Most existing studies about passive radar systems are based on the already known illuminator of opportunity (10)states.However,in practice,the receiver generally has little knowledge about the 10 states.Little research has studied this problem.This paper analyzes the observability and estimability for passive radar systems with unknown 10 states under three typical scenarios.Besides,the directions of high and low estim-ability with respect to various states are given.Moreover,two types of observations are taken into account.The effects of dif-ferent observations on both observability and estimability are well analyzed.For the observability test,linear and nonlinear methods are considered,which proves that both tests are ap-plicable to the system.Numerical simulations confirm the cor-rectness of the theoretical analysis.