JPS6221302A - Loop antenna for portable radio equipment - Google Patents

Abstract

PURPOSE:To improve the efficiency of antenna by using an air-core loop antenna and making a cross sectional area in a direction at a right angle to the coil axis nearly coincident with the maximum cross sectional area of a helmet. CONSTITUTION:The cross sectional shape of the loop antenna 20 in a direction at a right angle to the axis of the coil 21 is made nearly coincident with the cross sectional shape of the outermost circumferential shape of the helmet 10. Suppose that the cross sectional shape of the helmet 10 is a circle, then the cross sectional shape in the right angle direction of the coil 21 with respect to its axis is formed as a circle and the diameter is made nearly equal to the diameter of the largest cross sectional area of the helmet. Thus, the weight is light because of the adoption of the air-core regardless of the large-sized loop antenna and the antenna efficiency is improved without giving inconvenience to the carrying performance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a loop antenna for a portable radio device used in machine factories, construction sites, power-related work, and the like.

[Conventional technology]

BACKGROUND ART Loop antennas used in conventional portable radios (mainly inductive radios) are generally made by winding a conducting wire around a ferromagnetic core (magnetic core) such as ferrite to form a coil to provide desired characteristics.

Figure 2 shows a conventional example and its usage.
B shows the one built into the main body of the radio, and B shows the one separated from the main body of the radio. In these figures, (2) is the loop antenna, (21) is its coil, (22) is the ferrite core, (3) is the coaxial cable, and (4) is the main body of the radio. In the case of FIG. 2B, the antenna section is stored in, for example, a breast pocket, and the radio device main body (4) is attached, for example, to the waist.

[Problem that the invention seeks to solve]

Conventional loop antennas as described above are made small and lightweight in consideration of portability, and therefore generally have very low antenna efficiency of tJ4. Furthermore, when trying to improve antenna efficiency, the antenna inevitably becomes larger and heavier, making it unsuitable for portability.

[Means for solving problems]

The present invention focuses on the fact that users of portable radios often wear helmets, and the loop antenna has an air core instead of a magnetic core so that it can be detachably attached to the outer circumference of the helmet. The above-mentioned problem was solved by making the cross-sectional area in the perpendicular direction almost match the maximum cross-sectional area of the helmet.

[Effect]

By attaching the loop antenna to the outer periphery of the helmet, the cross-sectional area of the antenna is increased and antenna efficiency is improved.

Generally, the effective length he, which is a parameter of antenna efficiency, can be expressed by the following equation in the case of a loop antenna.

λ Here, N is the number of turns of the loop, S is the cross-sectional area, μe is the effective magnetic permeability of the magnetic core, and λ is the wavelength.

According to formula (1), to increase the effective length he, N or S
It turns out that you can make it larger. However, it is known that even if the number of turns N of the loop is increased, the antenna efficiency is not improved much.

Therefore, if we take the number of loops N and the wavelength λ constant and look at the efficiency ratio (improvement rate) η between the loop antenna wound around the magnetic core and the loop antenna attached to the outer periphery of the helmet, Since the effective magnetic permeability in the case of is approximately ], the following formula % formula % where hel is the effective length of the loop antenna wound around the magnetic core, Sl is the cross-sectional area of the magnetic core, μe is the effective magnetic permeability of the magnetic core, he
x is the effective length of the loop antenna attached to the helmet, S
2 is the cross-sectional area of the helmet.

Now, the cross-sectional area S1 of the magnetic core is 5 x 12 (H2) =
7.2X10-5 (durability), helmet cross-sectional area S2 is 0
．． 04 (rd), assuming that the effective magnetic permeability μe of the magnetic core is 30. It can be seen from this that the antenna efficiency is significantly improved.

〔Example〕

FIG. 1 is a schematic diagram illustrating an embodiment of the invention.

In the figure, (10) is a helmet. Helmet I-(10) is not limited to a safety helmet, but may be any other type of helmet or hat, as long as it can attach a loop antenna and is worn in a recessed part. is used for this laziness. (20)
is a loop antenna, and the cross-sectional shape of the coil (21) in the direction perpendicular to the axis is Helmet! - The cross-sectional shape of the maximum outer periphery of (10) is approximately the same. Hermeso 1-(1
Assuming that the cross-sectional shape of coil (21) is circular, the cross-sectional shape of coil (21) in the direction perpendicular to the axis is also circular, and its diameter is approximately equal to the diameter of the largest cross-sectional area of the helmet. however,
The maximum cross-sectional area of a helmet varies depending on the wearer, so
The cross-sectional area of the coil (21) of the loop antenna (20) may be prepared in various sizes in accordance with this, or may be set based on an average-sized helmet and adjusted to that cross-sectional area. (30) is a coaxial cable, (40
) is the main body of the radio, which is the same as the conventional one.

The radio main body (40) is attached to a chest pocket, waist belt, or the like.

〔Effect of the invention〕

As explained above, according to the present invention, although the loop antenna is large in size, it is lightweight due to its air core, and antenna efficiency can be significantly improved without impairing portability.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and FIG. 2 is a schematic diagram showing a conventional example and its usage situation. (10)... Helmet, (20)... Loop antenna, (21)... Its coil, (40)... Portable radio device body.

Claims (1)

[Claims] A loop antenna for a portable radio device, characterized in that the cross-sectional area in the direction perpendicular to the axis of the coil almost matches the maximum cross-sectional area of the helmet, so that it can be attached to and detached from the outer circumference of the helmet.