[invention Title]

BALUN INTERNAL TYPE LOOP ANTENNA

[Technical Field]

The present invention relates, in general, to loop antennas, and more particularly, to a balun internal type loop antenna, in which a radiation patch is helically formed on the outer circumference of a dielectric in a direction from the lower portion of the dielectric to the upper portion thereof, and a feeding part having a balun therein is inserted into the dielectric, thus preventing leakage current of the antenna, and realizing the miniaturization of the antenna.

[Background Art]

Generally, antennas are devices that efficiently radiate electric waves into space, or efficiently induce electromotive force in response to electric waves, thus achieving the object of communication in wireless communications. The antennas may be classified into a long-wave antenna, a medium-wave antenna, a short-wave antenna, an ultrashort-wave antenna, and a microwave antenna, according to the frequency used. The antennas may be classified into a standing wave antenna, a traveling wave antenna, and a log periodic antenna, according to the operational principle. The antennas may be classified into an isotropic antenna, an omni-directional antenna, a unidirectional antenna, and a bidirectional antenna, according to the directional characteristics. The antennas may be

classified into a linear polarization antenna, a circular polarization antenna, and an elliptical polarization antenna, according to the polarization. Further, the antennas may be classified into a broadband antenna, a narrowband antenna, a constant impedance antenna, and a tuned antenna, according to the frequency characteristics thereof.

The important characteristics required for the antennas are impedance characteristics and gain. When the impedance of an antenna is equal to that of a coaxial cable, electric waves are most efficiently transmitted. For this reason, impedance matching is very important. Further, when an antenna having a high gain is used, the antenna may communicate with a distant radio station even if the power thereof is low. Recently, an antenna having superior performance is required for an applied field, such as a Global Positioning System (GPS) , Digital Multimedia Broadcasting (DMB) , or Radio Frequency Identification (RFID) . Particularly, demand for an antenna having good impedance matching has increased.

As well known to those skilled in the art, RF signals are transmitted to an antenna through a coaxial cable or a strip line. Here, the coaxial cable or strip line is an unbalanced type line, but a loop antenna is a balanced type antenna. Thus, if the coaxial cable or strip line is connected to the loop antenna without taking special measures, leakage current occurs, so that the overall efficiency of the antenna is deteriorated.

Meanwhile, in order to overcome the problem, a balun is installed in an antenna patch, thus providing stable antenna

efficiency. However, such an antenna is problematic in that its size depends on the wavelength thereof, so that it is difficult to realize the miniaturization of the antenna.

[Disclosure] [Technical Problem]

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a balun internal type loop antenna, including a dielectric having a predetermined dielectric constant; an electrode patch helically formed on an outer circumference of the dielectric in a direction from a lower portion of the dielectric to an upper portion thereof; and a feeding part comprising a printed

circuit board inserted into the dielectric, having a shape, and having five layers.

The electrode patch includes a ring electrode part provided on the lower portion of the outer circumference of the dielectric, a plurality of helical electrode parts helically extending from the ring electrode part to the upper portion of the dielectric, and a folding part having as an end thereof extension ends of a group of helical electrode parts, and extending from the extension ends to a center of the dielectric, thus having a predetermined area.

Further, the folding part has a shape, and comprises a first folding portion and a second folding portion

which are symmetrical with respect to the dielectric.

A third layer of the feeding part includes a transformer and a stub for impedance matching, and a first layer and a fifth layer are connected at lower portions thereof to a second layer and a fourth layer, each comprising a GND layer, thus forming a balun.

Furthermore, the dielectric has a shape of a hollow cylinder or a rectangular shape.

[Technical Solution] In order to accomplish the object, the present invention provides a balun internal type loop antenna, in which a radiation patch is helically formed on the outer circumference of a dielectric in a direction from the lower portion of the dielectric to the upper portion thereof, and a feeding part having a balun therein is inserted into the dielectric, thus preventing leakage current of the antenna, and realizing the miniaturization of the antenna.

[Description of Drawings]

FIG. 1 is a perspective view of a balun internal type loop antenna, according to the present invention;

FIG. 2 is a perspective view of a balun internal type loop antenna having a rectangular dielectric, according to the present invention;

FIG. 3 is a sectional view of the balun internal type loop antenna, according to the present invention;

FIG. 4 is a view showing the entire construction of the balun internal type loop antenna, according to the present invention;

FIG. 5 is a detailed view showing a radiation patch, according to the present invention;

FIG. 6 is a side sectional view showing a feeding part having five layers, according to the present invention;

FIG. 7 is a graph showing the radiation pattern of the balun internal type loop antenna, according to the present invention; and

FIG. 8 is a graph showing the reflection loss of the balun internal type loop antenna, according to the present invention.

**Description of reference characters of important parts** 100: dielectric

200: electrode patch

210: ring electrode part

220: helical electrode parts

230: folding part 231: first folding portion

232 : second folding portion

300: feeding part

[Best Mode]

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

The construction of a balun internal type loop antenna,

according to the preferred embodiment of the present invention, will be described below with reference to FIGS. 1 to 6.

FIG. 1 is a perspective view of a balun internal type loop antenna, according to the present invention, FIG. 2 is a perspective view of a balun internal type loop antenna having a rectangular dielectric, according to the present invention, FIG. 3 is a sectional view of the balun internal type loop antenna, according to the present invention, FIG. 4 is a view showing the entire construction of the balun internal type loop antenna, according to the present invention, FIG. 5 is a detailed view showing a radiation patch, according to the present invention, FIG. 6 is a side sectional view showing a feeding part having five layers, according to the present invention, FIG. 7 is a graph showing the radiation pattern of the balun internal type loop antenna, according to the present invention, and FIG. 8 is a graph showing the reflection loss of the balun internal type loop antenna, according to the present invention.

As shown in FIGS. 1 to 4, the balun internal type loop antenna includes a dielectric 100, a radiation patch 200, and a feeding part 300.

The dielectric 100 has the shape of a hollow cylinder, is made of a ceramic material, and has a predetermined dielectric constant ( ε _r = 8 ~ 90) . According to this embodiment, the dielectric has the shape of a hollow cylinder. However, the present invention is not limited to the shape of a hollow cylinder. Thus, the dielectric may have the shape of a square pillar, as shown in FIG. 2.

Further, the radiation patch 200 is helically formed on the outer circumference of the dielectric 100 in a direction from the lower portion of the dielectric to the upper portion thereof. As shown in FIG. 5, the radiation patch includes a ring electrode part 210, a plurality of helical electrode parts 220, and a folding part 230. The ring electrode part is provided on the lower portion of the outer circumference of the dielectric. The helical electrode parts extend helically in the direction from the ring electrode part to the upper portion of the dielectric. The folding part has a group of helical electrode parts as an end of the folding part, and extends from the extension ends of the helical electrode parts to the center of the dielectric, thus having a predetermined area.

Here, the polarization of the antenna is determined according to the helical direction of the helical part. Thus, as shown in FIGS. 4 and 5, when the helical part is formed in a left-hand screw direction, the antenna has right hand circular polarization. When the helical part is formed in a right-hand screw direction, the antenna has left hand circular polarization.

According to this invention, the folding part 230 includes a first folding portion 231 and a second folding portion 232, which are symmetrical with respect to the center of the dielectric. Each of the first and second folding portions 231

and 232 has the shape of a

Further, the feeding part 300 is a printed circuit board

(PCB) which is inserted into the dielectric. The overall shape

of the feeding part is The feeding part has five layers, that is, first, second, third, fourth, and fifth layers.

FIG. 6 is a side sectional view showing the feeding part having the five layers. As shown in the drawing, the second, third, and fourth layers are feeding lines having a strip line structure. Especially, the third layer includes a transformer and a stub for impedance matching. The first and fifth layers are arranged to realize a λ./2 open type balun (bazooka balun) , and are connected at lower portions thereof to the second and fourth layers, which are connected to GND. That is, the antenna according to the present invention is the antenna having the balun (balance to unbalance transformer) therein. The balun of the antenna prevents leakage signals, thus increasing the overall efficiency of the antenna.

FIG. 7 is a graph showing the radiation pattern (2dB/div) of the balun internal type loop antenna. As shown in the graph, Half Power Beam Width (HPBW) exhibits superior characteristics even at a low angle of 180 degrees. Further, FIG. 8 is a graph showing the reflection loss of the balun internal type loop antenna. As shown in the graph, the reflection loss is -13.7dB at a GPS frequency (1.575GHz), and thus the matching of input impedance is very superior. The bandwidth thereof is 18.3MHz (1.2%). This is about twice as wide as the bandwidth of a conventional antenna having the same size as the antenna according to this invention. Further, superior characteristics

are exhibited in a wide frequency band in an axial ratio.

Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims .

[industrial Applicability]

As described above, the present invention provides a balun internal type loop antenna, in which a feeding part having a balun therein is inserted into a dielectric, thus preventing leakage current of the antenna, and realizing the miniaturization of the antenna, compared to a conventional antenna, which has a balun in an antenna patch.