Microstrip LPF Boasts Ultrawide Stopband

摘要

Lowpass filters (LPFs) with wide stopbands are often required in high-frequency communications systems to suppress unwanted harmonic and spurious signals. To meet some of these requirements, a compact LPF based on triangular patch resonators and a butterfly patch resonator with two 120-deg. radial wing patches was developed to provide ultrawideband (UWB) signal rejection. In demonstrating the design, a microstrip filter with 3-dB cutoff frequency at 1.78 GHz was designed, fabricated, and characterized, and was found to achieve an UWB stopband of 158.2% for suppression of unwanted signals as high as the 12th harmonic signals. The fabricated filter measures just 14.5 × 18.0 mm~2, which corresponds to 0.133λ_g × 0.165λ_g, where λ_g represented the guided wavelength at 1.78 GHz.