New grids for improved polarization diplexing of microwaves in reflector antennas

Grids of thin wires are mounted between a paraboloid and a microwave feed at its focus, so as to obtain linear polarization everywhere in the far-field of the paraboloid. Three types of grids are proposed: 1) a family of hyperbolae on an arbitrary plane
S
, 2) projections of these hyperbolae on an arbitrary surface, and 3) a set of straight lines that converge on a certain point
F'
on a plane
S
. If in cases 1) and 2) a point source is placed at the focus, the resulting plane wave reflected by the paraboloid will be polarized in one direction. In ease 3), there will also he a small cross-polarized component reflected by the paraboloid; the optimum choice of
F'
that minimizes this undesirable component is determined. Only for certain orientations of S will the optimum choice of
F'
be at infinity (in which case the grid is an ordinary parallel wire grid). A simple technique for fabricating grids on curved surfaces is also described. Using the grids discussed here, perfect (or nearly perfect, in case 3)) polarization diplexing at microwave frequencies can be achieved.