PLATE ANTENNA

Abstract: A plate antenna (1) comprising an upper radiator (3) and a lower radiator (4) electrically isolated from each other, the width of one (3) of said radiators increasing in the direction away from the other radiator as in a cone antenna, said radiators (3, 4) being film-like elements fitted in the same plane on a circuit board (5) made of a dielectric material. The other radiator (4) is of a rectangular shape while the first radiator (3) comprises a rectangular extension (7), so that the antenna also functions as a wide-band dipole antenna. With the antenna of the invention, a very simple and light construction is achieved.

Description: PLATE ANTENNA The present invention relates to a plate antenna. The traditional discone antenna consists of a metallic cone and a horizontal round metal disk placed symmetrically near its apex and electrically isolated from the cone. Instead of a disk and a cone, it is possible to use a corresponding construction consisting of a plurality of radial elements. The disk and the cone are fed in opposite phase. A discone antenna of this type is presented e.g. in US patent specification 4,851,859. Previously known discone antennas have the drawbacks of a large size and a complex construction. The object of the present invention is to eliminate the drawbacks of prior-art solutions and to achieve a completely new type of wide-band plate antenna that combines the advantages of the discone antenna, dipole antenna, Windom antenna as well as the slot antenna. The antenna of the invention is implemented using a film-like planar antenna pattern fitted on a printed circuit board or equivalent. The details of the features of the plate antenna of the invention are presented in the characterization part of claim 1. Other preferred embodiments of the invention are presented in the subclaims. With the antenna of the invention, a very wide frequency range is achieved, e.g. a range of 350 - 3000 MHz, and its width can be further increased e.g. towards lower frequencies by increasing the dimensions of the antenna, without simultaneously lowering the upper frequency. In addition, the antenna is of a very small size and simple and light construction in relation to its very wide frequency range and radiation efficiency. In addition, its dipole type radiation pattern is very advantageous in many uses, e.g. in underground tunnels where the radio field is weak. The antenna of the invention can also be provided with a protective casing, giving it a good protection against external damage. In the following, the invention will be described in detail by the aid of an example with reference to the drawings, wherein Fig. 1 presents a front view of an encased plate antenna with the casing sectioned longitudinally, Fig. 2 presents a side view of an antenna as in Fig. 1 with the casing longitudinally sectioned, and Fig. 3 presents an example of a radiation pattern for a antenna according to the invention. Fig. 1 and 2 illustrate a plate antenna 1 which can be used e.g. in the frequency range of 350 MHz - 3 GHz as radiators in an internal coverage system. The antenna 1 comprises an upper radiator 3 laid in a position transverse to the vertical center axis 2 of the antenna, and a lower radiator 4 electrically isolated from the upper radiator and having a downward tapering shape. Both the upper and the lower radiators 3,4 are films made of electrically conductive material, e.g. copper, arranged in the same plane on a vertical printed circuit board 5 of a rectangular form. The printed circuit board 5 may consist of P4 circuit board, which is cheap, and it may have a height of e.g. about 270 mm and a width of e.g. about 160 mm. The lower radiator 4 has a rectangular shape. Its width (in the horizontal direction) equals about 1/4 of the maximum wavelength in the frequency range of the antenna, e.g. about 140 mm, and its height e.g. about 85 mm. The upper radiator 3 comprises a pointed part 6 as in a discone antenna, whose width increases from the apex upwards at an angle A, e.g. 60 °, like the cross-section of a cone. In addition, above this part 6 there is a rectangular part 7 forming an extension of part 6 and having a width equal to its upper edge and also equal to the width of the lower radiator 3. Thus, besides working like a discone antenna, the antenna as a whole also functions as a wide-band dipole antenna^ The height of the upper radiator is about 2/3 and that of the lower radiator about 1/3 of the total height of the antenna radiators, and the upper radiator 3 may have a total height of e.g. 170 mm, in which case the antenna will also work as a Windom antenna. In addition, together with the radiators, the slot 8 between the upper and lower radiators forms a slot antenna. The printed circuit board 5 with the radiators 3, 4 has been fitted inside a plastic casing 9, the radiators and circuit board being thus mechanically well protected. The plastic casing 9 can be fastened e.g. with screws (not shown) to a base 10. A connection cable 11 can be connected from the radiators 3, 4 to a cable connector 12 at the lower edge of the protective casing 9. The inner conductor of the cable 11 is connected via a coupling 13 (soldered or the like) to the lower part of the upper radiator 3, and the shield is connected via a second coupling 14 to the upper part of the lower radiator 4. The matching impedance is directly 50 ohm, so connecting it to a standard high-frequency environment is very easy. Fig. 3 presents the vertical radiation pattern for an antenna according to the invention for a frequency of 451 MHz when the maximum amplitude is about 45.38 dB and the minimum amplitude 7.88 dB. The outermost circle corresponds to 45.31 dB. Measured from above, the horizontal radiation pattern 15 is a nearly circular pattern just inside the outermost circle, between 0 - 6 dB. Measured laterally, the radiation pattern 16 resembles the radiation pattern produced by a dipole at the frequency in question, the radiation at the extreme points almost reaching the outermost circle, so the antenna has directional properties corresponding to a dipole antenna. In addition, with the structure of the invention, the frequency range is extended at the lower end as compared with known discone antennas. It is obvious to the person skilled in the art that different embodiments of the invention are not restricted to the examples described above, but that they can be varied within the scope of the presented below.

Claims: CLAIMS 1. Plate antenna (1) comprising an upper radiator (3) and a lower radiator (4) electrically isolated from each other, the width of one (3) of said radiators inc- reasing in the direction away from the other radiator as in a cone antenna, said radiators (3,4) being film-like elements fitted in the same plane on a circuit board (5) made of a dielectric material, characterized in that the other radiator (4) is of a rectangular shape while the first radiator (3) comp- rises a rectangular extension (7), so that the antenna also functions as a wideband dipole antenna. 2. Antenna as defined in claim 1, characterized in that the height of one radiator is substantially 1/3 and the height of the lower radiator is substan- tially 2/3 of the total height of the radiators, so that the antenna also functions as a Windom antenna. 3. Antenna as defined in claim 1, characterized in that it has a slot (8) between the radiators, so that it also functions as a slot antenna. 4. Antenna as defined in claim 3, characterized in that the width of the antenna equals substantially 1/4 of the maximum wavelength in the frequency range of the antenna.

Inventors: HAAPANEN VEIJO, HAAPANEN, VEIJO
Applicants: CO JOT OY, HAAPANEN VEIJO, CO-JOT OY, HAAPANEN, VEIJO
Application year: 2000
Main classification: H01Q1
IPC codes: H01Q1, H01Q9, H01Q21