[time-nuts] DIY QFH

[Jim Lux]

On 11/26/13 8:51 AM, Attila Kinali wrote:
> On Tue, 26 Nov 2013 11:37:10 -0500
> "quartz55" <quartz55 at hughes.net> wrote:
>
>> Does anyone know what is inside the commercial units, like the PCTEL GPS-TMG-HR-26N I have?
>
> Three types of GPS antennas are common:
> * ceramic carrier patch antennas
> * cross dipole antennas
> * helical designs
>
> The patch antennas are even found in "expensive" antennas with cones
> or choke rings.


the challenge with a patch is getting a pattern that goes down to the 
horizon.

>
> The Trimble Bullet antenna is AFAIK a cross dipole type where the dipole
> ends are bend down for a more GPS like radiation pattern.

Crossed dipoles are very common in "survey grade" antennas. Typically 
the dipole elements are more "fan" like, wide at the end skinny in the 
middle, and the whole thing is shaped like it is draped across a dome. 
The "bowtie" improves the bandwidth, which is important in a 3 band 
antenna. Drooping the ends helps improve the pattern, and also changes 
the input Z.  I don't know how they do the phase quadrature.. do they 
make one dipole a bit longer and the other a bit shorter?  I don't know 
that this works over the whole L5,L2, L1 band, though.  Or some sort of 
quadrature hybrid.

>
> Helical designs vary greatly in their fabrication. I think most of the
> newer ones use some flex PCB that is bend into a pipe shape to form the
> helix (very cheap from a manufacturing point of view).
> High quality helix are either free space (like your QFH) or done on some
> ceramic pipe. I'm not aware of anyone using MID (molded interconnect device)
> for this kind of antenna. Although MID antennas have been the standard
> for cellphone antennas for quite some time already.

The classic helibowl antenna uses wire or copper foil tape wound on a 
plastic cup.  Helicals are pretty non critical in design, but don't 
necessarily have good patterns at the horizon.

don't forget the spiral pinwheel antenna, e.g. from Novatel.



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