JPH0373170B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-frequency antenna device, and particularly to an antenna device having a plurality of resonance bands.

[Prior art]

Generally, a linear antenna is used by resonating with the wavelength used, and this resonance occurs when the length of the antenna element is approximately 1/2 or n/2 (n is an integer) of the wavelength λ (lambda). Further, the range in which such resonance can be obtained is generally limited to the vicinity of the center frequency, and the applicable frequency band of one linear antenna is extremely narrow, at several percent of the center frequency used.

Furthermore, one antenna usually has only one resonant frequency band, and if it is used at a frequency that exceeds this range, not only will the antenna efficiency drop significantly, but the matching between the transmitter and receiver will shift and the transmission will be interrupted. There is even a risk of damaging the machine's power amplifier circuit.

Various countermeasures have been devised in the past, but
An example of this is explained below regarding a sleeve antenna.

That is, FIG. 6 is a diagram schematically showing the structure of a conventional sleeve antenna.
The antenna is constructed by erecting long positive electrode elements 2 insulated from each other, and the cylindrical negative electrode antenna 2 is used to feed power to both of these elements.
This is done in the vicinity of both antenna elements 4 via a coaxial feed line 3 that passes through the element 1.

The feature of this sleeve antenna is that two parallel lines newly formed by the cylindrical negative electrode element 1 and the outer conductor of the coaxial feed point 3 passing through it are connected to the lower end opening of the cylindrical negative electrode element. Since the impedance seen from the antenna becomes extremely large, this prevents unnecessary current induced from the antenna element from flowing into the outer sheath conductor of the coaxial feed line 3 connected to this antenna, thereby stabilizing the operation of the antenna. be.

The above-mentioned measure to widen the band in such a sleeve antenna is to increase the impedance by increasing the cylindrical diameter of the negative electrode element 1, thereby somewhat expanding the usable frequency band. It is.

In addition to expanding the applicable band, in order to use it in multiple bands, for example, by inserting an adjustable inductance in the middle of the antenna element and changing it according to the frequency used, the element can be used in multiple bands. One possibility is to adjust the electrical length of the In this case, the inductance is adjusted automatically by detecting the matching state of the transmitting signal power to the antenna, such as the amount of reflection of the feeding current, or by using a tuning means in conjunction with a channel changeover switch.

[Problem that the invention seeks to solve]

However, it is difficult to say that any of the conventional antenna broadbandization methods described above are optimal. That is, the former method of widening the band not only has its limitations but also increases the size and weight of the antenna.

In addition, the latter method requires a complicated and expensive device, and cannot be used as a portable antenna. Furthermore, none of the conventional antennas has a resonant frequency in a plurality of different frequency bands.

[Means and actions to solve the problem]

An object of the present invention is to provide a linear antenna having a wide band and a plurality of resonant frequency bands, based on a principle completely different from the conventional method of widening the band of a linear antenna as described above.

To achieve this objective, the present invention takes the following measures.

That is, a coil wound so that the high-frequency current flows in the opposite direction to the direction of the high-frequency current flowing through the antenna is added to the tip of the linear antenna, and the relationship between the inductance of the coil and the frequency is configured as desired. .

Although the exact operation of the antenna constructed in this manner is unknown, the effect of the coil attached to the tip is estimated as follows.

At the tip of a conventional linear antenna, for example, a sleep type antenna, a coil with the desired number of turns is placed with the tip of the positive element of the sleeve antenna as the central axis, and the upper end of the coil and the tip of the antenna positive element are positioned. In other words, consider a configuration in which a positive electrode element is added with a coil that hangs down from its tip end so as to surround the positive electrode element.

When a high frequency signal is applied to this antenna, a first resonance point is obtained that resonates with the length of the antenna element, similar to a conventional antenna. At this time, the coil hangs in the opposite direction to the extension direction of the antenna element. Therefore, the directions of the currents are opposite to each other, and it is thought that the antenna has a different effect from that of a conventional sleeve antenna in which a coil is simply added to the tip of the sleeve antenna in the direction in which the element extends.

Despite adding the coil in this way,
The reason why it can have the same resonant frequency as a conventional sleep antenna is that there is a stray capacitance between this coil and the tip of the antenna element to which it is attached, and this capacitance and the coil's own inductance create a parallel resonant circuit. By forming a parallel circuit and resonating in parallel with the resonance frequency when no parallel circuit is attached, it exhibits high impedance and has the same first resonance point as the conventional antenna. Furthermore, when the applied frequency is reduced, the parallel circuit moves away from the parallel resonance point and acts merely as an inductance, and a second resonance point can be obtained at a frequency position determined by the vertical and inner diameter dimensions of the coil. It is presumed that it is a thing.

〔Example〕

The present invention will be described in detail below based on illustrated embodiments.

FIG. 1 is an external view showing an embodiment of a 40 MHz band sleep antenna to which the present invention is applied.

In the figure, 1 is a λ/4 long cylindrical negative pole antenna element, 2 and 3 are a λ/4 long positive pole element and a coaxial feed line, respectively, as in FIG. A coil 4 having a diameter is attached to the tip of the negative antenna element 2 so as to be centered on the tip.

To specifically show the values of each element at this time, the length of the positive and negative antenna elements is about 1.87 m, the diameter of the coil is 10 mm, the coil is tightly wound, and the vertical dimension of the coil at this time is 100 mm. When the characteristics of the sleeve antenna constructed in this manner were measured, the results shown in FIG. 2 were obtained.

As is clear from the figure, the first
Obtain the resonance point of. This is the same resonant frequency as the conventional antenna, and shows that the coil 4 added in the present invention does not change the resonant frequency. Also, the point 5MHz lower from this point,
That is, a second resonance point occurs at 35MHz, resulting in two resonance points.

Therefore, the antenna can be used in two frequency bands with center frequencies of 40 MHz and 35 MHz.

Such an antenna is optimal for a duplex system that uses two frequencies, 40 MHz and 35 MHz, for transmission and reception, and by applying the present invention, the antenna that used to use separate antennas for transmission and reception can be improved. It is extremely economical as only one antenna is required.

For reference, we will examine the frequency characteristics when the above-mentioned coil 4 is simply added to the tip of the antenna element by extending it, as shown in Figure 3. Although not shown in the figure, the resonant frequency in this case is A conventional sleeve antenna, ie, one without a coil, only has one at a point lower than the resonant frequency, and its standing wave ratio is inferior to that of the conventional sleeve antenna.

As is clear from the comparison of the two, although both antenna elements have the same coil attached to the tip, it can be seen that they exhibit completely different phenomena depending on the direction in which the coil is attached.

The second resonant frequency can be arbitrarily selected by varying the number of turns and the diameter of the coil 4 constructed in this way, so it may be set as appropriate depending on the purpose of use.

For example, the vertical dimension of the coil 4 is set to 95 mm.
If it is shortened by mm, the second resonance frequency becomes 35.5MHz.
It has been confirmed that the frequency shifts to 0.5MHz higher.

Incidentally, although the above embodiment shows a case in which a coil is added to a sleeve antenna, the present invention need not be limited to this in any way, and can be applied to all linear antennas. Furthermore, it is applicable not only to vertically polarized waves such as a sleeve antenna, but also to horizontally polarized waves such as a dipole antenna.

That is, FIG. 4 is a schematic diagram of an antenna device showing another embodiment of the present invention, and FIG. Fig. 2(b) shows a coil 4 added to the tip of the positive element of an H-type antenna.

By configuring in this way, it is possible to realize a dipole antenna and an h-type antenna each having two resonance bands as described above.

Although the coil 4 may be attached in any structure, for example, the tip of the antenna element 7 may be attached as shown in FIG. A structure in which the coil 4 is inserted into an insulating material pipe 8 such as a dielectric material, and a copper wire or the like is wound around the surface of the pipe, and the tip thereof is connected to the antenna element 7.
Alternatively, as shown in FIG. 9(b), the extended portion of the antenna element 9 itself may be bent and integrally formed into a coil shape.

〔Effect of the invention〕

Since the present invention is configured and operates as described above, it is possible to realize an antenna device having a plurality of resonance points at arbitrary frequency intervals with a simple configuration, and is particularly applicable to duplex wireless communication equipment. This is very effective in making the antenna device extremely convenient as an antenna for a mobile phone or as an antenna for a wireless communication device using multiple frequencies.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an embodiment of the sleeve antenna to which the present invention is applied, Fig. 2 is a frequency characteristic diagram of the embodiment shown in Fig. 1, and Fig. 3 is a modification of the conventional sleeve antenna. FIG. 4 is a schematic diagram showing another embodiment of the present invention; FIG. b is a cross-sectional view and an external view showing an example of the structure of a coil added in the present invention, and FIG. 6 is a structural view of a conventional sleeve antenna. DESCRIPTION OF SYMBOLS 1... Positive antenna element, 2... Cylindrical negative antenna element, 3... Coaxial feed line, 4... Coil, 5, 6, 7 and 9... Antenna element, 8... Dielectric material.

Claims (1)

[Claims] 1. A multi-frequency antenna characterized in that a coil with a required number of turns is added to the tip of a linear antenna element so that current flows in the opposite direction to the current flowing through the element.