Design of thick frequency selective surfaces with complex apertures: Dichroics with cross-shaped and stepped rectangular apertures
Abstract
The unit cell shape of thick frequency selective surfaces, or dichroic plate, is dependent on its frequency requirements. One aperture shape may be chosen to give wider bandwidths, and another chosen for sharper frequency roll-off. This is analogous to circuits where the need for differing frequency response determines the circuit topology. Acting as spatial frequency filters, dichroics are a critical component in supporting the Deep Space Network (DSN) for spacecraft command and control up links as well as spacecraft down links. Currently these dichroic plates separate S-band at 2.0 - 232 GHz from X-band at 8.4 - 8.45 GHz. But new spacecraft communication requirements are also calling for an up link frequency at 7.165 GHz. In addition future spacecraft such as Craft/Cassini will require dichroics effectively separating K(sub a)-band frequencies in the 31 - 35 GHz range. The requirements for these surfaces are low transmission loss of less than 0.1 dB at high power levels. Also it is important to maintain a minimal relative phase shift between polarizations for circular polarization transmission. More current work has shown the successful demonstration of design techniques for straight, rectangular apertures at an incident angle of 30 deg. The plates are air-filled due to power dissipation and noise temperature considerations. Up-link frequency powers approach 100 kW making dielectrics undesirable. Here we address some of the cases in which the straight rectangular shape may have limited usefulness. For example, grating lobes become a consideration when the bandwidth required to include the new frequency of 7.165 GHz conflicts with the desired incident angle of 30 deg. For this case, the cross shape's increased packing density and bandwidth could make it desirable. When a sharp frequency response is required to separate two closely spaced K(sub a)-band frequencies, the stepped rectangular aperture might be advantageous.
- Publication:
-
NASA STI/Recon Technical Report N
- Pub Date:
- June 1992
- Bibcode:
- 1992STIN...9233965E
- Keywords:
-
- Apertures;
- Command And Control;
- Dichroism;
- Downlinking;
- Frequencies;
- Selective Surfaces;
- Shapes;
- Spacecraft Communication;
- Spacecraft Control;
- Spatial Filtering;
- Transmission Loss;
- Circular Polarization;
- Deep Space Network;
- Dielectrics;
- Noise Temperature;
- Phase Shift;
- Superhigh Frequencies;
- Ultrahigh Frequencies;
- Communications and Radar