alftel
Member level 1
I have RF design (three section Wilkinson splitter) that performs overall ok, but recently I acquired a small and very performant impedance and SWR measurement gadget that I am using not to test my antennas. I decided to try my splitter with this gadget, and to my surprise (it is 1:4 splitter design as shown at the picture below) Port 0 exhibits somewhat higher then 2:0 SWR and impedance curve somewhat jumpy (a big sine looking curve) in 2.4 - 2.5 GHz range (Test 1), while readings taken from P1, P2, P3, P4 are perfectly fine (test X).
- Test 1 - impedance/SWR test gadget connected to P0 with P1,P2,P3,P4 terminated with 50 ohm
- Test X - impedance/SWR test gadget connected to P1 or P2, or P3, or P4 with the rest of ports (including P0) terminated with 50 ohm
While being at Test 1 I tried "engineer finger" test and looks like placing human finger (dry) on top of isolation resistor R200A (middle section of first split from P0) brings readings to values similar to test X. I assumed that my finger presents capacitance in 0.1 pF - 0.7 pF range, and I saw people utilizing caps in parallel with isolation resistors in Wilkinson splitter designs in order to improve bandwidth, but soldering capacitor in parallel with this R200A didn't change a thing (tried values from 0.5pF to 100pF), and this R200A is identified as THE place that affects the whole P0 picture and does not affect any other ports.
Any advice/suggestion in terms how can I "replicate" this human finger test? I know that hands-on RF engineers aged >50 will understand what I am asking.
- Test 1 - impedance/SWR test gadget connected to P0 with P1,P2,P3,P4 terminated with 50 ohm
- Test X - impedance/SWR test gadget connected to P1 or P2, or P3, or P4 with the rest of ports (including P0) terminated with 50 ohm
While being at Test 1 I tried "engineer finger" test and looks like placing human finger (dry) on top of isolation resistor R200A (middle section of first split from P0) brings readings to values similar to test X. I assumed that my finger presents capacitance in 0.1 pF - 0.7 pF range, and I saw people utilizing caps in parallel with isolation resistors in Wilkinson splitter designs in order to improve bandwidth, but soldering capacitor in parallel with this R200A didn't change a thing (tried values from 0.5pF to 100pF), and this R200A is identified as THE place that affects the whole P0 picture and does not affect any other ports.
Any advice/suggestion in terms how can I "replicate" this human finger test? I know that hands-on RF engineers aged >50 will understand what I am asking.