Tishchenko, A.A. Sergeeva, D.Yu. JACoW Geneva, Switzerland 978-3-95450-177-9 10.18429/JACoW-IBIC2016-TUPG62 English 495-498 TUPG62 radiation target diagnostics electron plasma Contribution to a conference proceedings 2017 2017-02 http://dx.doi.org/10.18429/JACoW-IBIC2016-TUPG62 http://jacow.org/ibic2016/papers/tupg62.pdf We present the general theory of X-ray Smith-Purcell radiation from ultrarelativistic beams proceeding from our earlier results. The theory covers also the case of oblique incidence of the beam to the target, which leads to the conical effect in spatial distribution of Smith-Purcell radiation and allows one to count the divergence of the beam; also, the analytical description of the incoherent form-factor of the beam is given.