Tom Clark, K3IO wrote:
Lyle Johnson wrote:
I discussed some of these ideas with Eric, N7CL, at the TAPR meeting. Eric is very good at antenna system design, did S band stuff for us at MMS and does this sort of thing now for DoD.
Anyway, he suggested we consider Vivaldi's rather than patches. We used Vivaldi's on our trucks at S Band and they work well, are trivial to fabricate (a piece of PC board - I know, radiation, but it is the concept I am wanting us to consider). They are well behaved and have very little coupling to adjacent antennas. I'm not an antenna guy, but you might want to consider the Vivaldi and/or communicate with Eric.
Eric also assisted me with the design of the Microsat 2M rcvrs -- which bore a strange similarity to an MMS design.
AFAIK, the Vivaldi and antipodal antennas are linearly polarized. Multiple elements require crossed antennas, like Fig.9 in http://www.ansoft.com/news/articles/04.09a_MWJ.pdf#search=%22vivaldi%20anten... (note that the radiation is "endfire").
A PhD thesis for a 2-8 GHz describing this antenna used for a Snow radar is seen at http://profusion.ittc.ku.edu/research/thesis/documents/ravi_prakash_rajarama....
Having read the papers my first quickest impressions are
1) The vivaldi is attempting to solve a problem we do not have. We are not after an antenna that exhibits gain, low return loss, polarization isolation, etc. over several GHz. 2) It has gain a little lower than a vacuum dielectric patch at 4 dBi versus 6 dBi of our circular patches or cross dipoles or whatever. We have built in implementation loss in our calculations but I hate to give it up immediately. We would have to have 50% more area to make up for the lost gain over the patches with the increase complexity of feeding, etc. 3) I dont' know what substrate we could use that we could fly outside the spacecraft but we might be able to recess it into the structure in a tube and that would certainly reduce mutual coupling. What else it would do, is beyond my EM theory to guess. 4) It is a traveling wave antenna and/or end fire and according to recent authors "it is not well understood".
I am not rejecting them just giving my first impressions which might even be wrong but they are my first impressions.
Off to the salt mines Bob