Microwave Radio Bands

speed of light = 299.792 mm-GHz

Server Sky bands

Server sky will use three radio bands:

• Intra Array: very high bandwidth cellular connections between thinsats in one array
• Inter Array: long distance communication between thinsat arrays

• Ground Link: uplink and downlink to bulk (> 100m²) and consumer (1m²) ground stations

The server sky uplink/downlink bands will be in the advanced satellite Ka microwave bands; we will count on directionality to the equatorial MEO orbit to keep from interfering with LEO or GEO uses of this band. We will use relatively narrow band uplink and high bandwidth downlink, similar to assymetrical bandwidth usage on the internet now.

Server sky is NOT intended for bent-pipe communications, or for multipoint broadcast - uplinks contain mostly queries, requests, and ACK packets, while downlinks move bulk data in response to these data requests. Bulk data upload will mostly be from specialized large-antenna ground stations, not from average meter-scale consumer antennas.

The crosslinks between arrays will be in the 60GHz bands, and chosen specifically so they do not interfere with terrestrial and other uses because of the high atmospheric absorption ( 10dB/km ) in those bands, leading to > 100dB attenuation though the atmosphere. Specifically, if we choose a band between 57 GHz and 64 GHz for long distance beams, and assume signal coding providing bit rates of 8 bits/Hz, then the data bandwidth is 50Gbps and the attenuation is 7dB/km attenuation, but the attenuation at 30 degrees through the atmosphere will be > 60dB. Random-dithered sidelobe energy will probably peak at less than 30dB below our main beams to other arrays, so the peak interfering signal arriving at the ground in temperate latitudes will be 90 dB lower than the main beam.

Upwards beams towards GEO cross-array communication in these bands will be a problem; hopefully, agile radios in thinsat arrays can take over that function and extend the capabilities of those hypothetical GEO satellites rather than interfere with them.

If we choose microwatt intra-array communications in the 70-90 GHz range, very little will reach the the atmosphere or other orbits; microwave-band radiation from the sun will be much higher.

Space Power Satellites Bands

11.7 to 12.2 GHz is called the FSS-band and the 12.2 to 12.7 GHz range is called DBS band

Broadband satellite systems typically employ the 27.5-30.0 GHz SHF frequency range for uplink transmissions (earth-to-space) and the 17.7-20.2 GHz range for downlink transmissions (space-to-earth)

World Satellite Almanac 1987

... and many more

Distance from GEO to 45N, 38000 km, 1.8e16 m². 1W EIRP produces 5.5e-17 W/m² or 5.5e-18 mW/cm² at antenna dish.

2GW powersat produces 30mW/cm², 300W/m² an EIRP of 187 dbW on beam. Sidelobe power is 0.01mW/cm² or 0.1 W/m², an EIRP of 153 dBW, and the "floor" is 100nW/cm², 1μW/m², an EIRP of 103 dBW.

I don't know how much we must filter this spike of energy to keep it from degrading a signal. Chances are, a pure tone won't land directly in the signal band, but nonlinearities in LNA and mixer could shift the frequency into the baseband. Let's be very optimistic and assume that we can tolerate a signal or harmonic of the same power as the comsat signal.