Robohub.org
 

Antenna separation: How close can you go?


by
03 June 2016



share this:
robot_device-676x507

When building a new robot mechanical engineers always ask me: how close can different antennas be to one another? It is not uncommon to try squeezing 5+ antennas on a single robot (GPS, GPS2 for heading, RTK, joystick, e-stop, communications, etc..). So what is the proper response? The real answer is that it depends heavily on the environment. However, below are the rules of thumb I have learned and have been passed down to me for antenna separation. I do want to give a disclaimer some of this has been passed down as rules of thumb and may not be 100% correct.

Here is the rule: The horizontal distance between antennas should be greater than 1/4 of its wavelength (absolute minimum separation), but it should not be located at the exact multiples of its wavelength (maybe avoid the first 3-4 multiples). If multiple frequency antennas are near each other, then use the spacing distance of the lower frequency antenna, or even better, try to satisfy the rule for both frequencies.

Device Frequency Wavelength 1/4 Wavelength
WiFi 802.11 5.8GHz 5.17cm 1.29cm
WiFi 802.11 2.4GHz 12.49cm 3.12cm
GPS* 1.227GHz 24.43cm 6.11cm
Radios 900MHz 33.3cm 8.33cm

Here is a nice wavelength calculator I just found to generate the table above.

* If you are using two GPS antennas to compute heading then this does not apply. These numbers are strictly for RF considerations.

So, for example, if you have a GPS antenna and a WiFi 2.4GHz antenna you would want them to be separated by at least (more is better, within reason) 8.33cm. And you should avoid putting them at exactly 24.43cm or 33.3cm from each other.

This rule seems to work with the low power antennas that we typically use in most robotics applications. I am not sure how this would work with high power transmitters. For higher power transmitting antennas, you might want greater separation. The power drops off pretty quickly with distance (proportional to the square of the distance).

I also try to separate receive and transmit antennas (as a precaution) to try and prevent interference problems.

An extension of the above rule is ground planes. Ground planes are conductive reference planes that are put below antennas to reflect the waves to create a predictable wave pattern and can also help prevent multipath waves (that are bouncing off the ground, water, buildings, etc…). The further an antenna is from the ground (since the ground can act as a ground plane), the more likely having a ground place becomes necessary. In its simplest form, a ground plane is a piece of metal that extends out from the antennas base at least 1/4 wavelength in each direction. Fancy ground planes might just be several metal prongs that stick out. A very common ground plane is the metal roof of a vehicle/robot.

Note: Do not confuse ground planes with RF grounds, signal grounds, DC grounds, etc…

Aerial roof markings on London police car. Source: Wikimedia Commons

Aerial roof markings on London police car. Source: Wikimedia Commons

An example of building a ground plane can be with a GPS antenna. It should be mounted in the center of a metal roofed robot/car or on the largest flat metal location. This will minimize the multipath signals from the ground. If there is no flat metal surface to mount the antenna you can create a ground plane by putting a 12.22cm diameter metal sheet directly below the antenna (about 1/2 the signals wavelength, which gives 1/4 wavelength per side).

Note: Some fancy antennas do not require that you add a ground plane. For example, the Novatel GPS antennas do NOT require you to add a ground plane, as described above.

Other things to watch out for are shadowing between the antennas and sensors and the fresnel zone. For more information on the fresnel zone, and why antennas are not actually just line of site, click here.



tags: ,


Robots for Roboticists David Kohanbash is a Robotics Engineer in Pittsburgh, PA in the United States. He loves building, playing and working with Robots.
Robots for Roboticists David Kohanbash is a Robotics Engineer in Pittsburgh, PA in the United States. He loves building, playing and working with Robots.





Related posts :



Researchers are teaching robots to walk on Mars from the sand of New Mexico

  02 Sep 2025
Researchers are closer to equipping a dog-like robot to conduct science on the surface of Mars

Engineering fantasy into reality

  26 Aug 2025
PhD student Erik Ballesteros is building “Doc Ock” arms for future astronauts.

RoboCup@Work League: Interview with Christoph Steup

and   22 Aug 2025
Find out more about the RoboCup League focussed on industrial production systems.

Interview with Haimin Hu: Game-theoretic integration of safety, interaction and learning for human-centered autonomy

and   21 Aug 2025
Hear from Haimin in the latest in our series featuring the 2025 AAAI / ACM SIGAI Doctoral Consortium participants.

AIhub coffee corner: Agentic AI

  15 Aug 2025
The AIhub coffee corner captures the musings of AI experts over a short conversation.

Interview with Kate Candon: Leveraging explicit and implicit feedback in human-robot interactions

and   25 Jul 2025
Hear from PhD student Kate about her work on human-robot interactions.

#RoboCup2025: social media round-up part 2

  24 Jul 2025
Find out what participants got up to during the second half of RoboCup2025 in Salvador, Brazil.

#RoboCup2025: social media round-up 1

  21 Jul 2025
Find out what participants got up to during the opening days of RoboCup2025 in Salvador, Brazil.



 

Robohub is supported by:




Would you like to learn how to tell impactful stories about your robot or AI system?


scicomm
training the next generation of science communicators in robotics & AI


 












©2025.05 - Association for the Understanding of Artificial Intelligence