MICROSTRIP RADIATOR FOR CIRCULAR POLARIZATION FREE OF WELDS AND FLOATING POTENTIALS

Abstract: New type of planar antenna of microwaves appropriate for operating in linear or circular polarization, free of welds and floating potentials, and therefore free of electrostatic discharges and problems related to passive intermodulation products, whose application is of particular interest in aircraft and space technologies. Said antenna consists in the interconnection of a microstrip radiator with a spiral antenna of wires. For certain applications wherein said radiators are arranged in a same plane, the radiating effect of the patch may reduce the size of the spiral, whereby the radiator object of this invention degenerates into a circular slit in the ground plane of the supply line and wherein the helically arranged wires provide for the electric contact between the edges of the slit.

Description: MICROSTRIP RADIATOR FOR CIRCULAR POLARIZATION FREE OF WELDS AND FLOATING POTENTIALS The use of microstrip radiators in large alignments for use thereof in communication systems has been increasing little by little as new materials and new techniques appear, which aside from resolving problems, have notably cheapened the manufacturing processes. One of the main problems in space environment of antennas which operate in reception and transmission, is that one weld can generate a spurious signal in the reception band as a passive intermodulation product (PIMP) of signals coming from the transmission band. The fact that in certain alignments thee may be up to 6 welds per radiator makes it necessary to carry out a series of controls of non-existence of PIMP's by means of power tests in a vacuum chamber. French Patent Application FR-A-2 122 341 disclose an oscillating circuit including a patch (12) and a diode (14), where the patch is coupled - without welds - to radiating spirals (15, 16). However, as the oscillating circuit (12,14), a part of which (14) is formed integrally with the radiating elements (15,16), has to include welds necessary for connecting the diode (14) to the patch (12), the assembly will give rise to passive intermodulation products when used. German Patent Application DE-A-3 527 651 discloses a cavity backed antenna assembly with a radiating spiral (3). The German document does not indicate how to eliminate the passive intermodulation products induced by the welds that seem to be necessary in order to interconnect the different parts of the assembly. The studies carried out to avoid this matter have been basically directed towards eleminating welds, developing different alternatives to the supply system, which have been grouped together under the generic name of excitation by electromagnetic coupling (EMC), see the European Patent Application EP-A-0271458 and Barbero J., Martin C. and Vassal'lo J., "Circular patch with feeding through a circular slot", JINA'88, Nice (France). However, this type of excitation without welds, which is still based on a coupling between the feeding line and the radiant element tends to entail the existence of isolated conductive masses, capable of causing electric discharges upon being at an uncontrolled potential. This problem incapacitates these radiators for their use in aircraft and space technologies. A simple solution to this problem is to short-circuit the radiant element in points where the electric field is cancelled out, just as is done according to Haneishi M., Nakayama M., Saito S. and Hasegawa T., "Radiation Properties of Triplate-type planar antenna", ISAP'89, Tokyo (Japan), but this requires a well determined linear polarization of the radiated field, and except the including in the radiant system of a polarizing element, outside the radiator, this solution prevents the generating of circular polarization. The radiator as claimed is supplied by electromagnetic coupling from a stripline and it is inlaid in the same structure of the feeding line. This radiator does not have welds, therefore there are no problems of PIMP's; and it does not contain isolated metallic masses of the conductors belonging to the feeding line, thus, it is free of electrostatic discharges. Figure 1 shows a side view and top view of the device according to the present invention. Figure 2 shows the arrangement of the wires for the configuration of two feeding lines in the case of a circular slot. Figure 3 shows an alternative arrangement of the wires. Figure 4 shows two different radiation patterns. As can be seen in figure 1, the radiator whose application is described, consists of three layers (10), (11) and (12), separated from each other by two dielectric materials (13) and (14.) The radiant surface (layer (10) in figure 1) consists of a metallic plane which contains the radiant element, which consists of a circular or square slot, with four wires (15) (existing in the photoetching mask itself,) which put in contact both edges of the slot. The metallic part of this plane, outside the radiant element, is one of the ground planes of the feeding stripline. The layer (11) contains the central strip of the stripline where the feeding circuit is, which can consist of two feeding lines to generate circular polarization as shown in figure 2, or else one line with the adequate disturbance. The layer (12) consists of a totally metallic plane and is one of the ground planes of the feeding stripline. Figure 2 shows the arrangement of the wires for the configuration of two feeding lines in the case of the radiator with circular geometry. This arrangement is similar to that of the 4 wire antenna cited in Nakano H., "Research on Spiral and Helical Antennas at Hosei University", IEEE Antennas and Propagation Society Newsletter, June 1988. Following the philosophy put forth there, the operating of the antenna object of this patent can be reasoned as if the central metallic circle is a microstrip patch radiator which feeds a four wire antenna, providing the appropriate phases of excitation mode 1, according to the nomenclature cited in Nakano H., "Research on Spiral and Helical Antennas at Hosei University", IEEE Antennas and Propagation Society Newsletter, June 1988. For this reason, and in order to favour radiation of the wire antenna, it would be valid to resort to a design with longer wires, which would make it necessary to increase the size of the circular slot; then there is a compromise, since this increase involves a worsening of the coupling between the stripline and the microstrip patch, aside from considerably increasing the size of the radiator. Nevertheless, and above all when the substrate used is of a low dielectric constant, the overflow of the field itself of the patch, makes the contribution to the four wire radiation rather smaller than that due to the microstrip patch, thus, the performance of the radiator object of this patent, would in such a case be very similar to the classic one of the microstrip patch radiator, slightly modifying the gain thereof and the height in the side lobes, when it is used in array. As to the axial ratio , it does not have the same performance when it is used in dual polarization, since an arrangement of wires like that shown in figure 3, improves the left-hand circular polarization of the microstrip patch and worsens the right-hand one, just as it is shown in figure 4, where the radiation patterns of two radiators, separated in both cases, are represented. An application that is derived from what is described here is that in which the wire antenna is placed upon a conical or cylindric surface, the symmetry axis remaining parallel to the normal one of the patch. This arrangement, where the innovation is in the matching element of the wire antenna being a patch, having main application in the ground environment, where there are no problems with PIMP's due to the existence of welds.

Claims: A microstrip radiator for circular polarization free of welds and floating potentials, said antenna being based on a stripline, characterized in that it comprises a first conductive ground layer (10) and a second conductive ground layer (12); a radiating patch element separated from said first conductive ground layer (10) by a slot; a wire antenna comprising at least one spiral band (15) connecting said patch element to said first conductive ground layer (10); an electrical input layer (11); an input strip in said electrical input layer (11), said input strip terminating below said patch element; a first layer (13) of dielectric material separating said input layer (11) from said patch element, said first layer (13) of dielectric material also separating said input layer (11) from said first conductive ground layer (10); a second layer (14) of dielectric material separating said second conductive ground (12) layer from said input layer (11). A microstrip radiator according to claim 1, characterized in that the at least one spiral band (15) is placed upon a cylindrical surface, with the symmetry axis being parallel to the normal of said patch element. A microstrip radiator according to claim 1, characterized in that the at least one spiral band (15) is placed upon a conical surface, with the symmetry axis being parallel to the normal of said patch element. A microstrip radiator according to any of the preceding claims, characterized in that said patch element has a circular shape. A microstrip radiator according to any of claims 1-3, characterized in that said patch element has a square shape. A microstrip radiator according to any of the preceding claims, characterized in that said wire antenna comprises four spiral bands (15). A microstrip radiator according to any of claims 1-5, characterized in that it comprises an additional input strip terminating vertically below said patch element. A microstrip radiator according to any of the preceding claims, characterized in that said first layer of dielectric material (13) has, in the area where said patch element is situated, a dielectric constant different from the dielectric constant of the rest of said first layer of dielectric material (13).

Inventors: CASTILLO CUERVO-ARANGO PALOMA, LOPEZ LOPEZ GASPAR, MARTIN PASCUAL CARLOS, MONTESANO BENITO CARLOS, VASSAL LO SANZ JUAN, CASTILLO CUERVO-ARANGO, PALOMA DEL, LOPEZ LOPEZ, GASPAR, MARTIN PASCUAL, CARLOS, MONTESANO BENITO, CARLOS, VASSAL'LO SANZ, JUAN
Applicants: CONSEJO SUPERIOR INVESTIGACION, CONST AERONAUTICAS SA, CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS, CONSTRUCCIONES AERONAUTICAS, S.A.
Application year: 1991
Main classification: H01Q9
IPC codes: H01Q9, H01Q21