IMPROVEMENT OF MICROSTRIP BAND PASS FILTER HARMONIC SPURIOUS SUPPRESSION PERFORMANCE USING BAND STOP FILTER FEED LINES

บทคัดย่อ

In this paper, a simple design technique to suppress the 2^nd harmonic frequencies spurious responses of microstrip band pass filter (BPF) is presented. The technique is accomplished by using the parallel-coupled lines band stop filter (BSF) operating at 2f₀ frequency as feed lines. The practicable feasibility of the technique is demonstrated by the 3^rd order microstrip coupled line bandpass filter at 1.8 GHz with the 3.6 GHz coupled line band stop filters feed lines on AD600 microwave substrate. The experimental results of the proposed 1.8 GHz bandpass filters were evidently shown the spurious suppression improvement more than 30 dB at 2f₀.