direction coupler

look up directional coupler

Done that. That is why I ask it here.

-- Levente

PCB eh. I'm guessing VHF. Take a 100mm length of veroboard three tracks wide. Centre conductor is the through line and the outer ones the sense lines. Stick a diode at one end and a 50 Ohm resistor at the other end of the sense lines. Measure the voltage produced between the diode and resistor. The diodes should be at opposite ends of the board. Also half scale is 3:1 swr.

Now you need to understand some fundamental electronics to design one !

Download RFSim99. It includes a tool to design directional couplers of various sorts including coupled-line type. Look under tools>design>coupler. Both microstrip and stripline are included, as well as three other sorts. Note: the coupling given for the coupled- line type is for a quarter-wave long coupler. A shorter coupler will have less coupling but maintains directionality.

You can also use ATLC to design coupled lines of a more arbitrary cross-section, though uniform cross-section along the length of the coupler is still assumed.

You should be able to find on the web some description for coupled- line couplers that have flatter coupling versus frequency; it's done by adding sections with looser coupling on either end of a more tightly coupled section. You should also be able to find on the web a description of how the coupling varies with frequency. I've found both of those in the past. Google (or similar) is your friend.

Cheers, Tom