation is strongly generated differs depending on the frequency, and The higher the frequency range, the more it occurs in the outer part of the antenna electrode 1.

For example, if the radiation area is 21 for the antenna electrode 2 in FIG. As shown in FIG. 2 , it is concentrated near the antenna electrode surface 1. However, since the electric lines of force 22 have a slight spread above and below the antenna electrode surface 1, if there is a radio wave absorber 4 close to the antenna electrode 1, the electric wave absorber 4 will be absorbed, and as a result, the antenna gain will be reduced.

(C) Furthermore, in the radiation region 21 shown in FIG.
There are electric lines of force shown as , indicating strong radiation, but
When this electric line of force 23 crosses the radio wave absorber 4, it is absorbed and attenuated, resulting in a decrease in antenna gain.

For these reasons (A) to (C), even if the cavity is filled with a radio wave absorber and the radiation pattern can be maintained almost constant over a wide frequency band, there is a problem that the antenna gain will drop significantly. Ta.

(Means for Solving the Problems) The present invention was made in view of these conventional problems, and it absorbs radiation into the cavity while minimizing the decrease in antenna gain, and provides a wide frequency band. An object of the present invention is to provide a wideband antenna that can maintain an antenna radiation pattern in a substantially constant shape throughout the period.

In order to achieve this objective, the present invention includes:
In a wideband antenna that provides unidirectional antenna radiation characteristics by a combination of a wideband antenna element 1 and a cavity 2, a plurality of plate-shaped resistors 4 are used.
0 parallel to the central axis of cavity 2 and radially from the center of cavity 2.
It is placed inside.

(Function) According to the configuration of the present invention, the electromagnetic waves radiated from the antenna element into the cavity are considered to have a propagation mode close to the TEM mode within the cavity, and the electromagnetic waves are distributed in a radial or branch-like manner along the diameter of the cavity. Because a shaped resistor is provided, the electromagnetic waves radiated into the cavity are greatly attenuated by the resistor, and this cavity structure makes the broadband antenna unidirectional, relying on the direct waves from the antenna element. Therefore, even if the frequency changes, the radiation pattern hardly changes, making it possible to obtain a wideband antenna with a radiation pattern with extremely low frequency dependence.

(Example) FIG. 1 is an explanatory diagram showing an example of the present invention.

First, to explain the structure, 2 is a cavity, which has a cylindrical shape with an opening on the side where the antenna element is attached, and the inner wall surface of the cavity 2 is a good electrical conductor. As shown in Fig. 4, the opening of the cavity 2 is provided with an antenna electrode for, for example, a two-strand planar Archimedean spiral antenna. Antenna electrodes of periodic antennas and even antennas having a self-complementary structure are arranged.

A plurality of plate-shaped resistors 40 are arranged within the cavity 2 .

In this embodiment, the plurality of plate-shaped resistors 40 are arranged parallel to the central axis 2a of the cavity and radially from the center of the cavity.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

Cavity 2 of the present invention shown in the embodiment of FIG.
In this case, since a plurality of plate-shaped resistors 40 are provided inside parallel to the cavity center axis 2a and radially with respect to the cavity center, the proportion of the resistors 40 in the internal volume of the cavity 2 is very small. It is. As a result, even if the resistor 40 has a high dielectric constant, it occupies an extremely small volume within the cavity, so the equivalent dielectric constant within the cavity 2 is small.
Therefore, even if the resistor 40 is provided within the cavity, the impedance within the cavity can be maintained at a high value.

Furthermore, even if the resistor 40 is located at the end surface in contact with the antenna electrode, the area occupied by the end surface of the resistor 40 relative to the cavity opening area is extremely small, which poses a problem when the cavity is filled with a dielectric as in the past. The decrease in antenna gain can also be reduced.

Furthermore, even in the radiation region of the antenna electrode, the proportion of the resistor 40 in the cavity internal volume is extremely small, so radio wave absorption from a macroscopic perspective is suppressed to a small level, and the decrease in efficiency is small. In particular, when the cavity of the present invention is used for an antenna element having a structure in which current flows in an angular direction, such as a spiral antenna electrode, the current flows approximately perpendicularly to the resistor 40, so that the current flows through the resistor 40. Since the distance to the antenna electrode that undergoes absorption is extremely short, the reduction in efficiency due to the presence of the resistor 40 in the radiation region is more effectively improved.

On the other hand, considering the electromagnetic waves radiated from the antenna electrode into the cavity 2, it is considered that the electromagnetic waves have a propagation mode close to the TEM mode within the cavity, and therefore, the electromagnetic waves are propagated in a mode close to the TEM mode. Therefore, electromagnetic waves radiated into the cavity are greatly attenuated.

As a result, in the cavity of the present invention, indirect waves radiated into the cavity are sufficiently absorbed.
Since the antenna electrode provides a radiation pattern determined by direct waves to free space, it is a broadband antenna with a radiation pattern with extremely low frequency dependence that can maintain the shape of the radiation pattern almost the same over a wide frequency band. can be obtained.

FIG. 2 is an explanatory diagram showing another embodiment of the present invention, and is a plan view seen from the cavity opening side.

In the embodiment shown in FIG. 2, in addition to the plurality of plate-shaped resistors 40 provided parallel to the cavity center axis 2a and radially from the cavity center in the embodiment shown in FIG. shaped resistor 4
It is characterized in that plate-shaped resistors 42 are arranged in a branch-like manner.

In addition to the resistors 40 arranged radially in this way, by arranging the resistors 42 in branch shapes, it is possible to further reduce the attenuation and absorption of the electromagnetic waves, which are thought to have a propagation mode similar to the TEM mode radiated into the cavity. The objective is to realize a broadband antenna in which indirect waves can be sufficiently attenuated and absorbed within the cavity, and the frequency dependence of the radiation pattern is extremely small.

Furthermore, the plate-shaped resistors 40 and 42 placed in the cavity 2 in FIGS. 1 and 2 are designed to further suppress gain reduction due to current absorption on the antenna electrode as the resistor approaches the antenna electrode. 4
0 and 42 may not be set equal to the depth of the cavity 2, but may be set to a height that provides a predetermined space between the antenna electrode and both ends of the resistors 40 and 42.

In this way, when the height of the plate-shaped resistors 40, 42 is set to create a predetermined space between the antenna electrode and the upper end of the resistors 40, 42, the resistors 40, 42,
42 makes it impossible to provide the function of supporting and fixing the antenna electrode.

Therefore, as shown in FIG. 3, a plate-shaped resistor 40 or 42 disposed in the cavity has a structure having a portion 44 where the resistor is provided and a portion 45 where the resistor is not provided. If the cavity 2 is arranged so that the part 45 side without a resistor is located on the antenna electrode side, the provision of the part 45 without a resistor can prevent gain reduction due to current absorption on the antenna electrode. , the resistors 40 and 42 can have the function of supporting and fixing the antenna electrode.

(Effects of the Invention) As described above, according to the present invention, in the broadband antenna that provides unidirectional antenna radiation characteristics by the combination of the broadband antenna element 1 and the cavity 2, a plurality of plate-shaped resistors 40 are connected to the cavity. parallel to the central axis of 2 and cavity 2
Because they are arranged in the cavity 2 radially from the center of the antenna, the cavity impedance decreases, which causes a decrease in antenna gain when the cavity is filled with a radio wave absorber, and the antenna current outside the radiation area of the antenna electrode decreases. Minimize both the decrease in gain due to absorption and the decrease in antenna gain due to lines of electric force passing through the cavity from the radiation region of the antenna electrode crossing the radio wave absorber.
It is possible to absorb and attenuate the electromagnetic waves radiated into the cavity with almost no decrease in antenna gain, and as a result, the shape of the unidirectional antenna radiation pattern is maintained approximately constant over a wide frequency range with little decrease in gain. It is possible to obtain a wideband antenna that can be used.

Furthermore, plate-shaped resistors are placed radially inside the cavity.
Furthermore, since it is stretched around in a branch-like manner, the mechanical strength of the cavity itself can be increased.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing one embodiment of the present invention, Fig. 2 is a plan view showing another embodiment of the invention, and Fig. 3 is an explanatory diagram showing one embodiment of the present invention.
The figure is an explanatory diagram showing another example of the resistor used in the present invention, Fig. 4 is an explanatory diagram showing a conventional example, and Fig. 5 is an explanatory diagram showing the decrease in antenna gain when the cavity is filled with a radio wave absorber. It is a judgment diagram showing the cause. 1: antenna electrode, 2: cavity, 2a: cavity center axis, 40: resistor (radial arrangement),
42: Resistor (branch arrangement), 44: Portion with resistance, 45: Portion without resistance.

Claims (1)

[Claims] 1. In a wideband antenna that provides unidirectional antenna radiation characteristics by combining a wideband antenna element 1 and a cavity 2, a plurality of plate-like resistors 40 are arranged parallel to the central axis of the cavity 2 and A wideband antenna characterized in that it is arranged inside the cavity 2 so as to radiate from the center of the antenna. 2 The plurality of plate-shaped resistors 42 are connected to the plurality of plate-shaped resistors 4
2. The wideband antenna according to claim 1, wherein the antenna is arranged in a branch-like manner. 3. The broadband antenna according to claim 1, wherein a portion 45 having no resistance is formed on the antenna element 1 side as the plate-like resistors 40, 42.