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- TL;DR Summary
- I would like to increase the frequency range for which the impedance of my system is 50 ohms in order to reduce power losses due to impedance mismatch.

Hello,

Some trouble came up today with designing a 50 ohm system for a wireless powering project. I'd like to increase the frequency range for which my system impedance is 50 ohms in order to reduce power losses due to mismatch. I've simulated two RLC circuits in OrCAD SPICE to demonstrate my issue.

In one circuit, I simply simulated the RLC circuit by itself and measured the impedance. I did so by applying a 1A constant current and measuring the voltage. We know that Z=V/I, so the voltage I measure is proportional to impedance. In this circuit, I see what I expect to see: a constant real component of resistance (green) and a reactance (red) that crosses zero at the resonant frequency.

In the second circuit, I used an L network to match the impedance at resonance to 50 ohms.

The issue here is that my system impedance is only 50 ohms at the very peak. A very small mismatch in frequency can cause a very large mismatch in system impedance which can result in very large power losses.

I tried googling some terms to see if a topology exists to remedy such a problem, but I didn't find one. I'm basically looking for a "bandpass" transfer function where I have a 50 ohm pass band. I'm not looking to be spoon-fed the answer if a common one exists, but rather, I need some advice on where to start. Any references (textbooks, papers, articles, etc...) would be greatly appreciated. If not, your practical experience would be greatly beneficial. Do most RF engineers pick an exact system frequency and just stick to that?

Some trouble came up today with designing a 50 ohm system for a wireless powering project. I'd like to increase the frequency range for which my system impedance is 50 ohms in order to reduce power losses due to mismatch. I've simulated two RLC circuits in OrCAD SPICE to demonstrate my issue.

In one circuit, I simply simulated the RLC circuit by itself and measured the impedance. I did so by applying a 1A constant current and measuring the voltage. We know that Z=V/I, so the voltage I measure is proportional to impedance. In this circuit, I see what I expect to see: a constant real component of resistance (green) and a reactance (red) that crosses zero at the resonant frequency.

The issue here is that my system impedance is only 50 ohms at the very peak. A very small mismatch in frequency can cause a very large mismatch in system impedance which can result in very large power losses.

I tried googling some terms to see if a topology exists to remedy such a problem, but I didn't find one. I'm basically looking for a "bandpass" transfer function where I have a 50 ohm pass band. I'm not looking to be spoon-fed the answer if a common one exists, but rather, I need some advice on where to start. Any references (textbooks, papers, articles, etc...) would be greatly appreciated. If not, your practical experience would be greatly beneficial. Do most RF engineers pick an exact system frequency and just stick to that?