antennaimpedance-matching
I am fairly new to the RF world. It was certainly not my strongest subject. I am currently designing a board that uses the SIM868 module (GSM) and I need to design an antenna matching circuit. In the case above what size component should L1 be? 201, 402?
simulate this circuit – Schematic created using CircuitLab
There seems to be a remarkable lack of relevant on-web material. Maybe just hiding.
This looks highly apposite Design of New Multi Standard Patch Antenna GSM/PCS/UMTS/HIPERLAN for Mobile Cellular Phones with an interesting appearance
And tri-band !!!
GSM Dipole antenna - very informative
Designing a GSM dipole antenna
Commercial product.
LOOKS simple.
LOOKS good
LOOKs can be deceiving :-)
They say:
800/900/1800/1900/2100MHz
Omni Directional 1/2 Wave
Miniature 42 x 42 x 1mm
VSWR <3.0
RG178 Coax 50Ω Impedance
2-3dBi Gain (nominal)
Vertical Polarization
Admitted Radiation Power 1W
The free marvellous NEC RF software will probably do what you want.
Have a look here RF/Microwave Tools and here Tools and calculators - with RF writ large
If you have enough $ - Agilent ADS
Honestly, you're probably OK. The trace length is short enough that it's really not too significant, the important part is the balun and transceiver IC output impedance, which is probably only somewhat close to 100 Ohms differential. You may lose some range, but the fact that you're using a chip antenna is probably more significant.
Putting footprints in to play with the match might help, but it might also open up a big can of worms as well.
Best Answer
Depends on what "Q" your PI matching circuit needs. And the surrounding components that parasitically-couple to the inductor. Are larger inductors more accurate/stable?