Re: GPS antenna
davorin said:
Is it possible to use a small PCB as GPS antenna for testing?
Any good reference how they layout should look like if it is possible?
if you mean Printed Circuit Board by PCB (which i think you do!), i should tell you that Microstrip Antennas are actually PCBs, becouse they are printed on substrates. but there is some considerations.
1. simple printed antennas (such as edge fed p@tches) have very low band-width (say, 0.3%~ 2.5% with VSWR<2), but becouse of narrowband requirements of normal GPS antennas, i think they are practiacl.
2. usual RF substrates have high er to miniaturize the size of circuite. these high permittivity subs could be also used for p@tchs, and make it minature too, but consecuently a narrower band-width is gained.
3. better charasteristics could be reached by probe-fed p@tches, but manufacturing is then harder.
4. airgaps and very-low permittivity subs (such as foams) could be used to wide-banding the antenna, but a bigger p@tch is achieved (for example, as a 1.6GHz antenna, p@tch dimentiones will be about : 9.5cmx9.5cm), which is offen not practical.
5. miniaturization methods could be used to gain smaller p@tches (include loading with notches and lumped-elements). fractal miniaturized patches could be also practical.
6. due to Circular Polarization of many GPS antennas, some especial designs is proved to have better performance, such as square p@tchs or circular patches. here the main parameter which limit the bandwidth of the antenna is Axial-Ratio. typically 1% bandwidth could be achived with usual simple p@tchs.
7. as you know, most of these antennas are attached to an active RF section (may called active antennas), and thus higher VSWR is acceptable. having count this, a more miniaturized p@tches (with high er subs) could be used.
8. and finally, the p@tch antennas are not the only choice. one of my friends haa a very keen idea on merging RF parts with dielectric resonator antennas. if anybody interested in, please be free to pm me about.
hope be helpfull all these
,
cheers, marti