Communications: radio wave antennas – Antennas – Microstrip
Patent
1997-11-05
2000-02-01
Wimer, Michael C.
Communications: radio wave antennas
Antennas
Microstrip
343864, H01Q 138
Patent
active
06020852&
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an antenna element intended for transmission and reception of electromagnetic radiation having two orthogonal polarizations having a good purity of polarisation.
BACKGROUND OF THE INVENTION
Antenna elements of the kind that includes the present invention are called micro strip antennas or patch antennas and constitute an all round class of antenna elements. Hence, the basic building block of these antennas is a radiation disc in the shape of a flat, metallic plate. The plate was a shape that, in principle, is arbitrary, that is a patch, separated from a ground plane by means of air or a dielectric. By correctly choosing the dimensions of the plate it is made resonant for a chosen electromagnetic radiation frequency. Usually, the frequency, is in the microwave range. The plate can be used for absorbing or radiating energy at this frequency. It is often desirable that the antenna absorbs or radiates radiation solely having a particular polarization. It is required that the antenna has a good purity of polarization (a low cross polarization, a low axial ratio). It is often required that the antenna can obtain two orthogonal polarizations corresponding to two antenna ports, that is, two linear or opposed elliptical, in particular circular polarizations, having a good purity of polarization. It is clear that deviations from a geometrical symmetry can cause degradation of the polarization purity. The supply itself to the radiation disc can cause such an asymmetry. The problem related to polarization purity then becomes pronounced in the case when the antenna element is made a broad band, type since the effect from the supply in this case becomes marked.
A number of different solutions of the problem relating to polarization purity in antenna elements of the above type has been suggested.
The problem of geometrical asymmetry caused by the supply of the radiation disc can be solved by means a balanced supply, but this will add supply points. This is a complication that can not always be accepted. Balanced supply results in a doubling of the number of supply points for the antenna element, an increased complexity and the problem with potential build-up.
Cutting-outs and tongues at the edges of the antenna elements are often used to obtain a circular polarization using only one supply point. In the case of two polarizations they can, in principle, be used in order to improve the polarization purity. In practice it seems to be hard to design such radiation discs having cutting-outs and tongues since they also modify the electric dimensions of the antenna.
If the antenna element is to generate a circular, single or double that is, right and left rotating polarization and a quadrature hybrid is used, unbalance in the hybrid provides a method of improving the polarization purity. Unless circular polarisation is required and the hybrid already is a part of the antenna, the use of unbalanced hybrids seems to be of little value.
Sequential rotation of and supply to elements can be used as a method of improving the polarization purity in an array of antenna elements. It is a supplement to other methods and only works in the case when the antenna elements are used together with other elements in an array where cross-polarization of different antenna elements can be made to cancel each other at angles close to the broad side direction.
SUMMARY OF THE INVENTION
The object of the invention is to provide an antenna element of the kind mentioned in the introduction, which has a high polarization purity but still has a simple construction.
The present invention may include a ground plane and at least one radiation disc connected to two ports for supplying a desired electromagnetic radiation, preferably within the microwave range, the distance between the ground plane and the radiation disc being a fraction of the wavelength of the radiation.
According to the invention such an antenna element is primarily characterized in that the ports are located at an electrical dist
REFERENCES:
patent: 5539420 (1996-07-01), Dusseux et al.
Saab Ericsson Space AB
Wimer Michael C.
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