Vehicle antenna shadowed by its own chassis or payload
An antenna mounted low, or behind the vehicle's own body or load, loses line of sight to the access point in parts of the route, and the link fades even where a survey shows good coverage.
On this page5 sections
Is this your problem? It presents like this
- One vehicle type drops in places where a handheld, or a survey on the same route, sees good signal.
- The signal the vehicle reports sits well below a survey reading at the same spot.
- It is worse with a load on board, or in one direction of travel along the same aisle.
- Drops cluster in aisles and between machines, where the vehicle has no line of sight to any access point.
- Roams happen late or in odd places because the client sees weak signal from every access point.
- Bands
- 2.4 GHz5 GHz5 GHz DFS6 GHz
Why it happens
Plant floors rarely give a moving device a clear path. NIST measured propagation in an automotive factory, a steam plant, and a machine shop, and concluded that in industrial settings line of sight is seldom the case, especially for mobile platforms. The factories also lost power with distance faster than an open-area reference site.
The vehicle is one more obstacle, and it travels with the antenna. NIST describes shadowing as a deep attenuation wherever an object blocks the direct path. An antenna mounted low on a chassis, or behind a mast or a load, puts the vehicle’s own metal in that path whenever the access point sits on the far side. NIST’s first remedy for a device stuck in a machine canyon is to raise the antenna height until it sees the access point.
Multipath often rescues a blocked link indoors, and NIST notes that flat metal can be used as a reflector. The rescue costs data loss or delay, and a reflected path changes as the vehicle moves. An access point vendor’s antenna note says that changing the type of antenna and location of the antenna can remove a multipath problem outright.
Weak signal is what pushes an AGV into a roam. In a study of AGV disconnections at an automotive plant, roam trigger messages such as LOW RSSI and BEACON MISS appeared in 89.46%1 of the events. Survey the route the way the vehicle hears it, from where its antenna actually sits.
How to confirm it
- Log the vehicle's own signal along a route, and compare it with a survey taken at the vehicle's antenna height on the same route.
- Run the route loaded and unloaded, and in both directions, and compare the two logs.
- Inspect where each antenna sits relative to the chassis, mast, and load, and check cables and connectors for damage.
- Mount a temporary antenna high and clear of the body, repeat the run, and compare.
The fix
- Move the antenna up and clear of the chassis and the load, so it has line of sight to the access points.
- Change the antenna type or its position on the vehicle when the current mount cannot clear the body.
- If the vehicle cannot change, add an access point positioned to give the vehicle line of sight in the problem area.
Prevent it at design time
- Specify antenna position in the vehicle purchase, and review it with the wireless designer.
- Survey with the vehicle and its tallest load, at its real antenna height, not with a laptop on a cart.
- Plan access point mounting height with the vehicle antenna height in mind.
About this page
Built from 4 sources: 2 standards bodies and labs, 1 research paper or thesis and 1 vendor document. Researched and drafted with AI assistance, then reviewed and approved by Ben Rutter on . How pages are made
- First published
- Last updated
Change history (1)
- First published
Cite this page
Plain
Ben Rutter. "Vehicle antenna shadowed by its own chassis or payload." OT Wireless, published October 5, 2026. https://otwireless.com/causes/vehicle-antenna-placement/
APA 7
Rutter, B. (2026, October 5). Vehicle antenna shadowed by its own chassis or payload. OT Wireless. https://otwireless.com/causes/vehicle-antenna-placement/
BibTeX
@misc{rutter2026vehicleantennaplacement,
author = {Rutter, Ben},
title = {{Vehicle antenna shadowed by its own chassis or payload}},
year = {2026},
howpublished = {\url{https://otwireless.com/causes/vehicle-antenna-placement/}},
organization = {OT Wireless},
}