Thanks for your links. In the meantime I've made a passive probe. It has approximately flat response from DC to 3 GHz. Is someone is interested I can post some pictures with measurements...
I bought some nice old Tektronix P6056 and P6057 probes on eBay. Some specs from the instruction manual:
The P6056 is a 450 ohm series resistor, so it is a x10 probe. 3.5 GHz bandwidth. Input capacitance about 1 pF. 500 ohms DC to 300 MHz decreasing to 250 ohms at 1 GHz.
The P6057 is a 4950 ohm series resistor, so it is a x100 probe. 1.4 GHz bandwidth. Input capacitance about 1 pF. 5000 ohms DC to 350 MHz decreasing to 1500 ohms at 1 GHz.
Thanks for the S21 datas and realization pictures.
Just one question. Have the S21 datas been measured at an 50 ohm through-line enviroment ?
Thanks
g579
Yes, one port of network analyzer was connected to the 50 ohm microstrip transmission line terminated with the 50 ohm load. The second port was connected to the probe and i was holding its tip on the 50 ohm load at the end of the microstrip transmission line...
Very nice idea.
I would like to understand what is the input impedance of the probe to understand if the inserted probe affects the transmission line.
A test could be measuring the S21 of the microstrip with and without the probe inserted.
Thanks.
Mazz