KR100853994B1 - Low-profile antenna employing metamaterial structure - Google Patents

Abstract

A small antenna using a metamaterial structure is disclosed. The small antenna comprises a conductor connected between the feeding element and two inductive elements respectively connected to the ground plane and the inductive elements, the conductors comprising at least two parts spaced apart from each other and arranged substantially parallel to each other. The small antenna realizes a metamaterial structure without using a separate capacitor, thereby reducing the manufacturing cost of the antenna and achieving miniaturization. In addition, the resonance frequency of the antenna can be easily changed by changing the inductance of the inductive element.

Metamaterial, Conductor, Space Fill Curve, Inductance

Description

LOW-PROFILE ANTENNA EMPLOYING METAMATERIAL STRUCTURE}

1A and 1B show a conventional ring antenna.

2 illustrates a small antenna according to an embodiment of the present invention.

3 shows a Peano curve.

4 is a graph showing reflection coefficients of a small antenna of one embodiment of the present invention;

5 is a graph illustrating resonance frequency adjustment of a small antenna according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna for wireless communication, and more particularly, to a small antenna employing a metamaterial structure that operates as a zero order order resonator (ZOR).

An antenna is an essential component of a wireless communication device for transmitting / receiving electromagnetic waves, and is configured to resonate with electromagnetic waves of a specific frequency and to transmit / receive electromagnetic waves of that frequency. In this case, the resonance means that the impedance of the circuit is a real number at a specific frequency, and in practice, refers to a phenomenon in which the S11 parameter, which is the reflection coefficient of the circuit, decreases rapidly at a specific frequency.

Conventional antennas have a resonant structure in primary mode. That is, the conventional antenna has an electrical length of λ / 2 with respect to the wavelength λ corresponding to the desired frequency and is composed of a conductor (transmission line) whose one end is open or shorted. As a result, electromagnetic waves guided along the conductive wire form standing waves in the conductive wire, and resonance occurs. An antenna having a primary mode resonant structure is determined by the electrical length of the antenna entirely dependent on the resonant frequency, so that the size of the antenna changes according to the resonant frequency, and in particular, the antenna becomes larger as the desired resonant frequency is lowered.

In order to solve this disadvantage, a monopole antenna having an electrical length of λ / 4 has been proposed by forming the antenna on the ground plane, and in order to further reduce the size of the monopole antenna, a complex such as a helix form and a meander form has been proposed. An antenna having a shape has been proposed. However, the proposed antennas still do not escape the limit of size depending on the resonant frequency, and as the antenna becomes smaller, its shape becomes more complicated to form a fixed length antenna in a narrow space. In addition, as the shape of the antenna becomes more complicated, there is a difficulty in maintaining the performance of the antenna, such as the influence of coupling between the conductors formed increases.

In order to solve the shortcomings of the prior art using the first resonance, the use of a zero order resonance structure using a metamaterial has been attempted. Metamaterial refers to a material or electromagnetic structure that is artificially designed to have special electromagnetic properties that are not generally found in nature. In general, and in this specification, metamaterial refers to permittivity. Refers to a material or any such electromagnetic structure that is both negative and permeability negative.

It is possible to implement a zero-order resonator (ZOR) using such a metamaterial, and an example of zero-order resonator implementation using a metamaterial is described in U.S. Application No. 11 / 092,143 to Itoh et al. Unlike the conventional resonant structure, the zero-order resonator has a resonant frequency determined regardless of the electrical length of the resonant structure. The zero-order resonator has substantially the same resonant structure as the LC resonant circuit, so that the inductance and capacitance of the inductor and capacitor included in the circuit determine the resonant frequency. Therefore, the resonant frequency can be changed by adjusting the inductance and capacitance, and the antenna using the same does not increase in size even if the resonant frequency is lowered.

Ring antennas using metamaterials are known, which are shown in FIG.

Referring to FIG. 1A, a ring antenna 100 using metamaterials includes two transmission lines 106 and 108 and two capacitors 110 connecting these transmission lines 106 and 108 to each other. In addition, the conductors 106 and 108 are connected to the inductor 102 and the inductor 104, respectively. The conductors 106 and 108, the capacitor 110 and the inductors 102 and 104 may be manufactured by being printed or mounted on a printed circuit board. On the other hand, the inductor 102 is connected to a ground plane (not shown) arranged in parallel with the conductors 106 and 108 via a post (not shown), and the inductor 104 is connected to a power supply element through a post (not shown). Is connected to.

The antenna 100 having such a configuration is electrically interpreted as two antenna cells 200 shown in FIG. 1B connected in parallel, and the antenna cells 200 can operate as antennas by zero order resonance. In particular, the resonant frequency is determined by the zero-order resonator comprised by the conductors 106 ', 108', the inductors 102 ', 104' and the capacitor 110 '. Therefore, the antenna can be made compact regardless of the resonance frequency of the antenna.

However, since the antenna 100 of FIG. 1A connects the conductors 106 and 108 by using a separate capacitor 110, the manufacture of the antenna is complicated and the size of the antenna is limited.

It is an object of the present invention to provide an antenna that is more compact and easier to manufacture while using a metamaterial structure.

In addition, an object of the present invention is to provide a small antenna that can easily change the resonance frequency.

In order to achieve the above object, according to one embodiment of the present invention, there is provided an apparatus comprising: a first inductive element connected to a power feeding element; A second inductive element connected to the ground plane; And a conductor connected between the first inductive element and the second inductive element, the conductor comprising at least two portions spaced apart from each other and arranged substantially parallel.

Preferably the conductor is substantially in the form of a space-filling curve. More preferably, the conductor has a substantially Peano curve.

In addition, it is preferable that the inductance of the first inductive element or the second inductive element can be changed. More preferably, the first inductive element or the second inductive element is a variable inductor. The first inductive element or the second inductive element may include two or more inductors having different inductances; And a switch for selectively connecting one of the inductors with the conductor.

On the other hand, the inductance is preferably changed according to the operating environment of the antenna.

In order to achieve the above object, according to another embodiment of the present invention, a wireless communication device including the antenna is provided.

Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. The described embodiments are merely examples and the present invention is not limited thereto.

2 is a diagram illustrating a small antenna according to an embodiment of the present invention. The antenna of this embodiment includes a first inductive element 20 connected to a power feeding element (not shown), a second inductive element 22 connected to a ground plane (not shown) and inductive elements ( And a conductor 10 connected between 20 and 22. The conductor 10 may be formed by printing or etching on a printed circuit board, and the inductive elements 20 and 22 may be embodied as lumped elements and mounted on the printed circuit board. However, it is also possible to implement the inductive elements 20, 22 as distributed integer elements.

The first inductive element 20 and the second inductive element 22 are connected to the power feeding element and the ground plane, respectively, by a connecting conductor (not shown), and the connecting conductor acts as the main radiator of the antenna. When the antenna is formed on the printed circuit board, the connecting conductor can be connected with the inductive elements 20 and 22 through vias or through holes. On the other hand, the ground plane may be disposed substantially parallel to the conductor 10.

The conductor 10 is connected to the first inductive element 20 and the second inductive element 22 at both ends 18a and 18b, respectively, and forms an electrical path from the power feeding element to the ground plane. In addition, the conductor 10 comprises three parts 12, 14 and 16 spaced apart from one another and arranged substantially parallel to one another. Thus, capacitance is generated between them by the spacing between the conductor parts 12, 14 and 16. Therefore, unlike the conventional antenna, it is possible to implement a metamaterial structure without using a capacitor.

Specifically, by the antenna of the present embodiment, the capacitance between the first inductive element 20-the conductor part 12-the conductor parts 12 and 14-the capacitance between the conductor parts 14 and 16-the conductor part 16 ) An electrical path of the second inductive element 22 is formed. Thus, substantially similar to that shown in FIG. 1B, a metamaterial structure in which two inductors and capacitors are connected in series is formed, and operates as a zero-order resonator.

By substantially including the metamaterial structure, the antenna of the present embodiment can be miniaturized regardless of the resonance frequency of the antenna. In addition, by implementing the metamaterial structure without using a separate capacitor, the antenna can be manufactured more easily and at low cost, and the antenna can be made smaller.

On the other hand, the conductor 10 may substantially have the form of a space-filling curve. The space filling curve means a curve that can fill two-dimensional figures such as circles and rectangles. Since it was first described by Guiseppe Peano, many mathematicians have introduced various types of curves. That is, the conductor 10 of the present embodiment can be formed in the form of a single curve that can fill the area within the area in which the conductor 10 can be formed. Thereby, the conductor 10 of a long length can be efficiently formed in a limited area, and the electrical characteristic generate | occur | produced by a conductor can thereby be utilized to the maximum. In addition, since the conductor is efficiently formed within a predetermined area, miniaturization of the antenna can be achieved.

For example, the conductor 10 can be formed substantially in the form of a Peano Curve. Two exemplary Peano curves are shown in FIG. 3. As shown, both ends of the Peano curve can be used as both ends 18a and 18b of the conductor to form an antenna. In this case, various design changes can be brought about while using the conductor formation area efficiently. For example, when the first Peano curve of FIG. 3 (a) is used, the same antenna as shown in FIG. 2 can be obtained, while the capacitance generation portion is increased when the Peano curve of FIG. 3 (b) is used. Therefore, the resonant frequency may be changed in the zero-order resonator by the metamaterial structure.

However, one of ordinary skill in the art will readily recognize that the shape of the conductor 10 is not limited to that described and may be used as long as it can substantially generate capacitance and contribute to the formation of the metamaterial structure.

The antenna of the embodiment of FIG. 2 was actually implemented to simulate its characteristics, and the result is shown in FIG. 4. The implemented antenna is implemented to resonate at 1.77 GHz and its size is 9 mm × 9 mm. Meanwhile, the conventional metamaterial antenna was implemented to have the same resonance frequency and used as a comparative example, and the size thereof was 9.1 mm × 12.4 mm. As such, the antenna of the embodiment of the present invention is reduced in size by about 30% compared to the comparative example. Meanwhile, as shown in the graph of FIG. 4, the antenna of the embodiment has a bandwidth of 127.2 MHz based on the S11 value-10 dB, whereas the antenna of the comparative example has a bandwidth of 105.6 MHz, indicating that the antenna of the embodiment is superior in bandwidth. Confirmed.

Since the resonant frequency of the antenna is determined by the zero-order resonant structure, the resonant frequency can be changed by changing the inductance of the inductive elements 20, 22 in addition to the shape of the conductor 10. For example, one or more of the inductive elements 20, 22 may be a variable inductor. Alternatively one or more of the inductive elements 20, 22 may comprise two or more inductors with different inductances, and only one selected inductor thereof may be connected to the conductor 10 by a switch.

The change in inductance may be made by a user's input, or may be made automatically by detecting an operating state of the antenna. For example, when using a communication service using two different frequency bands as one device, the inductance may be changed by the service selection signal input by the user and the resonance frequency of the antenna may be appropriately adjusted. On the other hand, when the same service uses different frequency bands depending on the geographical location, or when different services are required according to the location of the device, the inductance is automatically changed according to the location of the device determined by a separate means and the resonance of the antenna The frequency can be adjusted.

By implementing the antenna of the present embodiment shown in FIG. 2, the resonance frequency change according to the inductance change was simulated, and the result is shown in FIG. First, an antenna having a resonant frequency of 1.77 GHz was obtained with an inductance of the first inductive element 20 at 15 nH and an inductance of the second inductive element 22 at 39 nH (implementation example 1). On the other hand, when the inductance of the first inductive element 20 was 27 nH and the inductance of the second inductive element 22 was 100 nH, the antenna had a resonance frequency of 1.29 GHz (implementation example 2). Therefore, it was confirmed that the resonance frequency of the antenna can be adjusted by changing the inductance.

As described above with reference to specific embodiments of the present invention, this is only an example and the present invention is not limited thereto. Those skilled in the art will be able to make various changes or modifications to the invention based on the principles described herein, and such changes or modifications are also within the scope of the invention. For example, a specific device type, inductance, capacitance, material of a conductor, type of substrate, size of an antenna, etc. for implementing an antenna can be easily selected by those skilled in the art. In addition, components described in specific terms such as metamaterials and conductors may be easily changed to functionally equivalent structures or materials. Therefore, the scope of the present invention should be defined by the matter described in the claims, not the description.

According to the present invention, it is possible to obtain an antenna which is further miniaturized and easy to manufacture by using a metamaterial structure and no capacitor.

Further, according to the present invention, a small antenna capable of easily changing the resonance frequency by changing the inductance can be obtained.

Claims (8)

A first inductive element connected to the power feeding element; A second inductive element connected to the ground plane; And A single conductor connected between the first inductive element and the second inductive element, Wherein the conductor comprises at least two portions spaced apart and parallel to each other. The method of claim 1, The conductor in the form of a space-filling curve. The method of claim 2, The conductor having the form of a Peano curve. The method of claim 1, Wherein the inductance of the first inductive element or the second inductive element can be varied. The method of claim 4, wherein The first inductive element or the second inductive element is a variable inductor. The method of claim 4, wherein The first inductive element or the second inductive element, Two or more inductors with different inductances; And And a switch for selectively connecting one of the inductors with the conductor. The method of claim 4, wherein The inductance is varied according to the operating environment of the antenna. A wireless communication device comprising the antenna of claim 1.

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