Multi-band internal antenna

[Technical Field]

0001The present invention relates to an antenna, more particularly to a multi band internal antenna.

[Background Art]

0002In current mobile terminals, there is a demand not only for smaller sizes and lighter weight, but also for functions that allow a user access to mobile communication services of different frequency bands through a single terminal. That is, there is a demand for a terminal with which a user may simultaneously utilize signals of multiple bands as necessary, from among mobile communication services of various frequency bands, such as the CDMA service based on the 824∼894 MHz band and the PCS service based on the 1750∼1870 MHz band commercialized in Korea, the CDMA service based on the 832∼925 MHz band commercialized in Japan, the PCS service based on the 1850∼1990 MHz commercialized in the United States, the GSM service based on the 880∼960 MHz band commercialized in Europe and China, and the DCS service based on the 1710∼1880 MHz band commercialized in parts of Europe. Furthermore, there is a demand for a composite terminal that allows the use of services such as Bluetooth, ZigBee, wireless LAN, GPS, etc. In this type of terminal for using services of multiple bands, a multi-band antenna is needed, which can operate in two or more desired bands. The antennas generally used in mobile terminals include the helical antenna and the planar inverted-F antenna (PIFA).

0003Here, the helical antenna is an external antenna that is secured to an upper end of a terminal, and is used together with a monopole antenna. In an arrangement in which a helical antenna and a monopole antenna are used together, extending the antenna from the main body of the terminal allows the antenna to operate as a monopole antenna, while retracting the antenna allows the antenna to operate as a λ/4 helical antenna. While this type of antenna has the advantage of high gain, its non-directivity results in undesirable SAR characteristics, which form the criteria for levels of electromagnetic radiation hazardous to the human body. Also, since the helical antenna is formed protruding outwards of the terminal, it is difficult to design the exterior of the terminal to be aesthetically pleasing and suitable for carrying, but a built-in structure for the helical antenna has not yet been researched.

0004[D6] <patcit id="pcit0001" dnum="EP0814535A"><text>EP0814535</text></patcit> addresses the problem of providing a surface-mount antenna in which excitation can occur without contact by using a capacitor, wherein matching can be performed even if the antenna size is reduced and which can be easily mounted on a surface by an input end formed on a side of a base member. For solving this problem, <patcit id="pcit0002" dnum="EP0814535A"><text>EP0814535</text></patcit> proposes a surface-mount antenna including a radiation electrode formed on one or more surfaces of a rectangular parallelopiped base member comprising a dielectric or a magnetic substance so as to have one end as an open end and another end as a first ground electrode; a feeding electrode formed on the surface or surfaces; and a second ground electrode formed in proximity to the open end of said radiation electrode.

0005[D7] <patcit id="pcit0003" dnum="WO2004057698A"><text>WO2004057698</text></patcit> addresses a multitude of improvements for capacitively loaded magnetic dipole (CLMD) antennas. One of the problems <patcit id="pcit0004" dnum="WO2004057698A"><text>WO2004057698</text></patcit> addresses is to provide CLMD antennas with reduced sizes without decrease in performance. For solving this problem, <patcit id="pcit0005" dnum="WO2004057698A"><text>WO2004057698</text></patcit> inter alia proposes an antenna element with a top portion, a middle portion and a bottom portion, wherein the top portion and the middle portion are provided with parallel ridges, such that the top portion and the middle portion maintain a constant gap size between them. According to <patcit id="pcit0006" dnum="WO2004057698A"><text>WO2004057698</text></patcit>, this ridged configurations allows the antenna element to maintain the electric field strength between the top portion and the middle portion while reducing the footprint of the antenna element.

0006[D8] <patcit id="pcit0007" dnum="JP2004236273B"><text>JP2004236273</text></patcit> addresses the problem of providing an antenna whose frequency characteristics are not changed owing to production variations. For solving this problem, <patcit id="pcit0008" dnum="JP2004236273B"><text>JP2004236273</text></patcit> proposes an antenna being equipped with a pattern coil formed on a substrate and a pattern capacitor composed of first and second electrode patterns formed on the same surface and adjacently disposed, and the pattern coil and the pattern capacitor are parallel or serially connected. In particular, <patcit id="pcit0009" dnum="JP2004236273B"><text>JP2004236273</text></patcit> teaches that thereby a change in an inductance value of the pattern coil is cancelled by a capacitance change of the pattern capacitor, thereby fixing a product of the inductance value and a capacitance value.

0007[D9] <patcit id="pcit0010" dnum="US5903240A"><text>US 5903240</text></patcit> addresses the problem of providing a surface mounting antenna in which a wider frequency bandwidth and a signal having a plurality of frequencies can be obtained without needing to enlarge the configuration of the overall antenna. For solving this problem, <patcit id="pcit0011" dnum="US5903240A"><text>US 5903240</text></patcit> proposes a surface mounting antenna comprising a substrate formed of at least one of a dielectric material and a magnetic material; at least two radiation electrodes for producing different resonant frequencies disposed on a first main surface of said substrate; a ground electrode disposed on a second main surface of said substrate; and a feeding electrode disposed on said substrate; said radiation electrodes each being open at first ends thereof and connected at second ends to said ground electrode, said feeding electrode and the open ends of said radiation electrodes being electromagnetically coupled to each other through capacitances.

0008The inverted-F antenna is an antenna designed to have a low profile structure in order to overcome such drawbacks. The inverted-F antenna has directivity, and when current induction to the radiating part generates beams, a beam flux directed toward the ground surface may be re-induced to attenuate another beam flux directed toward the human body, thereby improving SAR characteristics as well as enhancing beam intensity induced to the radiating part. Also, the inverted-F antenna operates as a rectangular micro-strip antenna, in which the length of a rectangular plate-shaped radiating part is reduced in half, whereby a low profile structure may be realized.

0009Because the inverted-F antenna has directive radiation characteristics, so that the intensity of beams directed toward the human body may be attenuated and the intensity of beams directed away from the human body may be intensified, a higher absorption rate of electromagnetic radiation can be obtained, compared to the helical antenna. However, the inverted-F antenna may have a narrow frequency bandwidth when it is designed to operate in multiple bands.

0010The narrow frequency bandwidth obtained when designing the inverted-F antenna to operate in multiple bands is resultant of point matching, in which matching with a radiator occurs at a particular point.

0011Thus, there is a demand for an antenna that maintains a low profile structure and overcomes the drawback of the inverted-F antenna of narrow band characteristics for more stable operation in multiple bands.

[Disclosure]

[Technical Problem]

0012To resolve the problems in prior art described above, an objective of the present invention is to provide a multi band internal antenna that exhibits wide-band characteristics even for multi-band designs.

0013Another objective of the present invention is to provide a multi band le internal antenna that provides wide-band characteristics using matching by coupling. Still another objective of the present invention is to provide a multi band internal antenna that is less affected by external factors, such as the hand effect.

0014Additional objectives of the present invention will be obvious from the embodiments described below.

[Technical Solution]

0015To achieve the objectives above, an aspect of the present invention presents a multi band internal antenna in accordance with claim 1, the antenna includes: a board, an impedance matching/feeding part formed on the board, and a first radiation element joined to the impedance matching/feeding part, where the impedance matching/feeding part includes: a first matching element of a particular length that is coupled to a ground, and a second matching element of a particular length that is arranged with a distance from the first matching element and is electrically coupled to a feeding point. The first matching element and the second matching element include a multiple number of coupling elements that protrude from the first matching element and the second matching element.

0016More specific aspects are defined in the dependent claims.

[Advantageous Effects]

0017Certain aspects of the present invention can provide a multi band internal antenna that utilizes coupling matching to achieve wide-band characteristics even for multi-band designs. Also, certain aspects of the present invention can provide a multi band antenna that is less affected by external factors, such as the hand effect.

[Description of Drawings]

0018<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Figure 1</figref> illustrates the structure of a multi band internal antenna according to a first disclosed example not being part of the present invention.</li><li><figref idref="f0002">Figure 2</figref> represents S11 parameters of the antenna illustrated in <figref idref="f0001">Figure 1</figref>.</li><li><figref idref="f0003">Figure 3</figref> illustrates the structure of a multi band internal antenna according to a second disclosed embodiment of the present invention.</li><li><figref idref="f0004">Figure 4</figref> represents S1 1 parameters of a multi band antenna according to the second disclosed embodiment of the present invention.</li><li><figref idref="f0005">Figure 5</figref> illustrates the structure of a multi band internal antenna according to a third disclosed embodiment of the present invention.</li><li><figref idref="f0006">Figure 6</figref> represents S1 1 parameters of an multi band antenna according to the third disclosed embodiment of the present invention.</li><li><figref idref="f0007">Figure 7</figref> illustrates the structure of a multi band internal antenna according to a fourth disclosed embodiment of the present invention.</li><li><figref idref="f0008">Figure 8</figref> represents S11 parameters of an multi band antenna according to the fourth disclosed embodiment of the present invention.</li><li><figref idref="f0009">Figure 9</figref> illustrates a structure in which a multi band internal antenna according to the third disclosed embodiment of the present invention is joined to an antenna carrier of a terminal.</li><li><figref idref="f0010">Figure 10</figref> illustrates a structure in which a multi band internal antenna according to the fourth disclosed embodiment of the present invention is joined to a PCB of a terminal.</li><li><figref idref="f0011">Figure 11 through Figure 13</figref> illustrate structures of the first matching elements and second matching elements according to embodiments of the present invention that provide high coupling.</li></ul>

[Mode for Invention]

0019The multi band internal antenna according to certain embodiments of the present invention or examples not being part of the present invention will be described below in more detail with reference to the accompanying drawings.

0020The embodiments or examples disclosed in the present specification will be presented using as an example a multi band antenna employed in GSM service bands, PCS service bands, and WCDMA service bands. However, the multi band internal antenna is not limited to the above bands, and can be made to operate for various frequency bands.

0021<figref idref="f0001">Figure 1</figref> illustrates the structure of a multi band internal antenna according to a first disclosed example not being part of the present invention. Referring to <figref idref="f0001">Figure 1</figref>, a multi band internal antenna can include a board 100, a radiation element 102 and an impedance matching/feeding part 104 formed on the board.

0022In <figref idref="f0001">Figure 1</figref>, the board 100 may be made of a dielectric material, and may serve as the antenna's main body, to which the other components may be joined. A variety of dielectric materials can be applied as the board 100. For example, the board can be a PCB, FR4 board, etc.

0023As described above, an antenna structured as an inverted-F antenna may utilize point matching with the radiation element by way of shorting pins, etc. This point matching, however, may narrow the frequency bandwidth.

0024To resolve the drawback of point matching stated above, a matching method based on coupling is presented, which includes an impedance matching/feeding part 104 having a particular length.

0025The impedance matching/feeding part 104 may include a first matching element 120, which may be electrically coupled to a ground, and a second matching element 130, which may be electrically coupled to a feeding point (not shown). Coupling feeding may be performed within the impedance matching/feeding part 104 from the second matching element 130 to the first matching element 120, while signals may be radiated by the radiation element 102, which is electrically coupled to the first matching element 120.

0026The first matching element 120 and the second matching element 130 may be formed with a particular gap in-between, and the interaction between the first matching element 120 and the second matching element may enable coupling matching. In the interaction between the first matching element 120 and the second matching element 130, the capacitance component may play a greater role than the inductance component, and as such the present example presents a structure that enables impedance matching for an wide-band by diversifying the capacitance component.

0027In order to diversify the capacitance component, the gap between the first matching element 120 and the second matching element 130 may be partially varied.

0028An example of partially varying the distance between the first matching element 120 and the second matching element 130 is shown in <figref idref="f0001">Figure 1</figref>, which illustrates a structure in which the first matching element 120 is bent several times, and the second matching element 130 is bent correspondingly.

0029Based on the bending positions, the first matching element 120 may be divided into three sections: section A1-A1', section A2-A2', and section A3-A3'. The second matching element 130 may be bent in correspondence with the first matching element 120, and may be divided into section B1-B1', section B2-B2', and section B3-B3'.

0030In an embodiment of the present invention, the distance <i>d1</i> between section A1-A1' and section B1-B1', the distance <i>d2</i> between section A2-A2' and section B2-B2', and distance <i>d3</i> between section A3-A3' and section B3-B3' are all different.

0031Thus, by implementing the first matching element 120 and the second matching element 130 as bending structures, and partially varying the distance in-between, wide-band characteristics by coupling matching and feeding can be obtained.

0032While <figref idref="f0001">Figure 1</figref> illustrates an example in which the distance between the first matching element 120 and the second matching element 130 varies partially due to bends in the first matching element 120 and the second matching element 130, it will be understood by the skilled person that this may be implemented in a variety of ways other than that illustrated in <figref idref="f0001">Figure 1</figref>.

0033Various embodiments that include varying distance between the first matching element and the second matching element are encompassed within the present disclosure, in one example the second matching element 130 may be formed as a straight line, while the first matching element 120 and the radiation element may be arranged diagonally, so that the distance is made to vary.

0034RF signals may be provide to the radiation element 102 by coupling feeding, as described above, and the radiation element 102 may radiate the signals to the exterior. The radiation element 102 may be connected to the first matching element 120 of the impedance matching/feeding part 104. Here, the transmission frequency band may be determined by the length of the radiation element 102 and the length of the impedance matching/feeding part 104.

0035<figref idref="f0002">Figure 2</figref> represents S11 parameters of the antenna illustrated in <figref idref="f0001">Figure 1</figref>.

0036Referring to <figref idref="f0002">Figure 2</figref>, it can be observed that the S11 parameters of the antenna illustrated in <figref idref="f0001">Figure 1</figref> represent relatively wide band characteristics.

0037In order to obtain wider band characteristics when utilizing matching by coupling, a structure is desired which can both diversify the capacitance component and provide a high capacitance in certain regions. This can also reduce the impact of external factors such as the hand effect by high capacitance..

0038<figref idref="f0003">Figure 3</figref> illustrates the structure of a multi band internal antenna according to a second disclosed embodiment of the present invention.

0039Referring to <figref idref="f0003">Figure 3</figref>, a multi band internal antenna according to the second disclosed embodiment of the present invention includes a board 300, a radiation element 302 and an impedance matching/feeding part 304 formed on the board 300, where the impedance matching part 304 includes a first matching element 320 and a second matching element 330.

0040Also, a multiple number of first coupling elements 306 are formed which may protrude perpendicularly to the lengthwise direction of the first matching element 320, and a multiple number of second coupling elements 308 are formed which may protrude perpendicularly to the lengthwise direction of the second matching element.

0041As in the first disclosed example described above, the first matching element 320 is electrically coupled to a ground, and the second matching element 330 is electrically coupled to a feeding point, and coupling feeding is performed from the second matching element 330 to the first matching element 320.

0042The multi band internal antenna according to the second disclosed embodiment of the present invention, as illustrated in <figref idref="f0003">Figure 3</figref>, is structured to allow coupling by a higher capacitance.

0043The structure of the internal antenna according to the second disclosed embodiment of the present invention includes first coupling elements 306 and second coupling elements 308, in addition to the structure of an antenna according to the first disclosed example.

0044The first coupling elements 306 and second coupling elements 308 enable coupling matching by a higher capacitance.

0045As illustrated in <figref idref="f0003">Figure 3</figref>, the first coupling elements 306 and second coupling elements 308 may be formed protruding from the first matching element and second matching element in a comb-like form. In certain embodiments, the first coupling elements 306 and the second coupling elements 308 may be formed alternately, to form generally comb-like shapes.

0046These coupling elements 306, 308 may substantially narrow the distance between the first matching element and the second matching element, to not only provide a higher capacitance, but also aid in diversifying the capacitance component, so as to enable matching for wider bands.

0047<figref idref="f0004">Figure 4</figref> represents S11 parameters of a multi band antenna according to the second disclosed embodiment of the present invention.

0048Referring to <figref idref="f0004">Figure 4</figref>, it can be observed that an antenna according to the second disclosed embodiment of the present invention exhibits wider band characteristics compared to the antenna of the first disclosed example illustrated in <figref idref="f0002">Figure 2</figref>.

0049A structure for achieving greater coupling between the first matching element and the second matching element can be implemented in various ways other than by the structures illustrated in <figref idref="f0001">Figure 1</figref> and <figref idref="f0003">Figure 3</figref>. <figref idref="f0011">Figure 11 through Figure 13</figref> are drawings that illustrate structures of first matching elements and second matching elements for obtaining greater coupling according to certain embodiments of the present invention.

0050As illustrated in <figref idref="f0011">Figure 11 through Figure 13</figref>, the widths and lengths of the coupling elements can be varied, and as shown in <figref idref="f0011">Figure 13</figref>, the coupling elements can also be implemented in shapes other than rectangles.

0051<figref idref="f0005">Figure 5</figref> illustrates the structure of a multi band internal antenna according to a third disclosed embodiment of the present invention.

0052Referring to <figref idref="f0005">Figure 5</figref>, a multi band internal antenna according to the third disclosed embodiment of the present invention includes a board 500, a first radiation element 502, an impedance matching/feeding part 504, and a second radiation element 506 formed on the board 500.

0053The impedance matching/feeding part 504 includes a first matching element 520, which is electrically coupled to a ground, and a second matching element 530, which is electrically coupled to a feeding point, where coupling elements 306, 308 are formed protruding from the first matching element 520 and second matching element to enable matching for wider bands.

0054The first radiation element 502 is formed extending from the first matching element 520 and feeding is performed by coupling.

0055In the third disclosed embodiment, the compositions of the first radiation element 502 and the impedance matching part 504 are substantially the same as those for the second disclosed embodiment described above, but the second radiation element 506 may be additionally included. The second radiation element 506 may be added for transmitting and receiving signals from different bands from those of the first radiation element 502. The second radiation element 506 may be separated by a particular distance from the first radiation element 502 and the impedance matching/feeding part 504 without electrical contact. The second radiation element 506 may be electrically coupled to a ground, and may receive power by coupling from the impedance matching/feeding part 504.

0056<figref idref="f0005">Figure 5</figref> illustrates an example in which the second radiation element 506 is shorter than the first radiation element 502, where the second radiation element 506 may be included to transmit and receive signals in a higher frequency band than that of the first radiation element 502.

0057While <figref idref="f0005">Figure 5</figref> illustrates the second radiation element 506 as having one bend, it will be apparent to the skilled person that the form of the second radiation element is not thus limited.

0058It will be understood by the skilled person that the approach of including additional radiation elements to form resonance points in other bands can be applied not only to the second disclosed embodiment but also to the first disclosed embodiment.

0059<figref idref="f0006">Figure 6</figref> represents S11 parameters of a multi band antenna according to the third disclosed embodiment of the present invention.

0060Referring to <figref idref="f0006">Figure 6</figref>, it can be observed that, due to the addition of a second radiation element, resonance points have been formed at high-frequency bands. Two resonance points have been formed at high-frequency bands, and the extra resonance point is caused by a parasitic component.

0061<figref idref="f0007">Figure 7</figref> illustrates the structure of multi band internal antenna according to a fourth disclosed embodiment of the present invention.

0062Referring to <figref idref="f0007">Figure 7</figref>, a multi band internal antenna according to the fourth disclosed embodiment of the present invention includes a board 700, and a first radiation element 702 formed on the board 700, an impedance matching/feeding part 704 formed on the board 700, and a second radiation element 706.

0063The impedance matching/feeding part 704 includes a first matching element 720 and a second matching element 730, the first matching element 720 electrically coupled to a ground, and the second matching element 730 electrically coupled to a feeding point.

0064Similar to the second and third disclosed embodiments, the first radiation element receives RF signals from the impedance matching/feeding part through coupling feeding.

0065In the fourth disclosed embodiment as compared to the third disclosed embodiment, the second radiation element 706 does not receive power by coupling but by direct feeding. The second radiation element 706 may be electrically joined to the second matching element 730 of the impedance matching/feeding part 704, which is electrically coupled to a feeding point, so that direct feeding may be provided to the second radiation element 706.

0066Thus, when there are additional radiation elements for transmitting and receiving signals in other bands, these radiation elements can be provided with power either by coupling, as in the third disclosed embodiment, or by direct power feeding, as in the fourth disclosed embodiment.

0067While <figref idref="f0007">Figure 7</figref> illustrates an example in which the second matching element 730 and the second radiation element 706 are electrically joined on the board, the second matching element 730 and the second radiation element 706 do not necessarily have to be joined on the board and can be electrically joined in another region.

0068Also, it will be apparent to the skilled person that the approach of including additional radiation elements to form resonance points in other bands can be applied not only to the second disclosed embodiment but also to the first disclosed example.

0069<figref idref="f0008">Figure 8</figref> represents S11 parameters of a multi band antenna according to the fourth disclosed embodiment of the present invention.

0070Referring to <figref idref="f0008">Figure 8</figref>, it can be observed that resonance points have been formed at high-frequency bands. Unlike the third disclosed embodiment shown in <figref idref="f0006">Figure 6</figref>, however, there is no extra resonance point caused by a parasitic component.

0071<figref idref="f0009">Figure 9</figref> illustrates a structure in which a multi band internal antenna according to the third disclosed embodiment of the present invention is joined to an antenna carrier of a terminal.

0072The antenna carrier may include a horizontal part 900 and a vertical part 902, where the vertical part 902 may be formed perpendicularly to the board 910 of the terminal to support the horizontal part 900, and the horizontal part 900 may be formed parallel to the board of the terminal, with the elements described above joined to the horizontal part 900.

0073In <figref idref="f0009">Figure 9</figref>, the first matching element may extend to the vertical part 902 and join a ground of the terminal's board 910, and the second matching element may extend and electrically connect with a feeding point. Also, in cases where the second radiation element is included, the second radiation element may extend to the vertical part 902 and join the ground of the terminal's board 910.

0074<figref idref="f0010">Figure 10</figref> illustrates a structure in which a multi band internal antenna according to the fourth disclosed embodiment of the present invention is joined to a PCB of a terminal. Referring to <figref idref="f0010">Figure 10</figref>, the second radiation element and the second matching element coupled to the feeding point, according to the fourth disclosed embodiment, may be electrically joined at point A, so that direct power feeding may be provided to the second radiation element.