Entire functions of exponential type, almost periodic in Besicovitch's   sense on the real hyperplane
  Suppose that an almost periodic in Besicovitch's sense function $f(x)$ of several variables is the restriction to the real hyperplane of an entire function of exponential type $b$. Then its spectrum is contained in the ball of radius $b$ with the center in the origin. 
S. Yu. Favorov, O. I. Udododva