The assembly process of the direct insertion package （SC04-06） filter is complex, and the trimming length of the pins and assembly vias affects the port impedance. This results in poor product consistency and hinders mass production of the frequency-selecting module. The surface mount package （SMD0705B） filter has a small size and a simple assembly process, but it suffers from poor stop-band suppression. This paper uses three-dimensional electromagnetic software to simulate the core surface acoustic wave （SAW） filter of the frequency-selective component. Through comparison of simulation results and physical measurements, the influence of filter packaging on stop-band suppression is verified. A method is proposed to add a shielding cover to the SMD0705B packaged filter, achieving high stop-band suppression in the P-band narrowband frequency-selecting module. The results indicate that the frequency-selecting module achieves stop-band suppression greater than 40 dBc, in-band ripple less than 1 dB, and amplitude consistency within 1 dB, making it suitable for mass production.