RF Antenna design and Metal Housing

[Andreas]

Dear All,

any opinion on attached antenna design (blue) to the outside of a metal housing?

• PCB that flows around an aluminium die cast housing
• External to aluminium housing there are plastic materials around PCB
• Antenna dimensions will be copied from nrf51-dk
• Any clearance requirements to metal housing...?

Thanks very much for your feedback in advance.

[Asbjørn]

I would recommend you to get some more clearance between the alu casing and the antenna. In general I would say that get as much distance as possible, but as a rule of thumbe a distance more than what's considered near field. This usually means about 1.0 cm from the main part of the antenna and metal objects. Far from all application have this luxury, so compromises has to be made. You can tune out the impedance changes caused by metal being closer. This can be done by antenna tuning. The metal casing will distort your radiation pattern, but it might not affect your application in a negative way over all. You get reflections from walls and rooms that will enable you to get a good coverage even though your radiation pattern in far from ideal. As @Charles states above, it will take some experimenting. If you have the time and luxury, I would recommend to make at least three versions of the board with three different distances between the metal housing and the main part of the blue antenna. For example, try one with 5 mm between the main part and the metal, the a second one with 10 mm and a third one with 15 mm. This should give you a good impression of what the distance from the metal casing towards the antenna will do to your application.