Better antennas

[mdodson]

The cover story for Aviation Week for Oct. 30th was about 'conformal arrays' - making a radar antenna part of an airplane's skin, instead of something that sticks out, or determines the size of the front of the airplane, e.g. F-15. This has implications for spacecraft, too, I believe. By putting such a device on the side of propellant tanks, you probably save weight, don't have to worry so much about pointing, since you're doing that electronically instead of mechanically, reduce the chances for a critical failure, and get a faster data rate from faraway places. Faster data rate (more information per second) is a good thing if you're teleoperating!

 

[CalliArcale]

As far as pointing electronically instead of mechanically (I presume you're referring to things like AESA radar, which is being investigated for possible use as very high bandwidth and very secure radio transceiver), I have only one point of doubt. What is the effective maximum range for focusing a radio beam in this way? That's an important question to answer if it is to replace traditional dish antennas. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[billslugg]

Calli<br /><br />The range of an antenna is determined by its forward gain.<br />That will be a function of size, accuracy of shape, accuracy of phasing. <br /><br />Big is better. Adapting to the shape of an airplane or a space ship would probably cause some loss of performance over a dedicated structure. <br /><br />Say you put phased elements wingtip to wingtip on an airplane. You would have an antenna maybe 100 feet wide. It would not be quite as good as a 100 foot wide dish, but would be far better than a 3 foot dish mounted in the nose.<br /><br />A similar strategy is used with the Very Large Arrays. Placing dishes across the world and phasing them. The result is an effective dish the size of the Earth. <br /><br />Proposals have been made to place elements in orbit around the Sun, making an antenna the size of the Earth's orbit. The trick is to know the location of each element to a high degree of precision. You must know the distance of each element from the other to within a fraction of the wavelength at which it operates. <br /><br />I think it might be possible to use the regular signals from pulsars to calibrate such a system. You need something distant, pervasive, of extremely short duration occurring at a high repetition rate. Or perhaps, as they occur, Britney Spears' marriage vows could be uploaded to each antenna. Comparison to an internal atomic clock and then sharing the data with each other antenna would allow a determination of each antenna's location in space. Then when the peaks and troughs come in from a distant source, and the antennas get together later to share signals, they know whether the peaks should reinforce or cancel out. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>