The wide application of a Majsner–Kronig–Penney (MKP) model is explained by analogy between distribution of waves in periodic structures, phenomenon of parametrical instability of oscillatory systems, electron properties in a crystal potential field, by a likeness of the differential equations and possibility to present solutions by elementary functions [1–5]. Characteristic features of the zonal theory, such as prohibited and permitted power bands, superficial condition have clear analogies for electromagnetic and sound waves in stratified–periodic medium and for parametric instabilities of a oscillatory system [5, 6].