KR100323394B1 - Broadband microstripline-fed circular slot antenna - Google Patents

Abstract

Improved annular ring slot antennas and circular slot antennas are disclosed. The annular ring-shaped slot is formed into an asymmetrical shape whose width is not uniform by separating the center of the circular patch formed from the inside of the conductive ground plate and the center of the circular slot. In addition, the circular slot antenna extends the area of the substantially circular slot by offsetting the center of the circular slot on the ground plate and the center of the circular patch by positioning the circular patch at the end of the feed line on the upper surface of the dielectric substrate, rather than placing the circular patch on the ground plate. Mismatch. Furthermore, more stub slots are formed in the circular slots or more subbs are added to the circular patches for wider bandwidth and better impedance matching characteristics. As a result, the narrowband characteristic, which is a disadvantage of the general microstrip antenna, is drastically improved, thereby realizing the structure of the antenna having the wideband frequency characteristic due to multiple resonances.

Description

Microstrip Circular Slot Antenna with Broadband Characteristics {BROADBAND MICROSTRIPLINE-FED CIRCULAR SLOT ANTENNA}

The present invention relates to an antenna, and more particularly to a microstrip circular slot antenna having broadband characteristics.

As the modern society has developed into an information society, various and rapid large-capacity information exchanges have been required. Accordingly, PCS (Personal Communication System), IMT-2000 (International Mobile Telecommunications-2000), WLL (Wireless Local Loop), and Satellite Many kinds of communication services such as telecommunications are being implemented. In addition, the development of a new communication system with the implementation of a variety of communication services is expected to rapidly increase the number of users of communication services, the need for a wider frequency band is emerging. Therefore, new communication systems need antennas capable of receiving signals in a wider frequency band. Accordingly, interest in microstrip antennas is increasing due to their small volume, light weight, and economical properties.

First proposed by Deschamps in 1953 and developed by Howell and Munson in the early 1970s, microstrip antennas have the advantages of being inexpensive, easy to make flat arrays, small cross-sections and easy to integrate with microwave circuits. However, the microstrip antenna has a big disadvantage of narrow bandwidth.

In order to remedy this drawback, a lot of research is in progress and various methods have been proposed. Among the microstrip antennas, many researches have been conducted on the microstrip slot antenna because of the advantage that the microstrip slot antenna has a relatively wide bandwidth and an antenna having a bidirectional radiation pattern or a single radiation pattern. Representative examples include a method of using a substrate having a low dielectric constant and a thickness, and a method of improving bandwidth by using parasitic coupled devices. However, the above methods have the disadvantage of increasing the size of the antenna.

In order to make up for this drawback, a method of widening bandwidth by changing the antenna structure itself has recently been proposed. Representatively, there is a study on a microstrip slot antenna having a relatively wide broadband characteristic as a single radiating element. Many studies focusing on the structural changes of microstrip slot antennas have been conducted mainly for rectangular slot antennas. As a representative example, a method of achieving impedance matching by changing a feeding structure of a rectangular slot antenna is proposed, and there is an example in which a feeding method exhibiting a broadband characteristic of 47% in the slot antenna is proposed through this method.

However, the rectangular slot antenna has a number of design variables, which makes it difficult to design and manufacture. On the other hand, the circular slot antenna has an advantage that the design and manufacturing is flat because the design parameters are smaller than the rectangular slot antenna.

On the other hand, as an example of the antenna having the broadband frequency characteristics disclosed in the prior art, the antenna disclosed in Japanese Patent Application Laid-open No. Hei 10-276033 entitled "antenna" proposed by Arai Hiroyuki et al. The antenna proposed by Arai Hiroyuki et al., As shown in FIG. 1, has a microstrip line 13 and a microstrip line 13 connected to the inner conductor pins of the coaxial connector 12 bonded to the side of the insulating board 10. A first printed disk 14 continuously formed at the tip of the bottom surface is provided on the first surface of the insulating board 10, and is connected to the matching pattern 15 and the matching pattern 15 connected to the outer conductor of the coaxial connector 12. The connected second printing disk 16 has a structure provided on the second surface of the insulating board 10. The two printing disks 14 and 16 are conductor patterns having the same diameter, and are positioned so that both circumferences of the projection plane are in contact with each other. By the way, the antenna has a characteristic that the diameter of the circular disk 16 and the feeder terminal circular disk 14 is the same, the offset or feedline termination circular radius optimization problem is not considered.

The present invention aims to provide a circular slot antenna that can obtain a wider bandwidth by widening the area of the circular slot to obtain multiple resonances by widening the area of the conventional antenna.

In addition, another object of the present invention is to provide a modified asymmetric annular annular slot antenna that can obtain a wider bandwidth by asymmetrically forming the annular annular slot.

1 shows the structure of a conventional antenna having broadband characteristics.

Figure 2a is a perspective view showing the structure of a conventional symmetrical annular ring antenna, Figure 2b is a perspective view showing a conductive ground plane in contact with the lower surface of the dielectric substrate.

3 shows a coordinate system for interpretation of a circular slot antenna.

4 shows a change in the reflection attenuation amount S ₁₁ according to the slot width W _s of the symmetric annular ring antenna.

Fig. 5A is a perspective view showing the structure of a modified asymmetric annular ring slot antenna according to the first embodiment of the present invention. Fig. 5B is a perspective view showing a conductive ground plate in contact with the lower surface of the dielectric substrate. 5A is a plan view of the antenna of FIG. 5A for illustrating an arrangement relationship between an antenna and a ground plate.

FIG. 6 is a graph showing a change in reflection attenuation with offset in the antenna of FIG. 5A.

FIG. 7 is a graph showing a change in reflection attenuation according to the radius of the circular patch of the ground plate in the antenna of FIG. 5A.

8A and 8B are graphs showing radiation patterns of electric and magnetic fields at respective resonance frequencies in the antenna of Fig. 5A, respectively.

FIG. 9A is a perspective view showing the structure of a circular slot antenna according to a second embodiment of the present invention, FIG. 9B is a perspective view showing a conductive ground plate in contact with a lower surface of the dielectric substrate, and FIG. 9A is a plan view of the antenna of FIG. 9A for illustrating an arrangement relationship.

Fig. 10 is a graph showing a change in reflection attenuation according to an offset in the circular slot antenna according to the second embodiment of the present invention.

11A and 11B are graphs showing changes in input impedance according to offsets in the circular slot antenna according to the second embodiment of the present invention.

FIG. 12 is a graph showing a change in the amount of reflection attenuation according to the radius R _in of the circular patch at the end of the feed line in the circular slot antenna according to the second embodiment of the present invention.

FIG. 13 is a graph showing an actual measurement result and a simulation result of the reflection attenuation amount in the optimized circular slot antenna according to the second embodiment of the present invention.

14A and 14B show the actual measurement results of the field emission pattern E _θ and the field emission pattern H _φ at 2.5 GHz in the optimized circular slot antenna according to the second embodiment of the present invention. It is a graph showing the simulation results.

Fig. 15A is a perspective view showing the structure of a circular slot antenna in which a stub is added to a circular patch at the end of a feeder line according to a third embodiment of the present invention, and Fig. 15B is a conductive ground plate in contact with the bottom surface of the dielectric substrate. Fig. 15C is a plan view of the antenna of Fig. 15A for illustrating an arrangement relationship between a feeder line and a ground plate.

16A and 16B respectively show the relationship between the frequency and the reflection attenuation when a stub is not added to the circular patch and when a stub is added to the circular patch at the end of the feed line according to the third embodiment. One graph.

FIG. 17A is a perspective view illustrating a structure of a circular slot antenna in which a stub slot is further formed in a circular slot of a conductive ground plane according to a fourth embodiment of the present invention, and a stub is formed in a circular patch at the end of a feed line; FIG. FIG. 17B is a perspective view showing a conductive ground plate in contact with the lower surface of the dielectric substrate, and FIG. 17C is a plan view of the antenna of FIG. 17A for illustrating an arrangement relationship between a feeder line and a ground plate.

18A and 18B respectively show the relationship between the frequency and the reflection attenuation when the stub slot is arranged to form 36 degrees and 60 degrees with the microstripline of the feed line in the circular slot in the antenna according to the fourth embodiment. It is a graph.

FIG. 19A is a perspective view illustrating a structure of a circular slot antenna in which a stub slot is further formed in a circular slot of a conductive ground plane according to a fifth embodiment of the present invention, and a conductive stub is further added to a circular patch at the end of a feed line; FIG. Fig. 19B is a perspective view showing a conductive ground plate in contact with the bottom surface of the dielectric substrate, and Fig. 19C is a plan view of the antenna of Fig. 19A for illustrating the arrangement relationship between the feeder and the ground plate.

<Description of the symbols for the main parts of the drawings>

Dielectric substrates: 56, 96, 156, 176, 196

Feed line: 54, 94, 154, 174, 194

Round Patches: 52B, 94B, 154B, 174B, 194B

Micro stripline: 54, 94A, 154A, 174A, 194A

Ground Plate: 52, 92, 152, 172, 192

Slots: 50, 90, 150, 170, 190

Stub slots: 171A, 171B

Stubs: 154C, 154D, 194C, 194D

In order to achieve the first object of the present invention, an antenna according to the present invention is a dielectric substrate, a conductive ground plate is provided on one side of the dielectric substrate and a circular slot formed therein, and the feeder is installed on the other side of the dielectric substrate And a circular patch having a diameter smaller than the diameter of the circular slot. Also, when viewed from above one side of the dielectric substrate, the centers of the circular slots and the circular patches do not coincide.

Further, according to an example of the present invention, the circular patch is located on the same plane as the circular slot. According to another example of the invention, the circular patch is located at the end of the feed line.

Furthermore, in order to improve the characteristics of the frequency band, the basic antenna structure as described above may be modified as follows. As a first example, an even number of conductive stubs radially protrude from the outer diameter of the circular patch, and the stubs are arranged to be symmetrical with respect to the feed line. As a second example, an even number of stub slots protrude radially at an outer diameter of the circular slot, and the stub slots are arranged to be symmetrical with respect to the feed line. As another example, the antenna may be configured by a combination of the first structure and the second structure.

In other words, when projecting from one side of the dielectric substrate by providing an offset of an arbitrary size between the circular slot and the center of the circular patch, the shape of the projection slot drawn on the projection plane becomes an asymmetric annular ring shape or the Very good frequency band characteristics appear when the projected outer diameter of the circular patch is slightly out of the outer diameter of the circular slot. Furthermore, a structure in which an offset such that the center of the circular patch does not leave the circular slot is given is preferable.

The present invention proposes a suitable feeding scheme for the modified asymmetric annular ring antenna and the new circular slot antenna to obtain a wider bandwidth. In other words, we propose an optimization structure to increase the bandwidth by changing the structure of the existing circular ring slot antenna. According to the experiment, the modified asymmetric annular ring antenna has a wide bandwidth by increasing the area of the slot of the conventional symmetric annular ring antenna. Considering this point, we proposed a circular slot antenna that can further expand the area of the slot. At this time, we proposed a suitable feeding structure to further expand the bandwidth. This circular slot structure is characterized in that multiple resonances can be obtained by increasing the slot area of the conventional circular ring slot antenna. With this structure, optimization process was performed to obtain wider bandwidth than the existing slot antenna. The optimized antenna has a broadband characteristic of 3.25 octave based on VSWR <2.

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

1. Structure and analysis theory of general annular ring slot antenna

The circular ring slot antenna has the advantage of simple feeding and easy matching and directional antenna beam, but has a big disadvantage of low bandwidth.

2A and 2B are structural diagrams of a conventional representative symmetric annular ring slot antenna. A circular ring slot 20 in which radiation occurs is located in the ground plane 22, above which the lower plane of the dielectric substrate 26 abuts, and the feed line 24 is grounded. It is located on the upper plane of the dielectric substrate 26 to face the plane (22).

In the symmetric annular ring slot antenna shown in FIGS. 2A and 2B, it can be assumed that the ground plane 22 is infinitely large because the slot 20 is symmetrical and the slot width is very small compared to the size of the ground plane 22. The relationship between the electric field and the magnetic field at this time can be expressed as follows by using FIG.

Magnetic Field Surface Current Distribution in Circular Ring Slots ( ) Is the same as Equation (1).

here Is the electric field of the slot, Denotes the unit normal vector of the slot. The magnetic field current distribution is expressed by dividing the ρ component and the φ 'component in the cylindrical coordinate system as follows.

Here, E _ρ and E _{φ '} are electric field components in the ρ and φ' directions in the slots, respectively. From the E _ρ and E _{φ '} components expressed in Equation (2), the remote electric field is expressed as follows using the vector electric potential method.

Where a is the inner radius of the slot.

Equations (3) and (4) can be further simplified as follows assuming that the slot width is much smaller than λ _o .

I) When W _s ≪λ _o , E _{φ '} = 0, E _ρ = constant

Ii) When W _s ≪λ _o , E _{φ '} = 0, E _ρ = E _o cos (nφ')

With θ component and φ component of the electric field expressed as in Equations (7) and (8), F (θ), which is a radiation power pattern, can be obtained through Equation (9) below.

2. First embodiment: asymmetrical annular ring slot antenna

(1) structure

An asymmetric annular ring slot antenna in which the structure of a conventional symmetric annular ring antenna is modified is disclosed in FIGS. 5A to 5C as a first embodiment of the present invention.

The asymmetric annular ring slot antenna is composed of a dielectric substrate 56, a ground plane 52 and a feed line 54. The ground plate 52 and the feed line 54 are made of a conductive material. The ground plate 52 is in contact with the lower surface of the dielectric substrate 56, the center portion is formed with an asymmetric annular ring-shaped slot 50. In order to form the slot 50 in an asymmetric annular ring shape, the first circle having a radius R and the radius R _in (where R _in <R) and the center of the first plate having a radius R are inconsistent with the first circle. Eliminates the asymmetric annular ring region 50 formed in binary. As a result, the position of the center of the circular patch 52B which is the inner region of the first circle has an offset from the center of the first circle. On the other hand, the feed line 54 is in contact with the upper surface of the dielectric substrate 56 to face the ground plane 52. Feed line 54 is formed of microstriplines and has a length that extends from the edge of the top surface of the dielectric to the top of circular patch 52B.

(2) frequency band characteristics

In the analysis of a conventional antenna having a ring-shaped or circular slot, it is possible to analyze using the above equations (1) to (9) only when the shape of the slot is symmetrical. However, in the case of the asymmetric annular ring antenna and the circular slot antenna proposed by the present invention, since the shape of the slot on the transparent surface is asymmetrical when viewed from the upper side of the dielectric substrate, it is impossible to interpret it using the above formula. In order to analyze the characteristics of the antennas having the structure according to the present invention, a full wave analysis method should be used. A representative method of the radio wave analysis method is the method of Moments. The present invention uses ensemble, which is commercial software written using the method of moments, in antenna design.

1) Design influence by slot width

FIG. 4 shows the change in the slot width (W _s ) when the radius (a + W _s ) including the slot is 26 mm based on the center of the symmetric annular ring antenna of FIG. 3. The change in reflection attenuation (S ₁₁ ) is shown. In the graph, the return loss refers to a value expressed in decibels between the power incident to the discontinuous portion in the transmission system and the power reflected therefrom. In the case of an antenna, a frequency band having a reflection attenuation value of -9.54 decibels or less, that is, a frequency band having a voltage standing wave ratio (VSWR) of 2 or less, may be defined as the bandwidth of the antenna. A frequency band with a voltage standing wave ratio (VSWR) of 1.5 or less may be defined as the bandwidth of the antenna.

In the case of the conventional symmetric annular ring antenna, it can be seen that the resonance frequency of the antenna varies greatly with the change of the slot width, but the bandwidth of the antenna does not change significantly. That is, based on the voltage standing wave ratio (VSWR) <2, the bandwidth is about 0.6 GHz, and as the slot width (W _s ) increases, the bandwidth decreases little by little and the center frequency decreases to the low frequency band. When the slot width (W _s ) is 15 mm, it is shown to resonate twice at 1.2 GHz and 2.1 GHz. The conclusion obtained in FIG. 4 is that when the widths of the slots are symmetrically equal, it is difficult to obtain broadband characteristics even if the width of the slots is widened.

2) Design influence due to offset

The offset is defined as the distance between the center of the slot 50 in the ground plane 52 and the center of the circular patch 52B. According to the experiment, it is confirmed that the change of the offset between the feed line and the slot in the slot antenna has a great influence on the antenna characteristics. That is, if the structure of the antenna is offset as shown in FIG. 5C without centering the center of the circular patch 52B with the center of the asymmetric annular ring-shaped slot 50, as shown in the graph shown in FIG. Similarly, the characteristic in which the resonant frequency changes with the offset is confirmed. As experimental conditions, R was 26 mm and R _in was 6.3 mm. In addition, the band characteristic shows that the larger the offset, the higher the resonant frequency shifts to the frequency band. It is noted that when the offset is 11 mm, the resonance is twice, and the band is 3.7 to 5.5 GHz, and the width thereof is 1.8 GHz, so that the broadband characteristics can be obtained when compared with the graph of FIG. 4.

3) Design influence according to the size change of circular patch 52B

In the antenna structure shown in FIGS. 5A to 5C, the offset is fixed to 7 mm and the radius R _in of the inner circular patch 52B is changed, so the result of comparing the characteristics of the reflection attenuation amount S ₁₁ is shown in FIG. 7. . Here the slot radius (R) is fixed at 26 mm.

As shown in FIG. 7, it can be seen that the change due to the radius R _in of the circular patch 52B affects the band characteristics of the antenna more than the change in offset. The larger the radius R _in of the circular patch 52B, the greater the bandwidth and the lower the frequency band. When R is 26 mm and R _in is 11 mm, a broadband characteristic of 1.35 octave is obtained with a bandwidth of 2 to 5 GHz based on the voltage standing wave ratio (VSWR) <2. In this case, it can be seen that three resonances occur at 2.2 GHz, 3.3 GHz, and 4.6 GHz.

The E-field radiation pattern and the H-field radiation pattern at the three resonance frequencies are shown in FIGS. 8A and 8B. As shown in FIG. 8A, in the case of the pattern of the electric field E _θ component, it was distorted to one side as the frequency was increased. In addition, as shown in FIG. 8B, the higher the frequency of the magnetic field _Hφ component, the narrower the beam width.

3. Second Embodiment: Circular Slot Antenna

(1) structure

The asymmetric annular ring antenna according to the first embodiment has proposed a method of obtaining a wide bandwidth by increasing the area of a slot of a conventional symmetric annular ring antenna. In consideration of this point, a circular slot antenna having a feeding structure suitable for widening the area of a slot can be further expanded and proposed as a second embodiment. The structure of the circular slot antenna according to the second embodiment is shown in Figs. 9A to 9C. As can be seen from the figure, the circular slot antenna according to the second embodiment is composed of a dielectric substrate 96, a ground plane 92 and a feed line 94. Ground plate 92 and feed line 94 are made of a conductive material. The ground plate 92 abuts on the lower surface of the dielectric substrate 96, and a circular slot 90 having a radius R is formed at the center thereof. The feed line 94 is composed of a circular patch portion 94B and a micro stripline portion 94A and abuts on the upper surface of the dielectric substrate 96 to face the ground plate 92. The radius of the circular patch 94B at the feeder end is R _in less than the radius R of the circular slot 90 (ie, R _in <R), the center of which is formed to be inconsistent with the center of the circular slot 90. do. The separation distance (offset) between the center of the circular slot 90 and the center of the circular patch portion 94B is the shape of the projection slot drawn in the projection plane when viewed from the top of the dielectric substrate 96 as shown in Fig. 9C. It is appropriate that the case becomes asymmetrical annular ring shape or that the projection outer diameter of the circular patch portion 94B slightly deviates from the outer diameter of the circular slot 90. However, depending on the size of the diameter of the circular slot 90 and the diameter of the circular patch 94B, even in a structure in which an offset such that the center of the circular patch 94B does not deviate from the circular slot 90 is given, a good frequency band is obtained. It can be characteristic because it can exhibit characteristics. This offset-related matter is commonly applied to other embodiments described later. The micro stripline portion 94A extends from the circumference of the circular patch portion 94B to the edge of the upper surface of the dielectric substrate 96 and the width of the micro stripline portion 94A is smaller than the diameter of the circular patch portion 94B. do.

The structural feature of the circular slot antenna according to the second embodiment is formed as part of the feed line 94 with the micro stripline 94A in the upper plane of the dielectric substrate 96 without forming the circular patch in the ground plane. By such a structure, similar characteristics to those of the modified asymmetric annular ring antenna can be obtained. The antenna of the second embodiment places the circular patch 94B in the plane where the feed line 94 is located, so that the slot area is substantially larger than that of the antenna of the first embodiment. As a result, as in the modified asymmetric annular ring antenna, the double resonance can be obtained when the slot width is increased. In the antenna of the second embodiment, multiple resonances can be obtained and wider bandwidth can be obtained. It was confirmed.

(2) Frequency band characteristics-influenced by design variables

1) Effect of Offset

The offset is defined as the distance between the center of the circular slot 90 of the ground plane 92 and the center of the circular patch 94B at the end of the feed line 94. 10 shows a change in the reflection attenuation amount S ₁₁ according to the change of the offset. Here, the radius R of the circular slot 90 is 26 mm and the radius R _in of the circular patch 94B at the feeder end is fixed at 11 mm and the offset is changed. As shown in Figure 10, the reflection attenuation (S ₁₁ ) continues to appear in the form of ripple (ripple), that is, the resonant frequency appears periodically, which means that multiple resonances occur. As a result, for example, with an offset of 13 mm, the bandwidth is very wide, ranging from 2 to 7.5 GHz. In addition, according to the experiment, when the circular patch 94B at the end of the feeder line is included in the circular slot 90, as the offset increases, the bandwidth of the antenna becomes wider.

11A and 11B show the change in normalized input impedance in the frequency band according to the offset. According to FIG. 11A, the real value of normalized input impedance converges to 1, and the imaginary value of normalized input impedance converges to 0 according to FIG. 11B. This confirms that the circular slot antenna of the second embodiment has an optimized structure that is well matched.

2) Effect of the radius of the circular patch at the end of the feeder

The effect on the antenna was examined while varying the radius (R _in ) of the circular patch 94B at the end of the feeder. As the size of the circular patch 52B acts as an important design variable in the annular ring slot antenna of the first embodiment, the size of the radius R _in of the circular patch 94B has a great effect on the matching even in the circular slot antenna of the second embodiment. Crazy FIG. 12 shows the amount of reflection attenuation according to the change _in the radius R _in of the circular patch 94B at the end of the feed line, when the radius R of the circular slot 90 is 26 mm and the offset is 13 mm. ₁₁ ) change.

The variation of the offset in the design of the circular slot antenna is also a large variable, but it can be seen from the comparison between FIG. 10 and FIG. 12 that the larger variable is the radius R _in of the circular patch 94B of the feed line 94. 12, it can be seen that the bandwidth becomes wider as the radius R _in of the circular patch 94B increases. In addition, in FIG. 12, the most optimized antenna structure according to the change in reflection attenuation S ₁₁ is, for example, when the radius R of the circular slot 90 is 26 mm, the radius R _in of the circular patch 94B. ) Is 11 mm and the offset is 13 mm. At this time, based on the voltage standing wave ratio (VSWR) <2, a broadband characteristic with a bandwidth of 2.16 octave is obtained.

3) Comparison of actual measurement and simulation results

As an example of optimized design data, the radius R of the circular slot 90 is 26 mm, the radius R _in of the circular patch 94B is 11 mm, and the offset is 13 mm, and the dielectric substrate has a dielectric constant. Is used, and the FR-4 having a thickness of 1 mm is used, and the size of the ground plate is 150 mm × 150 mm in consideration of the size of the circular slot 90. The reflection attenuation (S ₁₁ ) of the fabricated antenna was measured using an HP8510C network analyzer, and the radiation pattern was measured in an anechoic chamber having a size of 24 m × 8 m × 12 m.

FIG. 13 compares the result of measuring the reflection attenuation amount S ₁₁ of the optimized circular slot antenna with the simulation result. In FIG. 13, although the measurement result and the simulation result show similar characteristics as a whole, there is a slight difference. In the simulation tool, the result of the simulation and the actual fabrication measurement is different because the complete circle is not implemented, and the measurement value drops below -9.54 dB at the lower frequency than the simulation result. In addition, it can be seen from the analysis of the measurement that resonance occurs almost every 1.8 GHz, and the amount of reflection attenuation (S ₁₁ ) is 3.25 octave based on the voltage standing wave ratio (VSWR) <2 to obtain a very good broadband characteristic.

14 shows the electric field and magnetic field radiation pattern at 2.5 GHz of the circular slot antenna. Theoretically, the radiation pattern of the dipole antenna and the radiation pattern of the slot antenna are opposite to each other. 14A is a result of a measurement and simulation of the E _θ component of the electric field, and FIG. 14B is a result of a measurement and simulation of the H _φ component of the magnetic field. As can be seen in Figures 14a and 14b, it can be seen that the measurement results and simulation results also show some differences. This is because the simulation assumes an infinite ground plane, but the ground plane of the actual antenna is finite.

4. Third Embodiment: Circular Slot Antenna with Stubs on a Circular Patch

(1) structure

The structure of the circular slot antenna according to the third embodiment is the same as that of the circular slot antenna according to the second embodiment except that the shape of the circular patch at the end of the feed line is modified as shown in FIGS. 15A to 15C. That is, the circular slot antenna of the third embodiment has an even number of conductive stubs 154C and 154D protruding radially from the circumference of the circular patch 154B of the feed line 154 by the micro stripline 154A. It is further added to make symmetry with respect to. The protruding length of the stubs 154C and 154D is preferably 5 mm or less.

(2) frequency band characteristics

16A and 16B show frequency band characteristics according to the amount of reflection attenuation when and without the conductive stubs 154C and 154D to the circular patch 154B, respectively. Here, the specification of the antenna, that is, the dielectric substrate, the slot radius, the offset, the radius of the circular patch, and the like are the same as those in the above third embodiment. Comparing the above two figures, it can be seen that the frequency band characteristic when the conductive stubs 154C and 154D are attached to the circular patch 154B is obtained more broadly than that when it is not. In the former case, when the voltage standing wave ratio (VSWR) <2 is used, the band characteristic is 2 to 8 GHz, which shows that a very good broadband characteristic is obtained. The frequency band characteristics obtained are different depending on the position and length width of the stub, but the simulation results show that when the angle (θ) between the stubs 154C and 154D is formed with the micro stripline portion 154A of the feed line, the band is 60 to 80 degrees. The characteristics were the best. The relationship between the protruding length and the band characteristics of the stubs 154C and 154D was different depending on the substrate.

5. Fourth Embodiment: a tubed circular slot antenna having a stub slot in a circular slot

(1) structure

The structure of the circular slot antenna according to the fourth embodiment is the same as that of the circular slot antenna according to the second embodiment except that the shape of the circular slot formed in the ground plate is modified as shown in FIGS. 17A to 17C. Do. That is, in the circular slot antenna of the fourth embodiment, the circular slot 170 of the ground plate 172 has an even number of stub slots 171A and 171B which protrude slightly from the circumference in the outer diameter direction. Symmetrically further on both sides of 174A).

(2) frequency band characteristics

18A and 18B illustrate the frequency band characteristics of the antenna according to the fourth embodiment. In the former case, the angle θ of the position of the stub slot with the feed line is 36 degrees. Each case of 60 degrees is shown. Based on the voltage standing wave ratio (VSWR) <2, the frequency band characteristic of the antenna is about 1.7 ~ 7.8 GHz in the latter case, which is wider and better than the former, and the latter has better degree of impedance matching. It can be seen. From this result, it can be seen that the frequency bandwidth of the antenna can be adjusted according to the position of the stub slot formed in the circular slot, and the impedance matching can be better achieved. Furthermore, it has been found that the size of the stub slot also affects the frequency bandwidth and impedance matching.

6. Fifth Embodiment: Stubd circular slot antenna with stubs on a circular patch by forming a stub slot in a circular slot and adding a stub to the circular patch.

(1) structure

19A to 19C, the structure of the circular slot antenna according to the fifth embodiment is in the form of the circular slot formed in the ground plate according to that of the fourth embodiment, and the form of the circular patch of the feeder is the third embodiment. The structure of the circular slot antenna according to the second embodiment is the same as that of the example. That is, in the circular slot antenna of the fifth embodiment, an even number of stub slots 191A and 191B projecting slightly in the outer diameter direction from the circumference of the circular slot 190 of the ground plate 192 are provided with the micro stripline portion ( Are further formed symmetrically on both sides of 194A). In addition, an even number of conductive stubs 194C, 194D protruding radially from the circumference of the circular patch 194B of the feed line 194 is further added to both sides of the micro stripline portion 194A.

(2) frequency band characteristics

It was confirmed in the third and fourth embodiments that the addition of more stubs to the circular patch of the feeder and the formation of more stub slots to the circular slots result in better frequency band characteristics and better impedance matching of the antenna. As can be seen, the broadband structure and excellent impedance matching can be obtained from the combination of the above two antenna structures.

7. Fabrication process

First, an antenna sample is prepared by stacking a conductive metal layer on the upper and lower surfaces of the dielectric substrate. Using such an antenna sample, a similar process to a semiconductor manufacturing process, that is, a mask preparation, photoresist coating, mask alignment and exposure, development, and etching may be sequentially performed to fabricate an antenna of a desired shape. An example thereof is as follows. Models of the antenna according to the above-described embodiments, that is, patterns of the conductive metal layers stacked on the upper and lower surfaces of the dielectric substrate are floated with a film to form a mask for the upper and lower surfaces. Next, the photoresist is evenly coated on the upper surface of the antenna sample, and then the upper surface model is attached to the metal layer by attaching a mask for the upper surface and extracting ultraviolet rays. The exposed photoresist surface is reacted with a developer and then etched using an etchant such as ferric chloride solution. The same process is performed for the bottom surface. By this process, slots, feeders and stubs of a desired shape can be formed. The photoresist, developer and etchant can be variously selected and it can be embossed or engraved depending on the type of photoresist.

As described above, the present invention provides various optimization structures of the antenna to have a wideband frequency characteristic. Various types of antennas proposed by the present invention are easier to design and manufacture due to smaller design variables than rectangular slot antennas, and have excellent broadband characteristics. In particular, the structure of the circular slot antenna has a large slot area, and by causing multiple resonances through the slot, it is possible to drastically improve the narrow band characteristic, which is a major disadvantage of the microstrip antenna. In addition, since the available frequency band is from 1.68 GHz to 15.96 GHz, it is expected that it can be integrated into one antenna without the inconvenience of using different antennas according to each frequency band.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the present invention without departing from the spirit and scope of the invention described in the claims below. I can understand that you can.

Claims (5)

A dielectric substrate, a conductive ground plate disposed on one side of the dielectric substrate and having a circular slot formed therein, a feeder provided on the other side of the dielectric substrate, and a circular patch having a diameter smaller than the diameter of the circular slot. And the center of the circular slot and the circular patch do not coincide with each other when viewed from above one side of the dielectric substrate. The antenna of claim 1, wherein the circular patch and the circular slot are located on the same plane. 2. The antenna of claim 1 wherein said circular patch is located at the end of said feed line. The antenna of claim 3, wherein an even number of conductive stubs are radially protruded in an outer diameter of the circular patch, and the stubs are arranged to be symmetrical with respect to the feed line. The antenna of claim 3 or 4, wherein an even number of stub slots protrude radially at an outer diameter of the circular slot, and the stub slots are arranged to be symmetrical with respect to the feed line. .