In this letter, a novel high selectivity microstrip filter with source-loaded coupling is proposed using the dual-mode resonator. The resonator can generate one odd mode and one even mode in the desired band. The folded stepped-impedance open stub at the central plane can control the even mode resonant frequencies, whereas the odd mode ones are fixed. A transmission zero is created near the lower cut-off frequency due to the main path signal counteraction. Two additional transmission zeros attributed to source-loaded coupling are generated near the upper cut-off frequency and in the upper-stopband. A dual-mode filter prototype is simulated, fabricated and measured. The EM simulated and measured results are presented and excellent agreement is obtained.
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