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Re: Designing antenna matching circuit - newbie question

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Newbie level 2
Aug 20, 2009
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antenna matching circuit

In fact here is the sonnet design file I'm using for the murata footprint

50 ohms matching cuircuit for gsm modules

Now that is odd - my first post seems to have disappeared so I'll retype my question.

I'm designing a PCB with a GSM modem and a ceramic chip antenna. The modem connects to the PCB via a 50ohm cable assembly and a Murata RF cable connector mounted on the PCB. From the murata connector the antenna tech spec says I need a 50 ohm coplanar transmission line to the antenna pad using a short microstrip.

No my problem is that I'm trying to use SonnetLite to design the microstrip however when I enter the recommended murata connector footprint by itself into sonnet on a 1mm thick FR4 material with copper metal conductors, and calculate
it's characteristic impedance at 1-2GHz using a 3 port configuration consisting
of (1) ground (2) antenna feed point (3) cable connection point, the magnitude
of the characteristic impedance of port 2 is about 130 ohms and of port 3 is about 90 ohms. I assume the characteristic impedance of the manufacturer's recommended footprint should be 50 ohms so I guess I must be doing something wrong. I can achieve a 50ohm impedance but using a very different geometry from the recommended one.

I guess when I add the microstrip itself to connect to the antenna feed point the
total imedance will radically change anyway but I'm not sure whether I should design it to have 50ohms impedance on port 2 or 3. Any ideas?

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