The input impedance of the resonant box was measured when an RF combiner was attached to the box.
Indeed the combiner makes the impedance more 50 Ohm and reduces the reflection.
**** measurement conditions ****
* The output of box, where the EOM will be connected, was open so that the box tries resonating with a parasitic capacitor instead of the real EOM.
* ZFSC-3-13, a 3-way combiner from mini circuit, was used.
* The S-port of the combiner was directly attached to the box with a short connector (~ 30 mm).
* Port 1 and 2 are terminated by 50 Ohm.
* The input impedance was measured on port 3 with AG4395A net work analyzer.
* Reflection coefficient 'Gamma' were calculated from the measured impedance 'Z' by using an equation Gamma = (50-Z)/(50+Z).
The resonances are found at 11, 29 and 73 MHz (55 MHz resonance was shifted to 73 MHz because of no EOM).
Note that the resonances are at frequencies where the notches appear in the reflection coefficient plot.
Don't be confused by a peak at 70 MHz in the impedance. This is an extra resonance due to a leakage inductance from the transformer in the circuit.
An RF combiner should be included in the triple resonant box because it eases impedance mismatching and hence lowers undesired RF reflections.