RTK rover – helical vs patch antennas

Q&A forumCategory: QuestionsRTK rover – helical vs patch antennas
cfnomad asked 1 year ago
I’m looking for a compact RTK rover antenna and am looking for recommendations.
Specifically, we’re trying to decide between the helical dual-band antenna and OEM patch antenna. I‘ve heard that helical antennas are often worse at rejection multi-path, but am not sure that’s actually the case.
About our requirements: For our base, we’re planning a simpleRTK2 with survey grade antenna. Distance to the rover is <10km. We’ll need very good position accuracy: <1cm, and are particularly interested in the vertical/height position on that level.
It would be easier to fit a helical antenna on our rover, but CEP/accuracy is the first priority. Do you have any recommendations?
Many thanks 😉
replied 1 year ago

I’m guess someone needs to invest some time and capital in testing.

One guy I worked with over the years was relatively dismissive of quad-helix GPS antennas (volutes) whilst another went on to start Sarantel. As the former did post-processing, and RTK, work decades ago, and also used choke-ring antenna’s too, I’m apt to take his word for the fact that the phase-center variation and stability was “not good” in the volute antennas. The gain, and the RF design was excellent, and as I recall it had good directional/upward performance.

replied 12 months ago

I’m looking into this too, and the first practical results show that the mixing of the two types of antennae produces worse results than if both are of the same type. First reasoning could be that the phase-center difference in height of the stacked patch antennae mismatches to the unique phase-center of the better helicals. Would love to have some inputs from specialists in the field.

replied 12 months ago

Interesting, so you’re saying that the phase-center is more well-defined in the helical than in the patch antenna. Did you just look at horizontal or also at vertical positions?

replied 12 months ago

>>Would love to have some inputs from specialists in the field.
I think RF/Antenna experts are generally quite rare and expensive, expect to have to contract services.

Volutes are generally vertically orientated, picking up signals which are circularly polarized. Satellites being directly overhead, and at zero doppler frequency shift, is not the dominant case.

Most designs in this class have a ground plane, with the spiral/helix come off perpendicular. The ones on the GPS satellites are grouped in an array, to get a directional beam, and rotating wave-front.

Trimble used to have what I’d describe as a crown shaped element, ie perhaps two pairs of dipoles, at perhaps 1/4 wavelength, bent/curved to meet the circular ground plane.

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