Good afternoon everyone,
I'm currently studying the impedance matching between a microstrip line that lies on both typical (orange) and ferrimagnetic (blue) substrates (see figure below).
I assume that the characteristic impedance Zo of the line is given by Zo = P/I², where P is the power flowing along the line, and I is the electrical current. In order to evaluate the power, I integrate the poynting vector over the different surfaces (green faces) that you can see above. The first section of the line (on the left) lies on a classical dielectric substrate; in this case, i find by integrating the Poynting vector a power of 0.488 W which is very close to the classical stimulated power of half a Watt. The current is then taken as the circulation of H around the line. As a result, i reach a 50 Ohms characteristic impedance, as expected for the line's dimensions. My problem appears when applying this method on the part of the line lying on the ferrimagnetic substrate. The integration of Poynting vector gives me either negative values, or very high values compared with the stimulated power (theta corresponds to the angle between the integration plan and the line, theta = 0 corresponding to the perpendicular configuration).
The negative values wouldn't surprise me if only the line would experience any reflexion, which is not the case according to my S parameters (S11 < -19 dB | S12 > -0.06 dB). In addition, the magnitude of the integral of Poynting vector is always bigger than half a Watt, that should be the maximum power flowing onto the line.
Would someone have any experience about ferrimagnetic material could help me with this ?
Thank you in advance !
Vincent Muzzupapa
