Radioastronomy Antennas
the term "Astronomy" call for passive sky observation. Some "active" scientific project are called "radar-astronomy". The transmission of high power signal for SETI or communication with human interplanetary missions is called "deep space communication".
In Astronomy , also in radioastronomy, it's important both sensitivity and angle of view.
To increase sensitivity, if the radiosource emission is a black body (in most cases are black body) increase collecting Area, decrease Noise Temperature, increase Bandwidth and increase observing time.
So the first answer to your question is: the antennas are largest as possible. 10 m - to 100 m antennas are typically paraboliod with F/D=0.3 - 0.4.
But for the beam of view, to be scientifically competitive, no one antenna is pratical !
Astronomers combine (in phase) the signals coming from far antennas located around the world, to get a "virtual" antenna that have a extremally thin lobe of interference (i.e. 0.001 arcsec).
The tendency for the new one single single antenna are growing into the following main directions:
-Larger, fully steareable paraboloid
-Multibeam.
Spacecraft Radiotelescope.
The multibeam is close displacement of an array of illuminators on the focal plane (focal zone) of the dish. In this manner the observer may look simultaneously to many points on the sky.
With the spacecraft antennas, the observer may look at frequency masked by the atmosphere.
But remember: every radiotelescope is unique, there isn't a "typical" mode to build antennas.
The 4K cooled Maser ( 40+ y.o. tecnhology) is unsurpassed in low noise, but is narrowband.
The tecnology used to receive signals is criogenically cooled GaAs or InP
HEMT LNA. Observers may get Maser like performances with BW large up to 1/2 octave and more.
Another thing that is done is to combine antennas to get a null pattern which gives better angular measurement accuracy than using the main lobe.
Start your exploration here if you are interested in playing with amateur radio astronomy.
http://a.webring.com/hub?ring=radioastro
You can download a very interesting book on the subject,
Large Antennas of the Deep Space Network
https://www.edaboard.com/ftopic85609.html
check this site it may helps ;)
http://www.astrosurf.com/lombry/radioastronomy2.htm
HI!
Since i'm interested also in radioastronomy i can give you a ery good
website, there is all you need:
http://www.nitehawk.com/rasmit/ws1_4.html
you'll find a lot of projects, experiments and homebrew equipment,
Have fun!
There is another design you might be interested to know which is in use now these years for radio-astronomy. Hot-electron direct balometer detector.
It is a special made device which electron-phonon is the only mechanism for heat interaction.
They couple balometer detector in antennas or waveguides an most of the cases in these last ones. They put these space ships and are very good to sub-milimeter fine detection.
dear djalli,
you are rigth!
Really as the spectrum is continuum also the detecting instruments "continuosly" cover the entire EM spectrum. Bolometers may be considered the joint between radio spectrum and IR spectrum.
But strictly speaking Bolometres are detectors, not Antennas.
You are right it is called "bolometer" not balometer I was calling it.
They are very expensive.
New EDAboard link to Radioastronomy Antennas Book:
Large Antennas of the Deep Space Network, William A. Imbriale, ISBN: 0-471-44537-1
Hardcover, 302 pages, Wiley, February 2003, ￡75.95 / ?116.70
https://www.edaboard.com/ftopic112225.html
Parabolic antennas are used for their high dectivity