Recent advances in additive manufacturing of viscoelastic materials have paved the way towards the design of increasingly complex structures. In particular, emerging biomedical applications in acoustics involve structures with periodic micro-architectures, which require a precise knowledge of both longitudinal and transverse bulk properties of the constituent materials. However, the identification of the transverse properties of highly soft and attenuating materials remains particularly challenging. Thereby, the present work provides a methodological framework to identify the frequency-dependent ultrasound characteristics (i.e., phase velocity and attenuation) of viscoelastic materials. The proposed approach relies on an inverse procedure based on angular measurements achieved in double through-transmission, referred as θ-scan. Towards this goal, a forward modeling of the double transmitted waves through a homogeneous solid is proposed for any incidence angle based on the global matrix formalism. The experimental validation is conducted by performing ultrasound measurements on two types of photopolymers commonly employed for additive manufacturing purposes: a soft elastomer (Elastico™Black) and a glassy polymer (VeroUltra™White). As a result, the inferred dispersive ultrasound characteristics are of interest for the computational calibration and validation of models involving complex multi-material structures in the MHz regime.