Electromagnetic bandgap structure and printed circuit board

An electromagnetic bandgap structure and a printed circuit board that solve a mixed signal problem are disclosed. In accordance with embodiments of the present invention, the electromagnetic bandgap structure includes a first metal layer; a first dielectric layer, stacked in the first metal layer; a second metal layer, stacked in the first dielectric layer, and having a holed formed at a position of the second dielectric layer; a second dielectric layer, stacked in the second metal layer; a metal plate, stacked in the second dielectric layer; a first via, penetrating the hole formed in the second metal layer and connecting the first metal layer and the metal plate; a third dielectric layer, stacked in the metal plate and the second dielectric layer; a third metal layer, stacked in the third dielectric layer; and a second via, connecting the second metal layer to the third metal layer.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2007-0041993, filed on Apr. 30, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed circuit board, more specifically to a printed circuit board that can solve a mixed signal problem between an analog circuit and a digital circuit.

2. Background Art

Various apparatuses such as mobile communication terminals, personal digital assistants (PDA), laptop computers and digital multimedia broadcasting (DMB) devices have been launched in order to meet today's trend that mobility is considered as one of the most important issues.

Such apparatuses include a printed circuit board, which is configured to compound analog circuits (e.g. radio frequency (RF) circuits) and digital circuits for wireless communication.

FIG. 1is a sectional view showing a printed circuit board including an analog circuit and a digital circuit. Although a 4-layered printed circuit board is illustrated, various printed circuit boards such as 2 and 6-layered printed circuit boards can be applied. Here, the analog circuit is assumed to be an RF circuit.

The printed circuit board100includes metal layers110-1,110-2,110-3and110-4(hereinafter, collectively referred to as110), dielectric layers120-1,120-2and120-3(hereinafter, collectively referred to as120) stacked in between the metal layers110, a digital circuit130mounted on the top metal layer110-1and an RF circuit140.

If it is assumed that the metal layer110-2is a ground layer and the metal layer110-3is a power layer, a current passes through a via160connected between the ground layer110-2and the power layer110-3and the printed circuit board100performs a predetermined operation or function.

Here, an operation frequency of the digital circuit130and an electromagnetic (EM) wave150by harmonics components are transferred to the RF circuit140, to thereby generate a problem mixed signals. The mixed signal problem is generated due to the EM wave, having a frequency within the frequency band in which the RF circuit140is operated, in the digital circuit130. This problem results in obstructing the accurate operation of the RF circuit140. For example, when the RF circuit140receives a signal ranging a certain frequency band, transferring the EM wave150including the signals ranging the certain frequency band from the digital circuit130may make it difficult to accurately receive the signal ranging the certain frequency band.

Solving the mixed signal problem becomes more difficult due to the increased complexity of electronic apparatuses and the higher operation frequency of the digital circuit130.

The decoupling capacitor method, which is a typical solution for power noise, is not adequate for high frequencies. Accordingly, it is necessary to intercept or decrease the noise of the high frequencies between the RF circuit140and the digital circuit130.

FIG. 2is a sectional view showing an electromagnetic bandgap structure that solves a problem mixed signals between an analog circuit and a digital circuit in accordance with a conventional art, andFIG. 3is a plan view showing a metal plate configuration of the electromagnetic bandgap structure shown inFIG. 2.FIG. 4is a perspective view showing the electromagnetic bandgap structure shown inFIG. 2, andFIG. 5is a schematic view showing an equivalent circuit of the electromagnetic bandgap structure shown inFIG. 2.

The electromagnetic bandgap structure200includes a first metal layer210-1, a second metal layer210-2, a first dielectric layer220aa second dielectric layer220b, a meal plate232and a via234.

The first metal layer210-1and the metal plate232are connected to each other through the via234. A mushroom type structure230is formed to include the metal plate232and the via234(refer toFIG. 4).

If the first meal layer210-1is a ground layer, the second metal layer210-2is a power layer. Also, if the first metal210-1is the power layer, the second layer210-2is the ground layer.

In other words, the repeated formation of the mushroom type structure230(refer toFIG. 3) results in a bandgap structure preventing a signal having a certain frequency band from being penetrated. At this time, the mushroom type structures230, including the metal plates232and the vias234, are repeatedly formed between the ground layer and the power layer.

The function preventing a signal having a certain frequency band from being penetrated, which is based on resistance REand RP, inductance LEand LP, capacitance CE, CPand CGand conductance GPand GE, is approximated to the equivalent circuit shown inFIG. 5.

A mobile communication terminal is a good example for an electronic apparatus employing the board realized with the digital circuit and the RF circuit together. In the case of the mobile communication terminal, solving the problem mixed signals needs the noise shielding of an operation frequency band of the RF circuit between 0.8 and 2.0 GHz. The small sized mushroom type structure is also required. However, the foregoing electromagnetic bandgap structure may not satisfy the two conditions needed to solve the problem mixed signals.

Since the smaller sized mushroom type structure causes the bandgap frequency band shielding the noise to be increased, the mobile communication terminal is not effectively operated in the operation frequency band of the RF circuit between 0.8 and 2.0 GHz.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an electromagnetic bandgap structure and a printed circuit board that can allow the size not to be increased and have a low bandgap frequency band.

The present invention also provides an electromagnetic bandgap structure and a printed circuit board that can solve a problem mixed signals in an electronic apparatus (e.g. a mobile communication terminal) employing the board having the digital circuit and the RF circuit, realized therein together.

In addition, the present invention provides an electromagnetic bandgap structure and a printed circuit board that can allow the noise having a certain frequency band not to penetrate it.

An aspect of present invention features an electromagnetic bandgap structure including a first metal layer; a first dielectric layer, stacked in the first metal layer; a second metal layer, stacked in the first dielectric layer and having a hole formed at a predetermined position; a second dielectric layer, stacked in the second metal layer; a metal plate, stacked in the second dielectric layer; a first via, penetrating the hole formed in the second metal layer and connecting the first metal layer and the metal plate; a third dielectric layer, stacked in the metal plate and the second dielectric layer; a third metal layer, stacked in the third dielectric layer; and a second via, connecting the second metal layer to the third metal layer.

Here, the second via can connect the second metal layer to the third metal layer through an area excluding the area in which the metal plate is stacked.

A plurality of second vias can be formed. Here, the plurality of second vias can be symmetrically formed based on the first via as a reference axis.

The first via can be formed to have an identical center axis to the hole. Here, a diameter of the hole can be set to be larger than that of the first via

A plurality of mushroom type structures including the metal plates and the first vias can be placed between the first metal layer and the third metal layer. Here, a plurality of holes can be formed in the second metal layer, according to a position of each first vias of the mushroom type structures.

The plurality of holes can be formed to be away from each other at regular intervals.

The metal layers of the plurality of mushroom type structures can be placed on a same planar surface.

The third dielectric layer can be formed by using an identical dielectric material to the second dielectric layer.

Another aspect of the present invention features a printed circuit board having an analog circuit and a digital circuit. Here, the printed circuit board can include an electromagnetic bandgap structure which is disposed between the analog circuit and the digital circuit, the electromagnetic bandgap structure including a first metal layer; a first dielectric layer, stacked in the first metal layer; a second metal layer, stacked in the first dielectric layer, and having a hole formed at a predetermined position; a second dielectric layer, stacked in the second metal layer; a metal plate, stacked in the second dielectric layer; a first via, penetrating the hole formed in the second metal layer and connecting the first metal layer and the metal plate; a third dielectric layer, stacked in the metal plate and the second dielectric layer; a third metal layer, stacked in the third dielectric layer; and a second via, connecting the second metal layer to the third metal layer.

Here, the first metal layer can be any one of a ground layer and a power layer, and the second metal layer and the third metal layer can be the other.

The second via can connect the second metal layer to the third metal layer through an area excluding the area in which the metal plate is stacked.

A plurality of second vias can be formed. Here, the plurality of second vias can be symmetrically formed based on the first via as a reference axis.

The first via can be formed to have an identical center axis to the hole. Here, a diameter of the hole can be set to be larger than that of the first via.

A plurality of mushroom type structures including the metal plates and the first vias can be placed between the first metal layer and the third metal layer. Here, a plurality of holes can be formed in the second metal layer, according to a position of each first via of the mushroom type structures.

The plurality of holes can be formed to be away from each other at regular intervals.

The metal layers of the plurality of mushroom type structures can be placed on a same planar surface.

The third dielectric layer can be formed by using an identical dielectric material to the second dielectric layer.

The analog circuit can be an RF circuit receiving a wireless signal from an outside.

DESCRIPTION OF THE EMBODIMENTS

Since there can be a variety of permutations and embodiments of the present invention, certain embodiments will be illustrated and described with reference to the accompanying drawings. This, however, is by no means to restrict the present invention to certain embodiments, and shall be construed as including all permutations, equivalents and substitutes covered by the spirit and scope of the present invention. Throughout the drawings, similar elements are given similar reference numerals. Throughout the description of the present invention, when describing a certain technology is determined to evade the point of the present invention, the pertinent detailed description will be omitted.

Terms such as “first” and “second” can be used in describing various elements, but the above elements shall not be restricted to the above terms. The above terms are used only to distinguish one element from the other. For instance, the first element can be named the second element, and vice versa, without departing the scope of claims of the present invention. The term “and/or” shall include the combination of a plurality of listed items or any of the plurality of listed items.

When one element is described as being “connected” or “accessed” to another element, it shall be construed as being connected or accessed to the other element directly but also as possibly having another element in between. On the other hand, if one element is described as being “directly connected” or “directly accessed” to another element, it shall be construed that there is no other element in between.

The terms used in the description are intended to describe certain embodiments only, and shall by no means restrict the present invention. Unless clearly used otherwise, expressions in the singular number include a plural meaning. In the present description, an expression such as “comprising” or “consisting of” is intended to designate a characteristic, a number, a step, an operation, an element, a part or combinations thereof, and shall not be construed to preclude any presence or possibility of one or more other characteristics, numbers, steps, operations, elements, parts or combinations thereof.

Unless otherwise defined, all terms, including technical terms and scientific terms, used herein have the same meaning as how they are generally understood by those of ordinary skill in the art to which the invention pertains. Any term that is defined in a general dictionary shall be construed to have the same meaning in the context of the relevant art, and, unless otherwise defined explicitly, shall not be interpreted to have an idealistic or excessively formalistic meaning.

Hereinafter, some embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 6is a perspective view showing an electromagnetic bandgap structure which solves a mixed signal problem between an analog circuit and a digital circuit, and FIG. is a plan view showing a metal plate configuration of the electromagnetic bandgap structure shown inFIG. 6.FIG. 8is a sectional view showing an electromagnetic bandgap structure of the present invention according to the A-A′ line ofFIG. 7, andFIG. 9is another sectional view showing an electromagnetic bandgap structure of the present invention according to the B-B′ line ofFIG. 7.

Referring toFIG. 6thoughFIG. 9, the electromagnetic bandgap structure300in accordance with an embodiment of the present invention can include a first metal layer210-1, a second metal layer210-2, having a hole350formed at a predetermined position, a third metal layer210-3, a first dielectric layer220a, a second dielectric layer220b, a third dielectric layer220c, a metal plate330, a first via340and a second via360.

In other words, the first dielectric layer220acan be stacked in the first metal layer210-1, and the second metal layer210-2can be stacked in the first dielectric layer220a. The second dielectric layer220bcan be stacked in the second metal layer210-2, and the metal plate330can be stacked in the second dielectric layer220b. The first metal layer210-1and the metal plate330can be connected to each other through the first via340penetrating the hole350, formed in the second metal layer210-2. The third dielectric layer220ccan be stacked in the metal plate330and the second dielectric layer220b, and the third metal layer210-3can be stacked in the third dielectric layer220c. The second metal layer210-2and the third metal layer210-3can be connected to each other through the second via360. Here, the metal plate330and the first via340can be arranged in a mushroom form between the first metal layer2210-1and the third metal layer210-3(which is referred to as a mushroom type structure370). Each of the elements will be described as follows.

The first metal layer210-1, the second metal layer210-2and the third metal layer210-3can be used as means for connecting an electrical power. For example, if the first metal layer210-1is a ground layer, the third metal layer210-3(including the second metal layer210-2, connected to the third metal layer210-3through the second via360, and the same shall apply hereinafter.) can be a power layer. If the first metal layer210-1is the power layer, the third metal layer210-3can be the ground layer. In other words, the first metal layer210-1and the third metal layer210-3can be each one of the ground layer and the power layer, which are placed close to each other, and the dielectric layer220can be placed between the ground layer and the power layer. Accordingly, it is natural that any metal material capable of being provided with the power and transferring an electrical signal can be used without any limitation. The same can be applied to the metal plate330, the first via340and the second via360, which are described below.

The dielectric layer220can be formed between the first metal layer210-1and the second metal layer210-2and between the second metal layer210-2and the third metal layer210-3. The dielectric layer220can be distinguished into the first dielectric layer220a, the second dielectric layer220band the third dielectric layer220caccording to their formation time. At this time, the second metal layer210-2can be placed between the first dielectric layer220aand the second dielectric layer220b, and the metal layer210-3can be placed between the second dielectric layer220band the third dielectric layer220c. Here, the first dielectric layer220a, the second dielectric layer220band the third dielectric layer220c, respectively, can consist of materials having different dielectric constants, but alternatively, at least one dielectric layer can consist of materials having the same dielectric constant.

For example, the second dielectric layer220band the third dielectric layer220ccan be formed by using the same dielectric material for the convenience of the stacking process and the adjustment of the bandgap frequency. As such, selecting or adjusting the dielectric material (i.e. the corresponding dielectric constant) included in each dielectric layer adequately can make it possible to approach a desired bandgap frequency band (i.e. between 0.8 and 2.0 GHz) in accordance with the present invention. Of course, each stacked thickness of the three dielectric layers220a,220band220ccan also be adequately adjusted to approach the desired bandgap frequency band.

For example, even though the electromagnetic bandgap structures300have the same size, the corresponding bandgap frequency band can approach the desired frequency band by largely decreasing the stacked thickness of the third dielectric layer220cand increasing the stacked thickness of the first dielectric layer220aor the second dielectric layer220bas much as the stacked thickness of the third dielectric layer220cis decreased. Here, the bandgap frequency can refer to the frequency prevented from being transferred among the electromagnetic wave transferred from one side to the other side.

The first via340can connect the first metal layer210-1and the metal plate330by penetrating the hole350formed in the second metal layer210-2. Accordingly, the process removing a part of the second metal layer210-2to form the hole350can performed before the first via340is formed. For example, the hole350can be formed at a position in the second metal layer210-2by using the below-described drilling process. Then, the second via345penetrating the hole350can be formed. At this time, the process forming the hole350can be performed after or before the second dielectric layer220bis stacked in the second metal layer210-2. Hereinafter, the method of forming the first via340will be described taking an example.

The first metal layer210-1, the first dielectric layer220a, the second metal layer210-2, the second dielectric layer220band the metal plate330can be successively stacked in. Then, a via land (not shown) can be formed at a position in the metal plate330. Here, the position of the metal plate330can be the position in which the first via340is desired to be formed for being electrically connected to the first metal layer210-1. The via land, which is to reduce the position error in the drilling process for forming the first via340, can be formed more largely than the sectional area size of the first via340.

Then, through the drilling process, the via can be formed to penetrate the via land, the dielectric layer220b, the hole350formed on the second metal layer210-2and the first dielectric layer2202a. After the via is formed, the plating process can be performed to allow a plating layer to be formed on the internal wall of the via in order to electrically connect the first metal layer210-1to the metal plate330. According to the plating process, a plating layer can be formed on the internal wall of the via excluding the center part among the inside part of the via or the entire inside part of the via can be completely filled. In case that the inside part of the via has an empty center part, the empty center part can be filled with the dielectric material or air. Through the foregoing processes, the first via340can have one end part340a, connected to the first metal layer210-1, and the other end part340b, connected to the metal plate330.

Here, the first via340can be formed to have the same axis as the hole30in order to penetrate the hole350formed in the second metal layer210-2and connecting the first metal layer210-1to the metal plate330. Similarly, the hole350formed in the second metal layer210-2can have a larger diameter than the first via340in order to allow the first via340to penetrate the hole350formed in the second metal layer210-2and to connect the first metal layer210-1and the metal plate330.

AlthoughFIG. 6throughFIG. 9illustrate the mushroom type structure370in which one first via340is connected to one metal plate330as an example, a plurality of first vias340can be connected to one metal plate330. Also, even thoughFIG. 6andFIG. 7illustrate the metal plate330having a regular square shape, the metal plate330can have various shapes such as polygons, for example, triangles and hexagons, circles and ellipses. Below are described the mushroom type structure370with reference toFIG. 6throughFIG. 9.

At least one mushroom type structure370having the metal plate330and the first via340can be arranged between the first metal layer210-1and the third metal layer210-3. At this time, the metal plate330of the mushroom type structure370can be arranged on the same planar surface or the different planar surface between the first metal layer210-1and the third metal layer210-3. Even ifFIG. 6throughFIG. 9illustrate that the first via340of the mushroom type structure370is connected to the first metal layer210-1, the first via340can be connected to the third metal layer210-3.

Also, a plurality of mushroom type structures370can be connected to the first metal layer210-1or the third metal layer210-3through the first via340. Alternatively, some of the plurality of mushroom type structures can be connected to the first metal layer210-1and the other can be connected to the third metal layer210-3.

FIG. 7illustrates that the mushroom type structures370can be away from each other at predetermined intervals and be repeatedly arranged. The repeated formation of the mushroom type structures370can make it possible to block a signal having a frequency band corresponding to an operation frequency band of an analog circuit (e.g. an RF circuit) among an electromagnetic wave proceeding from a digital circuit to the analog circuit. For this, the second metal layer210-2can form a plurality of holes350, and the mushroom type structures370can be arranged one by one at a position corresponding to a position in which each hole350is formed. At this time, the metal plates330of the plurality of arranged mushroom type structures can be arranged on the same or different planar surface. Also, the plurality of holes350can be away from each other in regular intervals and be formed on the second metal layer210-2.

The second via360can connect the second metal layer210-2to the third metal layer210-3. The second via360can be formed through the similar processes to the aforementioned processes of forming the first via340. Through the processes, the second via360can have one end part360a, which is connected to the second metal layer210-2, and the other end part360b, which is connected to the third metal layer210-3. Here, since the second via360is for the electric connection between the second metal layer210-2and the third metal layer210-3, the second via360can be required to be disconnected to the metal plate330. Accordingly, the second via360can be formed by penetrating an area of an upper surface of the second dielectric layer220b. In the electromagnetic bandgap structure300, a plurality of second vias360connecting the second metal layer210-2to the third metal layer210-3can be also formed. At this time, the plurality of second vias360can be symmetrically formed based on the first via340as a reference axis as illustrated inFIG. 6andFIG. 7.

AlthoughFIG. 6throughFIG. 9are related to the case that the second via360connects the second metal layer210-2to the third metal layer210-3, the second via360can be formed to connect the first metal layer210-1to the second metal layer210-2. In this case, the first metal layer210-1and the second metal layer210-2can function as one of the power layer and the ground layer, and the third metal layer210-3can function as the other.

As such, in the electromagnetic bandgap structure, if the structure connecting any one metal layer to another layer of 3 metal layers by additionally having the second via360(i.e. the structure having one more ground layer (or power layer), and hereinafter, referred to as ground layer adding structure) is used, the inductance value can be acquired more enough corresponding to the added second via360, to thereby lower the bandgap frequency band as compared with the conventional structure (refer toFIG. 4). This will be described more clearly with reference toFIG. 10.

As described above, the electromagnetic bandgap structure300of the present invention can be arranged inside the printed circuit board having the analog circuit and the digital circuit. In other words, in accordance with an embodiment of the present invention, the printed circuit board can have the analog circuit and the digital circuit. At this time, the analog circuit can be the RF circuit such as an antenna receiving a wireless signal from an outside.

In the printed circuit board of the present invention, the electromagnetic bandgap structure300illustrated inFIG. 6andFIG. 7can be arranged between the analog circuit and the digital circuit. For example, the electromagnetic bandgap structure300can be arranged between the RF circuit140and the digital circuit130of the printed circuit board illustrated inFIG. 1. This is to block an electromagnetic wave having a frequency band which is similar to the operation frequency band (e.g. 0.8-2.0 GHz) of the RF circuit140among the transferred electromagnetic wave by arranging the electromagnetic bandgap structure300to allow the electromagnetic wave generated from the digital circuit130to necessarily pass through the electromagnetic bandgap structure300before being transferred to the RF circuit140.

Accordingly, the electromagnetic bandgap structure300of the present invention can be arranged in a closed curve shape about the RF circuit140and the digital circuit130. Alternatively, the electromagnetic bandgap structure300can be arranged in a signal transferring path between the digital circuit and the analog circuit. It is obvious that the electromagnetic bandgap structure300can be arranged in various ways.

As described above, arranging the electromagnetic bandgap structure300inside the printed circuit board can make it possible to prevent an electromagnetic wave having a frequency band of the electromagnetic wave transferred from the digital circuit to the analog circuit from being transferred. This can solve the mixed signal problem.

FIG. 10is graphs showing results that are computer-simulated by using electromagnetic bandgap structures in accordance with a conventional art and an embodiment of the present invention.

FIG. 10and the below table 1 show computer-simulated results that compare the case of the conventional electromagnetic bandgap structure200(refer to (a) ofFIG. 10) with the case of the electromagnetic bandgap structure300of the present invention (refer to (b) ofFIG. 10).

Here,FIG. 10and the below table 1 assume that the conventional electromagnetic bandgap structure200and the electromagnetic bandgap structure300of the present invention have the same size and the same configuration. However, it must be understood clearly that despite the same design condition,FIG. 10and the below table 1 is merely examples showing that the simple design change into the ground layer adding structure such as the electromagnetic bandgap structure300of the present invention can makes it possible to lower the bandgap frequency bandgap band largely as compared with the conventional electromagnetic bandgap structure200.

Accordingly, in the present invention, it is natural that adjusting various conditions such as the shape and size of the structure, and the thickness, dielectric constant and configuration of each element appropriately can design the electromagnetic bandgap structure to have a lower bandgap frequency band than the bandgap frequency bands shown inFIG. 10and the following table 1.

Referring toFIG. 8and table 1, although the conventional electromagnetic bandgap structure200and the electromagnetic bandgap structure300of the present invention have the same design conditions such as the size of the structure, it can be recognized that the electromagnetic bandgap structure300of the present invention has the bandgap frequency band that is lower than approximately 0.3 to 0.4 GHz or more as compared with the conventional electromagnetic bandgap structure. This can be because the electromagnetic bandgap structure300of the present invention has the structure in which has one more ground layer or power layer by connecting one to another of three metal layers through the second via360in addition to arranging the electromagnetic bandgap structure370. This can be described below with reference to the equivalent circuit ofFIG. 5.

The electromagnetic bandgap structure300of the present invention can acquire an inductance component corresponding to the lengthwise direction of the second via360(refer to LEcomponent by the via234ofFIG. 5) more as compared with the conventional electromagnetic bandgap structure200due to having the ground layer adding structure through the second via360. As such, the bandgap frequency band blocked through the electromagnetic bandgap structure300of the present invention by the inductance value additionally acquired by the second via360can be lowered as compared with the conventional structure. Accordingly, if the electromagnetic bandgap structure300having the ground layer adding structure like the present invention forms a lot of second vias360connecting metal layers, since the acquired inductance value is increased, it can be easily recognized that it is possible to lower the bandgap frequency band more largely.

As described above, when manufacturing the electromagnetic bandgap structure, the present invention can lower the bandgap frequency band more or select a desired bandgap frequency band by simply changing the configuration by the method of adding the second metal layer210-2and the second via360without the design process of minutely adjusting or changing the size, quantity and material of the structure to lower the bandgap frequency band.

FIG. 11AthroughFIG. 11Eillustrate various configuration types of a second via connecting a second metal layer to a third metal layer in an electromagnetic bandgap structure. In particular,FIG. 11AthroughFIG. 11Eillustrate that a plurality of second vias360are symmetrically arranged (or formed) based on the first via340as a reference axis. However, it shall be obvious that the configuration of the second via360is not limited to the foresaid description and it is unnecessary to symmetrically arrange the second vias360based on the first via340as the reference axis.

FIG. 12AthroughFIG. 12Care graphs showing results that are computer-simulated by using electromagnetic bandgap structures in accordance with a conventional art and an embodiment of the present invention according to each configuration type of the second via shown inFIG. 11AthroughFIG. 11E. Refer toFIG. 12AthroughFIG. 12C, it can be recognized that the electromagnetic bandgap structure300of the present invention according to configuration shown inFIG. 11AthroughFIG. 11Ehas the bandgap frequency band of approximately 1.0 to 2.5 GHz or so on a (−) 50 dB basis (refer to (a) through (e) ofFIG. 12AthroughFIG. 12C). However, the conventional electromagnetic bandgap structure200has the bandgap frequency band of approximately 1.5 to 3.5 GHz or so on the (−) 50 dB basis (refer to (f) ofFIG. 12C). Accordingly, it is recognized again that the electromagnetic bandgap structure300of the present invention can lower the bandgap frequency band due to having the ground layer adding structure as compared with the conventional structure.

Hitherto, although some embodiments of the present invention have been shown and described for the above-described objects, it will be appreciated by any person of ordinary skill in the art that a large number of modifications, permutations and additions are possible within the principles and spirit of the invention, the scope of which shall be defined by the appended claims and their equivalent.