Pi Networks: What they can do
I am reading about pi networks and I would like to understand what they can be used for (lets do a bit more functionality level discussion)
1. They can match antenna for narrowband (100MHz or so) transmissions
2. They can be also used as LPF (low pass filters) cutting out harmonics
3. anything else?
What is not clear is if 1,2 can be combined with an AND or with an OR (match antennas and filters harmonics, or do just one of the two jobs).
For now I am learning smith charts and VNA and today I am excited to report that I found which capacitor to add in series to kill some reactance :) Big times.!
Thanks
Alex
1. In fact the Pi matching network is narrowband if the input and output impedances are not far from each other.
If the inp/output impedances are very different, the Pi matching network have wider bandwidth than other networks, as L-type (due to loaded-Q seen by each component).
2. All the matching network types (L, Tee, Pi, etc) can be used as low-pass or high-pass filters in the same circuit.
3. Phase sifter is another place where Pi networks can be used:
A Pi matching network can be designed for different bandwidths. The maximal achievable bandwidth reduces with increased impedance ratio, respectively the minimal Q increases.
It is a lot to be combined. It is maybe a bit advertising myself but AnTune software is as far as I know the only software that is specialized to simplify this and other related tasks.
Finding best antenna matching both wide and narrow-band, even when both source and load are complex freq.depending impedances, suppress harmonics, auto select network topology for lowest transmission loss, using non ideal LC component data. Doing all these calculations fully automatic up to 10 times/sec by reading real time data from a VNA is very useful as it allows for live antenna adjustments for finding optimized antenna/network combination. Sometimes must antenna matching be optimized for two or more special cases such as free space and handheld. That is typical the case for cellphones.
Matching goal is sometimes not for lowest VSWR but for best TRP and TIS. All these functions and more are included in AnTune software.
For full use of these functions must VNA be able to communicate with a PC over GPIB, LAN or USB.