Resonant-Grid Quasi-Optical Diplexers

In many millimeter-wave systems associated with communicationsatellite antennas or Hertzian cables,1 quasi-optical filters and diplexers are attractive. Because of their large areas, quasi-optical devices have large power-handling capability and the multimoding problem is, in a sense, avoided. The ohmic losses can be small, and the grids are easy to manufacture by photographic techniques. A simple type of diplexer is the plane-parallel Fabry-Perot resonator, incorporating parallel inductive grids and operating under oblique incidence.2 The transmission of a plane-parallel Fabry-Perot resonator is essentially the same as that of a single-pole filter. This type of diplexer, however, suffers from the walk-off effects associated with the diffraction and lateral displacement of the incident beam. 3,4 This effect is aggravated if more than two grids are used to obtain a maximally flat response. The number of grids required, and therefore the walk-off effects, are minimized if the grids have resonant properties of their own. Narrow-band resonant crosses have been used in the far-infrared region.5 No diplexing operation, however, was considered. The special features of the grid patterns considered here are their broadband characteristics and their capability of operating under oblique incidences. Preliminary results were reported in Ref. 6. In the present paper, new experimental results concerning the transmission, reflection, and depolarization of resonant-grid diplexers are reported.