Compact Microstrip IF Lossy Filter With Ultra-Wide Stopband

A novel compact six-pole intermediate frequency lossy filter based on double-layer microstrip coupled microstrip resonators is proposed in this paper. A detailed theoretical analysis for the performance operation mechanism is illustrated. Significant advantages of the proposed structure over existing lossy filters include its low passband insertion loss variation, compact footprint, and ultra-wide stopband bandwidth. Excellent experimental results are provided to confirm these improvements, by using LCP bonded PCB multilayer technology. In general, the fabricated prototype filter operates at 0.97 GHz, with 0.19-dB insertion loss variation in the passband. In addition, it obtains a sharp selectivity with a pair of transmission zeros, as well as the 10th harmonic suppression with better than the 32-dB rejection level. Good agreement between the measured and simulated results can be observed finally.