Effect of mitering/ reflections by making microstrip smaller

Hi,

I'm currently designing a 868 MHz-circuit and my 50 ohms microstrip line is too bold to directly connect it to the input pin of an IC. I only have a 0.8mm FR4 board and unfortunately can't use another one.

Can I do something like I've drawn in the attached graphic or do I get too much reflections by doing that?
The width of the microstrip line is about 1.5mm, the width of the IC pin about 0.5mm. I've checked several books (Pozar, etc.) but couldn't find anything of help there.


Thanks alot in advance!

arefeidi

Just figured out I can simulate this with Ansoft Designer SV - if I keep the length of the tapered line short (about 0.5mm) I still have a S11 of -50dB. So I guess it is possible to solve my problem with a tapered microstrip line.

If I'm wrong please correct me :)

Well, my comment is that it can not possibly be 50 dB return loss, so you are simulating it wrong.

The reality is that you have to live with necking down a line to connect to the chips, and at 800 MHz it really is not a problem. You can taper, or step, or whatever.

Thanks!

Well, I've simulated a microstrip line of about 20mm (as it will be in my layout) followed by a tapered line of 0.5mm (width 1.5mm -> 0.5mm).

S11 is about -50dB in that case - though, making the tapered line shorter rapidly decreases S11.

Usually the two pins to both side of
the input pin are ground. this is make
this way so it can resemble a CPW for
design. If both transmission lines are
match should not be a problem.

Thanks, yes - indeed the neighbouring pins are GND. I'll put as much of ground area near the tapered line then.