Slotted waveguide antenna for near-field focalization of electromagnetic radiation
A radial slot antenna comprising a radial waveguide, which includes an upper plate, having a centroid and an edge region and provided with a plurality of radiating apertures, formed as slots in the upper plate, which develop around the centroid. The radiating apertures are arranged to form first and second radiating regions, which are distinct and radially separated by a dwell region without radiating apertures and wherein, in the first and second radiating regions, radially adjacent radiating apertures are separated from one another by a radial distance, the dwell region having a radial width greater than the radial distances of the radiating apertures in the first and second radiating regions. The slot antenna further comprises a signal feeder for supplying am electromagnetic field to assume, in the first and second radiating regions, opposite phases, so that the electromagnetic field emitted by the slot antenna can be expressed via Bessel functions.
1. A radial slot antenna comprising:
a radial waveguide including an upper plate having a centroid and an edge region and provided with a plurality of radiating apertures formed as slots in the upper plate and positioned around the centroid, the plurality of radiating apertures comprising a plurality of first radiating apertures and a plurality of second radiating apertures;
wherein the plurality of first radiating apertures is arranged in such a way as to form at least one first radiating region, and the plurality of second radiating apertures is arranged in such a way as to form at least one second radiating region, the first and second radiating regions being distinct and radially separated by a dwell region without radiating apertures;
wherein the plurality of first radiating apertures of the first radiating region develops along a first spiral path forming a plurality of first turns, and the plurality of second radiating apertures of the second radiating region develops along a second spiral path forming a plurality of second turns;
wherein radially adjacent turns in the first spiral are separated from one another by a first mutual radial distance, and radially adjacent turns in the second spiral are separated from one another by a second mutual radial distance; and
wherein the first radiating apertures and the second radiating apertures each comprise first grooves and second grooves, (a) the first grooves being arranged immediately one after another along the first spiral path or the second spiral path and being rotated with respect to one another in a counter clockwise direction by a first angular value that increases with a distance from the centroid, and (b) the second grooves being arranged immediately one after another along the first spiral path or the second spiral path and being rotated with respect to one another in a counter clockwise direction by a respective second angular value that increases with the distance from the centroid;
said slot antenna further comprising a signal feeder operable for supplying an electromagnetic field so as to assume, in the first and second radiating regions, opposite phases, in such a way that the electromagnetic field emitted by the slot antenna can be expressed via Bessel functions.
2. The antenna according to claim 1 , further comprising a lower plate, made of electrically conductive material, set facing the upper plate, and a dielectric layer extending between the upper plate and the lower plate,
wherein said signal feeder extends between the upper plate and the lower plate, which are substantially aligned, in a direction of alignment orthogonal to the radial direction, with the centroid so as to supply said electromagnetic field in the dielectric layer.
3. The antenna according to claim 2 , wherein the upper plate and the lower plate form a flat-parallel-plate waveguide, said electromagnetic field being a circularly polarized wave.
4. The antenna according to claim 1 , wherein the electromagnetic field is a uniform field.
5. The antenna according to claim 1 , wherein said first and second spirals have the characteristics, in the first and second radiating regions, of an Archimedean spiral.
6. The antenna according to claim 1 , wherein said waveguide has a circular shape with a diameter larger than approximately 40λ , where λ , is the wavelength of the electromagnetic field supplied.
7. The antenna according to claim 1 , wherein the radiating apertures are formed in pairs, each pair including a first slot and a second slot, which are formed in the upper plate, the first slot and the second slot having a substantially rectangular shape and extending at a distance from one another in respective main directions of extension substantially orthogonal to one another, each pair being set according to said ideal annular pattern.
8. The antenna according to claim 1 , wherein the first and second radiating regions are located between consecutive zeros of the Bessel function that describes the electromagnetic field emitted by the slot antenna when considered at the upper plate.