CLAIM OF PRIORITY 
   This application claims priority to an application entitled “PLANNER ANTENNA HAVING LINEAR AND CIRCULAR POLARIZATION”, filed in the Korean Industrial Property Office on May 27, 2002 and assigned Serial No. 2002-29322, the contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to an antenna that is located at the end of a wireless communication system, or other radio system, and more particularly, to a wideband planar antenna having linear and circular polarization, which uses different polarization for transmission and reception to increase the isolation between transmission and reception by suggesting and using a type of a radiation element. 
   2. Related Art 
   A dish antenna is commonly used for a satellite communication service because the dish antenna has a simple structure and it can easily form dual circular polarization. Dish antennas are sometimes cumbersome due to their bulkiness. For this reason, various kinds of planar array antennas with a low height have been introduced. However, most planar antennas can only utilize one of linear and circular polarization, not both. 
   This characteristic limits the use of the planar antenna such that the antenna cannot be used for both transmission and reception. In most cases, planar array antennas for satellite communication are used only for the purpose of reception. 
   I have found that there are disadvantages to current dish antennas and current planar antennas. Efforts have been made to improve antennas. 
   Exemplars of recent efforts in the art include U.S. Pat. No. 4,475,107 for CIRCULARLY POLARIZED MICROSTRIP LINE ANTENNA issued on Oct. 2, 1984 to Makimoto et al., U.S. Pat. No. 4,816,835 for PLANAR ANTENNA WITH PATCH ELEMENTS issued on Mar. 28, 1989 to Abiko et al., U.S. Pat. No. 4,614,947 for PLANNER HIGH-FREQUENCY ANTENNA HAVING A NETWORK OF FULLY SUSPENDED-SUBSTRATE MICROSTRIP TRANSMISSION LINES issued on Sep. 30, 1986 to Rammos, U.S. Pat. No. 6,166,701 for DUAL POLARIZATION ANTENNA ARRAY WITH RADIATIN SLOTS AND NOTCH DIPOLE ELEMENTS SHARING A COMMON APERTURE issued on Dec. 26, 2000 to Park et al., U.S. Pat. No. 5,241,321 for DUAL FREQUENCY CIRCULARLY POLARIZED MICROWAVE ANTENNA issued on Aug. 31, 1993 to Tsao, U.S. Pat. No. 6,107,956 for AUTOMOTIVE FORWARD LOOKING SENSOR ARCHITECTURE issued on Aug. 22, 2000 to Russell et al., U.S. Pat. No. 4,922,263 for PLATE ANTENNA WITH DOUBLE CROSSED POLARIZATIONS issued on May 1, 1990 to Dubost et al., U.S. Pat. No. 5,005,019 for ELECTROMAGNETICALLY COUPLED PRINTED-CIRCUIT ANTENNAS HAVING PATCHES OR SLOTS CAPACITIVELY COUPLED TO FEEDLINES issued on Apr. 2, 1991 to Zaghloul et al., and U.S. Pat. No. 5,321,411 for PLANAR ANTENNA FOR LINEARLY POLARIZED WAVES issued on Jun. 14, 1994 to Tsukamoto et al. 
   While these recent efforts provide advantages, I note that they fail to adequately provide an improved planar anntenna having linear and circular polarization. 
   SUMMARY OF THE INVENTION 
   To solve the above-described problems, it is an object of the present invention to provide an antenna having linear and circular polarization, which uses dipoles as radiation elements, and has an orthogonal characteristic in both linear and circular polarization, the antenna being embodied by using two plates and the front and back sides of the plates effectively. 
   An object of the present invention is to provide a planar antenna having linear and circular polarization, comprising: a plate with a conductor coated on both surfaces of a dielectric substance; a first branch positioned on a first surface of the plate; and a second branch positioned on a second surface of the plate. 
   Another object of the present invention is to provide a planar antenna having linear and circular polarization, comprising: a first plate with a conductor coated on both surfaces of a dielectric substance; a second plate with a conductor coated on both sides of the dielectric substance, the second plate being positioned under the first plate; a plurality of first symmetrical radiation elements which are on both surfaces of the first plate, for transmitting or receiving a radio wave; a plurality of second symmetrical radiation elements which are on both surfaces of the second plate, for transmitting or receiving a radio wave; a ground plate which supports the whole antenna and is used as a ground for the entire circuit; and a support for supporting the whole antenna by connecting the overlapped first and second plates and the ground plate. 
   Still another object of the present invention is to provide a radiation element comprising two branches and one stem, wherein the branches meet at the stem at an angle of 45° to the surface that is perpendicular to the stem, and the branches are in the shape of a symmetric dipole. 
   The present invention discloses a planar antenna that accommodates either linear or circular polarization having an orthogonal characteristic during transmission and reception in a wideband. By using two folds of printed-circuit-board type plates, the antenna of the present invention can minimize insertion loss, weight, and thickness. However, since isolated radiation elements are insufficient, the frequency band has a limitation. 
   The planar antenna of the present invention comprises a ground plate, two micro strip plates, and a support for connecting the ground plate and the micro strip plates. The space between the plates and the support is filled with a material such as polystyrene foam. 
   On each plate, there are dipoles, which are radiation elements, power supply circuits, slots, and stubs. The entire antenna is divided into rooms in the shape of a lattice, in which a ground circuit surrounds a pair of dipoles. The collection of lattice-shaped rooms is called a subarray. The subarrays positioned on the same surface have linear polarization characteristics independently from each other. Since the dipoles of each subarray are orthogonal to each other, the polarization vectors of two subarrays are orthogonal to each other. In addition, a subarray has an independent power supply circuit, and since the coupling of the orthogonal dipoles is very small, various forms of polarization can be embodied depending on how the subarrays are connected. 
   The power supply circuit in a single subarray includes a 90° phase shifter. Accordingly, the polarization of each of the subarrays combines to form circular polarization. The power supply circuit is connected to each of the subarrays and the power supply connections are orthogonal to each other. A termination of a subarray is connected to a circular waveguide through a probe, and it excites the Transverse Electric 11 (TE11) mode. Therefore, the two modes before and after the excitation are orthogonal to each other, and the overall mode is determined by overlapping the two modes. The polarization slope of the overall mode determines the correlations between the signal powers of orthogonal modes, and by the result of it, the polarization characteristic of an antenna is determined. 
   In other words, if Transverse Electric 11 (TE11) mode signals connected to the subarrays have the same linear polarization, the overall polarization has a characteristic of linear polarization, and if the phase difference of the Transverse Electric 11 (TE11) mode signals connected to the subarrays is 90°, the overall polarization has a characteristic of circular polarization. A single subarray has a characteristic of linear polarization. 
   To achieve these and other objects in accordance with the principles of the present invention, as embodied and broadly described, the present invention provides a planar antenna having linear and circular polarization, the antenna comprising: a plate having a dielectric substance with a conductor coated on side surfaces of the dielectric substance; and at least one radiation element comprising: a first branch being positioned on a first surface of said plate; and a second branch being positioned on a second surface of said plate different from the first surface. 
   To achieve these and other objects in accordance with the principles of the present invention, as embodied and broadly described, the present invention provides a planar antenna having linear and circular polarization, the antenna comprising: a first plate having a first dielectric substance with a conductor coated on side surfaces of the first dielectric substance, said first plate having a first side surface and a second side surface; a second plate having a second dielectric substance with a conductor coated on side surfaces of the second dielectric substance, said second plate having a first side surface and a second side surface, said second plate being under said first plate, said first side surface of said second plate facing said second side surface of said first plate; a plurality of first symmetrical radiation elements being on said first and second side surfaces of said first plate, said first elements performing at least one selected from among transmitting radio waves and receiving radio waves; a plurality of second symmetrical radiation elements being on said first and second side surfaces of said second plate, said second elements performing at least one selected from among transmitting radio waves and receiving radio waves; a ground plate corresponding to a local reference potential for said first and second elements, said ground plate being under said second plate; and a support supporting the antenna by connecting said first plate, said second plate, and said ground plate. 
   To achieve these and other objects in accordance with the principles of the present invention, as embodied and broadly described, the present invention provides a radiation element, comprising: a pair of branches; and a stem being joined to said pair of branches, each one of said branches forming a 45° angle with a surface that is perpendicular to said stem, said pair of branches corresponding to a symmetric dipole. 
   The present invention is more specifically described in the following paragraphs by reference to the drawings attached only by way of example. Other advantages and features will become apparent from the following description and from the claims. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, which are incorporated in and constitute a part of this specification, embodiments of the invention are illustrated, which, together with a general description of the invention given above, and the detailed description given below, serve to exemplify the principles of this invention. 
       FIG. 1  is a diagram illustrating a radiation element, in accordance with the principles of the present invention. 
       FIG. 2  is a schematic view describing a planar antenna, in accordance with the principles of the present invention; 
       FIG. 3  is a diagram showing a radiation circuit in a 2×2 subarray of the planar antenna, in accordance with the principles of the present invention; 
       FIG. 4  is a diagram depicting the arrangement of dipoles on the upper surface of the upper plate, in accordance with the principles of the present invention; 
       FIG. 5  is a diagram depicting the arrangement of dipoles on the lower surface of the upper plate, in accordance with the principles of the present invention; 
       FIG. 6  is a diagram depicting the arrangement of dipoles on the upper surface of the lower plate, in accordance with the principles of the present invention; 
       FIG. 7  is a diagram depicting the arrangement of dipoles on the lower surface of the lower plate, in accordance with the principles of the present invention; 
       FIG. 8  is a side view of the planar antenna, in accordance with the principles of the present invention; 
       FIGS. 9A and 9B  are diagrams showing the probe and the polarization propagating direction of the planar antenna, in accordance with the principles of the present invention; 
       FIG. 10  is a graphical view showing a voltage standing wave ratio of the upper and lower plates of the planar antenna, in accordance with the principles of the present invention; 
       FIG. 11  is a graphical view representing the isolation between subarrays, in accordance with the principles of the present invention; 
       FIG. 12  is a graphical view showing antenna gains and cross polarization isolation, in accordance with the principles of the present invention; and 
       FIG. 13  is a view showing a general arrangement and orientation of the components of  FIGS. 4-7  stacked up in order, in accordance with the principles of the present invention. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the present invention are shown, it is to be understood at the outset of the description which follows that persons of skill in the appropriate arts may modify the invention here described while still achieving the favorable results of this invention. Accordingly, the description which follows is to be understood as being a broad, teaching disclosure directed to persons of skill in the appropriate arts, and not as limiting upon the present invention. 
   Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described. In the following description, well-known functions, constructions, and configurations are not described in detail since they could obscure the invention with unnecessary detail. It will be appreciated that in the development of any actual embodiment numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill having the benefit of this disclosure. 
   The present invention will now be described more fully with reference to the accompanying drawings, in which a preferred embodiment of the invention is shown. This invention may be embodied in many different forms and should not be construed as being limited to the embodiment set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thickness of the layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can either be directly on the other layer or substrate or has intervening layers present. The same reference numerals in different drawings represent the same elements, and thus their descriptions will be omitted. 
   One type of planar antenna can be associated with linearly polarize waves. Such an antenna can include a ground plate, power supply circuit plate, and radiation plate, and has a high gain, but it is used for the purpose of reception only. 
   Another type of planar antenna can be associated with circular polarization. Such an antenna is used for either transmission or reception due to its single polarization characteristic. Such an antenna will have a generally simple configuration. However, such an antenna does not embody the characteristic of dual polarization. 
   Some planar radiation elements can form both linear and circular polarization. An antenna that has linear and circular polarization may have all its radiation elements and power supply points existing on one plane, and a requested polarization is embodied by properly exciting in the power supply points. Accordingly, two power supply circuits are needed to obtain two kinds of polarization. This would be made possible by arraying the two power supply circuits appropriately on one plane. 
   A joint array could address some of the above-mentioned problems. An antenna that relates to a dual polarization antenna array using a common aperture can have the common aperture involving a micro strip dipole array and a plurality of centered slot arrays positioned in the aperture. Such a dual polarization array antenna could have radiation elements in the common apertures and multiple folds of power supply circuits. 
   Another antenna could have a fully suspended-substrate micro strip line, and two folds of power supply circuits for the common aperture of circular waveguide radiation elements. That type of antenna would be disadvantageous due to the complicated configuration, excessive height, and mechanically delicate fabrication process. 
   Another planar antenna could be formed of patch elements that make up a complete printed-circuit-board type dual polarization antenna. Such an antenna could be formed of a radiation element circuit unit, first and second power supply circuit units, and a ground plate stacked on one another, each layer being positioned independently by a dielectric substance layer. The patch elements of the radiation element circuit unit could be connected to the power supply circuit unit electromagnetically. Such a planar antenna could use a transmission signal or a reception signal in a different polarization mode, so that the polarization mode of transmission could be different from that of reception, and it could minimize loss so as to obtain high antenna gain. 
   Referring to  FIG. 1 , which illustrates a radiation element in accordance with the principles of the present invention, a radiation element has two branches  110  and  120 , and a stem  130 . Each branch forms an angle of 45° with a surface that is perpendicular to the stem  130 , as shown in FIG.  1 . 
   In accordance with the principles of the present invention, the branches  110  and  120  are not required to form an angle that is 45° with the surface that is perpendicular to the stem  130 . The branches  110  and  120  could form any angle less than 90° with the surface that is perpendicular to the stem  130 . 
   As shown in  FIG. 1 , grooves  140  are formed where the ranches  110  and  120  meet the stem  130 . Each groove  140  is called a slot, and this is to compensate for the reactance of a dipole. As shown in  FIG. 1 , each branch  110 ,  120  meets the stem  130  at a right angle at the region of the slot  140 . Each of the branches forms a 90° angle with the stem  130 . 
   Referring to  FIG. 2 , which shows a schematic view of a planar antenna in accordance with the principles of the present invention, the planar antenna of the present invention comprises two plates  210  and  220 , a ground plate  230 , a support  240  for connecting the plates  210  and  220  and the ground plate  230  at the center, and polystyrene foam  250  for filling the empty space between the lower plate  220  and the ground plate  230 . 
   A circuit unit of the upper plate  210  is formed of a conductor, such as copper (Cu), aluminum (Al), silver (Ag), astatine (At), iron (Fe), and gold (Au), covering the surface of a dielectric substance. Since the side surfaces of the dielectric substance are covered with the conductor, radiation circuits are placed on both sides of the plates, just as a circuit is placed on a printed circuit board (PCB). Radiation circuit  260  is placed on the upper surface of the upper plate  210 . Radiation circuit  270  is placed on the lower surface of the upper plate  210 . Dielectric substances that can be used here include polyethylene, polyester, acrylic resin, polycarbonate, ammonium bicarbonate (ABC), polyvinyl chloride (PVC), and a mixture thereof. The dielectric substance has an upper side surface and a lower side surface. 
   The lower plate  220  and the upper plate  210  are formed in a similar manner. Radiation circuit  270  is placed on the upper surface of the lower plate  220 . Radiation circuit  280  is placed on the lower surface of the lower plate  220 . One part of radiation circuit  270  may be placed on the lower surface of the upper plate  210 , and another part of radiation circuit  270  may be placed on the upper surface of the lower plate  220 . In some cases, the entire radiation circuit  270  may be placed on the lower surface of the upper plate  210 , or the entire radiation circuit  270  may be placed on the upper surface of the lower plate  220 . Thus, if the entire radiation circuit  270  is placed on the lower surface of the upper plate  210 , then the radiation circuit  270  does not exist on the upper surface of the lower plate  220 . 
   The ground plate  230  is made of aluminum (Al). It supports the entire antenna and it is used as a ground of all of the circuits. The support  240  connects the two plates  210  and  220  and the ground plate  230 . Within the support  240  exists a probe, and the probe is connected to the termination of the power supply circuit connected to the power supply circuit of each radiation element. A more detailed description will be provided with reference to FIG.  3 . 
   Between the lower plate  220  and the ground plate  230  is a supporting substance such as polystyrene foam  250  for supporting the antenna. The supporting substance  250  also performs a function of insulating the ground plate  230  from the other plates  210  and  220 . 
   A middle layer can exist between the lower surface of the upper plate  210  and the upper surface of the lower plate  220 . 
   The upper plate  210  has an upper surface and a lower surface. The upper and lower surfaces of the upper plate  210  can be referred to as an upper side surface and a lower side surface, or can be referred to merely as side surfaces of the upper plate  210 . 
   The lower plate  220  has an upper surface and a lower surface. The upper and lower surfaces of the lower plate  220  can be referred to as an upper side surface and a lower side surface, or can be referred to merely as side surfaces of the lower plate  220 . 
     FIG. 3  illustrates a radiation circuit in a 2×2 subarray of the planar antenna in accordance with the principles of the present invention. The items shown in  FIG. 3  include radiation elements and other components located on various layers of the plates  210  and  220 , and located between those plates. If someone could see directly through the plates  210  and  220 , then they would be able to see the items included in FIG.  3 . 
   The items in  FIG. 3  are surrounded by a dotted line  290 . The dotted line  290  is also shown in FIG.  2 . The dotted line  290  in  FIG. 2  surrounds 4 branches on the upper surface of the upper plate  210 . That is, the dotted line  290  in  FIG. 2  surrounds four radiation elements on the upper surface of the upper plate  210 . The dotted line  290  shown in  FIG. 3  surrounds 16 branches (that is, 16 radiation elements) because  FIG. 3  shows all radiation elements on all surfaces of the plates  210  and  220 . The 16 radiation elements shown in  FIG. 3  include the 4 radiation elements shown in the dotted line  290  in FIG.  2 . 
   The 16 radiation elements in  FIG. 3  are surrounded by a ground circuit  360 . The ground circuit  360  is approximately at the location of the dotted line  360 , and thus is in the shape of a square or a large window. The ground circuit  360  includes 4 square-shaped ground circuits. Each one of the 4 square-shaped ground circuits surrounds  4  radiation elements, as shown in FIG.  3 . In  FIG. 3 , one of the 4 square-shaped ground circuits is surrounded by the dotted line  395   b  (window  395   b ). The window  395   b  shown in  FIG. 3  is similar to the thick black squares shown in FIG.  2 . The window  395   b  of portion  290  is not shown in FIG.  2 . However, a differently located window  395   a  is indicated in FIG.  2 . The window  395   a  in  FIG. 2  is very similar to the window  395   b  in  FIG. 3 , except window  395   a  is located in a different position than window  395   b.    
   In  FIG. 3 , the parts  310  and  320  hatched with oblique lines represent a circuit on the upper surface of the upper plate  210 . The circuit unit is formed of radiation elements  310  and power supply wires  320 . The parts  330  and  340  filled with grey cal in the drawing correspond to a circuit located on the bottom surface of the lower plate  220 . This circuit unit is formed of radiation elements  330  and power supply wires  340 , just as in the upper plate  210 . The parts  350  and  360  that are not filled with any hatching or color indicate circuits located on the bottom surface of the upper plate  210  and the upper surface of the lower plate  220 . These circuits include radiation elements  350  and ground circuits  360 . 
   The radiation elements located at both sides of the plates are in the form of a symmetrical dipole. One branch  310  of the dipole lies on one surface of the upper plate  210  with the power supply wire  320 , and the other branch  350   a  lies on the ground circuit  360 , which is on the opposite surface of the upper plate  210 . Accordingly, one branch  310  of the dipole and the other branch  350   a  corresponding thereto are located at opposite surfaces of a plate  210 . That is, a subarray has dipoles arranged on one side of a plate  210  as shown in FIG.  4  and another subarray has dipoles arranged on the other side of the plate  210  as shown in  FIG. 5 , so that the dipoles of the subarrays overlap with each other. Unlike general dipoles, the branches of the dipoles are formed at an angle of 45° to obtain optimal performance. In accordance with the principles of the present invention, the dipole branches are bent at 45° to reduce the dipole area. However, in general, dipoles are not bent. 
   The other plate  220  is just the same as the plate  210  described above. In other words, one branch  330  of the dipole lies on one surface of the plate  220  with the power supply wire  340 , and the other branch  350   b  lies on the ground circuit  360 , which is on the opposite surface of the plate  220 . Accordingly, one branch  330  of the dipole and the other branch  350   b  of the same dipole are located on opposite sides of a plate  220 . That is, a subarray has a shape in which the dipoles of FIG.  6  and the dipoles of  FIG. 7  overlap in the plate. Unlike general dipoles, the branches of the dipoles are formed bent at an angle of 45° to obtain optimal performance. In accordance with the principles of the present invention, the dipole branches are bent at 45° to reduce the dipole area. However, in general, dipoles are not bent. 
   The power supply wires  320  and  340  are converted into micro strip lines through a balloon  370 . A slot  380  is formed to compensate for the reactance of the dipole. It is formed in the shape of a groove where the branches of the dipole are bent. A stub  390  is formed to compensate for the coupling impedance, and it is positioned at the branch of the dipole. All the dipoles are supplied with power through the branch power supply wires, which diverge from the main power supply wire. 
     FIG. 4  is a diagram depicting the arrangement of dipoles on the upper surface of the upper plate  210 , in accordance with the principles of the present invention.  FIG. 4  show that the radiation elements  350   a  of the upper plate  210  shown in  FIG. 3  are arranged in one subarray.  FIG. 5  is a diagram depicting the arrangement of dipoles on the bottom surface of the upper plate  210 , in accordance with the principles of the present invention. That is, the drawing show that the radiation elements  310  of the upper plate  210  shown in  FIG. 3  are arranged on one subarray. Each square window in portion  201  in  FIG. 5  is a ground window containing a pair of dipoles (that is, containing 4 radiation elements). Each square window in  FIG. 5  only shows a part of one dipole. When the 4 surfaces are stacked up on top of each other, as shown in  FIG. 13 , then it is apparent that each square window has a pair of dipoles as depicted in window  395   b  in FIG.  3 . 
     FIG. 6  is a diagram depicting the arrangement of dipoles on the upper surface of the lower plate  220 , in accordance with the principles of the present invention. The drawing shows that the radiation elements  350   b  of the lower plate shown in  FIG. 3  are arranged in one subarray.  FIG. 7  is a diagram depicting the arrangement of dipoles on the bottom surface of the lower plate  220 , in accordance with the principles of the present invention. It shows that the radiation elements  330  of the lower plate shown in  FIG. 3  are arranged in one subarray. 
   When the dipoles of  FIGS. 4 through 7  are stacked up in order, the dipole arrangement of the planar antenna of the present invention is formed.  FIG. 13  is a view showing the general arrangement and orientation of the components of  FIGS. 4-7  stacked up in order, in accordance with the principles of the present invention. 
     FIG. 8  is a side view of a planar antenna formed in accordance with the principles of the present invention. The ground circuit  360  is embodied in the form of a window surrounding the dipoles. For example,  FIG. 3  shows a window  295   b  with two dipoles in the window  395   b . All of the ground windows include a pair of dipoles that are orthogonal to each other. The windows minimize the effect of the dipole radiation on a screen circuit. The ground windows form a lattice, and the power supply wires are arranged on the windows. Accordingly, two plates with a similar dipole arrangement form a subarray of a separate antenna, and two folds of subarrays, which are orthogonal to each other, form an antenna.  FIG. 8  shows the longitudinal end of power supply circuit  820 , probe  830 , ground plate  840 , and support assembly  850 . The support assembly  850  corresponds generally to the support  240  shown in FIG.  2 . 
   A power supply wire for one subarray is positioned on the upper plate  210 , and a power supply wire for the other subarray is positioned on the lower plate  220 . The ground circuit  360  is located between the two plates  210  and  220 , and it is for both use for both subarrays. 
   The ground windows should be sufficiently thicker than the power supply wire to reduce the coupling between the power supply wires for the subarrays. The power supply circuit for each plate includes a phase shifter embodied with a micro strip line stub to have a phase difference of 90° with respect to the corresponding subarray. The phase shifter used here is a conventional phase shifter. In this case, when the two subarrays both operate, circular polarization can be obtained, whereas when only one subarray operates, linear polarization is obtained. 
   The termination  820  of the power supply circuit is located at the center of each plate, and the termination of the upper plate  210  is positioned to be orthogonal to the termination of the lower plate  220 . The terminations  820  are connected to the probes  830  located at the center of the array antenna. Accordingly, all the subarrays include a pair of terminations in the same direction. 
   The pair of terminations is excited by the Transverse Electric 11 (TE11) mode of a circular waveguide combiner through the probes  830 . When the two pairs of terminations  820  are orthogonal to each other, the two Transverse Electric 11 (TE11) modes become orthogonal to each other too. 
     FIGS. 9A and 9B  are diagrams showing the probe and the polarization propagation direction of the planar antenna in accordance with the principles of the p sent invention.  FIG. 9A  shows the direction of polarization when the polarization of the Transverse Electric 11 (TE11) mode is parallel to another pair of probes and only one subarray operates.  FIG. 9B  illustrates the direction of polarization when the polarization of the Transverse Electric 11 (TE11) mode is rotated by 90° with respect to another probe and two subarrays operate. If the phase shifter operates while the two subarrays operate, the polarization of the array antenna becomes circular, either leftward or rightward. 
   Therefore, the two orthogonal Transverse Electric 11 (TE11) modes always correspond to two types of antenna polarization, i.e., linear (vertical or horizontal) polarization, or circular leftward or rightward polarization. One polarization is used for the purpose of transmission, and the other one is used for reception. 
     FIG. 10  is a graphical view showing a voltage standing wave ratio (VSWR) of the upper plate and the lower plate of the planar antenna, in accordance with the principles of the present invention. The voltage standing wave ratio (VSWR) is measured in the bandwidth of 7.25 gigahertz (GHz) to 8.4 GHz. As shown in the drawing, the maximum value of the voltage standing wave ratio (VSWR) is under 1.7. 
     FIG. 11  is a graphical view representing an isolation between the subarrays, in accordance with the principles of the present invention. As shown in the drawing, the isolation between the subarrays is more than −25 decibels (dB) over the entire bandwidth. 
     FIG. 12  is a graphical view showing antenna gains and cross polarization isolation, in accordance with the principles of the present invention. As shown in the drawing, the antenna gains are at least 28.5 dB, and the cross polarization isolation is over −25 dB at maximum. 
   As described above, the present invention provides an antenna having linear and circular polarization, which has an orthogonal characteristic in both linear and circular polarization, and whose height can be lowered by embodying a micro strip planar antenna having dual polarization which has high gain over a wide frequency band, and transmits or receives linear or circular polarization. 
   While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant&#39;s general inventive concept.
An antenna is located at the end of a wireless communication system, or other radio system, and more particularly, a wideband planar antenna with linear and circular polarization uses different polarization for transmission or reception to increase the isolation between the transmission and reception by suggestion and using a type of radiation element. The disclosed antenna is more efficient than other similar antennas that can transmit/receive linear or circular polarization. The disclosed invention makes it possible to pr vide an antenna having dual polarization, which has an orthogonal characteristic in both linear and circular polarization, and which can lower the height of the antenna by embodying a micro strip planar antenna which has linear and circular polarization that has high gain over a wide frequency band, and which transmits/receives linear or circular polarization.