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Good design practise for RF PCB info wanted?

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Advanced Member level 3
Jun 19, 2001
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Hello, can someone please advise me on what is good practise for the design of an RF transciever on a PCB.

Using 0603/0805 smt components on an 1.6mm 1oz FR4 board at 870mhz with groundplane underneath.
I would like to know things like.

I.E. in the transmit line from an RF IC through the filters to the antenna, where I have a connection of


IC= transciever IC
LG=inductor to ground
CG=cap to ground
ANT=antenna. (Green dot on the left) (chip antenna)

What would be the best way to lay the components out.

LAYOUT 1 - all in a line?

LAYOUT 2 - Split in cross fashion?

LAYOUT 3 - taking smallest board area up.

I can tell from the various books etc that layout 1 would be best however I would
prefer layout 3 as it takes less space.

Also should the L & C that go to ground be next to each other or are they OK as in layout 2?

As a newby to RF I would appreciate opinions from some that have experience of RF layout.

Thank you,

Added after 27 minutes:

Also, at the IC end, is it more important for the RF lines and components to be close to the PCB or the decoupling caps?

As there are VCC lines that when the cap is next to them make it so that the RF line cap is further away

The third one is OK.
1) Do you get same ESR/SRF for the 0603 as for 0804
2) Why do you have a separate track for the smaller cap? You can combine pads


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Being new to RF boards I dont understand the meaning of the question about the ESR/SRF ?
My boards are normally just either plain digital or power supplies etc, nothing above 50mhz.

By smaller cap I take it you mean c14.
I'm used to keeping pads seperate so that we get the best soldering & equal (ish) pulling forces in reflow.

So you think that even #3 will work OK?

I would like to give you a recommendation,
"You better see a doctor(RF Engineer) before
it gets worst". First, the separation between
upper plane and ground will determine the
impedance of the transmission line. Granted,
probable the distances are not so important
but then again you would need to check that.
Second, adding lines for the purpose of
routing will probably add changes on phase
and undesirable effects on the IC even create
an oscillator or at minimum reflections that
render the PCB unuseful. Thirst, and probable
the most important, for 0603/0805 SMT
components the fringe effects of the edges will
have a completely different meaning or value
for capacitance or inductances.

Probably at 870 MHz are not important but its
better to check them out.

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