Structured frames such as wavelet and Gabor frames in L 2 (R) have been extensively studied. But L 2 (R +) cannot admit wavelet and Gabor systems due to R + being not a group under addition. In practice, L 2 (R +) models the causal signal space. The function-valued inner product-based F a-frame for L 2 (R +) was first introduced by Hasankhani Fard and Dehghan, where an F a-frame was called a function-valued frame. In this paper, we introduce the notions of F a-equivalence and unitary F a-equivalence between F a-frames, and present a characterization of the F a-equivalence and unitary F a-equivalence. This characterization looks like that of equivalence and unitary equivalence between frames, but the proof is nontrivial due to the particularity of F a-frames.