Abstract:
Provided are a microstrip stack patch antenna using multilayered metallic disk array and a planar array antenna using the same. The microstrip stack patch antenna of the present research concentrates beam patterns and acquires a high gain characteristic by finitely depositing metallic disks in a bore-sight on a conventional microstrip stack patch radiator. The microstrip stack patch antenna includes: a microstrip stack patch directly connected to the feed line; and a mask conductor layer for improving side lobe and gain characteristics, the mask conductor being formed on the microstrip stack patch.

Description:
FIELD OF THE INVENTION  
   The present invention relates to a microstrip stack patch antenna using a multilayered metallic disk array; and, more particularly, to a microstrip stack patch antenna using a multilayered metallic disk array which has a concentrated beam pattern and a high gain property by depositing metallic disks on the microstrip stack patch radiator in a direction that electromagnetic waves are propagated, and a planar array antenna using the same. 
   DESCRIPTION OF RELATED ART 
   Generally, medium and long-range communication/broadcasting application fields, such as Wireless Local Area Network (WLAN) antenna, and satellite broadcast receiving antenna, require a high-gain and broadband planar array antenna. 
   Generally, the planar array antenna can obtain a required level of gain by increasing the number of radiating elements. According to the method, however, if the gain of a radiating element is low, the array space between radiating elements is narrow and thus the number of radiating elements should be increased. As a result, the feed network becomes complicated. Also, due to the loss caused by the mutual coupling effect between the radiating element and the feed line and the loss caused by a long feed line, the antenna efficiency is decreased. 
   On the contrary, if the gain of a radiating element is increased, the array space between the radiating elements is increased in proportion to the increased gain. Thus, the feed circuit network is simplified and the length of the feed line is shortened and, as a result, high antenna efficiency can be obtained. 
   Due to the advantages that the microstrip patch antenna can be easily fabricated, small in size, lightweight and thin, the microstrip patch antenna is most commonly used in terrestrial broadcasting and satellite broadcasting and communication. However, it has a disadvantage that it has a narrow operation band. 
   Particularly, it requires a plurality of antennas to receive domestic and overseas satellite signals simultaneously due to a difference in frequency used for the satellite broadcasting and communication. 
   Also, in case where circular polarization is used, there is an additional condition that the microstrip patch antenna should satisfy the axial ratio characteristic in a corresponding band as well as the characteristic of impedance bandwidth. Therefore, it is hard to improve the performance of the antennas. 
     FIGS. 1A and 1B  present a cross-sectional view and a plane figure of a conventional microstrip single patch antenna. 
   As illustrated in  FIGS. 1A and 1B , the conventional microstrip single patch antenna includes a conductive ground layer  1  in the lower part of a dielectric substrate  2 , and a conductive feed line  3  and a first patch  4  which are formed on the upper surface of the dielectric substrate  2 . 
   However, the conventional microstrip single patch antenna has a narrow operation bandwidth and a small element gain of 5 to 7 dBi. 
     FIG. 2A  shows a cross-sectional view of the conventional microstrip stack patch antenna; and  FIG. 2B  presents plane figures showing a first patch and a second patch of the conventional microstrip stack patch antenna. 
   As shown, the conventional microstrip stack patch antenna includes a conductive ground layer  21  in the lower part of a dielectric substrate  20 , a conductive feed line  22  and a first patch  23  which are formed on the upper surface of the dielectric substrate  20 , and a dielectric foam layer  24  formed on the first patch  23  to isolate it from a second patch. 
   On top of the dielectric foam layer  24 , a think dielectric film  25  is placed and then the second patch  26  is formed thereon. 
   The microstrip stack patch antenna has a broadband impedance characteristic and has a single radiator gain of 7 to 9 dBi, which is relatively high, compared to the microstrip single patch antenna of  FIG. 1 . 
   The gain characteristic of the microstrip stack patch antenna is dependent on the electric and physical characteristics of the used dielectric medium. However, if design parameters are optimized to excite input power in a desired frequency bandwidth, single element gain of around 9dBi can be acquired typically. 
     FIG. 3  is a cross-sectional view showing a conventional microstrip single patch antenna using a dielectric cover having a high dielectric constant. 
   As shown, the conventional microstrip single patch antenna using a dielectric cover having a high dielectric constant includes a dielectric foam layer  34  having a thickness a little thinner than 0.5λ 0  on the microstrip single patch antenna of  FIG. 1A . The thickness makes the electrical wavelength between the single patch and the dielectric foam layer  34  be 180°. On top of the dielectric foam layer  34 , a dielectric layer  35  which has a high dielectric constant and a thickness of 0.25λg is formed. Herein, the dielectric layer  35  and a first patch  33  will be not described further, since they perform the same operations as the dielectric layer  1  and the first patch  4  of  FIG. 1 . 
   The antenna gain of the microstrip single patch antenna using a dielectric cover having a high dielectric constant can acquire a high gain characteristic, but it has a shortcoming that it has a narrow impedance bandwidth. 
     FIG. 4  is a cross-sectional view showing a conventional microstrip stack patch antenna using a dielectric cover having a high dielectric constant. 
   As shown, the conventional microstrip stack patch antenna using a dielectric cover having a high dielectric constant includes a dielectric foam layer  47  having a thickness of 0.35 to 0.45 λ 0  on the microstrip stack patch antenna of  FIG. 2A . The thickness makes the electrical wavelength between the stack patch and the dielectric foam layer  47  be 180°. On top of the dielectric foam layer  47 , a dielectric layer  48  which has a high dielectric constant and has a thickness of 0.25λg is formed. Herein, the dielectric layer  48  and a second patch  46  will be not described any more herein, since they perform the same operations as the dielectric layer  20  and the second patch  26  of  FIG. 2A . 
   The microstrip stack patch antenna using a dielectric cover having a high dielectric constant has a relatively high antenna gain and an improved impedance bandwidth, compared to the microstrip single patch antenna of  FIG. 3  which also uses a dielectric cover having a high dielectric constant. 
   However, the high-gain radiators of  FIGS. 3 and 4  which use the dielectric cover utilize a dielectric material having a high dielectric constant. This is the reason that it has a shortcoming of a narrow bandwidth. 
   In addition, such conventional antennas have a little restriction in high-frequency applications due to their sensitivity to temperature-based electrical characteristics. When the conventional antennas are also used in low-frequency applications, they have a shortcoming that the dielectric material is relatively heavy and expensive. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide a microstrip stack patch antenna using a multilayered metallic disk array with a concentrated beam pattern and a high gain property by depositing metallic disks on the conventional microstrip stack patch radiator in a direction that electric waves are propagated, and a planar array antenna using the same. 
   In accordance with an aspect of the present invention, there is provided a microstrip stack patch antenna, which includes: a microstrip stack patch including feed line and a patch connected to the feed line electrically; and a mask conductor layer for improving side lobe and gain characteristics, the mask conductor being formed on the microstrip stack patch. 
   In accordance with another aspect of the present invention, there is provided a planar array antenna, which includes: a microstrip stack patch radiator, wherein, when the microstrip stack patch radiator is used to extend the planar array antenna, the distance d between the microstrip stack patch radiators in a direction orthogonal to an excitement or feeding direction can be approximately determined based on 0.9L e ≦d≦1.1L e , where 
             L   e     =         λ   0       2   ⁢     π         ⁢     10     D   20               
and D (dBi) is directivity.
 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: 
       FIG. 1A  is a cross-sectional diagram showing a conventional microstrip single patch antenna; 
       FIG. 1B  is a top view showing the conventional microstrip single patch antenna; 
       FIG. 2A  is a cross-sectional diagram showing a conventional microstrip stack patch antenna; 
       FIG. 2B  is a top view showing a first patch and a second patch of the conventional microstrip stack patch antenna; 
       FIG. 3  is a cross-sectional diagram showing a conventional microstrip single patch antenna using a dielectric cover with a high dielectric constant; 
       FIG. 4  is a cross-sectional diagram showing a conventional microstrip stack patch antenna using a dielectric cover with a high dielectric constant; 
       FIG. 5A  is a cross-sectional diagram illustrating a microstrip stack patch antenna using a multilayered metallic disk array in accordance with an embodiment of the present invention; 
       FIG. 5B  is a top view describing a first patch and a second patch of the microstrip stack patch antenna using a multilayered metallic disk array in accordance with an embodiment of the present invention; 
       FIG. 5C  is a top view illustrating a mask conductor with the center opened and a metallic disk in accordance with an embodiment of the present invention; 
       FIG. 6  is a graph presenting an input return loss of a microstrip stack patch antenna using a multilayered metallic disk array in accordance with an embodiment of the present invention; 
       FIGS. 7A to 7D  are graphs illustrating radiation patterns dependent on the number of metallic disks deposited in the microstrip stack patch antenna using a multilayered metallic disk array in accordance with an embodiment of the present invention; and 
       FIG. 8  is a graph describing gain characteristic dependent on the number of metallic disks deposited in the microstrip stack patch antenna using a multilayered metallic disk array in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings. Thus, those skilled in the art can easily embody the technological concept of the present invention. If any detailed description on a widely known technology in relation to the present invention is determined to blur the point of the present invention, it will be omitted. Hereinafter, preferred embodiments of the present invention will be described with reference to accompanying drawings. 
   In the present invention, it is assumed that a dielectric material used in a dielectric foam layer has nearly an ideal dielectric constant, i.e., ε r =1.05, and the thin thickness of a dielectric film is neglected. 
     FIG. 5A  is a cross-sectional diagram illustrating a microstrip stack patch antenna using a multilayered metallic disk array in accordance with an embodiment of the present invention, and  FIG. 5B  presents a top view describing a first patch and a second patch of the microstrip stack patch antenna using a multilayered metallic disk array in accordance with an embodiment of the present invention. 
   Referring to  FIG. 5B , the microstrip stack patch of the present invention comprises a first patch  53  and a second patch  56 . The first patch  53  is an active patch with linear polarization, while the second patch  56  is a passive patch with linear polarization. 
   The first patch  53  is formed on a dielectric layer  50  and a ground layer  51  in the bottom surface and input power is fed to the first patch  53  through an input feed line  52  from an input port. 
   The second patch  56  is formed on a thin dielectric film  55  and a dielectric foam layer  54  is placed between the first and second patches  53  and  54 . 
   Design parameters of the microstrip stack patch are determined as values having optimal input impedance and gain characteristics through simulation. Although the present invention suggests the square-shaped first and second patches which adopt a direct feeding method and radiate linear polarization, diverse patches and feeding forms can be used according to a required type of polarization. 
   As illustrated in  FIG. 5A , the microstrip stack patch antenna using multilayered metallic disk array, which is suggested in the present invention, includes a mask conductor layer  58 ,  59  between the microstrip stack patch and the multilayered metallic disk array. The mask conductor layer  58 ,  59  includes a mask conductor  59  and a dielectric film layer  58 . 
   Hereinafter, the multilayered metallic disk array will be described by taking an example of a case where a metallic disk is used as a conductor. 
   Between the mask conductor  59 , the microstrip stack patch and the multilayered metallic disk array, dielectric foam layers  57  and  60  are inserted. 
   The multilayered metallic disk-array has a plurality of metallic disks, which are directional radiators, perpendicularly to the microstrip patch radiator with a predetermined space between them in order to obtain a high gain property. 
     FIG. 5C  is a top-view illustrating a mask conductor with the center opened and a metallic disk in accordance with an embodiment of the present invention. 
   As depicted in the left diagram of  FIG. 5C , the central part of the mask conductor  59  of the present invention is opened with a diameter of about one wavelength in order to efficiently transmit the power excited from the microstrip stack patch to the multilayered metallic disk array. 
   The mask conductor  59  improves a side lobe characteristic of a radiation pattern when there is no multilayered metallic disk array and concentrates the radiation pattern into a forward direction. Therefore, it has an effect of improving an antenna gain characteristic. 
   If there is the multilayered metallic disk array, the mask conductor  59  reradiates reflecting electromagnectic waves into free space through a proper match of the reflecting electromagnectic waves. The gain characteristic is different a little bit according to whether or not the mask conductor  59  is grounded. 
   As illustrated in the right diagram of  FIG. 5C , the metallic disks of the multilayered metallic disk array are arrayed on the same thin dielectric films  61 ,  64 ,  67 , and  70  in the same center. 
   As shown in  FIG. 5A , it is possible to form the first patch, the second patch, the mask conductor, and the metallic disks to have their centers in the same position or otherwise. 
   The metallic disks are perfect conductors and the optimal diameter is in the range of 0.25 λ to 0.35 λ, i.e., a non-resonance size. The diameter is one of significant design parameters for determining the antenna gain characteristic. 
   The thickness of the dielectric foam layer  60  on which a first metallic disk  62  is placed works as a design parameter, too, which is significant for determining the antenna gain characteristic. 
   In addition, the thicknesses of dielectric foam layers  63 ,  66  and  69  from the dielectric foam layer  63  on which a second metallic disk  65  is placed to the dielectric foam layer  69  on which an N th  metallic disk  71  is placed are significant design parameters for determining the antenna gain characteristic. In the embodiment of the present invention, the dielectric foam layers are deposited in the same and uniform thickness. 
   However, the dielectric foam layers can be optimized in different thicknesses generally. Also, the metallic disks  62 ,  65 ,  68  and  71  are omitted partially and periodically and the position and period of the omitted disk work as design parameters for determining the antenna gain characteristic. 
   The following table 1 presents a result obtained by simulating the microstrip stack patch, the mask conductor, and the multilayered metallic disk array by using an Ensemble™, which is a commercial simulator, in accordance with an embodiment of the present invention. The design parameters were optimized in an operating frequency of 9.2 to 10.8 GHz (f 0 =10 GHz). 
   
     
       
             
             
           
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               Description of 
                 
             
             
               Design parameter 
               Value of Design Parameter 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               microstrip 
               Substrate Spec. 
               ε x  = 2.17, H l  = 0.508 mm, T = 0.018 mm 
             
             
               stack 
               (TLY5A) 
             
             
               patch 
             
             
                 
               2 nd  Patch 
               11.15 mm(W) × 11.15 mm(L) 
             
             
                 
               (Passive Patch) 
             
             
                 
               1 st  Patch 
               10.15 mm(W) × 10.15 mm(L) 
             
             
                 
               (Active Patch) 
             
             
               Mask 
               Diameter of 
               30 mm 
             
             
               Conductor 
               Circular Opening 
             
             
                 
               Isolation Height 
               H = 1.0 mm 
             
             
               Metallic 
               Diameter of 
               2r = 9 mm 
             
             
               Disk 
               Metallic Disk 
             
             
               Array 
               Number of 
               N = 1~15 
             
             
                 
               Metallic Disks 
             
             
                 
               Initial Position 
               z l  = 9 mm 
             
             
                 
               Final Position 
               z L  = 9~51 mm 
             
             
                 
               Space between 
               ds = 3 mm 
             
             
                 
               Metallic Disks 
             
             
                 
             
           
        
       
     
   
   In the dielectric substrate with the dielectric constant (ε x ) of 2.17, the height (H 1 ) of 0.508 mm and the conductor thickness (T) of 0.018 mm, the design parameter values of the microstrip stack patch are optimized in the operation frequency of 9.2 to 10.8 GHz. It can be seen from the table 1 that the first patch has a width (W) of 10.15 mm and a length (L) of 10.15 mm, while the second patch has a width (W) of 11.15 mm and a length (L) of 11.15 mm. 
   Also, the mask conductor  59  has the optimal design parameter values when the diameter of the circular opening is 30 mm and the isolation height (H), which corresponds to the height of a dielectric foam layer  57 , is 1.0 mm. 
   In addition, the metallic disks of the metallic disk array have the optimal design parameter values when metallic disks have a diameter of 9 mm, the initial position (z 1 ), which is the height of a reference numeral ‘ 60 ,’ of 9 mm, and the spacing (ds) of 3 mm between the metallic disks. 
     FIG. 6  is a graph presenting an input return loss of a microstrip stack patch antenna using a multilayered metallic disk array in accordance with an embodiment of the present invention. 
   As shown, the input return loss of the microstrip stack patch antenna having the mask  59 , i.e., perfect conductor mask (PCM) and the input return loss of the microstrip stack patch antenna using the array of the metallic disks  62 ,  65 ,  68  and  71  stacked on the mask conductor  59 , i.e., disk  1  and disk  8 , tend to have a partially improved or degraded electric characteristics in the bandwidth, compared with the input return loss of a simple microstrip stack patch antenna, i.e., a stack microstrip patch (SMP). However, since the changes in the performance are not significant, the characteristics can be regarded to be in the range of acceptance. 
     FIGS. 7A and 7B  are graphs illustrating radiation patterns based on the number of metallic disks deposited in the microstrip stack patch antenna using a multilayered metallic disk array in accordance with an embodiment of the present invention. 
   Referring to  FIG. 7A , the microstrip stack patch antenna having the mask conductor  59 , i.e., PCM, has a higher antenna gain value than the conventional microstrip stack patch antenna, i.e., SMP. 
   The microstrip stack patch antennas using the metallic disk array, i.e., the disk  1  and disk  8 , has a higher antenna gain value than the microstrip stack patch antenna having the mask conductor  59 , i.e., PCM. That is, the main and side lobes go up, as the main beam becomes narrower. 
   As shown in  FIGS. 7B ,  7 C and  7 D, the antenna gain is increased as the metallic disks (the disks 1 to 15) are further deposited. 
     FIG. 8  is a graph describing gain characteristic based on the number of metallic disks deposited in the microstrip stack patch antenna using a multilayered metallic disk array in accordance with an embodiment of the present invention. 
   It can be seen from  FIG. 8  that the antenna gain is increased and decreased periodically, as the metallic disks  62 ,  65 ,  68  and  71  are deposited. This is because the power excited by the microstrip stack patch is periodically and electromagnetically coupled under the equi-phase with the metallic disk array placed in a direction that electromagnectic waves propagate. Also, although the number of metallic disks continues to be increased, the gain is scarcely changed. This is because parasitic disks apart from the microstrip patch exciting radiators have small current amplitude excited. 
   As presented in the graph of the embodiment, the gain can be improved about 4.5 to 5.0 dB by arraying the metallic disks which have a size smaller than the resonance size on top of the microstrip stack patch. 
   If the high gain radiators of the present invention is used for extending the planar array antenna, the distance d between the radiators in a direction orthogonal to the excitement direction is determined approximately based on 0.9L e ≦d≦1.1L e  to reduce interference between radiators. Herein, if it is assumed that current is distributed uniformly in the antenna aperture, L e  can be expressed as the following equation 1: 
                   L   e     =         λ   0       2   ⁢     π         ⁢     10     D   20                 Eq   .           ⁢   1               
wherein D (dBi) is directivity.
 
   The actual distance is selected through simulation to make the coupling quantity between adjacent elements be more than at least 25 dB. 
   The present invention described above provides a wide impedance bandwith, concentrates electromagnetic waves into a desired direction, and improves the antenna gain by solving the shortcomings of the conventional microstrip patch antenna in the application of the low-frequency and the high-frequency by using the multilayered metallic disk array. 
   Also, when the radiator of the present is used to extend the planar array antenna, the feeding circuit can be simplified as the distance between the radiators becomes widened relatively and high feeding efficiency can be obtained as the coupling characteristics between the radiators becomes weak. Consequently, the size of the antenna for a required level of gain can be reduced relatively. 
   The present application contains subject matter related to Korean patent application No. 2004-042594, filed in the Korean Intellectual Property Office on Jun. 10, 2004, the entire contents of which is incorporated herein by reference. 
   While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.