Abstract The main purpose of this paper is introducing a new method based on the transmission line approach for designing FSS-backed reflecarray antennas. For this reason a dual band reflectarray antenna is designed. This antenna contains a conventional single layer RA and a FSS backed double layer RA with 54% and 50% efficiency operating at X band and K band, respectively. A double layer FSS is used between RAs to isolate them. K band cell element is designed and analyzed using transmission line method and consideration of equivalent circuit for elements of each layer. Then the results obtained using this technique is compared to those found by CST and ADS. The comparison shows a good agreement. Jerusalem cross dipole with variable size is employed as radiation element in both bands. The most important properties of our suggested array are low cross polarization and high efficiency.