JPS63208308A - Cavity for wide-band antenna - Google Patents

Abstract

PURPOSE:To maintain a radiation pattern nearly in a constant shape over a wide frequency range by arranging plural plate type resistors in a cavity in parallel to the cavity center shaft and radially from the cavity center. CONSTITUTION:The plural plate type resistors 40 are arranged in the cavity 2 in parallel to the center shaft 2a of the cavity 2 and radially from the cavity center. Consequently, the ratio of the resistors 40 to the internal capacity of the cavity 2 is a little. Consequently, the equivalent dielectric constant in the cavity is small and the impedance in the cavity 2 is held high, so that a decrease in antenna gain is small. An electromagnetic wave radiated by an antenna electrode in the cavity, on the other hand, is at a propagation attitude close to a TEM mode in the cavity 2, so the electromagnetic wave radiated by the resistors 40 in the cavity 2 is attenuated greatly. Thus, a wide-band antenna is obtained which has a radiation pattern with small frequency dependency.

Description

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

(Prior art) Conventionally, cavities for this type of wideband antenna include:
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.

As for the shape of the antenna electrode 1, a multi-filament log spiral antenna, a log-periodic antenna, and a wideband antenna having a self-complementary structure are also used.

Reference numeral 2 denotes a cavity, which is used to make the directional characteristics of the broadband antenna made of 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. This makes the 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, resulting in a unidirectional antenna directivity in the direction shown by arrow 3. give.

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. ing. That is,
At frequencies where the depth of the cavity 2 is an odd multiple of λ/4 of the antenna excitation wavelength λ, the direct wave and the indirect wave are similar to each other as indicated by arrow 3.
Because of the constructive interference in the front direction of the antenna as shown in , a radiation pattern with a narrow beam width with a peak in the front direction of the antenna is generated. Further, at frequencies where the cavity depth is an even multiple of λ/4, direct waves and indirect waves interfere to cancel each other, generating 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, the conventional broadband antenna equipped with such a cavity, especially the broadband antenna equipped with the cavity 2 which serves as a lossless reflector as shown in FIG. In this case, as mentioned above, strong interference between direct waves and indirect waves occurs, so the antenna radiation pattern shows strong frequency dependence, and it is necessary to keep the shape of the radiation pattern almost constant over a wide band. The problem is that it cannot be used for other purposes.

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. Actually, in the structure shown in Figure 4,
One octave is the limit for maintaining a substantially constant radiation pattern.

On the other hand, a method can also be considered in which the cavity 2 is filled with a radio wave absorber to absorb all the energy propagating into the cavity, thereby eliminating 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 than the impedance of free space, and the impedance of the cavity becomes lower in the ratio of the direct wave to the wave into the cavity, and the wave into the cavity is absorbed, increasing the efficiency. descend.

(B) When the radio wave absorber approaches the vicinity of 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 broadband antenna electrode 1, the position where radio wave radiation is strongly generated differs depending on the frequency, and in the low frequency region The more it becomes, the more it occurs in the outer part of the antenna electrode 1.

For example, the radiation area for the antenna electrode 2 in FIG.
If this is the case, the current on the antenna electrode 1 does not radiate inside the radiation region 21 and is in a propagation mode, and the electric lines of force at this time are as shown in 22, on the antenna electrode surface 1.
concentrated in the vicinity.

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, they will be absorbed, resulting in a decrease in antenna gain.

(C) Furthermore, in the radiation region 21 shown in FIG. When it crosses the line, it undergoes absorption attenuation, 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 approximately 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 has been made in view of such conventional problems, and it absorbs radiation into the cavity while minimizing the decrease in antenna gain, and provides a wide frequency range. It is an object of the present invention to provide a cavity for a wideband antenna that can maintain an antenna radiation pattern in a substantially constant shape over a period of time.

In order to achieve this object, the present invention provides a wideband antenna cavity that provides unidirectional antenna radiation characteristics in combination with a wideband antenna element.
A plurality of plate-shaped front resistors are arranged in the cavity so as to be parallel to the center axis of the cavity and radially or even branch-like from the center of the cavity.

(Function) According to the configuration of the present invention, the electromagnetic waves radiated from the antenna element into the cavity are TE
It is thought that the propagation mode will be close to M mode, and since plate-shaped resistors are provided radially or branch-like on the diameter of the cavity, the electromagnetic waves radiated into the cavity will be greatly attenuated by the resistors, and this cavity Due to its structure, a wideband antenna relies on direct waves from the antenna element and is unidirectional, so the radiation pattern hardly changes even when the frequency changes, making it possible to create a wideband antenna with a radiation pattern that has extremely low frequency dependence. Obtainable.

(Example) FIG. 1 is an explanatory diagram showing one embodiment 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 surface of the cavity 2 is provided with an antenna electrode of, for example, a two-strand planar Archimedean spiral antenna. periodic antenna,
Furthermore, antenna electrodes of 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.

In the cavity 2 of the present invention shown in the embodiment shown in FIG.
Since the resistor 40 is provided parallel to a and radially with respect to the center of the cavity, the resistor 40 occupies the inner volume of the cavity 2'.
The proportion is very small. As a result, even if the resistor 40 has a high dielectric constant, the volume occupied in the cavity is extremely small, so the equivalent dielectric constant in the cavity 2 is small.
Therefore, even if the resistor 40 is provided inside the cavity, the impedance inside 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 causes a problem when the cavity is filled with a dielectric material as in the past. The decrease in antenna gain can also be reduced.

Furthermore, 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 is absorbed by the resistor 40. Since the distance to the receiving antenna electrode 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 cavity 2, the electromagnetic waves are TE
It is thought that the propagation state is close to the M mode, and therefore, the electromagnetic waves radiated into the cavity are greatly attenuated by the resistors 40 arranged radially in the radial direction.

As a result, in the cavity of the present invention, the indirect waves radiated into the cavity are sufficiently absorbed, and the antenna electrode provides a radiation pattern determined by the direct waves to free space, so that the radiation is transmitted over a wide frequency band. It is possible to obtain a wideband antenna having a radiation pattern with extremely small frequency dependence, which can maintain substantially the same pattern shape.

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, C
In addition to a plurality of plate-shaped resistors 40 that are parallel to the pull cavity center axis 2a and radially provided from the center of the pull cavity, plate-shaped resistors 42 are branched from the plate-shaped resistors 40 that are arranged radially. The feature is that it is arranged so that

In addition to the resistors 40 arranged radially in this way, by arranging the resistors 42 in branch shapes, it is possible to attenuate and absorb the electromagnetic waves that are thought to have a propagation mode close to the EM mode radiated into the cavity. The objective is to realize a broadband antenna in which the indirect waves are 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. Cavity 2 with a height of 40°42
antenna electrode and resistor 40 without having a height equal to the depth of
, 4 and 2 may be set at a height that provides a predetermined space between them.

In this way, when the height of the plate-shaped resistor 40.42 is set to create a predetermined space between the antenna electrode and the upper end of the resistor 40.42, the antenna electrode is supported and fixed by the resistor 40°42. It will no longer be possible to provide the functionality to do so.

Therefore, as shown in FIG. 3, a plate-shaped resistor 40 or 42 placed 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. By arranging the cavity 2 in such a way that the part 45 where no resistor is provided is located on the antenna electrode side, the provision of the part 45 where no resistor is provided prevents gain reduction due to current absorption on the antenna electrode. , the resistor 40 has the function of supporting and fixing the antenna electrode.
It can be held up to 42.

(Effects of the Invention) As described above, according to the present invention, in a cavity for a wideband antenna that provides unidirectional antenna radiation characteristics in combination with a wideband antenna element, a plurality of plate-shaped resistors are arranged along the center axis of the cavity. By arranging them in the cavity so that they are parallel and radial from the center of the cavity, the cavity impedance decreases and antenna electrode radiation causes a decrease in antenna gain when the cavity is filled with radio wave absorbers. Both the decrease in gain due to the absorption of antenna current outside the area, and the decrease in antenna gain due to the electric field lines passing through the cavity from the radiation area of the antenna electrode crossing the radio wave absorber are minimized, and the decrease in antenna gain is minimized. A wideband antenna that can absorb and attenuate the electromagnetic waves radiated into the cavity with almost no interference, and as a result, the shape of the unidirectional antenna radiation pattern can be kept almost constant over a wide frequency range with little loss of gain. can be obtained.

Furthermore, since the plate-shaped resistors are arranged radially or even branch-like within the cavity, 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 a further embodiment of the present invention, and Fig. 3 shows another embodiment of the resistor used in the present invention. FIG. 4 is an explanatory diagram showing a conventional example, and FIG. 5 is a judgment diagram showing the cause of antenna gain reduction when the cavity is filled with a radio wave absorber. 1: Antenna electrode 2: Cavity 2a: Cavity central axis 40: Resistor (radial arrangement) 42: Resistor (branch arrangement) 44: Part with resistance 45: Part without resistance

Claims (3)

[Claims] (1) In a wideband antenna cavity that provides unidirectional antenna radiation characteristics when combined with a wideband antenna element, a plurality of plate-shaped resistors are arranged parallel to the center axis of the cavity and radially from the center of the cavity. A cavity for a wideband antenna, characterized in that it is placed inside the cavity. (2) The cavity for a wideband antenna according to claim 1, wherein the plurality of plate-shaped resistors are arranged in a radiating state from the center of the cavity and further branched. (3) The cavity for a wideband antenna according to claim 1, wherein the plate-like resistor is a portion having no resistance on the antenna electrode side.