A local converse Theorem for U(2,2)

Let $F$ be a $p$-adic field and $E\mathrm{/}F$ be a quadratic extension. In this paper, we prove the local converse theorem for generic representations of ${\text{U}}_{E\mathrm{/}F}(2,2)$ if $E\mathrm{/}F$ is unramified or the residue characteristic of $F$ is odd. Our method is purely local and analytic, and the same method also gives the local converse theorem for ${\text{Sp}}_4(F)$ and $\widetilde {$\text{Sp}$}_4(F)$iftheresiduecharacteristicof$F$ is odd.