I am designing a board that includes a WiFi module (TI CC3000) and chip antenna (Johanson 2500AT44M0400). My board is a 4 layer-board based on TI's CC3000EM reference design. This design includes a basic Pi filter matching network. I have selected similar components to what TI used, however, I realize that I will likely end up needing to do a bit of tuning to match the antenna perfectly to my board.
In the past few days, I have been doing lots of reading on the subject and have learned a ton about the required measurements and tuning methodologies. After lots of reading and lots more head scratching, I think that I am starting to understand the underlying concepts. Here is my current understanding of the antenna tuning process:
1. Measure the complex reflection coefficient S11.
2. Plot S11 on a Smith chart (and admittance chart).
3. Select parallel or series components that will move the plotted point to the center of the chart.
a. Series inductors move clockwise along circles of constant resistance
b. Series capacitors move counter-clockwise along circles of constant resistance
c. Parallel inductors move counter-clockwise along circles of constant conductance
d. Parallel capacitors move clockwise along circles of constant conductance
My big question at this point is how to accomplish number 1. I know that the normal way to accomplish this is to use a VNA, but I don't have access to one or the funds to buy one. Copper Mountain Technologies'
Planar R54 Vector Reflectometer that looks like it would do the job for around $3k. I have also seen mention of using a dual directional coupler to measure return loss, but does this just give you the magnitude? What is the minimum equipment required to perform this type of measurement?