The introduction of new modulations on the global navigation satellite systems brings potential improvements for ground positioning. Clever receiver designs taking advantage of the characteristics of the new signals will be able to achieve better accuracy, higher sensitivity, improved multipath mitigation and tracking robustness. In this context, this paper focuses on the Galileo E5a signal and study different acquisition architectures that can be applied on this signal. Their performances are discussed in terms of detection sensitivity and by a theoretical characterization of the false alarm and detection probabilities. The theoretical results are validated by measurements using a Spirent constellation simulator, a Fraunhofer triple band frontend and a non real time software receiver.