In RF PCB design ~1GHz, when should I worry about orientation of inductors in relation to the magnetic fields, I have seen application notes from manufactures where they pointed out, that it was very important to orient inductors correctly, or else the induced magnetic field would effect the design performance.

In a differential signal path, it is understandable that two inductors placed in close range, could affect each other and degrade performance.

But when does this apply, should I always place inductors right angles, or how do I determine when it is necessary ?

Snapshot from TRC105 reference design, just as an example. TRC105 reference design


I have had problems in the past with lumped filters where there has been unwanted coupling between the inductors which has adversely affected the frequency response. The stray magnetic fields from the inductors couple more if they are aligned, so mounting them at right angles (orthogonally) is a good idea in this case.

Having referred to the datasheet and reference design for the device you mention - the layout does not have the inductors placed orthogonally.

L1 and L2 are arranged so that the mutual coupling is anti-phase, whereas for L4 and L5 the mutual coupling is in phase - this is by design - I would suggest you follow it.


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