The dilation property of modulation spaces and their inclusion relation with Besov spaces

We consider the dilation property of the modulation spaces Mp,q. Let Dλ :f (t) →f (λt) be the dilation operator, and we consider the behavior of the operator norm Dλ Mp,q→Mp,q with respect to λ. Our result determines the best order for it, and as an application, we establish the optimality of the inclusion relation between the modulation spaces and Besov spaces, which was proved by Toft [J. Toft, Continuity properties for modulation spaces, with applications to pseudo-differential calculus, I, J. Funct. Anal. 207 (2004) 399–429]. © 2007 Elsevier Inc. All rights reserved.