RF Matching Networks Project: Week 1 (6/2/2015): L Networks and Future Plans

This week is the first week of our project. Our aim is to build and test several designs for radio frequency impedance matching circuits, with the ultimate goal of designing a network to supply high power RF energy to a gas discharge for use in plasma experiments. Here's our plan for the next five weeks:

Part 1: Testing simple matching networks

In this part of the project, we'll build and test some simple matching networks using three common topologies, with the aim of finding out which topology will work best for our final design. To make this a fair test, all these matching networks will have the same source and load - the 50 ohm output from the signal generator as the source, and a 100 ohm resistor as the load. They'll be designed around a frequency of 1 MHz, but aiming for as wide a bandwidth as possible, so they should still work reasonably well on other, nearby frequencies.

Hopefully we can complete this section in two weeks:

In week 1, we plan to design and test both high-pass and low-pass L networks - the simplest matching network design.
During week 2, our aim is to design and test both high-pass and low-pass Pi networks, and band-pass T networks and LCC networks.

Part 2: Designing a network for gas discharge experiments

By this point, we'll hopefully have some idea of what type of matching network will work best for our needs. Then we've just got to design a new network that will work with a gas discharge as the load. Of course we won't be using an actual gas discharge in the lab, instead we'll be testing with a model load - a circuit made from capacitors, resistors and inductors which looks like a gas discharge to an electrical signal, but without all the high voltages and toxic ozone.

First, we'll design a low power version of our matching network during week 3, then test it and make sure it works okay.
Week 4 will be spent doing some research and coming up with a theoretical design for a high power network. This should work the same as the low power version, so we just need to find some parts that won't explode or catch fire if you try to send hundreds of watts through them!
Finally, in week 5 we'll make sure everything is documented properly and get our presentations ready.

So on with week 1...

Week 1 started off with a bit of a problem - we couldn't find our components! Fortunately, it didn't take us long to realise what had happened - somehow they'd ended up in the fourth floor labs instead of on the third floor. That could have been a lot worse...

With that out the way, we got to work on designing some L networks. Our internet research had revealed some helpful formulas so choosing component values was easy. We also made a spreadsheet to calculate component values. When we found both results matched, we knew we were on the right track.

In the morning, we designed a high-pass L network. There was just one problem - the ideal component values our formulas told us we needed didn't quite match up with the real component values that we could buy. This meant we had to make a compromise by choosing the next nearest values. To investigate the effects of this compromise, we decided to build three high-pass L networks - one with the closest possible component values, on with the next highest values, and one with the next lowest values.