JP2007019572A - Densely wound helical antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a densely wound helical antenna whose gain can be enhanced while attaining downsizing and that can properly be applied also to an antenna for transmitting/receiving a radio wave in a microwave band. <P>SOLUTION: In the densely wound helical antenna comprising a straight wire shaped inner conductor 20 and a densely wound coil shaped outer conductor 30 arranged coaxially around the inner conductor 20 wherein one end of the inner conductor 20 is freely connected to a feeding side conductor of a 50Ω feeder and one end of the outer conductor 30 is freely connectable to a parasitic side conductor, the wires configuring the outer conductor 30 are wound in a form of a coil, the cross-sectional shape of which is rectangular or nearly rectangular, the longer sides configuring the coil inner diameter and the coil outer diameter, so that the height of the antenna is relatively increased and the antenna gain is improved while attaining downsizing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a small antenna suitable for application to, for example, a mobile communication terminal station.

  In recent years, with the development of mobile communication, there is an increasing demand for miniaturization and high efficiency of antennas in terminal stations (mobile communication terminal stations). However, when the wavelength ratio of the conventional antenna is reduced due to miniaturization, the radiation efficiency is drastically reduced and the antenna gain is reduced. In addition, impedance matching with a 50Ω feed line that is common in mobile communication terminal stations is achieved. I can't take it. Therefore, a small antenna having a wavelength ratio dimension of 1/20 or less generally requires a transformer for matching with a 50Ω feed system. Therefore, as a small antenna that does not require a transformer, has a simple feeding structure, and can be used by being mounted on a small communication device such as a mobile phone, a straight wire-shaped inner conductor 2 as shown in FIG. A small densely wound helical antenna 1 having a densely wound coil shape and an outer conductor 3 whose surface is insulated and disposed coaxially with the inner conductor 2 as the center has been developed (see, for example, Non-Patent Document 1 and Patent Document 1). .)

  This closely wound helical antenna 1 shortens the length in the antenna axial direction (antenna height) by using a closely wound coiled (closely wound helical) conductor element as an external conductor (the element length is constant and the antenna height is high). The feed point impedance is stepped up by the configuration in which the linear inner conductor 2 (primary conductor) to be fed is coaxially arranged at the center of the non-feed tightly wound helical outer conductor 3 (secondary conductor). In addition, the outer conductor 3 (secondary conductor) is thickened and the ratio of the inner diameter of the outer conductor 3 (secondary conductor) to the inner conductor 2 (primary conductor) is increased to increase the transformation ratio and match. Even if there is no device, the 50Ω feed line can be matched. In this case, as a feeding method, a method of short-circuiting the tips of the outer conductor 3 and the inner conductor 2 and a method of opening the tip are possible. When the tip is short-circuited, the antenna height is about 1/26 wavelength, the tip If the antenna is opened, the antenna height can be reduced to about 1/80 wavelength. In either case, the antenna has directivity similar to that of a normal monopole antenna (dipole), the antenna gain can be suppressed to about −15 dBd in terms of dipole ratio, and no ground plane is required.

“Journal of the Institute of Electronics, Information and Communication Engineers”, April 2004, Vol. J87-B, no. 4, p. 524-534) JP 2003-152427 A

  As described above, the tightly wound helical antenna formed by coaxially arranging a tightly wound coil-shaped outer conductor with a straight wire-shaped inner conductor as the center can be reduced in size and requires a transformer. In addition, the power supply structure is simple, and it is suitable as a small antenna to be used by being mounted on a small communication device such as a mobile phone as a mobile communication terminal station. However, the technology of the above-described conventional closely wound helical antenna assumes an antenna that transmits and receives radio waves in the vicinity of the VHF band of, for example, 200 to 500 MHz, and generally has a high frequency band of, for example, 2400 MHz that exceeds 1000 MHz, which is called a microwave. Problems remain when applied to antennas that transmit and receive radio waves.

  In other words, in the case of an antenna that transmits and receives microwave band radio waves, it is possible to reduce the diameter of the conductor (wire) so as to further reduce the height of the antenna depending on the wavelength. When the diameter is reduced and the antenna height is shortened, the antenna gain is reduced and the effectiveness as an antenna is reduced.

  The present invention solves such a problem, and can obtain a tightly wound helical antenna that can improve antenna gain while reducing the size of the antenna and can be suitably applied as an antenna for transmitting and receiving microwave radio waves. With the goal.

  The closely wound helical antenna of the present invention comprises a straight wire-like inner conductor and a densely wound coil-like outer conductor disposed coaxially with the inner conductor as the center, and one end portion of the inner conductor is formed by insulating coating on the surface. A tightly wound helical antenna that can be connected to a power supply-side conductor of a 50 Ω power supply line and one end of the external conductor can be connected to a non-power-supplying side conductor, and the external conductor is a wire whose cross-sectional shape is rectangular or substantially rectangular It is formed, and the long side of the rectangle or the substantially rectangle is coiled in a direction that constitutes a coil inner diameter portion and a coil outer diameter portion.

  Thus, as a wire (wire) constituting the coil-shaped outer conductor, a rectangular or substantially rectangular cross-section wire is adopted instead of the circular cross-section wire in the prior art, and the long side thereof has a coil inner diameter portion and a coil outer diameter. When the thickness dimension on the short side is equal to the diameter of the wire having a circular cross section in the prior art, the length in the antenna axial direction (antenna height) is larger than that of the prior art. Increasing the size and decreasing the thickness on the short side increases the antenna axial length (antenna height) and improves the antenna gain compared to the conventional method of reducing the diameter of the wire with a circular cross section. To do.

  The resonance frequency of a closely wound helical antenna formed by coaxially arranging a coil-shaped outer conductor centering on a straight wire-shaped inner conductor depends on the total length of the wires constituting the coil of the outer conductor. A predetermined impedance characteristic is obtained by making the ratio of the coil inner diameter of the non-powered secondary conductor (outer conductor) to the diameter of the primary conductor (inner conductor) to be fed constant. Therefore, in order to equalize the resonance frequency, it is necessary to make the total length of the wires constituting the coil substantially constant, and in order to make the impedance characteristics equal, the ratio needs to be made substantially constant. Therefore, since the impedance characteristics are equal and the above ratios are approximately equal, the closely wound helical wire of the present invention has a dimension in the antenna radial direction (antenna thickness) compared to the closely wound helical wire using a circular cross-section wire as the outer conductor. ) Is substantially unchanged (the antenna thickness changes if the short side dimension or diameter of the wire changes, but the changes are the same and there is no relative change). Only) becomes relatively large, and the antenna gain is improved.

  Therefore, when applied to an antenna that transmits and receives radio waves in a high-frequency band exceeding 1000 MHz, which is generally called microwaves, for example, 2400 MHz, in order to further reduce the size of the antenna, the conductor (wire) is made thinner and the antenna thickness is reduced. Even if the antenna height is reduced, the antenna height is not as small as that of a conventional closely wound helical antenna, and a required antenna gain can be obtained, so that the effectiveness as an antenna can be obtained. Conventional tightly wound helical antennas are not reasonable to apply to antennas that transmit and receive microwave radio waves.

  The closely wound helical antenna of the present invention may be one in which the other end of the inner conductor and the other end of the outer conductor are connected by a conductor (short-circuit type), and the other end of the inner conductor and the outer conductor It may be one that does not connect to the other end (open type).

  As is apparent from the above description, the closely wound helical antenna of the present invention uses a wire having a rectangular or substantially rectangular cross section instead of a circular cross section wire in the prior art as a wire (wire) constituting the coiled outer conductor. By adopting and winding the coil in the direction in which the long side of the coil constitutes the coil inner diameter part and the coil outer diameter part, the thickness dimension on the short side side is reduced to reduce the size of the antenna as a whole, and the circular shape in the prior art The antenna gain can be improved by relatively increasing the length (antenna height) in the antenna axial direction compared to the case where the diameter of the cross-section wire is reduced, and in particular, an antenna for transmitting and receiving microwave band radio waves. When applied to the antenna, it is possible to improve the antenna gain while reducing the size of the antenna and not to reduce the effectiveness of the antenna.

  In the closely wound helical antenna of the present invention, the wire (wire) constituting the coiled outer conductor is a wire having a rectangular or substantially rectangular cross section, and its short side dimension is the diameter of a conventional circular cross section wire. Since the cross-sectional area is relatively large with respect to the outer conductor of the conventional closely wound helical antenna, the mechanical strength is improved.

  Further, in the closely wound helical antenna of the present invention, the wire (wire) constituting the coiled outer conductor is a wire having a rectangular or substantially rectangular cross section, and the short side dimension is the diameter of the conventional circular cross section wire. Since the surface area is relatively large compared to the outer conductor of the conventional closely wound helical antenna, the so-called skin effect, in which the current tends to concentrate and flow near the surface as the frequency increases, is relatively Loss is reduced and antenna gain is further improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a closely wound helical antenna according to an embodiment of the present invention, and FIGS. 2A and 2B are cross-sectional shapes of wires constituting an outer conductor of the closely wound helical antenna according to the embodiment. It is explanatory drawing which shows the 1st example of this and a 2nd example.

  The tightly wound helical antenna of this embodiment indicated by reference numeral 10 in FIG. 1 comprises a straight wire-like inner conductor 20 and a tightly wound coil-like outer conductor 30 arranged coaxially with the inner conductor 20 as the center, One end of the internal conductor 20 can be connected to a power supply side conductor (not shown) of the 50Ω feed line, and one end of the external conductor 30 can be connected to a non-power supply side conductor (not shown). And the wire which comprises the outer conductor 30 is a rectangle which cross-sectional shape has a round part in four corners, and as shown in FIG. 1, the long side of a rectangle is a coil in the direction which comprises a coil inner diameter part and a coil outer diameter part. It is wound.

  The wire constituting the outer conductor 30 is a copper wire, and an enamel insulating film 31 is formed on the surface thereof as shown in FIG. The rectangular cross-sectional shape has a ratio (h / w) of the dimension (height) h on the long side to the dimension (thickness) w on the short side is 1.1 or more, more preferably, for example, 1 .5 or more.

  The cross-sectional shape of the wire constituting the outer conductor 30 is a flat wire formed by rolling a wire (copper wire) having a circular cross-section as shown in FIG. It may be a cross-sectional shape.

  The closely wound helical antenna 10 may be formed directly on a 50Ω connector (not shown), and the inner conductor 20 and the outer conductor 30 are fixed by another means, and one end side (lower end side) is a printed circuit board. It may be connected to the upper transmission line and ground (GND).

  In addition, the closely wound helical antenna 10 may be a short-circuit type in which the other end of the inner conductor 20 and the other end of the outer conductor are connected by a conductor. What does not connect with the other end part of a conductor (open type) may be sufficient. Further, a synthetic resin insulator such as Teflon (registered trademark) or styrene may be interposed between the inner conductor 20 and the outer conductor 30.

  This closely wound helical antenna 10 has a constant ratio of the coil inner diameter D of the non-powered outer conductor 30 (secondary conductor) to the diameter d of the inner conductor 20 (primary conductor) to be fed (in the “short-circuit type”, for example, D / In the case of d = 2.5 and “open type”, for example, D / d = 4.8), impedance matching with the Ω50 feeder is obtained. Then, the short side dimension (thickness) and the long side dimension (height) of the rectangular cross-sectional wire constituting the coil-shaped outer conductor 30 according to the wavelength of the radio wave of the applied frequency (for example, 2400 MHz). ) By setting the total length of the wire and the total length of the coil, the antenna gain is improved while reducing the size.

It is a schematic block diagram of the closely wound helical antenna of embodiment of this invention. It is explanatory drawing (a), (b) which shows the 1st example and 2nd example of the cross-sectional shape of the wire which comprises an external conductor in the closely wound helical antenna of embodiment of this invention. It is a schematic block diagram of the conventional closely wound helical antenna.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Closely wound helical antenna 20 Inner conductor 30 Outer conductor 31 Insulation film d Inner conductor diameter D Inner conductor coil inner diameter h Long side dimension (height)
w Dimensions on the short side (thickness)

Claims (3)

Consists of a straight wire-shaped inner conductor and a densely wound coil-shaped outer conductor that is coaxially arranged with the inner conductor as the center, and one end of the inner conductor is connected to the power supply side conductor of the 50Ω feeder A tightly wound helical antenna that can be freely connected to one end of an external conductor to a non-feed-side conductor, wherein the external conductor is formed of a wire having a rectangular or substantially rectangular cross section, and the rectangular or substantially rectangular The closely wound helical antenna is characterized in that the long side of the coil is wound in the direction of the coil inner diameter portion and the coil outer diameter portion. 2. The closely wound helical antenna according to claim 1, wherein the other end of the inner conductor and the other end of the outer conductor are connected by a conductor. 2. The closely wound helical antenna according to claim 1, wherein the other end of the inner conductor is not connected to the other end of the outer conductor.

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