11. Electrical Interface
11.1 Transmission Line
All transmission lines should be designed to have a characteristic impedance of 50Ω.
• The length of the transmission lines should be kept to a minimum.
• Any other parts of the RF system like transceivers, power amplifiers, etc, should also
be designed to have an impedance of 50 Ω.
Once the material for the PCB has been chosen (PCB thickness and dielectric constant), a
coplanar transmission line can easily be designed using any of the commercial software
packages for transmission line design. For the chosen PCB thickness, copper thickness
and substrate dielectric constant, the program will calculate the appropriate transmission
line width and gaps on either side of the track, so the characteristic impedance of the co-
planar transmission is 50 Ω.
11.2 Matching Circuit
The antenna requires a matching circuit that must be optimized for each product. The
matching circuit will require up to six components, the following circuit should be designed
into the host PCB. Not all components may be required but should be included as a
precaution. The matching network must be placed close to the antenna feed to ensure it
is more effective in tuning the antenna.