Jinze,
My understanding is you used mini-circuits RF transformer that has winding ratio 1:1 to connect VNA to your designed LZ1AQ amplifier with balanced input and measured Z input of your antenna amplifier.?
Your plot shows a peak of measured impedance |Z| = 244.5 ohm at frequency 22 MHz.
I do not follow? your explanation "this is more in line with the impedance matching expactation of the loop". How come ?
Impedance matching for a broad band application can be discussed? when Ra + j Xa of? antenna impedance can transformed in R inp + j X inp in such way to achieve a maximum power transfer when?4 R a x R inp / | Z a + Z inp | ^ 2 = 1 - |Gamma|^2 for a specified bandwidth from f min to f max of design interest. Have you ascertained that ? That is the function of matching network between antenna and input of your amplifier.
Raphael
