ttc antenna
I need help to design a simple antenna for amateur satellite Telemetry and control use. The antenna must be conformal and have a beamwidth of 70 degrees. It can operate in 432Mhz or 850MHz. Anyone can help or recommed any links on how to build one of these antenna? I have read the ARRL Antenna book but can't find any suitable antenna. I also cannot use a helix because of its height. Any links to some examples?
Thanks in advance.
Cheers,
Element7k
hi,
the antenna could be the quadrifilar helix antenna.
You can find al lot of stuff on the subject... very easy to build... good patter specially for those "birds" in polar orbit, circular polarization.
It shows a little directivity (cardioid pattern) i think it is better than crossed dipoles.
The band is 435 MHz.... i don't think that amateurs have the 850 Mhz....
you likely meant something else....
ciao
PS. I have a nec file for that antenna... if you're interested
at §21 of
Lo Y T, Lee S W, Antenna Handbook, Vol 3, Applications, Chapman & Hall, 1993
you can find a paragraph on TT&C.
Good luck!
Hi scoppulal,
thanks for the nec example. Very much appreciated. However, I notice that there are two source in the quadrifilar. Does this mean the antenna operate in phase quadrature and a phase shifter is needed? Is is possible to use a single feed?
I will like to simulate a x dipole in nec to compare performace. How do I feed this x dipole then? Again with 2 feeds? It will be brilliant if you have an example of a cross dipole as well.
Thanks in advance.
Element7k
quote="satellite"]at §21 of
Lo Y T, Lee S W, Antenna Handbook, Vol 3, Applications, Chapman & Hall, 1993
[/quote]
Hi satellite,
Most of the antenna in this book are waveguide and array antennas. They are not quite comformal and are too complicated for me to build. Thanks for you help anyway.
Cheers,
Element7k
Perhaps you could find interesting the following:
The Design of the Radio Frequency (RF) Subsystem Printed Circuit Boards for the Petite Amateur Navy Satellite (PANSAT)
ciao,
NO phase shifter is needed for the quadrifilar helix (maybe a balun).
I hope the attached helps to understand the feed... the wiring is on the top (it works back fire).
I don't have a nec simulation for crossed dipole (or crossed yagi).
For the crossed system you could simulate two dipole in "+" position and use two separete feed, but one must be a quarter wavelength shifted to obtain circular polarization.
Otherwise you could use in-phase feed but you have to put one dipole a quarter wavelength behind (or beyond) the other, always mainteining the "+" structure.
In any case, to have circular polarization, there must be a phase shift of a quarter wavelength between dipoles. After simulation if you're going to built the dipole system take in account the media used to obtain the shift: air and cables have different velocity factor.
Hope it helps.
Ciao
Hi scoppulal,
thanks very much for you advise. I have managed to obtain a nec simulation of a 20m turnstile from cbik website and I plan to modify that to my operating frequency. However, I do not quite understand how the loads are calculated. For those who do not have nec and is able to help, I attach a diagram of the antenna with dim and load values.
Many thanks in advance.
Regards,
Element7k
Dear friends,
perhaps you are the most suited people to whom I can ask!
Do you have the following book?
Telemetry Systems Engineering
Frank Carden, Russ Jedlicka, and Robert Henry
Artech House
632 pages.
ISBN 1-58053-257-8
For what I konw, it should exist in PDF.
Thanks,
Pieropaolo
I don't have.
There is a sample chapter:
http://www.artechhouse.com/Default.a...=1-58053-257-8