We present the design of a tunable wavelength filter based on an active arrayed waveguide grating (AWG). We show a novel layout and simulated performance of a tandem filter configuration that covers 43 nm in C band with 0.2-nm (25-GHz) channel spacing at –35-dB crosstalk level. Design of the device is based on Fourier-Fresnel formalism with special emphasis on tuning mechanisms. The Gerchberg-Saxton phase retrieval method is used to estimate phase errors and generate phase patterns required for device tuning. A polarization insensitive filter is presented with its main parameters and simulation results. The technological considerations of achieving nanoseconds-scale tunability by exploiting the electro-optical effect in LiNbO3 crystals are discussed in detail. Such a filter may find various applications in packet-switched coarse and dense multiwavelength dynamic networks.