Microstrip-Wider track width-Effect on RF Performance

[vibhatomar]

Hi,

What will be the effect on RF performance if i use wider track width than the actual calculated one?

For e.g. if at 2.45GHz, for 50 ohm impedance microstrip width is coming as 0.36mm for a particular PCB layer stack but i am using 0.5mm width for RF signals, what will be the impact on RF performance?

Cheers,

 

[BigBoss]

Characteristic impedance won't be 50 Ohm anymore and some reflections occur and in according with this, of cours losses..

 

[jiripolivka]

It looks to me that your substrate thickness makes the "live" line width not practical.
RF lines should preferably have 50 OHms for the lowest loss. If you have a situation like this, I would suggest replacing your PCB "microstrip" with a section of a good thin coaxial cable with 50-Ohm impedance.

In general, PCBs used as RF transmission lines are poor due to loss. One good choice is using the FR-4 Teflon substrate for your RF line, or, a coaxial cable. You will still need that cable to connect your device to an antenna.

 

[volker_muehlhaus]

what will be the impact on RF performance?

It all depends on the length of the line relative to the wavelength.

If the line is 1/20 wavelength or shorter (effective wavelength including substrate epsilon), then the impedance transformation due to the wrong Z0 can be neglected. If your line is longer than that, you will see a frequency dependent impedance transformation as calculated below.

For the effective wavelength, you can do an estimate where you calculate wavelength in air divided by SQRT(epsilon). This is not exact because some of the field is in air, but it's good enough for an estimate if the line length is critical or not.