# Does bidirectional impedance matching matter?

For my own learning, I derived the following relationships for basic two-element impedance-matching networks. Apologies that I cannot create diagrams; they are not supported by touch devices.

If $R_S < R_L$: put Ra in parallel with Rs; then Rb in series with Rl.

$$R_A = \frac {R_S} {\sqrt {1-R_S/R_L}} \\ R_B = R_L {\sqrt {1-R_S/R_L}}$$

In the opposite case, if $R_S > R_L$, make Ra in series with Rs, and Rb in parallel with Rl, and in the equations exchange Rs with Rl and Ra with Rb.

In both cases, Rs will see an impedance of Rs looking forward, and Rl will see an impedance of Rl looking backwards.

But is the backwards criterion necessary if power is only ever transferred from source to load? Would this criterion only need to be enforced on a bidirectional line?

• I'm not sure what you mean by "backwards criterion." Could you please clarify that? Commented May 18, 2018 at 16:46
• As in, how important is it that the load see a resistance equal to its own resistance? Commented May 18, 2018 at 17:09