- W2AEW Tutorial about directional couplers (Very very good)
- QEX Article about a SWR meter using AD8307 logamps
- Microstrip and Stripline Design Analog Devices Tutorial
- Directional Couplers / SWR detectors for 145MHz - 435MHz
- Multi-Teknik Impedance calculator
- How to measure transmission line impedance
- Introduction to transmission lines
- Smith chart tutorial
- Determine the dielectric constant
The plan is to make a test setup, somewhat like what W2AEW did, but with an embedded microstrip design like in the QEX article. The idea is then to measure properties with my N2PK VNA. Or at least, try to.
So, the big problem, how wide should the traces be. According to the calculator from Multi-Teknik, referencenced in the QEX calculator, I get a width that varies a bit around 2.1mm (trace thickness = 0.035mm, h=1.6mm, total height = 3.2mm, Er=4.2...4.8).
After constructing the PCB, measurements indicate it works very well up to 60 MHz (the very limit of my measurement capabilities with the N2PK VNA). Coupling factor is 30dB (or should I say -30dB? idk), Directivity is another 30dB. Then, measuring at the radio club, I noticed that the directivity diminished with frequency, leaving only 12dB at 500MHz.
Next step is measuring the impedance of the embedded microstrip lines as described here. I know who to call for this.