JP4649486B2 - Mobile terminal antenna - Google Patents

Description

  The present invention relates to an antenna for mobile terminals, and more particularly to an antenna for mobile terminals in which mutual coupling between a plurality of antenna elements is suppressed.

  In recent years, with the miniaturization of mobile terminals, mobile terminal antennas have been reduced in space, that is, downsized, built-in, and thinned. In addition, mobile terminals, especially mobile phones, can be applied to various applications such as support for multiple bands in international roaming, GPS, Bluetooth, Wireless LAN, and 1 segment partial reception services for mobile phones and mobile terminals. It has been demanded. In addition, there is a growing demand for improved skills for improving communication quality and high-speed mobile communications. From such a background, research and development of an antenna device in which a plurality of antenna elements are combined with a mobile terminal have been conducted recently.

  When a plurality of antenna elements are loaded on a portable terminal, the antenna elements influence each other, and the characteristics of the antenna can be deteriorated. This is mainly due to the mutual coupling between the antenna elements. Therefore, the antenna characteristic degradation can be solved by suppressing the mutual coupling between the elements. In order to reduce mutual coupling between elements of the antenna, for example, it is conceivable to increase the distance between the antenna elements. However, in a limited space such as a portable terminal, it is necessary to arrange the antenna elements close to each other. Against this background, various methods for reducing mutual coupling between antenna elements have been considered.

  For example, Patent Document 1 discloses a technique in which an inverted F antenna and a microstrip antenna are arranged close to each other, and radiation electrodes are arranged so as to cross each other at 90 degrees to reduce mutual coupling between elements. Patent Document 2 discloses a technique for reducing mutual coupling between elements by providing a dielectric separator between antenna elements. In addition, there are those provided with slots between patch antenna elements, those provided with metal walls, those provided with electromagnetic band gaps, and the like.

  Further, Non-Patent Document 1 discloses a technique of reducing the mutual coupling between elements by short-circuiting between feeding points or short-circuit points of two planar inverted F antenna elements with a suspension line (suspended line).

  On the other hand, Non-Patent Document 2 discloses a configuration in which a plurality of L-shaped folded monopole antenna elements are arranged. The L-shaped folded monopole antenna element extends in parallel from the feeding strip to the ground plate, and the radiating strip that is folded back and connected to the shorting strip is L-shaped when viewed from the plate surface of the ground plate. It is formed into a mold. Non-Patent Document 2 examines such an L-shaped folded monopole antenna element arranged symmetrically, and can be downsized as compared with an inverted F antenna element or the like, and is also advantageous in terms of bandwidth. Can be realized.

JP 11-31923 A JP 2006-517073 A Allusion, Jalo (Aliou Diallo), Cerro Laksi (Cyril Luxey), et al., "Study and Reduction of the Mutual Coupling Between Two Mobile Phone PIFAs Operating in the DCS1800 and UMTS Bands", IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 54, NO. 11, 2006, November 11, p. 3063-3074 Hiroshi Kinyo, Hisashi Morishita, Yoshio Koyanagi “Basic Study on L-shaped Folded Monopole Antenna for Mobile Terminals” IEICE General Conference, March 07, 2007, p. 128

  However, among the prior arts using the inverted F antenna element, the band is narrow and the mutual coupling between elements cannot be sufficiently suppressed. Further, a patch antenna provided with a slot, a metal wall, or the like can be applied only to a directional antenna in a single direction because of the characteristics of the patch antenna. Furthermore, in such a thing, the space for providing a separator, a slot, and an electromagnetic band gap is required, and the space for arranging an electronic circuit or the like on the ground plate has been reduced. There is also a problem that the height of the antenna device increases.

  Further, the antenna element short-circuited by the suspension line disclosed in Non-Patent Document 1 is an antenna having a narrow band because it uses an inverted F antenna element. Further, the structure is not such that the reflection coefficient (impedance characteristics) can be adjusted while adjusting the mutual coupling between elements, and such a study has not been made.

  In addition, the L-shaped folded monopole antenna element disclosed in Non-Patent Document 2 has not been studied for mutual coupling between elements when a plurality of elements are arranged, and deterioration of antenna characteristics can be a problem. there were.

  In view of such circumstances, the present invention is an antenna for a portable terminal that can be reduced in size while having a wide band and can improve the deterioration of the antenna characteristics by adjusting mutual coupling between elements when a plurality of elements are arranged. Is to provide.

  In order to achieve the above-described object of the present invention, an antenna for a mobile terminal according to the present invention includes a ground plate made of a conductor and a pair of L-shaped folded monopole antenna elements arranged symmetrically on the ground plate. Each of the pair of L-shaped folded monopole antenna elements includes an L-shaped radiating strip portion formed of a folded strip formed in an L-shape parallel to the ground plate, and the L-shaped radiating strip portion. A pair of L-shaped folded monopole antennas having a feeding strip portion that is connected to one end of the antenna and rises at a right angle from the ground plate, and a short-circuit strip portion that is connected to the other end of the L-shaped radiation strip portion and rises at a right angle from the ground plate A bridge portion connected to the element and a side to which a feeding strip portion of each L-shaped radiation strip portion is connected; It is intended to comprise.

  Here, the pair of short-circuit strip portions may be disposed between the pair of power supply strip portions.

  In addition, the mutual coupling between elements may be adjusted by the distance from the end of each L-shaped radiating strip to which the feeding strip is connected to the position to which the bridge is connected.

  In addition, the impedance characteristics may be adjusted by the distance between the feeding strip portion and the short-circuit strip portion of each L-shaped folded monopole antenna element.

  Further, the resonance frequency of the antenna may be adjusted by the length of the L-shaped radiation strip portion.

  Further, the pair of L-shaped folded monopole antenna elements may have different frequency bands.

  The antenna for a portable terminal of the present invention can be miniaturized while adopting an L-shaped folded monopole antenna element, and can be reduced in size, and by short-circuiting between radiating strip parts by a bridge part, There is an advantage that mutual coupling can be reduced.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a schematic perspective view for explaining the configuration of the mobile terminal antenna of the present invention. As shown in the figure, the mobile terminal antenna of the present invention is mainly composed of a ground plate 1, a pair of L-shaped folded monopole antenna elements 2, and a bridge portion 3.

  The ground plate 1 is composed of a conductor corresponding to the substrate of the mobile terminal. In the illustrated example, the ground plate 1 is shown to be somewhat large, but the present invention is not limited to this and may be a ground plate having a size on which an antenna element can be placed.

  A plurality of L-shaped folded monopole antenna elements 2 are provided to realize a plurality of channels such as a plurality of bands or MIMO (Multiple Input Multiple Output). As shown in the figure, in the mobile terminal antenna of the present invention, a pair of L-shaped folded monopole antenna elements 2 are arranged symmetrically on the ground plate 1. The L-shaped folded monopole antenna element 2 includes an L-shaped radiating strip portion 21, a feeding strip portion 22, and a short-circuit strip portion 23. The L-shaped radiation strip portion 21 is formed of a folded strip formed in an L shape in parallel with the ground plate 1. More specifically, the L-shaped radiating strip portion 21 extends in parallel with the ground plate, and the radiating strip that is folded back and returns to the original in parallel is L-shaped when viewed from the plate surface of the ground plate 1. It is formed. In other words, the strip extending parallel to the ground plate is folded 90 degrees while being parallel to the ground plate, further extended, folded back 180 degrees upward so as to overlap the folded strip, and returned to the original state. . The L-shaped radiation strip portion 21 in the illustrated example is disposed along the corner portion of the ground plate 1. As an example of the dimensions of the L-shaped radiation strip portion 21, the line width of the strip is 5 mm, the length until the 90-degree folded portion is 14 mm, and the length from the 90-degree folded portion to the 180-degree folded portion is as follows. 13 mm. Moreover, the thickness (interval between the upper strip and the lower strip) when folded back by 180 degrees is 0.5 mm. In addition, since each dimension changes also with target frequencies etc., it is not limited to the dimension quoted, but these dimensions are given for reference to the last.

  Further, in the illustrated example, the pair of L-shaped folded monopole antenna elements 2 is an antenna for a mobile terminal that realizes a plurality of channels of the same frequency band by arranging the same shape symmetrically on the ground plate. It was. However, the present invention is not limited to this, and is an antenna for a portable terminal that realizes a plurality of bands of different frequency bands by arranging a pair of L-shaped folded monopole antenna elements having different shapes substantially symmetrically on the ground plate. There may be. In this case, different frequency bands are obtained by changing the length of each L-shaped radiation strip portion. A pair of L-shaped folded monopole antenna elements is grounded by arranging the feeding strip portion and the short-circuit strip portion connected to such an L-shaped radiating strip portion to be symmetrical on the ground plate. It will be arranged substantially symmetrically on the plate.

  A feeding strip portion 22 and a short-circuit strip portion 23 are connected to both ends of the L-shaped radiation strip portion 21. The feeding strip portion 22 and the short-circuit strip portion 23 are each raised from the ground plate 1 at a substantially right angle, and are connected to the end portions of the L-shaped radiation strip portion 21.

  Since the L-shaped radiation strip portion 21, the feeding strip portion 22, and the short-circuit strip portion 23 are only required to be electrically connected, they may be integrally formed by bending one strip line. Further, for example, a double-sided substrate or the like may be used to form a folded strip using a through hole, and the L-shaped radiation strip portion may be formed by patterning.

  In the mobile terminal antenna of the present invention, the pair of L-shaped folded monopole antenna elements 2 are arranged symmetrically on the ground plate 1. In the illustrated example, the ground plate 1 is arranged to be line symmetric in the longitudinal direction. More specifically, each L-shaped folded monopole antenna element 2 is arranged along both corners of the ground plate 1. In the illustrated example, a structure in which the pair of power supply strip portions 22 are disposed outside is shown. That is, a pair of short-circuit strip portions 23 is disposed between the pair of power supply strip portions 22. More specifically, the feeding strip portion 22 is connected to the lower strip end of the L-shaped radiation strip portion 21, and the short-circuit strip portion 23 is connected to the upper strip end. However, the present invention is not limited to this, and is a structure in which a pair of power strip portions 22 are disposed inside, that is, a structure in which a pair of power strip portions 22 are disposed between a pair of short-circuit strip portions 23. Also good. In addition, when both structures are compared, the one in which the feeding strip portion 22 is disposed on the outside is more preferable because the mutual coupling between elements is generally low.

  As the distance between the pair of L-shaped folded monopole antenna elements is narrowed, the mutual coupling between the elements increases. However, even if the antenna for a mobile terminal of the present invention is close to about 1 mm, the mutual coupling between the elements is increased. Is kept at a level that is practically acceptable. Therefore, since a plurality of antenna elements can be arranged close to each other, they can be accommodated in a smaller area.

  In the portable terminal antenna of the present invention, the antenna characteristics can be adjusted by the distance between the feeding strip portion 22 and the short-circuit strip portion 23. As the distance between the feeding strip portion 22 and the short-circuit strip portion 23 is increased, the resonance frequency is increased and the antenna is matched. Details of the characteristics will be described later.

  Now, the mobile terminal antenna of the present invention has the bridge portions 3 respectively connected to the side to which the feeding strip portion 22 is connected of the pair of L-shaped radiation strip portions 21 configured as described above. Yes. The bridge part 3 short-circuits each L-shaped radiation strip part 21. More specifically, both ends of the bridge portion 3 are connected to the L-shaped radiation strip portion 21, but the connection position is present on the strip on the side to which the feeding strip portion 22 is connected. The mobile terminal antenna of the present invention can adjust the magnitude of mutual coupling between elements according to this connection position. In addition, the bridge | bridging part 3 is comprised by the stripline of 0.5 mm, if an example is given. However, the bridge portion is not limited to the dimensions given, and these dimensions are given for reference only.

  Hereinafter, a method for adjusting antenna characteristics for a portable terminal according to the present invention will be described. FIG. 2 is a schematic perspective view for explaining an example of dimensions and parameters of the portable terminal antenna according to the present invention. In the figure, the portions denoted by the same reference numerals as those in FIG. The ground plate 1 was 120 mm × 45 mm, and the L-shaped folded monopole antenna element 2 was sized as shown. Based on such a configuration, three parameters, parameter g, parameter d, and parameter L, were adjusted. As shown in the figure, the parameter g is an interval between the feeding strip portion 22 and the short-circuit strip portion 23. The parameter d is a distance from the feeding strip portion 22 to a position where the bridge portion is connected. The parameter L is the length of the portion of the L-shaped radiation strip portion 21 bent into an L shape. In the following description, the target frequency is adjusted so that the antenna operates in the 2 GHz band. For the analysis, an electromagnetic field simulator IE3D (manufactured by Zeland) based on the moment method was used.

  FIG. 3 is an S parameter characteristic diagram when the parameter g is changed to 1 mm, 3 mm, 5 mm, and 7 mm in the mobile terminal antenna of the present invention. In the figure, the solid line represents the S11 parameter that is the antenna reflection coefficient, and the broken line represents the S21 parameter that is the mutual coupling between elements. As shown in the figure, it is understood that when the parameter g is increased, the resonance frequency is increased and at the same time the antenna is matched. That is, the antenna matching (impedance characteristic) can be adjusted by the parameter g.

  Next, FIG. 4 is an S parameter characteristic diagram when the parameter d is changed to 0 mm, 2 mm, 4 mm, and 6 mm in the mobile terminal antenna of the present invention. In the figure, the solid line represents the S11 parameter that is the antenna reflection coefficient, and the broken line represents the S21 parameter that is the mutual coupling between elements. FIG. 4 is a graph when the parameter g is 5 mm. As shown in the figure, it can be seen that as the parameter d is increased, the resonance frequency of the antenna and the frequency at which the mutual coupling between the elements becomes the minimum approach. That is, it is possible to adjust the parameter d so that the resonance frequency of the antenna is close to the frequency at which the mutual coupling between elements is minimized.

  As shown in the characteristic diagram of FIG. 3, when the parameter g is set to 5 mm, the antenna matching can be adjusted. However, the resonance frequency of the antenna and the frequency at which the mutual coupling between the elements is the smallest match. Not. However, as shown in the characteristic diagram of FIG. 4, by adjusting the parameter d to 6 mm, for example, it is possible to make the resonance frequency of the antenna and the frequency at which the mutual coupling between the elements is minimized substantially coincide.

  FIG. 5 is an S parameter characteristic diagram when the parameter L is changed to 13 mm, 16 mm, and 18 mm in the portable terminal antenna of the present invention. In the figure, the solid line represents the S11 parameter that is the antenna reflection coefficient, and the broken line represents the S21 parameter that is the mutual coupling between elements. FIG. 5 is a graph when the parameter g is 5 mm and the parameter d is 6 mm. As shown in the figure, it can be seen that as the parameter L is increased, the resonance frequency of the antenna decreases. In other words, the resonance frequency of the antenna can be adjusted to the target frequency by the parameter L. The resonance frequency of the antenna is adjusted by the parameter L in the above example, but it may be adjusted by the length (full length) of the L-shaped radiation strip portion including the parameter L.

  As shown in the characteristic diagram of FIG. 4, when the parameter g is 5 mm and the parameter d is 6 mm, it is possible to adjust the resonance frequency of the antenna and the frequency at which the mutual coupling between the elements is minimized. However, it is greatly deviated from the target frequency of 2 GHz band. However, as shown in the characteristic diagram of FIG. 5, it is possible to adjust the resonance frequency to the 2 GHz band by adjusting the parameter L to 18 mm, for example.

  In the mobile terminal antenna of the present invention, by adjusting the parameters g, d, and L in this way, the resonance frequency can be matched with the desired target frequency, and the mutual coupling between elements can be reduced. Become. As shown in FIG. 5, it can be seen that the mutual coupling between elements at this time can be reduced to -24 dB.

  Here, the characteristic change by the presence or absence of a bridge part is demonstrated using FIG. FIG. 6 is a diagram for explaining a characteristic change when the bridge portion of the portable terminal antenna of the present invention is loaded, and FIG. 6A is an S parameter characteristic diagram, and FIG. ) Is an impedance characteristic diagram. Here, the characteristic diagram of the illustrated example is that of an antenna designed with the parameters g, d, and L being g = 3 mm, d = 7 mm, and L = 16 mm, respectively. In the figure, the broken line represents the S11 parameter that is the antenna reflection coefficient, and the solid line represents the S21 parameter that is the mutual coupling between the elements. The black line is a characteristic when the bridge portion is loaded, and the gray line is a characteristic when the bridge portion is not loaded. As shown in the figure, in the mobile terminal antenna of the present invention, it is understood that the S21 parameter, which is the mutual coupling between elements, is greatly reduced from -11 dB to -20 dB by loading the bridge portion in this way.

  FIG. 7 is a radiation pattern characteristic diagram with and without loading the bridge portion of the portable terminal antenna of the present invention. As shown in the figure, the radiation characteristics of each plane are substantially the same regardless of the presence or absence of the bridge portion, and it can be seen that there is almost no influence on the radiation characteristics due to the loading of the bridge portion.

  Further, FIG. 8 is a characteristic diagram of mutual coupling between elements and antenna efficiency when the bridge portion of the portable terminal antenna of the present invention is loaded. In the figure, the horizontal axis represents the distance between the L-shaped folded monopole antenna elements, and represents the characteristics of mutual coupling between elements and antenna efficiency at 2.1 GHz with respect to the change in the distance. The antenna efficiency was obtained by multiplying the radiation efficiency by the reflection coefficient and the efficiency due to mutual coupling. The broken line represents the S21 parameter indicating mutual coupling between elements, and the solid line represents the antenna efficiency. The black line is a characteristic when the bridge portion is loaded, and the gray line is a characteristic when the bridge portion is not loaded. As shown in the figure, it can be seen that the mutual coupling between the elements can be greatly reduced by loading the bridge portion at every element interval, and the antenna efficiency can be greatly improved. In particular, it can be seen that a low coupling characteristic of about −10 dB is obtained even when the distance between the L-shaped folded monopole antenna elements is very close to 1 mm.

  As described above, the portable terminal antenna of the present invention can be miniaturized while adopting an L-shaped folded monopole antenna element, and can be short-circuited between the radiating strip portions by the bridge portion. Therefore, there is an advantage that mutual coupling between elements can be reduced. In addition, the mutual coupling between elements can be adjusted by the position where the bridge portion is connected, and further, the desired antenna characteristics can be determined depending on the distance between the feeding strip portion and the short-circuit strip portion and the length of the L-shaped radiation strip portion. It is possible to adjust so that.

  Note that the portable terminal antenna of the present invention is not limited to the illustrated examples described above, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

FIG. 1 is a schematic perspective view for explaining the configuration of the mobile terminal antenna of the present invention. FIG. 2 is a schematic perspective view for explaining an example of dimensions and parameters of the portable terminal antenna according to the present invention. FIG. 3 is an S parameter characteristic diagram when the parameter g is changed in the mobile terminal antenna of the present invention. FIG. 4 is an S parameter characteristic diagram when the parameter d is changed in the mobile terminal antenna of the present invention. FIG. 5 is an S parameter characteristic diagram when the parameter L is changed in the mobile terminal antenna of the present invention. FIG. 6 is a diagram for explaining the characteristic change when the bridge portion of the portable terminal antenna of the present invention is loaded and not loaded. FIG. 7 is a radiation pattern characteristic diagram with and without loading the bridge portion of the portable terminal antenna of the present invention. FIG. 8 is a characteristic diagram of inter-element mutual coupling and antenna efficiency when the bridge portion of the portable terminal antenna of the present invention is loaded and not loaded.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ground plate 2 L-shaped folding monopole antenna element 3 Bridge part 21 L-shaped radiation strip part 22 Feeding strip part 23 Short-circuit strip part

Claims (5)

A mobile terminal antenna built in a mobile terminal, the mobile terminal antenna is
A ground plate made of a conductor;
A pair of L-shaped folded monopole antenna elements disposed on the ground plate in a substantially line symmetrical manner in a predetermined direction on the ground plate plane , wherein the pair of L-shaped folded monopole antenna elements Each of them has an L-shaped radiating strip portion formed of a folded strip formed in an L shape in parallel to the ground plate, and a power supply that is connected to one end of the L-shaped radiating strip portion and rises at a right angle from the ground plate A pair of L-shaped folded monopole antenna elements having a strip portion and a short-circuited strip portion connected to the other end of the L-shaped radiating strip portion and rising at a right angle from the ground plate;
A bridge portion for short-circuiting each L-shaped radiation strip portion connected to a side to which the feeding strip portion of each L-shaped radiation strip portion is connected , A bridge part in which mutual coupling between elements is adjusted by a distance from an end part to which the feeding strip part is connected to a position to which the bridge part is connected ;
An antenna for a portable terminal comprising:   The portable terminal antenna according to claim 1, wherein the pair of short-circuit strip portions are disposed between the pair of feeding strip portions. In the mobile terminal antenna of claim 1 or claim 2, characterized in that the distance by the impedance characteristics of the feeding strip portion and the short circuit strip portion of each of said L-shaped folded monopole antenna element is adjusted Antenna for mobile terminals. In the mobile terminal antenna according to any one of claims 1 to 3, an antenna for a portable terminal, wherein the resonance frequency of the antenna by the length of each said L-shaped radiating strip portion is adjusted. In the mobile terminal antenna according to any one of claims 1 to 4, wherein the pair of L-shaped folded monopole antenna element is an antenna for a portable terminal, each of the frequency bands are different from each other.