Planar antenna

Abstract: A planar antenna (10) in multilayered arrangement of a grounding conductor plate (11), a power supplying circuit plate (12) and a radiating circuit plate (13) as separated from one another, radiating elements of which the radiating circuit plate (13) being a plurality of apertures (13a,b) electromagnetically coupled to power supply probes (12a,b) of the power supplying circuit plate (12), is provided on the radiating circuit plate (13) with a polarizer (14) capable of converting linear polarized waves into circular polarized waves, whereby the antenna is enabled to ensure a high efficiency and wide-band cross polarization characteristics.

Description: SPECIFICATION BACKGROUND OF THE INVENTION This invention relates to planar antennas and, more particularly, to a planar antenna which realizes a high radiation efficiency and cross polarized wave characteristics over a wide band range. The planar antenna of the kind referred to can be effectively employed with respect to broadcasting satellite or communication satellite. DESCRIPTION OF RELATED ART Generally, in place of conventional palabolic antennas involving cumbersome installation work and questionable in external appearance, there has been suggested such a planar antenna as has been disclosed in, for example, U.S. Patent No. 4,475,107 (corresponding German Application P 31 49 200.2). In all events, it has been demanded for the planar antenna of this kind that the antenna realizes a higher gain in the reception and, for this purpose, there have been made a variety of attempts to reduce insertion loss. In U.S. Patent No. 4,851,855 (corresponding to German Patent No. 37 06 051), for example, the present inventors K. Tsukamoto et al have suggested a planar antenna in which power supplying and radiating circuits and grounding conductor are mutually held separated through a space retaining means while rendering both of the power supplying and radiating circuits to be electromagnetically coupled for a power supply, instead of direct connection between them. With this arrangement, the power supplying circuit can be disposed in an internal space of the antenna so as to effectively reduce the insertion loss. Further, in U.S. Patents Nos. 4,929,959 and 5,005,019 to A.I. Zaghloul et al, there have been suggested further planar antennas in which the radiating circuit is formed with many annular slots provided in each of their center portions with a patch element, and the patch elements are electromagnetically coupled to power supply probes of the power supplying circuit one by one so that the insertion loss can be reduced and assembling ability can be improved. According to these U.S. patents of Tsukamoto et al and Zaghloul et al, it is possible to attain the reduction of the insertion loss and the improvement in the assembling ability in contrast to any other known planar antenna. On the other hand, in these U.S. patents, too, the radiating circuit comprises slots of a square; circular or other shape and patch elements centrally disposed respectively in each of the slots so that a high precise etching process will be required therefor with a required etching pattern of the radiating plate made much complicated, and there have arisen such problem that manufacturing fluctuation due to an unevenness of printed circuit board or the like becomes large to lower the yield of resultant products and required manufacturing costs are generally elevated. Further, in an earlier invention disclosed in U.S. Patent Application No. 07/509,820 (corresponding German Patent Application P 40 14 133.0), the present inventors K. Tsukamoto et al have suggested a planar antenna in which the radiating circuit plate is provided only with fully open apertures which are electromagnetically coupled to the power supplying probes of the power supplying circuit plate so that the function of radiating element can be attained only by the apertures without aid of such patch element as disclosed in the foregoing U.S. Patents. According to this earlier invention, any high precision manufacturing is no more required so as to render the manufacturing to be simpler, the radiating circuit can be formed simply through a punching work or the like with respect to a metal plate instead of the etching process with respect to the printed circuit board, and the productivity can be effectively improved. In receiving the circular polarized wave with the antenna of the earlier invention, however, there has arisen a deterioration in the efficiency due to a leakage of electric wave of parallel plate mode between the radiating circuit plate and the grounding conductor plate as a result of the electromagnetic coupling between the power supplying probes and the radiating elements formed only by the apertures of a special contour. Further, this leakage has involved a risk that the electric wave leaked out of any one of the apertures is coupled to another aperture so as to have the cross polarization characteristics deteriorated. These have been bars to the attainment of the higher efficiency than in the case of the palabolic antenna and the excellent cross polarization characteristics over a wide-band. SUMMARY OF THE INVENTION A primary object of the present invention is, therefore, to provide a planar antenna which is excellent in the antenna efficiency over a wide band and in the cross polarization characteristics. According to the present invention, this object can be realized as set out in the appended claims. Other objects and advantages of the present invention shall be made clear in following description of embodiments of the invention detailed with reference to accompanying drawings. BRIEF EXPLANATION OF THE DRAWINGS FIGURE 1 shows in a fragmentary perspective view as disassembled the planar antenna in an embodiment according to the present invention; FIG. 2 shows in a fragmentary plan view as magnified a positional relationship between each pair of the apertures in the radiating circuit plate and each power supply probe in the power supplying circuit plate in the planar antenna of FIG. 1; FIG. 3 is an explanatory view for the arrangement of the apertures of the radiating circuit plate in the planar antenna of FIG. 1; FIG. 4 is a fragmentary, schematic sectioned view of the planar antenna of FIG. 1; FIG. 5 is a fragmentary plan view of the polarizer in the planar antenna of FIG. 1; FIG. 6 is a diagram for graphically showing the gain characteristics of the planar antenna of FIG. 1 and of a conventional planar antenna; Fig. 7 shows in a fragmentary, schematic plan view the polarizer in another embodiment according to the present invention; and FIG. 8 shows in a fragmentary plan view as magnified a positional relationship between each pair of the apertures of the radiating circuit plate and each power supply probe of the power supplying circuit plate in still another embodiment of the present invention. While the present invention shall now be described with reference to the embodiments shown in the accompanying drawings, it should be appreciated that the intention is not to limit the invention only to these embodiments shown but rather to include all alterations, modifications and equivalent arrangements possible within the scope of appended claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring here to FIGS. 1 through 5, there is shown a planar antenna 10 in an embodiment according to the present invention, which antenna 10 comprises a grounding conductor plate 11, a power supplying circuit plate 12 and a radiating circuit plate 13, which plates 11-13 are sequentially disposed to flatly face one another in the order mentioned, as mutually separated with spacers 15a and 15b of such plastic material as a foamed sheet interposed between the respective plates 11-13 to mutually separate them by the thickness of these spacers. Further, in front of the radiating circuit plate 13, there is provided a polarizer 14 capable of converting linear polarized wave into circular polarized wave. For the grounding conductor plate 11, it is possible to employ, for example, an aluminum plate of a thickness 2mm and available in the market, while a plate of such other electrically conducting material as copper, silver, astatin, iron, gold and the like may be employed. The power supplying circuit plate 12 is placed at a predetermined interval with respect to the grounding conductor plate 11 with the spacer 15a of the foamed plastic sheet or the like interposed between them. This power supplying circuit plate 12 comprises preferably a polyester substrate of 50µm thick and a power supplying circuit pattern 12a formed on the substrate with a copper foil laminated thereon and subjected to an etching process for the pattern 12a including power supply probes 12b respectively disposed for electromagnetic coupling with the radiating elements in the radiating circuit plate 13. Further, for the radiating circuit plate 13, an aluminum plate of 0.4mm thick, preferably, is employed, and rectangular apertures respectively 13mm long and 2mm wide are made in the plate in pairs 13a and 13b as mutually separated in width direction by 9mm. According to an optimum aspect, the paired rectangular apertures 13a and 13b are formed as punched through the aluminum plate in 16 lines and 16 columns at intervals of 20mm. Further, the radiating circuit plate 13 is placed at a desired interval with respect to the power supplying circuit plate 12 with such spacer 15b as the foamed plastic sheet interposed between them as required. The power supply probes 12b of the power supplying circuit plate 12 and the apertures 13a and 13b in the pairs of the radiating circuit plate 13 should preferably be effectively electromagnetically coupled to each other, in particular, by disposing each of the power supply terminals 12b to intersect one aperture 13b of the paired apertures 13a and 13b and to position tip end of the terminal intermediate between the paired apertures 13a and 13b as seen in the plan view of FIG. 2. As a result of the electromagnetically coupling between the power supply probes 12b of the power supplying circuit plate 12 and the paired apertures 13a and 13b of the radiating circuit plate 13, there occurs such electric wave of the parallel plate mode as has been partly described with reference to the related art, between the radiating circuit plate 13 and the grounding conductor plate 11, but this electric wave of the parallel plate mode will propagate in a linear direction since the paired apertures 13a and 13b are formed for the linear polarized wave. In this case, it is preferable that the respective pairs of the apertures 13a and 13b are arranged in the propagating direction of the parallel plate mode so that the electric wave occurred in the parallel plate mode will have a phase substantially of 1 wavelength or an integral multiple thereof, as shown in FIG. 3. With the above arrangement, the leakage electric wave occurring between the radiating circuit plate 13 and the grounding conductor plate 11 in the parallel plate mode is made to be radiated again out of other adjacent apertures 13a and 13b, as also matched in the same phase. That is, there can be realized a planar antenna structure capable of re-utilizing the leakage electric wave, and the leakage can be eliminated seemingly as a whole. Accordingly, it is possible to realize a highly efficient planar antenna. In respect of the arrangement of the paired apertures 13a and 13b for rendering the phase of the foregoing electric wave of the parallel plate mode to be an integral multiple of the 1 wavelength, it is of course not always required to have the respective pairs of apertures 13a and 13b spaced physically by 1 wavelength. Further, while effective value of the wavelength is made to vary in accordance with the dielectric constant of the dielectric spacer 15b employed or a dimension of the apertures 13a and 13b, it will suffice the purpose to set the spacing of the paired apertures 13a and 13b optimumly in accordance with design requirements. Further, the polarizer 14 provided in front of the radiating circuit plate 13 comprises a flexible printed-circuit board on which a circuit pattern 14a of so-called meander conductor lines formed through an etching process, as will be specifically seen in FIGS. 1 and 5. Here, the polarizer 14 may be formed with, for example, three of the flexible printed-circuit boards respectively having circuit pattern 14a of meander conductor lines and with an insulating layer constituted by an optimum foamed plastic sheet interposed between the respective printed-circuit boards. Accordingly, it is possible to realize a polarizer arrangement capable of converting into the circular polarized wave highly efficiently over a wide-band the linear polarized wave of the linear polarized wave antenna which highly efficiently re-utilizing the leakage electric wave of the parallel plate mode. According to the planar antenna 10 in the instant embodiment of the present invention as described in the above, therefore, measurement of VSWR, gain and cross polarized-wave characteristics has proved that, as shown graphically in FIG. 6, an efficiency of more than 80% and cross polarized-wave characteristics of more than about 32 dBi as represented by a solid line curve PRET could be obtained. In this case, it has been confirmed that the maximum efficiency has shown to be more than 96%, and has been found that the antenna 10 is remarkably improved in the antenna characteristics in contrast to a conventional planar antenna of circular polarized wave type as represented by a curve PRIR of a single dot chain line in FIG. 6. It should be appreciated further that the apertures 13a and 13b constituting the radiating elements of the radiating plate 13, in particular, are full open holes or complete through holes made as punched off in the metal plate, without any provision of such patch elements in the openings as shown in, for example, the foregoing U.S. Patent 4,929,959 to A.I. Zaghloul et al, and are still effective to maintain the high efficiency with the electromagnetic coupling of the power supply probes 12b to the apertures 13a and 13b realized, to remarkably improve the productivity with the arrangement very simplified, and also to sufficiently reduce required manufacturing costs. While in the foregoing embodiment shown in FIGS. 1-5 the polarizer 14 having the circuit pattern of the meander conductor lines is shown to be employed, it will be also possible to employ another polarizer 14A comprising a stack of three foamed plastic sheets, preferably, on which such biased lattice type circuit pattern 14Aa as shown in FIG. 7 is printed with a conducting ink. While in the foregoing embodiment of FIGS. 1-5 the aluminum plate is employed as the radiating circuit plate 13, further, it is also possible to employ any market-available flexible printed-circuit board, as shown in FIG. 8 a copper foil of which is subjected to an etching process, so as to form the radiating elements. In this case, too, it is possible to attain substantially the same function and effect as in the foregoing embodiment. According to the present invention, as will be clear from the foregoing description, it is made possible to effectively re-utilize the leakage electric wave of the parallel plate mode which has been hitherto rendering the antenna characteristics only to be deteriorated, whereby it is enabled to realize a remarkably high efficiency, and to ensure the excellently wide-band cross polarization characteristics by the combination of antenna elements with the polarizer.

Claims: A planar antenna in a multilayered structure comprising a grounding conductor plate (11), a power supplying circuit plate (12), and a radiating circuit plate (13), wherein said plates (11,12,13) are respectively stacked in the order referred to as mutually separated by a dielectric layer (15a,15b) interposed between them (11-13), and said radiating circuit plate (13) is formed with a metal plate which including a plurality of radiating elements for generation of linear polarized waves as electromagnetically coupled to power supply probes (12b) of said power supplying circuit plate (12) in physically non-contact relationship, characterized in that a polarizer (14) is disposed on said stack to be in front of the radiating plate (13) for converting the linear polarized waves into circular polarized waves, and in that said radiating elements of the radiating circuit plate (13) are made in said metal plate in the form of a plurality of pairs of rectangular apertures (13a,13b) mutually separated in their width direction, said pairs of the rectangular apertures (13a,13b) being respectively arranged at intervals of substantially 1 wavelength of the linear polarized waves. A planar antenna according to claim 1, wherein said polarizer comprises a stack of printed-circuit boards each having a conductor circuit pattern, and of insulating sheets interposed respectively between said boards. A planar antenna according to claim 3, wherein said polarizer comprises an insulating sheet having a conductive circuit pattern. A planar antenna according to claim 2, wherein said circuit pattern of said polarizer is formed with meander conductor lines. A planar antenna according to claim 3, wherein said circuit pattern of said polarizer is formed with meander conductor lines. A planar antenna according to claim 2, wherein said circuit pattern of said polarizer is formed with lattice conductor lines. A planar antenna according to claim 3, wherein said circuit pattern of said polarizer is formed with lattice conductor lines.

Inventors: SAITO TAKESHI, TSUKAMOTO KATSUYA, SAITO, TAKESHI, TSUKAMOTO, KATSUYA
Applicants: MATSUSHITA ELECTRIC WORKS LTD, MATSUSHITA ELECTRIC WORKS, LTD.
Application year: 1992
Main classification: H01Q15
IPC codes: H01Q21, H01Q15, H01Q13, H01P1