KR20090111103A - Uni-Planar Antenna using CRLH structure - Google Patents

Abstract

PURPOSE: A uni-planar antenna using a CRLH(Composite Right/Left-Handed) transmission line is provided to use a low resonance frequency lower than a half wavelength resonance frequency, thereby miniaturizing an antenna. CONSTITUTION: A serial inductance and a serial capacitance are serially connected. A shunt inductance(420) and a parallel capacitance are connected in parallel. A transmission line has a unit cell which is a structure that the shunt inductance and the parallel capacitance are connected in parallel. The unit cells are arranged on both wings of a parallel T-shaped circuit.

Description

Uni-Planar Antenna using CRLH structure}

The present invention relates to a planar antenna, and more particularly, to a single planar antenna that can be miniaturized using a CRLH transmission line.

Today, portable wireless terminals are becoming a necessity in our daily lives, and consumers' interests and demands in the wireless industry, especially portable terminals, are increasing day and night. In line with this, researches on improving the performance and function of the terminal are being actively conducted. On the other hand, in order to easily use on the go, it is necessary to keep the size and lightness without affecting the performance and function, so miniaturization and light weight is essential. In particular, since the miniaturization of communication components ensures a space in which other electronic components are to be mounted, research on the miniaturization and weight reduction of terminals has been actively conducted since the terminal can also be multifunctional. The miniaturization of a terminal can be achieved through a process of highly integrating RF components, but miniaturization of an antenna is recognized as the biggest problem among several RF components. In general, the size of the antenna is determined by the operating frequency, and since the terminal frequency operates at a relatively low frequency in the microwave band, the antenna size occupies a large proportion in the terminal.

Conventionally, a monopole antenna or a helical antenna has been used as a terminal antenna, and intenna, in which an antenna is hidden inside a terminal, is used for external reasons. The antenna may be implemented as a ceramic chip antenna or a Planar Inverted F Antenna (PIFA), and has the advantage of easy integration as well as an external advantage. In addition, many studies have been conducted from various angles to achieve miniaturization of antennas.

However, miniaturization of antennas is constantly required, and furthermore, due to a multi-input multi-output (MIMO) antenna technology, in order to arrange multiple antennas in a terminal, the antenna size needs to be further reduced. In the actual implementation of the multi-communication technique, the efficiency is reduced due to the mutual interference between the antennas, and to reduce the mutual interference, a sufficient distance between the antennas is required, but this causes an increase in the overall space occupied by the antenna. As the number of antennas in the terminal increases, the effect of miniaturization becomes more maximized. As a result, in order to achieve miniaturization of the antenna, it is necessary to develop a new technology that is one step up from the technology developed so far.

Current terminal size is determined by antenna size. According to the prior art, since the resonant antenna uses half-wave resonance, the size of the antenna is determined by the frequency. The present invention implements a CRLH transmission line including a series capacitance and a parallel inductance in a general transmission line, thereby providing a small planar antenna that can operate at a low resonance frequency.

As a first aspect of the present invention, a planar antenna includes a transmission line having a structure in which a series inductance and a series capacitance are connected in series, and a parallel inductance and a parallel capacitance are connected in parallel.

Preferably, the transmission line is characterized in that the plurality of unit cells cascaded.

Preferably, the serial capacitance is implemented by an interdigital structure.

Preferably, the parallel inductance is implemented by a via structure.

Preferably, in the via structure, by adjusting the diameter of the via, it characterized in that the size of the parallel inductance is adjusted.

Preferably, the planar antenna is characterized in that in the case of a high frequency, the phase speed and the group speed are characteristic of the forward direction, that is, the RH (Right-Handed) transmission line.

Preferably, the planar antenna is characterized in that, in the case of low frequency, the phase speed and the group speed exhibit opposite characteristics, that is, characteristics of a left-handed transmission line.

In order to solve the problems of the prior art, it is possible to realize the miniaturization of the antenna by using a low resonant frequency below the half-wave resonant frequency while maintaining the physical size of the antenna as it is.

FIG. 1 illustrates a general transmission line that shows properties of a right-handed (RH) material, and FIG. 2 illustrates a transmission line that shows properties of a left-handed (LH) meta material.

In the case of lossless transmission lines, which are common materials, that is, right-handed (RH) materials, they can be modeled as an equivalent circuit, as shown in FIG. have. On the other hand, when the equivalent circuit of the transmission line is represented by the series capacitance and its parasitic resistance 200 and the parallel inductance and its parasitic resistance 210 as shown in FIG. 2, the characteristics of the left-handed (LH) metamaterial are shown.

However, to implement the LH metamaterial must be implemented on the existing transmission line, that is, the RH material. As a result, when LH metamaterials are implemented on top of RH materials, one can no longer expect pure LH metamaterial properties.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

3 illustrates an equivalent circuit model for implementing an LH metamaterial according to a preferred embodiment of the present invention. The equivalent circuit shown in FIG. 3 is called a Composite Right / Left-Handed (CRLH) transmission line, meaning that the RH transmission line and the LH transmission line are combined. Referring to FIG. 3, a series inductance 300 and a parallel capacitance 320 representing a property of an RH material, and a series capacitance 310 and a parallel inductance 330 representing a property of an LH material are combined to be modeled as an equivalent circuit. Can be. Due to the characteristics of the reactance parameter, the series capacitance and parallel inductance dominate at low frequencies, indicating the characteristics of the LH metamaterial, while the series inductance and parallel capacitance prevail at the high frequencies, indicating the properties of the RH material.

4 illustrates an LH metamaterial having a periodic structure using a CRLH transmission line as a unit cell. Unlike the conventional PBG structure, the LH metamaterial does not have to have a periodic structure, but since the implementation is easy when the periodic structure is used, a method of implementing a periodic structure using the LH metamaterial is required. Referring to FIG. 4, the LH metamaterial may be implemented by cascading a CRLH transmission line periodically to a unit cell. In the unit cell, the parallel capacitance and the parallel inductance 420 are proportionally distributed to the lower portion of the T-shaped circuit and the series inductance and the series capacitances 400 and 410 are disposed on both wings of the T-shaped circuit. It is possible to periodically connect this T-shaped circuit as a unit cell.

In practice, in order to implement a CRLH unit cell, it is necessary to artificially create series capacitance and parallel inductance. 5A, 5B, and 5C illustrate a CRLH unit cell implementation method. Referring to FIG. 5A, a method of implementing a CRLH unit cell using the concentrator 510 is illustrated. This method is implemented using a chip inductor and a chip capacitor, which are lumped elements. The desired reactance can be easily obtained, but the operating frequency is limited due to the resonance frequency of the chip itself.

Referring to FIG. 5B, a method of implementing a CRLH unit cell using the mushroom structure 520 is illustrated. In this way, planar patches can produce series capacitance at narrow intervals between patches and parallel inductance through vias. This method has the disadvantage of making high reactance, but it is widely used in two-dimensional structure.

Referring to FIG. 5C, a method of implementing a CRLH unit cell using the interdigital structure 530 is illustrated. This method can make high capacitance value by using interdigital capacitance and high inductance value through short stub, but it takes up a lot of area compared to other structures.

The LH metamaterial may be implemented in a symmetrical periodic structure using the CRLH transmission line of the T network as a unit cell as shown in FIG. 4. The dispersion diagram based on this equivalent circuit can explain the principle of small antenna design using metamaterials.

,

일 때, ABCD 행렬은 다음과 같이 주어진다. If N CRLH transmission lines are connected in one dimension, FIG. 4

,

, The ABCD matrix is given by

　 식 (1)

Formula (1)

Using periodic boundary conditions, the following formula can be derived.

식 (2)

Formula (2)

If we take the real part of the solution of equation (2),

식 (3)

Formula (3)

식 (4)

Formula (4)

In Equation (4), a relationship between frequency and transmission constant can be obtained, and when the graph is plotted, a dispersion curve of a general CRLH transmission line can be obtained as shown in FIG. 6.

Referring to FIG. 6, the high frequency shows the effect of the inductance of the series impedance and the capacitance of the parallel admittance, and thus exhibits the characteristic of the RH mode (600), while the low frequency shows the large influence of the capacitance of the series impedance and the inductance of the parallel admittance. Therefore, the characteristic 610 of the LH mode is shown.

인 곳에서 공진이 발생한다. On the other hand, in the periodic structure consisting of three unit cells

Resonance occurs where.

, 즉 RH 모드 영역인 고주파에서 공진이 발생하는 반면, CRLH 전송선로의 경우 LH 모드에서 낮은 공진 주파수를 얻을 수 있다.

에서 공진하는 모드는 일반적인 전송선로(RH 모드)에서는 얻을 수 없는 모드이다. 구조물의 물리적 길이를 일정하게 유지하면서 낮은 주파수의 공진 모드를 이용할 수 있다는 장점을 공진 안테나에 응용할 경우 안테나의 크기를 줄일 수 있는 이점이 있다. In case of general transmission line

That is, while the resonance occurs at the high frequency, which is the RH mode region, a low resonance frequency can be obtained in the LH mode in the case of the CRLH transmission line.

Resonant mode is a mode that cannot be obtained in a general transmission line (RH mode). The advantage of using a low frequency resonant mode while keeping the physical length of the structure constant has the advantage of reducing the size of the antenna when applied to the resonant antenna.

On the other hand, since the Dispersion curve is determined as the reactance parameter of the equivalent circuit, the trend of the Dispersion curve can be analyzed through the reactance parameter. First, in the RH region, the transmission line is determined by LR and CR. On the other hand, as the frequency increases, the transmission constant also increases, so that the wavelength length becomes smaller. On the other hand, in the LH region of the CRLH transmission line, it is determined by LL and CL. In particular, since the transmission constant is negative, the wavelength length increases with increasing frequency.

Looking at the change of the dispersion curve according to the change of each reactance parameter, the following phenomenon occurs. First, when increasing LL, the parallel resonance frequency and the LH cutoff frequency are taken. Second, when CL increases, the parallel resonance frequency and the LH cutoff frequency are taken. If both LL and CL increase, the dispersion curve shifts to a lower frequency. That is, for the small antenna design, both LL and CL should have a high value. For example, if the physical length is constant but the LL and CL values can be greatly increased, the operating frequency of the small antenna may be further lowered.

7 shows a 2-D interdigital CRLH structure according to the present invention. Referring to FIG. 7, the upper patch is L _R , the interdigital coffee sheet is C _L , the via is L _L 700, and the capacitor and the capacitor between the patch and the lower ground plate may be equivalently modeled as C _R.

FIG. 8 is an equivalent circuit diagram of the 2-D interdigital CRLH structure of FIG. 7 as shown above. Referring to FIG. 8, the parallel capacitance and the parallel inductance 800 are connected in parallel, the series inductance and the series capacitance are proportionally distributed in series, and connected in two dimensions.

The 2-D interdigital CRLH structure according to the present invention is particularly designed to increase CL, and LL can also be adjusted through the diameter of the via.

9 illustrates an embodiment in which the CRLH structure according to the present invention is designed as an antenna operating in the LH mode. Since the interdigital capacitance is related to the serial capacitance CL and the capacitance increases with the number of fingers, eight fingers are used in four directions per unit cell.

Since the structure shown in the embodiment of FIG. 9 is a 3 × 3 periodic structure 900, n = 0, ± 1, ± 2 modes can be expected. For miniaturization of the antenna, observe the resonant frequencies in the modes n = -1, -2. In particular, since the lowest physical frequency is obtained when n = -2 mode in the same physical length, a two-dimensional CRLH structure is designed in which the resonance frequency of n = -2 is 1.1-GHz band. n = -2 in size (0.07λ 0.07λ _g X _g) of the radiating plane it is only occupied 7.8% of a conventional half wavelength antenna radiation plane (0.5λ _g X 0.5λ _g) As shown in FIG.

10 shows the results of S-parameter simulation using Ansoft HFSS. Referring to the simulation result 1000, it can be observed that resonance occurs at 1.684 GHz in n = 0 mode, 1.406 GHz in n = -1 mode, and 1.131 GHz in n = -2 mode. At 1.131 GHz, the return loss is -23.68 dB.

The present invention has been limited to the embodiments of the present invention, but it is obvious that the technology of the present invention can be easily modified by those skilled in the art. Such modified embodiments should be included in the technical spirit described in the claims of the present invention.

1 illustrates a general transmission line, which is characteristic of a right-handed (RH) material,

2 illustrates a transmission line showing characteristics of left-handed (LH) metamaterials.

3 illustrates an equivalent circuit model for implementing an LH metamaterial according to a preferred embodiment of the present invention.

4 illustrates an LH metamaterial having a periodic structure using a CRLH transmission line as a unit cell.

5A, 5B, and 5C illustrate a CRLH unit cell implementation method.

6 shows a dispersion curve of a typical CRLH transmission line.

7 shows a 2-D interdigital CRLH structure according to the present invention.

FIG. 8 is an equivalent circuit diagram of the 2-D interdigital CRLH structure of FIG. 7 as shown above.

9 illustrates an embodiment in which the CRLH structure according to the present invention is designed as an antenna operating in the LH mode.

10 shows the results of S-parameter simulation using Ansoft HFSS.

Claims (6)

In the flat antenna, Series inductance and series capacitance are connected in series, It includes a transmission line having a structure in which parallel inductance and parallel capacitance are connected in parallel as a unit cell, The series capacitance is a single plane antenna, characterized in that implemented by an interdigital (interdigital) structure. The method of claim 1, The transmission line is a planar antenna, characterized in that the plurality of unit cells cascaded. The method of claim 1, The parallel inductance is a planar antenna, characterized in that implemented by a via (via) structure. The method of claim 1, In the via structure, by adjusting the diameter of the via, the planar antenna, characterized in that for adjusting the size of the parallel inductance. The method of claim 1, The planar antenna is characterized in that the phase speed and the group speed in the case of a high frequency characteristics of the forward direction. The method of claim 1, The planar antenna is characterized in that the phase speed and the group speed is characterized in the opposite direction in the case of low frequency.

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