Narrowband filters that are utilized in the IF stages are almost the most effective components when the performance parameters such as the Intermodulation Spurs (IMS) and noise floor of the entire strip are considered. Thus, selectivity of the IF filters should be as high as possible. Required sharpness and ultimate rejection often dictate high Q-structures like cavity or waveguide structures, but these type of filters fail to comply with physical parameters such as space and weight that planar filters do. On the contrary, other problems arise in this type of filters. The most severe ones are dispersion and bandwidth enlargement. In this paper, a technique to control the bandwidth of the planar filter while keeping loss and the length same is told.