A novel, dual-band frequency-selective surface (FSS) is presented. The designed and fabricated FSS structure has closely spaced operation bands and high selective frequency response at each operation band. Two-dimensional compact U-shaped slot resonators are used in each FSS unit cell to obtain this ability. Also, each slot resonator is composed of straight slot section at the centre connected to two U-shaped arms at each end. The dimensions of the slot resonators are optimised using via full-wave electromagnetic simulations using CST Microwave Solver. The proposed FSS structure is independent of incident polarisation and angle because of 90 degrees rotation of the unit cell. The validity of the proposed FSS is confirmed by both simulation and measurement results. In the experimental verification, a waveguide measurement setup is chosen. Both measurement and simulation results show that the FSS structure operates at the designed frequencies of 8.80 and 9.54 GHz, which are very close to each other.