This paper is concerned with the design of robust filters that ensure minim
um filtering error variance bounds for discrete-time systems with parametri
c uncertainty residing in a polytope. Two efficient methods for robust Kalm
an filter design are introduced. The first utilizes a recently introduced r
elaxation of the quadratic stability requirement of the stationary filter d
esign. The second applies the new method of recursively solving a semidefin
ite program (SDP) subject to linear matrix inequalities (LMIs) constraints
to obtain a robust finite horizon time-varying filter. The proposed design
techniques are compared with other existing methods. It is shown, via two e
xamples, that the results obtained by the new methods outperform all of the
other designs.