S11 to Return Loss Calculator

Use this tool to calculate the Return Loss (RL) from S11.

Return Loss is a measure of mismatch at a transition in an RF circuit.

Enter

  • S11 – either linear or dB value can be used

	

			

		

						

				

				

                

			

			
						

		

		






Background





S11 is the input reflection coefficient [1] with a value between 0 and 1. (Entering values outside this range will result in meaningless output). Referring to the picture of a two port network shown below, S11 = b1/a1 (when a2=0)










Formula





If a1, b1 and S11 are all linear numbers,





Return Loss = 10*Log10(a1/b1)





or





RL = -10*Log10(S11)





On the other hand, if S11 is expressed in dB





RL = -S11dB





Return Loss is always a positive number as a1 > b1





Example Calculations





If the reflected signal b1 = 0, then all of the input signal a1 is transmitted forward and the return loss RL = ∞.





If all of the input signal is reflected back, then b1=a1 and none of it is transmitted forward. This is the poorest match possible and RL = 0.





If S11 = 0.1, the Return Loss is calculated to be 20 dB.





Related Calculators









References





[1] Scattering Parameters on Wikipedia