JP2008160366A - Balanced wide band antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna which attains a balanced wide band antenna and has an improved matching state and whose directivity has no frequency characteristics. <P>SOLUTION: A projection (stub) is provided on a grounded element, namely, a ground plate to solve the problem. That is, in the balanced wide band antenna which has a radiation element formed with a symmetrical conductor pattern on the front face of a dielectric substrate and has the grounded element formed of a conductor pattern on the rear face of the dielectric substrate, the radiation element being connected to an external circuit through a balun, the grounded element has a rectangular conductor pattern and includes conductor patterns projecting from end parts in the longitudinal direction of the rectangular conductor pattern or their neighbors in directions orthogonal to the longitudinal direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to the structure of a balanced broadband antenna using a balun, and relates to the shape of a conductor pattern formed on a dielectric substrate.

  There are various types of antennas, and they are used according to the system application. In antennas used in mobile devices for mobile communication, there is a strong demand for miniaturization and thinning, and antennas composed of a conductor pattern formed on a dielectric substrate or a laminated structure have been studied. It has been put into practical use. In addition, it is necessary to change the shape of the radiating element in order to meet the demand for wider bandwidth such as UWB.

  FIG. 8 shows an example of such a wide-band antenna, in which the antenna is composed of a conductor pattern formed on the front and back surfaces of a dielectric substrate. Antenna elements, that is, radiating elements 81 and 82 having a copper foil conductor pattern are formed symmetrically on the surface of the dielectric substrate 80. In order to increase the bandwidth, the shape is not a rectangle but the width gradually increases. These two radiating elements 81 and 82 are connected to a coaxial line (not shown) via a balun 84 such as a laminated balun mounted in a chip and mounted on a dielectric substrate 80 to supply power.

  A ground element 86 having a rectangular conductor pattern is formed on the back surface of the dielectric substrate 80 so as to cross between the two radiating elements. The ground element 86 is connected to an outer conductor of a coaxial line (not shown). The actual connection is made via a coaxial connector attached to the back surface of the dielectric substrate.

An antenna that performs balanced feeding using the balun as described above has a poor matching state when the grounding element as shown in FIG. 8 is formed in a rectangular shape, and improves the matching state even if the size of the grounding element is changed. It is not possible. In order to improve the matching state, there is a method of making the two radiating elements different in size and shape so that they are asymmetrical. However, if the symmetry of the radiating elements is broken, another problem arises that the directivity has frequency characteristics. . FIG. 9 and FIG. 10 show the problem state of these characteristics. The shape of FIG. 8 cannot satisfy the return loss characteristic in a part of the target frequency range, and the real part in the frequency range. The impedances of (Real: solid line) and imaginary part (Imaginary: broken line) vary greatly from 50Ω and 0Ω, respectively, indicating that no matching is obtained.
JP 2005-130292 A

  The present invention realizes a balanced broadband antenna, and provides an antenna with improved matching state and directivity having no frequency characteristics.

  The present invention solves the above-mentioned problems by providing protrusions (stubs) on a ground element, that is, a ground plate. Namely, a balanced broadband antenna comprising a radiating element formed with a symmetric conductor pattern on the surface of a dielectric substrate and a grounding element formed with a conductor pattern on the back surface thereof, the radiating element being connected to an external circuit through a balun. The grounding element is a rectangular conductor pattern, and is characterized in that it has a conductor pattern protruding in a direction perpendicular to the longitudinal direction from the longitudinal end of the rectangular conductor pattern or its vicinity. is there.

The following effects can be obtained by the present invention.
(1) Improvement of matching state of balanced antenna using balun (2) Realization of antenna whose directivity does not have frequency characteristics By changing the shape of the grounding element, the frequency change of the Real component and Imaginary component of the input impedance Suppresses fluctuations and maintains a stable state in which the Real component is 50Ω and the Imaginary component are close to 0Ω even in the high frequency band, and the matching state is stabilized. In addition, an antenna having ideal dipole directivity in a predetermined frequency band and having no frequency characteristic in the directivity is realized.

The components of the balanced broadband antenna according to the present invention are as follows.
(1) Dielectric substrate: A conductor pattern of a radiating element and a ground element is formed, and a balun is mounted.
(2) Radiation element: It is composed of a symmetrical conductor pattern on the surface of a dielectric substrate.
(3) Balun: Performs balanced-unbalanced conversion between the radiating element and the feed line.
(4) Grounding element: It is composed of a rectangular conductor pattern that is formed on the back surface of the dielectric substrate and has a protruding portion that serves as a ground plate for the antenna. Various shapes such as symmetrical and asymmetrical shapes can be adopted as the shape of the protruding portion.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a plan view and FIG. 1B is a bottom view showing an embodiment of the present invention. In this example, pentagonal radiating elements 11 and 12 are formed of copper foil on the surface of a dielectric substrate (dielectric constant = 4.4) 10 having a thickness of 24 mm × 60 mm and a thickness of 0.6 mm. The radiating elements 11 and 12 have a shape in which the width gradually increases in order to increase the bandwidth. The two radiating elements 11 and 12 are each connected to a balun 14 that performs balanced-unbalanced conversion. The balun 14 can be configured by mounting a multilayer chip balun usable in a frequency range of 3.2 GHz to 4.8 GHz on a dielectric substrate.

  A ground element 16 serving as a ground plate is formed with a copper foil conductor pattern at the center of the back surface of the dielectric substrate 10. In this example, a 6.5 mm width pattern is formed across the width direction of the dielectric substrate, and a 2 mm wide conductor pattern that protrudes about 7 mm is added to both ends of the 22.4 mm length. Since the protrusions 17 are formed symmetrically at four locations, the shape of the grounding element is H-shaped. The difference from the conventional antenna shown in FIG. 8 is that this protrusion 17 is provided.

  The characteristics of the antenna configured as described above will be described. When the matching state is shown by the return loss characteristic of FIG. 2, it was confirmed that the return loss in the target frequency range from 3.2 GHz to 4.8 GHz was cleared to −10 dB, and matching as an antenna was obtained. In addition, in the target frequency range of the input impedance characteristic of 3.2 GHz to 4.8 GHz in FIG. 3, the Real component is approximately 50Ω and the Imaginary component is approximately 0Ω, indicating that the input characteristics are improved.

  Next, the measurement result about the directivity of the balanced broadband antenna according to the present invention will be described. FIG. 4 shows the directivity of vertical polarization (solid line) and horizontal polarization (broken line) in the horizontal plane of the antenna shown in FIG. It was confirmed that the directivity does not have frequency characteristics and the omnidirectionality of the horizontal vertical polarization can be obtained by making the conductor pattern of the grounding element H-shaped. FIG. 5 shows vertical polarization (solid line) and horizontal polarization (broken line) on the vertical plane.

  The shape of the grounding element of the balanced broadband antenna according to the present invention is not limited to the shape shown in FIG. 1, and any shape as shown in FIGS. 6 and 7 can be adopted. In the example of FIG. 6, conductor patterns are formed symmetrically in both the length direction and the width direction, and in FIG. 7, at least one is formed asymmetrically.

  The present invention can be used for antennas that require a wider band, such as UWB-compatible antennas, and can meet the demand for small and thin antennas.

The top view (a) and bottom view (b) which show the example of the present invention Illustration of its return loss characteristics Illustration of its input impedance characteristics Illustration of directional characteristics in the horizontal plane Illustration of directivity characteristics within the vertical year Bottom view showing another embodiment of the present invention Bottom view showing another embodiment of the present invention Plan view (a) and bottom view (b) showing a conventional example Illustration of its return loss characteristics Illustration of its input impedance characteristics

Explanation of symbols

10, 80: Dielectric substrate
11, 12, 81, 82: Radiation element
14, 84: Balun
16, 86: Grounding element
17: Projection

Claims (3)

In a balanced broadband antenna comprising a radiating element formed with a symmetric conductor pattern on the surface of a dielectric substrate and a grounding element formed with a conductor pattern on the back surface, the radiating element being connected to an external circuit via a balun,
The grounding element is a rectangular conductor pattern, and includes a conductor pattern that protrudes in a direction perpendicular to the longitudinal direction from or near the longitudinal end of the rectangular conductor pattern. . 2. The balanced broadband antenna according to claim 1, wherein the protruding conductor patterns are formed symmetrically. 2. The balanced broadband antenna according to claim 1, wherein the protruding conductor pattern is formed asymmetrically.

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