JP2017092663A - Broadband non-directional antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable further band widening while simplifying and downsizing a structure to be disposed on a reflector.SOLUTION: An element 2 consisting of a rotational symmetry body having a longitudinal cross-sectional shape of an index curve is used as a radiation element. Around the radiation element 2, four parasitic elements 31-34 are radially disposed in parallel with a ground plate 1 and with the radiation element 2 defined as a center while being spaced apart from each other at an interval of 90 degrees. The parasitic elements 31-34 consist of: meander parts 313-343 of which the one-side ends are disposed on a peripheral surface of the radiation element 2 while being spaced apart from each other by a gap Δg; horizontal parts 312-342 which are formed while being folded at an angle of 90 degrees in a horizontal direction from other-side ends of the meander parts 313-343; and short-circuiting parts 311-341 which are connected to the ground plate 1 while being folded and formed vertically downwards from other-side ends of the horizontal parts 312-342.SELECTED DRAWING: Figure 1

Description

  The present invention relates to, for example, a relay device that relays a radio signal wave of a mobile phone or a terrestrial wave of a television broadcast, a mobile station such as a ship, a vehicle, or an aircraft, or a broadband omnidirectional antenna used for a land base station.

  In general, antennas used in repeaters that retransmit radio waves from mobile phone systems and terrestrial waves such as television broadcasts to dead zones such as underground shopping malls are small and lightweight due to problems such as installation location and aesthetics. Required. In addition, as a relay antenna, a vertically polarized horizontal omnidirectional antenna is often used.

  As an antenna device that satisfies this requirement, a bidirectionally polarized antenna device is known. This antenna device is, for example, a plurality of linear or planar impedance matching element portions that are excited by one-point feeding from the back side, and are arranged perpendicularly to the matching element portion and arranged to ground the tip. A horizontally polarized bi-directional antenna having a linear radiating element is arranged on a ground plate (see, for example, Patent Document 1).

  On the other hand, as a communication antenna used in a mobile station such as a ship, a vehicle, an aircraft, or a land base station, the horizontal plane directivity is omnidirectional in order to receive radio waves from all directions of arrival, From the viewpoint of general installation strength, etc., it is required to have a low attitude and to have a wide band in order to reduce the number of antennas. Further, in recent years, in order to reduce the RCS (Rader Cross Section) of ships and aircraft, it has been required to integrate the hull and fuselage shapes with the antenna shape. Yes.

  As a technique for flattening the antenna while maintaining a wide bandwidth, for example, four radiating elements are provided radially on a conductor plate formed in a square shape, and a plate-like short-circuit element is provided at the end of each radiating element as a conductor. A technique is known in which a low-profile and wide-band characteristic can be obtained by mounting vertically on a plate and feeding power to the lower central portion of the radiating element via a feeding element (for example, Patent Document 2). 3 or 4).

In addition, as another example of a wideband omnidirectional antenna with a low bandwidth, as shown in FIG. 15 of Patent Document 5, it corresponds to the lower limit operating frequency f _L at a predetermined interval on the ground plate. There has also been proposed an antenna in which four radiating elements set to a length of ¼ of the wavelength λ _L are arranged radially at equal angles and a feeding point is provided below the center of the radiating element. . According to this antenna, vertical polarization horizontal plane directivity can be obtained with a low attitude.

  Furthermore, as another example of the wideband omnidirectional antenna, an antenna that realizes a low attitude and wideband by a structure above the feeding point as shown in Patent Document 6, 7 or 8 has been proposed.

Japanese Patent Laid-Open No. 11-20503 JP 2008-219853 A JP 2011-239094 A JP 2007-336296 A JP 2014-179859 A Japanese Patent No. 3793456 Japanese Patent No. 4287293 Japanese Patent No. 3927680

However, the wide-band omnidirectional antenna described in Patent Document 5 enables a low attitude, but the deviation in the horizontal plane directivity band, particularly the deviation at 250 MHz and 400 MHz, is as large as 5 to 10 dB. Therefore, stable omnidirectionality cannot be obtained, and sufficient wideband characteristics cannot be obtained with respect to the specific bandwidth. Further, the radial dimension is as large as 0.75λ _L with respect to the wavelength λ _L corresponding to the lower limit operating frequency f _L , and further miniaturization is required.

  In addition, the antennas described in Patent Documents 6 and 7 are all complex or large in structure, and it is difficult to increase the dimensions in response to a request for lowering the operating frequency band. Although the antenna described in Patent Document 8 can realize a low-profile antenna, it is difficult to obtain a sufficient broadband property.

  The present invention has been made paying attention to the above circumstances, and its object is to provide a wide-band omnidirectional antenna that can be further broadened while the structure disposed on the reflector is simple and small. It is to provide.

  In order to achieve the above object, a first aspect of the present invention includes a ground plate having a polygonal or circular shape that is equal to or greater than a quadrangle and provided with a power feeding portion at a central portion, and the ground plate directly above the power feeding portion. A radiating element that is erected and has a longitudinal cross-sectional shape formed of an exponential curve or a rotationally symmetric conductor that forms a polygonal line that approximates the exponential curve, and a lower end portion connected to the feeding portion, and the radiating element as a center and the periphery thereof And a plurality of parasitic elements arranged radially at a certain angle from each other. Then, each of the plurality of parasitic elements is arranged in parallel to the ground plate with a certain distance from the peripheral surface of the radiating element, and from the meander portion to the ground plate A horizontal portion that is held in a parallel state and formed at least one diffraction curve, and a short-circuit portion that is bent perpendicularly to the ground plate from the horizontal portion and connected to the ground plate. is there.

  According to a second aspect of the present invention, the plurality of parasitic elements are arranged in four directions at an angle of 90 degrees with respect to the periphery of the radiating element.

According to a third aspect of the present invention, when the meander unit has a target value of the minimum operating frequency as f _M , the width dimension is 0.0327 f _M (excluding the wire diameter) and the length dimension is outside. Is set to 0.0358 f _M (excluding the wire diameter), the center position is set to 0.0302 f _M , the element diameter is set to 0.00406 f _M , and the anti-plurality is set to 4 times (interval 0.005 f _M ).

  According to the first aspect of the present invention, it is possible to obtain a very wide VSWR ratio band and a horizontal plane direction ratio band with a low feeding impedance while having a low profile and a small structure, and in particular, the lower limit operating frequency is reduced. It becomes possible to set it lower.

  According to the second aspect of the present invention, it is possible to obtain desired band characteristics and directivity characteristics at a low cost with a simple and compact structure with the necessary and sufficient number of parasitic elements.

According to a third aspect of the invention, when the VSWR is the lower limit operating frequency when the 3.0 and f _L, with respect to the target value f _M of the minimum operating frequency, be f _L = 0.853f _M Can do.

1 is a perspective view showing the overall configuration of a wideband omnidirectional antenna according to a first embodiment of the present invention. 2A and 2B are diagrams for explaining the size of a parasitic element of the broadband omnidirectional antenna illustrated in FIG. 1, in which FIG. 2A is a plan view, and FIG. 2B is an enlarged view of a part of a meander unit. The figure for demonstrating the size of the radiation | emission element of the broadband omnidirectional antenna shown in FIG. The figure which shows the specific example of the size of the parasitic element and radiation | emission element which were shown in FIG. 2 and FIG. The figure which shows the VSWR characteristic of the broadband omnidirectional antenna shown in FIG. The characteristic view which shows the vertical surface directivity and horizontal surface directivity of the broadband omnidirectional antenna shown in FIG. The figure which shows the best value of the size of the meander part of the broadband omnidirectional antenna shown in FIG. The figure which shows the VSWR characteristic of the broadband omnidirectional antenna shown in FIG. The figure for demonstrating the effect of the broadband omnidirectional antenna shown in FIG. 1 in contrast with the conventional antenna. The figure for demonstrating the effect of the broadband omnidirectional antenna shown in FIG. 1 in contrast with the conventional antenna. The figure for demonstrating the effect of the broadband omnidirectional antenna shown in FIG. 1 in contrast with the conventional antenna. The figure for demonstrating the effect of the broadband omnidirectional antenna shown in FIG. 1 in contrast with the conventional antenna. The figure for demonstrating the effect of the broadband omnidirectional antenna shown in FIG. 1 in contrast with the conventional antenna.

Embodiments according to the present invention will be described below with reference to the drawings.
[First Embodiment]
FIG. 1 is a perspective view showing the overall configuration of a wideband omnidirectional antenna according to a first embodiment of the present invention.
In the wide-band omnidirectional antenna according to the first embodiment of the present invention, the radiating element 2 is erected directly above the power feeding portion 4 disposed at the center of the ground plate 1 having a disc shape. The radiating element 2 is composed of a conductor made of a rotationally symmetric body whose longitudinal section forms an exponential curve, and its lower end is connected to the power feeding section 4. The power feeding unit 4 is connected to a wireless circuit (not shown) through a power feeding pattern formed on the ground plate 1.

  Further, around the radiating element 2, four parasitic elements 31 to 34 are arranged radially at an angle of 90 degrees with respect to the radiating element 2 in the horizontal direction. These parasitic elements 31 to 34 are all made of a linear conductor, and meander parts 313 to 343 having one end arranged on the peripheral surface of the radiating element 2 with a predetermined gap (gap), and the meander part 313. The horizontal portions 312 to 342 that are bent at an angle of 90 degrees in the horizontal direction from the other end of ˜343, and the lower portions of the horizontal portions 312 to 342 are bent vertically downward and connected to the ground plate 1. The short circuit parts 311 to 341 are configured. The parasitic elements 31 to 34 are not limited to linear wires, and may be, for example, strip-shaped or fan-shaped plates.

  FIGS. 2A and 2B are diagrams for explaining the sizes of the parasitic elements 31 to 34. FIG. 2A is a plan view, and FIG. 2B is an enlarged view of a part of the meander part. FIG. FIG. 3 is a diagram for explaining the size of the radiating element 2.

For example, if the target value of the lowest operating frequency in the frequency band to be transmitted / received is f _M and the wavelength corresponding to the target value f _M is λ _M , the radius 2a of the parasitic elements 31 to 34, the short-circuit part 311 A height H of 341, an interval (gap) Δg between the tip of the meander parts 313 to 343 and the peripheral surface of the radiating element 2, a total length L _{0 of} the meander parts 313 to 343 and the horizontal parts 312 to 342, and the meander part The total length L _bent of 313 to 343, the dimensions M and M / 2 of the individual bent portions of the meander parts 313 to 343, the maximum diameter 2X _p of the upper end of the radiating element 2, the total height Z _{p of} the radiating element 2, Z _q and X ₀ are set as shown in FIG. 4 in terms of the wavelength λ _M corresponding to the target value f _M of the minimum operating frequency.

  Further, the exponential curve of the cross section of the radiating element 2 can be obtained by the rotationally symmetric body curve formula shown in FIG. The rotationally symmetric curve is not limited to an exponential curve, and a polygonal line approximating the exponential curve may be used.

The dimensions of each part of the configuration wideband omnidirectional antenna as described above is set to the values shown in FIG. 4, the voltage standing wave ratio with respect to the frequency ratio (f _M ratio): the (Voltage Standing Wave Ratio VSWR) When measured, the characteristics shown in FIG. 5 were obtained. As is apparent from this VSWR characteristic, it can be seen that an extremely wide frequency characteristic having a specific bandwidth of 177% or more can be obtained when the VSWR is 2.0 or less.

As for directivity, first, in the vertical plane, for example, as shown in FIG. 6A, at 0.967λ _M , −5.00 dB or more in the range of 30 ° to 90 ° with the vertical upward being 0 °. gain is obtained, as shown in FIG. 6 (b) for example in the horizontal plane, when the 0.967λ _M, 0dB or more gain can be obtained over the entire azimuth.

By the way, this inventor confirmed that there exist the following best values in the structure of the said meander parts 311-341.
That is, in the case of the meander parts 311 to 341 having a shape as shown in FIG. 7A, the constituent elements are an outer dimension A in the width direction and an outer dimension B in the length direction as shown in FIG. 7B. And the center position C, the element diameter D, and the number of repetitions E. Then, when the target value of the minimum operating frequency is f _M ,
A = 0.0327f _M (excluding wire diameter)
B = 0.0358f _M (excluding wire diameter)
C = 0.0302f _M
D = 0.00406 f _M
E = 4 times (interval 0.005 f _M )
Set to each.

FIG. 8 is a diagram showing simulation values of the VSWR characteristics from the low frequency region to the medium frequency region when the above best value is adopted. As can be seen from the figure, when the above-mentioned best value is adopted as each element of the meander units 311 to 341, the lower limit operating frequency f _L when the VSWR is 3.0 is set to the target value f _M of the minimum operating frequency. On the other hand, f _L = 0.853 f _M.

Incidentally, increasing the external dimensions A in the width direction of the meander portions 311-341, becomes maximum in the vicinity 1.2f _L lower limit operating frequency f _L decreases, VSWR exceeds 3.0. Also, when increasing the length direction of the outer dimensions B, the lower limit operating frequency f _L becomes maximum in the vicinity 1.2f _L decreases, VSWR exceeds 3.0. When the center position C was brought close to the radiating element 2, the VSWR tended to increase over the entire operating frequency band. When the element diameter D is increased, the lower limit operating frequency f _L is asymptotically decreased, and when the element is in contact with an adjacent element, the lower limit operating frequency f _L is increased. On the other hand, when the element diameter D is reduced, the VSWR tends to increase over the entire operating frequency band. Increasing the number of iterations E, the lower limit operating frequency f _L unchanged, VSWR becomes maximum in the vicinity 1.2f _L exceeds 3.0.

  As described in detail above, the broadband omnidirectional antenna according to the first embodiment uses the element 2 made of a rotationally symmetric body having a longitudinal section of an exponential curve as the radiating element, and around the radiating element 2. In the state parallel to the ground plate 1, the four parasitic elements 31 to 34 are arranged radially at an angle of 90 degrees with the radiating element 2 as the center. Then, the parasitic elements 31 to 34 are arranged at 90 degrees in the horizontal direction from the meander parts 313 to 343 arranged at one end with a gap Δg on the peripheral surface of the radiating element 2 and the other ends of the meander parts 313 to 343. The horizontal portions 312 to 342 are bent at an angle of 3 mm and the short-circuit portions 311 to 341 are bent vertically downward from the other ends of the horizontal portions 312 to 342 and connected to the ground plate 1. ing.

Therefore, when the feed impedance is 50Ω, it is possible to obtain a very wide VSWR ratio band and horizontal plane directivity ratio band, and in particular, the lower limit operating frequency f _L can be set lower. In addition, since the overall height H of the antenna element portion excluding the ground plate 1 is 0.1λ _L and the width dimension is 0.29λ _L, a low-profile and compact structure can be maintained, so that both weight and wind receiving load are significantly reduced. An antenna having high wind-resistant performance can be provided. In particular, it is possible to reduce the cost of the antenna by reducing the material cost by reducing the weight.

  Furthermore, since a dielectric material is not required, it has fire resistance and can be adapted to flame retardancy and heat resistance design. Therefore, it is possible to provide an antenna suitable for an environment with fire resistance regulations such as underground facilities and tunnels. Further, since the antenna element and the feed line are arranged on the same plane (front surface) of the ground plate 1 and the back surface of the ground plate 1 is a reflective surface, it can be directly attached to a metal housing or a wall surface. Therefore, it is possible to provide an antenna suitable for an ultra-wideband wireless communication system that employs UWB (Ultra Wide Band) or the like.

That is, the antenna element portion has a low profile and a small structure with an overall height H of 0.1λ _L and a width dimension of 0.29λ _L , but with a feed impedance of 50Ω, the ratio of the extremely wide VSWR ratio band to the horizontal plane directivity It is possible to provide a wideband omnidirectional antenna that can obtain a band and that can set the lower limit operating frequency f _L even lower.

Next, the effect of the broadband omnidirectional antenna according to the first embodiment will be described in comparison with various conventional antennas.
First, at the most basic monopole antenna 20 as shown in FIG. 9, when the wavelength corresponding to the reference working frequency f _A and lambda _A, element length is increased and λ _A / 4. On the other hand, with the antenna according to the first embodiment, as described above, the overall height H can be reduced to 0.1λ _L with respect to the wavelength λ _L of the lower limit operating frequency f _L.

Next, in order to reduce the height of the antenna, as shown in FIG. 10, the element 21 is bent into a U shape to form a half of the loop antenna. In this way, the height H of the antenna can be reduced to the equivalent of λ _A / 8. However, the antenna 21 having this structure cannot obtain omnidirectionality in a horizontal plane.

  Therefore, as shown in FIG. 10, it is assumed that a cross antenna having elements 211 to 214 arranged radially at equal angles in four directions is configured from the tip of the vertical element 210 connected to the power feeding unit 4. In this case, it is possible to obtain omnidirectionality in the horizontal plane while lowering the antenna height. However, this cross-shaped antenna has another problem that the feeding impedance is increased to 200 to 1 kΩ, and further broadband characteristics cannot be obtained.

On the other hand, in order to obtain wideband characteristics, a gap-loaded cross-shaped antenna in which four parasitic elements 221 to 224 are arranged with a gap between them and a radiating element 22 connected to the feeder 4 as shown in FIG. It has been known. In this antenna, two resonance frequencies are coupled by a capacitance formed by a gap, and thereby, a wide band of about twice the ratio (f _H / f _L ) between the upper limit operating frequency f _H and the lower limit operating frequency f _L. Characteristics can be obtained. However, since the antenna having this structure has the widest band when the feeding impedance is about 90Ω, it is difficult to obtain a wide band with the feeding impedance set to 50Ω.

In order to set the feeding impedance to 50Ω, a gap-loaded folded cross antenna in which intermediate portions of the four parasitic elements 231 to 234 are bent in the horizontal direction as shown in FIG. 12 can be considered. With an antenna having this structure, the feeding impedance is adjusted to 50Ω, and the antenna diameter can be reduced. However, it is not possible to further increase the upper limit operating frequency f _H.

Therefore, in order to further increase the upper limit operating frequency f _H , it has been proposed to configure the radiating element with a rotationally symmetric body having a cross-sectional shape of an exponential curve as shown in FIG. When the radiating element 2 made of a rotationally symmetric body having an exponential cross-sectional shape is used, the high frequency region can be further broadened. However, it is difficult to increase the bandwidth in the low frequency range.

In contrast, in the high-frequency omnidirectional antenna according to the first embodiment, the meander portions 341 to 344 are provided in the horizontal portions of the four parasitic elements 31 to 34 as described above. The element length of .about.34 can be increased without increasing the antenna diameter, which makes it possible to further widen the low frequency range. For example, when the VSWR is 3.0, the lower limit operating frequency f _L can be lowered from 3.16 GHz to 2.84 GHz. Thereby, the height ratio of the operating frequency can be 19 or more. When the lower limit operating frequency f _L is lowered to 2.84 GHz, the antenna height H is further lowered to 0.095λ _L without changing the element diameters of the parasitic elements 31 to 34 while being 0.2 mm. can do.

[Other Embodiments]
In the first embodiment, the horizontal portions 312 to 342 of the parasitic elements 31 to 34 are bent at 90 degrees once in a state parallel to the ground plate 1 with respect to the meander portions 313 to 343. A plurality of diffraction curves may be formed in parallel with the ground plate 1. In addition, the shape of the ground plate, the radiating element, and the dimensions of each parasitic element may be set in any manner according to the target operating frequency.

  Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Ground plate, 2 ... Radiation element, 31-34 ... Parasitic element, 311-341 ... Short-circuit part, 312-342 ... Horizontal part, 313-343 ... Meander part, 4 ... Feed part.

Claims (3)

A ground plate with a polygonal or circular shape that is equal to or greater than a quadrangle, and a power feeding portion is provided in the center,
A radiating element that is erected immediately above the power feeding portion of the ground plate, and that is configured by a rotationally symmetric conductor having a longitudinal cross-sectional shape forming an exponential curve or a polygonal line approximating the exponential curve, and having a lower end connected to the power feeding portion; ,
A plurality of parasitic elements arranged radially around the radiating element at a certain angle around the radiating element;
Each of the plurality of parasitic elements includes a meander portion arranged in parallel to the ground plate in a state spaced from the peripheral surface of the radiating element, and parallel to the ground plate from the meander portion. A horizontal portion formed with at least one diffraction curve while maintaining a simple state, and a short-circuit portion that is bent perpendicularly to the ground plate from the horizontal portion and connected to the ground plate. Broadband omnidirectional antenna.   The broadband omnidirectional antenna according to claim 1, wherein the plurality of parasitic elements are arranged in four directions around the radiating element at an angle of 90 degrees with each other. The meander section, when the target value of the minimum operating frequency and f _M, (excluding diameter) 0.0327f _M the outer dimension of the width direction, the 0.0358f _M (wire diameter the external dimensions in the length direction excluded), the center position 0.0302f _M, 0.00406f the element size _M, claim 2, wherein the broadband omnidirectional antenna, characterized in that respectively set in the counter several four times (interval 0.005F _M) .