WO2008117898A1

WO2008117898A1 - Broad band antenna

Info

Publication number: WO2008117898A1
Application number: PCT/KR2007/001456
Authority: WO
Inventors: Byung Hoon Ryou; Won Mo Sung; Gi Ho Kim
Original assignee: E.M.W. Antenna Co., Ltd.
Priority date: 2007-03-26
Filing date: 2007-03-26
Publication date: 2008-10-02

Abstract

The present invention relates to a broadband antenna. The antenna includes a first radiation element constructed in a meander shape so as to resonate at a high frequency band, a second radiation element constructed in a spiral shape so as to resonate at a frequency band lower than the first radiation element, a stub having one end short-circuited with the first radiation element and the other end grounded and short-circuited, the stub being coupled with the first radiation element so as to match impedance, and a feed terminal electrically short-circuited with the first radiation element and the second radiation element and supplied with power at the same time. Therefore, the present invention can obtain a broadband antenna, which can minimize the length of an antenna employing a coupling effect and also operate at a low frequency band, such as the DVB-H band, as a broadband through one antenna.

Description

BROADBAND ANTENNA Technical Field

[1] The present invention relates to an antenna that forms a broadband in the DVB-H band, and more particularly, to a broadband antenna which can obtain a broadband characteristic by generating dual resonance using a pair of radiation elements covering neighboring bands. Background Art

[2] Along with the development of communication technology, in particular, a wireless communication technology in line with the advancement of the electronic industry, a variety of portable terminals enabling voice and data communication with anyone anywhere and anytime have been developed and generalized. Furthermore, in order to improve the portability of the portable terminals, a variety of technologies for the miniaturization of the portable terminals (for example, the development of high- density integrated circuit elements, a miniaturization method of an electronic circuit board, etc.) have been developed. As the purposes of using the portable terminals are diversified, terminals performing various functions, such as terminals for navigation and terminals for Internet, have bee developed.

[3] Meanwhile, one of the important technologies in the wireless communication technology is technology regarding the antenna. Antennas employing various schemes, such as a coaxial antenna, a rod antenna, a loop antenna, a beam antenna, and a super gain antenna, have now been known.

[4] The antennas are adapted for use of specific frequency bands. When a user tries to employ various services using different frequency bands, such as voice, data communication and Internet, by using portable terminals, there was inconvenience that the user must use different portable terminals per on a service basis.

[5] In particular, the DVB-H band is a relatively low frequency band, and hence has a limitation in using a loop antenna or a patch antenna in order to transmit and receive signals of the DVB-H band.

[6] Therefore, in order to solve the above inconvenience, there is a need for the development of technologies that enable the use of different frequency bands using one antenna.

[7] In particular, in order to obtain a broadband radiation characteristic, the size (length, etc.) of an antenna is increased, which becomes an obstacle in not only the miniaturization of an antenna, but also the miniaturization of a portable terminal in which a corresponding antenna is mounted. [8] Therefore, there is an urgent need for the development of an antenna that can be miniaturized while having a broadband characteristic. Disclosure of Invention

Technical Problem

[9] The present invention has been made in view of the above problems occurring in the prior art, and an object of the present invention is to provide a broadband antenna, which can minimize the length of an antenna employing a coupling effect and also operate at a low frequency band, such as the DVB-H band, as a broadband through one antenna, by generating resonance at different frequencies using a plurality of radiation elements covering different radiation bands.

[10] Furthermore, another object of the present invention is to provide a broadband antenna, which can diversify terminal functions and improve the marketability of products by allowing different services to be provided in one terminal. Technical Solution

[11] To achieve the above objects, the present invention provides a broadband antenna, including a first radiation element constructed in a meander shape so as to resonate at a high frequency band; a second radiation element constructed in a spiral shape so as to resonate at a frequency band lower than the first radiation element; a stub having one end short-circuited with the first radiation element and the other end grounded and short-circuited, the stub being coupled with the first radiation element so as to match impedance; and a feed terminal electrically short-circuited with the first radiation element and the second radiation element and supplied with power at the same time.

[12] Preferably, a ground body that shields the first radiation element and the second radiation element in order to minimize electrical interference between the radiation elements is further included.

[13] Furthermore, a base coupled to the first radiation element and the second radiation element is further included.

[14] More preferably, the first radiation element has patterns formed on two or more faces of the base so as to maximize an electrical length within a permitted space.

[15] Furthermore, a coating body is formed on one surface of the spiral pattern of the second radiation element.

[16] Meanwhile, the impedance is matched by controlling the length of a distal extension portion extending from the spiral pattern of the second radiation element.

[17] Furthermore, the second radiation element operates as a stub of the first radiation element.

[18] Furthermore, a detailed frequency is tuned by controlling the length of the stub.

[19] Furthermore, the first radiation element and the second radiation element resonate at a DVB-H band. [20] Furthermore, the first radiation element resonates at a third resonant frequency band, that is, a harmonic component of a first resonant frequency. [21] Furthermore, a via hole is formed in a predetermined portion of the coating body, and a distal extension portion of the second radiation element penetrates the via hole. [22] Meanwhile, the present invention provides a wireless communication apparatus including the broadband antenna.

Advantageous Effects

[23] The present invention has been made according to the above needs, and generates resonance generates at different frequencies using a plurality of radiation elements covering different radiation bands. Therefore, the present invention can obtain a broadband antenna, which can minimize the length of an antenna employing a coupling effect and also operate at a low frequency band, such as the DVB-H band, as a broadband through one antenna.

[24] Furthermore, the present invention allows one antenna to be applied to different portable terminals. Accordingly, the available range and application objects of a corresponding antenna can be expanded, so the marketability and compatibility of an antenna can be improved.

[25] Furthermore, the present invention can diversify terminal functions and improve the marketability of products by allowing different services to be provided in one terminal. Brief Description of the Drawings

[26] Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

[27] FIG. 1 is a front perspective view showing a broadband antenna in accordance with a first embodiment of the present invention;

[28] FIG. 2 is a rear perspective view showing the broadband antenna in accordance with a first embodiment of the present invention;

[29] FIG. 3 is a front view showing the broadband antenna in accordance with a first embodiment of the present invention;

[30] FIG. 4 is a rear view showing the broadband antenna in accordance with a first embodiment of the present invention;

[31] FIG. 5 is a lateral view showing the broadband antenna in accordance with a first embodiment of the present invention;

[32] FIG. 6 is a perspective view showing the broadband antenna in accordance with a first embodiment of the present invention;

[33] FIG. 7 is a rear perspective view showing a broadband antenna in accordance with a second embodiment of the present invention;

[34] FIG. 8 is a front perspective view showing the broadband antenna in accordance with a second embodiment of the present invention;

[35] FIG. 9 is a perspective drawing of the broadband antenna in accordance with a second embodiment of the present invention;

[36] FIG. 10 is a rear perspective view showing a broadband antenna in accordance with a third embodiment of the present invention;

[37] FIG. 11 is a diagram showing the Smith chart and the standing- wave ratio at the time of conventional single resonance;

[38] FIG. 12 is a diagram showing the Smith chart and the standing-wave ratio at the time of conventional dual resonance;

[39] FIG. 13 is a diagram showing gains and efficiency at the time of conventional dual resonance;

[40] FIG. 14 is a diagram showing the Smith chart and the standing- wave ratio at the time of resonance of the present invention; and

[41] FIG. 15 is a diagram showing gains and efficiency at the time of resonance of the present invention. Best Mode for Carrying Out the Invention

[42] In order to fully understand the present invention, the operational advantages of the present invention, and the objects accomplished by the implementations of the present invention, reference should be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents written in the accompanying drawings.

[43] The present invention will now be described in detail in connection with the preferred embodiments with reference to the accompanying drawings. The same reference numbers will be used throughout the drawings to refer to the same or like parts.

[44] FIG. 1 is a front perspective view showing a broadband antenna in accordance with a first embodiment of the present invention. FIG. 2 is a rear perspective view showing the broadband antenna in accordance with a first embodiment of the present invention. FIG. 3 is a front view showing the broadband antenna in accordance with a first embodiment of the present invention. FIG. 4 is a rear view showing the broadband antenna in accordance with a first embodiment of the present invention. FIG. 5 is a lateral view showing the broadband antenna in accordance with a first embodiment of the present invention. FIG. 6 is a perspective view showing the broadband antenna in accordance with a first embodiment of the present invention.

[45] Referring to FIGS. 1 to 6, the broadband antenna of the present invention includes a board 100 in which a ground body is formed, a first radiation element 200 resonating at a high frequency band, a second radiation element 300 resonating at a frequency band lower than that of the first radiation element, a stub 500 branched from a predetermined portion of an electrical path of the first radiation element 200 and configured to match impedance of the first radiation element 200, a feed terminal 600 feeding power to the first radiation element 200 and the second radiation element 300, and a ground terminal 700 connected to the ground body of the board 100 and grounded.

[46] More specifically, the first radiation element 200 is formed in a meander shape and can maximize its electrical length. The second radiation element 300 is formed in a spiral shape and can maximize its electrical length at a relatively narrow space. In more detail, the second radiation element 300 can include two or more spiral patterns on a surface facing the first radiation element 200. The spiral patterns restrict electrical interference with the first radiation element 200 thereto, thus improving radiation efficiency.

[47] Patterns of a spiral form, which are applicable to the second radiation element 300, are described in detail in Korean Patent Application Nos. 10-2006-0029327 and 10-2006-0033029. The specifications of the applications are incorporated herein by reference. The second radiation element 300 has an increased inductance component and a reduced capacitance component due to its spiral patterns and therefore can have a low quality factor and reflection loss value. Describing this phenomenon from a viewpoint of an equivalent circuit, the antenna can be equalized as a parallel LC resonant circuit.

[48] In the present drawings, the second radiation element 300 has a coil wound from a quadrilateral outer side to a quadrilateral inner side and has a square spiral shape in which four quadrilateral edges are vertical to each other. However, the present invention is not limited to the above construction, but the second radiation element 300 may have the coil wound from the inner side to the outer side. Main radiators of the respective spiral sides are parallel to each other and therefore an electric wave can be radiated and received in all direction of the main radiators. However, the spiral shape proposed in the above embodiment is not limited thereto, but may include even a scroll of a typical circular arc form not including a straight- line portion.

[49] More specifically, the first radiation element 200 can resonate at a first resonant frequency, for example, a 500MHz band used in the digital video broadcasting- handheld (DVB-H). The first radiation element 200 is supplied with power through the feed terminal 600. The first radiation element 200 can reduce signal interference with the second radiation element 300 using the ground body at the DVB-H frequency band, thus realizing a band expansion effect. Furthermore, the first radiation element 200 can realize a secondary band expansion effect through the length of the stub 500, so it can cover a very wide DVB-H bandwidth.

[50] The first radiation element 200 can also resonate at a third resonant frequency band, such as the L-band of the harmonic components of the first resonant frequency. Therefore, a broadband characteristic can be obtained employing overlapping of the frequency bands and a multi-band can be realized using the harmonic components as the third resonant frequency, enabling the miniaturization of an antenna. Here, a detailed frequency can be tuned by controlling the length of the stub 500.

[51] The second radiation element 300 has an electrical length shorter than that of the first radiation element 200, so that the second radiation element 300 can resonate at a second resonant frequency, for example, at the BANDIII (T-DMB) band.

[52] Meanwhile, the first and second radiation elements 200, 300 can be formed using a metal sheet of various materials depending on a person skilled in the art.

[53] The board 100 can include the ground body. The ground body functions as a ground with respect to the plurality of radiation elements 200, 300. The ground body is interposed between the first radiation element 200 and the second radiation element 300 and functions to shield signals radiated from both the radiation elements 200, 300. The ground body does not have a limited shape and can be modified in various forms, including a sheet type ground body.

[54] The feed terminal 600 is a transmission line of signals that are transmitted and received by the plurality of radiation elements 200, 300 and can be connected to a cable such as a coaxial cable. The cable consists of a central conductor that transmits signals and an external conductor serving as a ground. More specifically, the feed terminal 600 is connected to the central conductor of the coaxial cable. The external conductor of the coaxial cable, which serves as the ground of the cable, is connected to the ground body.

[55] Meanwhile, when the antenna comprising the plurality of radiation elements 200,

300 is connected to a portable terminal, phenomena, such as the change of a resonant frequency, can be generated due to several factors upon impedance matching or coupling with the portable terminal. Thus, the antenna undergoes a tuning process for controlling the change of the resonant frequency and reducing reflection loss.

[56] This tuning process can be performed by controlling the shape or length of each radiation element, a distance between respective radiation elements, the size of the stub 500 formed at one side of a radiation element and coupled thereto, a distance between the stub 500 and the radiation element, and so on.

[57] Meanwhile, impedance can be matched by controlling the length of a distal extension portion of the second radiation element 300, which extends from the spiral patterns. Here, the amount of radiation generated from the second radiation element 300 is very smaller than that of the first radiation element 200, so the second radiation element 300 can operate as a kind of a stub.

[58] The broadband antenna of the present invention is described from another point of view. The broadband antenna of the present invention can be interpreted as an antenna having two branches including an inverse F antenna and an L type antenna. Here, the first radiation element 200, that is, the inverse F antenna operates as a main radiation element and the second radiation element 300, that is, the L type antenna operates as an assistant radiation element. At this time, for the purpose of impedance matching, the length of the stub 500, which is branched from a predetermined portion of the first radiation element 200, bent several times and then short-circuited with the ground terminal 700, can be controlled.

[59] FIG. 7 is a rear perspective view showing a broadband antenna in accordance with a second embodiment of the present invention. FIG. 8 is a front perspective view showing the broadband antenna in accordance with a second embodiment of the present invention. FIG. 9 is a perspective drawing of the broadband antenna in accordance with a second embodiment of the present invention.

[60] Referring to FIGS. 7 to 9, a first radiation element 200 and a second radiation element 300 can be integrally formed with a base 800. More specifically, the first radiation element 200 and the second radiation element 300 can be insert-molded with the base 800 or plated on the base 800.

[61] The base 800 can be fabricated using a PCB or can be formed using ceramics or

PPS with a high dielectric constant. More specifically, the base 800 can be formed from ceramics, such as BaTiO base, Ba(Mg Ta )O base or Ba(Zn Ta )O based

3 1/3 2/3 3 1/3 2/3 3 having a relative permittivity ε of about 20 to 120. A wavelength shortening effect can r be obtained through ceramics of a high dielectric constant and an antenna can be further miniaturized. If dielectric ceramics having a relative permittivity exceeding the above range is used, the wavelength shortening effect can be expected. However, when the relative permittivity is 20 or less, the wavelength shortening effect is small, which makes it difficult to entirely miniaturize the size of the antenna. When the relative permittivity exceeds 120, characteristics such as dielectric loss or temperature coefficient are degraded. Accordingly, a problem in that the utilization of the dielectric ceramics as the base 800 is lowed may occur. The base 800 may also be formed from inorganic/ organic complex material.

[62] Meanwhile, the first radiation element 200 can be bent several times in a meander form and then formed on the base 800. Here, in order to maximize the electrical length of the first radiation element 200 within a permitted space, patterns of the first radiation element 200 can be extended by utilizing two or more faces of the base 800.

[63] FIG. 10 is a rear perspective view showing a broadband antenna in accordance with a third embodiment of the present invention.

[64] Referring to FIG. 10, one end of the spiral pattern of the second radiation element

300 can extend from the base with it being spaced apart from the base at a specific interval. A coating body 900 can be formed in the space that is spaced apart from the based, as shown in FIG. 10.

[65] A valid wavelength of electromagnetic waves reduces as the dielectric constant increases. Thus, the electrical length of the second radiation element 300 can be increased by disposing the coating body 900 of a high dielectric constant. In other words, a signal of a long wavelength can be transmitted or received using a smaller antenna. The coating body 900 is formed to cover at least part of the second radiation element 300. The coating body 900 can be formed from material having a dielectric constant higher than that of the board 100 and can employ, preferably, polyphenilyne sulfide (PPS) material. PPS is polymer material comprised of an aromatic ring and sulfur atoms. PPS is high-dielectric material having a relative permittivity of about 20. PPS can be easily processed through injection molding, etc. and is suitable for the material of the coating body 900 since it is high resistant to shock. The layout of the coating body 900 is described in detail in Korean Patent Nos. 10-2006-0005629 and 10-2006-0033029 filed by the applicant of the present invention, the entire contents of which are incorporated herein by reference.

[66] Meanwhile, for easy coupling of the second radiation element 300 and the coating body 900, a via hole is formed at a predetermined portion of the coating body 900 and the distal extension portion of the second radiation element 300 penetrates the via hole. Thus, the structure and the fabrication process of the antenna can be simplified.

[67] FIG. 11 is a diagram showing the Smith chart and the standing- wave ratio at the time of conventional single resonance. FIG. 12 is a diagram showing the Smith chart and the standing- wave ratio at the time of conventional dual resonance. FIG. 13 is a diagram showing gains and efficiency at the time of conventional dual resonance.

[68] Referring to FIG. 11, in the case of a radiation pattern employing the conventional one radiation element, there are some problems in covering the DVB-H band of a broadband since the bandwidth of the radiation element is narrow.

[69] Meanwhile, referring to FIG. 12, a dual resonant antenna made to solve the above problem also can obtain only a physical overlapping effect of both bands and therefore has a relatively narrow bandwidth. The dual resonant antenna inevitably experiences degradation in terms of the gain and efficiency, as shown in FIG. 13.

[70] FIG. 14 is a diagram showing the Smith chart and the standing- wave ratio at the time of resonance of the present invention. FIG. 15 is a diagram showing gains and efficiency at the time of resonance of the present invention.

[71] Referring to FIG. 14, as in the present invention, the first radiation element 200 and the second radiation element 300 are formed to face each other. Here, the first radiation element is formed on at least two faces of the base 800 in the meander form in order to increase its electrical length, and the second radiation element 300 is formed in the spiral structure in order to minimize interference with the first radiation element 200 and can obtain the radiation patterns of a broadband when between-both the radiation elements 200, 300 is shielded by the ground body. Furthermore, as shown in FIG. 15, high gain and efficiency can be obtained when compared with FIG. 13.

[72] The broadband antennas of the present invention have been described above. It will be appreciated that the technical constructions of the present invention can be modified in various ways by those skilled in the art without changing the technical spirit or indispensable characteristics of the present invention.

[73] Furthermore, it is evident that a variety of portable terminals, transmitting/receiving devices for wireless communication, and so on, which employ the broadband antenna of the present invention, may fall within the scope of the present invention. Therefore, it should be understood that the above embodiments are only illustrative in all aspects, but the present invention is not limited to the disclosed embodiments. Therefore, Therefore, the scope of the present invention is not limited by or to the embodiments as described above, and should be construed to be defined only by the appended claims and their equivalents.

Claims

[I] A broadband antenna, comprising: a first radiation element constructed in a meander shape so as to resonate at a high frequency band; a second radiation element constructed in a spiral shape so as to resonate at a frequency band lower than the first radiation element; a stub having one end short-circuited with the first radiation element and the other end grounded and short-circuited, the stub being coupled with the first radiation element so as to match impedance; and a feed terminal electrically short-circuited with the first radiation element and the second radiation element and supplied with power at the same time. [2] The broadband antenna of claim 1, further comprising a ground body for shielding the first radiation element and the second radiation element so as to minimize electrical interference between the radiation elements. [3] The broadband antenna of claim 1, further comprising a base coupled to the first radiation element and the second radiation element. [4] The broadband antenna of claim 3, wherein the first radiation element has patterns formed on two or more faces of the base so as to maximize an electrical length within a permitted space. [5] The broadband antenna of claim 3, wherein a coating body is formed on one surface of the spiral pattern of the second radiation element. [6] The broadband antenna of claim 1, wherein the impedance is matched by controlling the length of a distal extension portion extending from the spiral pattern of the second radiation element. [7] The broadband antenna of claim 1, wherein the second radiation element operates as a stub of the first radiation element. [8] The broadband antenna of claim 1, wherein a detailed frequency is tuned by controlling the length of the stub. [9] The broadband antenna of claim 1, wherein the first radiation element and the second radiation element resonate at a DVB-H band. [10] The broadband antenna of claim 1, wherein the first radiation element resonates at a third resonant frequency band, that is, a harmonic component of a first resonant frequency.

[I I] The broadband antenna of claim 5, wherein: a via hole is formed in a predetermined portion of the coating body, and a distal extension portion of the second radiation element penetrates the via hole. [12] A wireless communication apparatus comprising a broadband antenna according to any one of claims 1 to 11.