Gumussoy, S.Özbay, Hitay2019-02-212019-02-2120182405-8963http://hdl.handle.net/11693/49882It is shown that strictly proper neutral time delay systems having at least one asymptotic pole chain converging to a vertical line Re(s) = σ > 0 cannot be stabilized by a proper controller. A special coprime factorization can be obtained for such systems with infinitely many unstable poles, provided they are bi-proper (i.e. proper, but not strictly proper). From this factorization, stabilizing feedback controllers are obtained. Necessarily, all stabilizing controllers for this type of plants are also bi-proper.EnglishCoprime factorizationFactorization methodsFeedback stabilizationTime delayUnstable systemsArticle10.1016/j.ifacol.2018.07.209