E-band: 60-90 GHz

Because of various unknowns in the 60 - 90 GHz band, the choice of single dish antenna for both the satellite and earth station can simplify the design and minimize cost. The Cassegrain antenna is chosen for the link because it has better illuminating efficiency with dual reflector. This use can minimize the shift of the phase center especially in the millimeter-wave range. The most important design parameter of the antenna is the diameter, which affects the received power and fade margin. The beamwidth is also desired to be smaller, however that also results in difficult aligning of the main beam axis. Therefore, both antennas of the satellite and of the earth station will be equipped with a high precision stepper motor for rotation to perform the alignment of the space-earth link. Other factors considered in this design include low sidelobe levels, surface precision

The main reflector has a highly accurate surface and is designed from aluminum. The sub-reflector is a machined aluminum hyperboloid or ellipsoid which is rigidly supported by special plastic cylinder. Some low cost and high performance commercial solutions are available from ELVA-1 Millimeter Wave Division [1]. The antennas have minimal cross-section to reduce aperture blockage resulting in low sidelobe levels (about 18 dB). The antenna of the earth station can also be custom designed with bigger dish to further increase the gain to 55 - 60 dBi. In the initial development and for cost analysis purposes, the specifications of the antennas below are listed in this proposal.

Table 1: Specifications for ELVA-1 Millimeter Wave Division Antenna

The rectangular feed waveguides are chosen to send polarized signals to the sub-reflector. We will employ the rectangular waveguide WR-12 operating in 60 - 90 GHz band. The polarization can be adjusted by rotation to separate the horizontal and vertical signals with an ortho-mode transducer (OMT), which is a polarization duplexer. The OMT can separate two microwave signal paths.

K-band: 20-30 GHz

In addition, we will have Cassegrain K-band antennas for the supplemental beacon channel. It will cover 30/20 (uplink/downlink) GHz bands. The antenna gains are 65.8 dB at 19.45 GHz and 68.7 dB at 29.25 GHz. The antenna diameter is 11.5 m. [2]

References

[1] http://www.elva-1.com/products/microwave/dual_reflect.html
[2] T. Takano, E. Ogawa, M. Shinji, N. Ishida, "20, 30 GHz Band Cassegrain Earth Station Antenna for the Japanese Domestic Satellite Communication System," IEEE Trans. Comm., Nov 1979, pp. 1728 – 1731.