Complementary Compact Microstrip Resonant Cell and Its Applications to Microwave Single- and Dual-Band Bandpass Filters

This paper presents the complementary compact microstrip resonant cell (CCMRC), which behaves as a bandpass filter with good selectivity. Investigations reveal that CCMRC consists of λ/2 and λ/4 resonators. By using the traditional coupled resonator theory, the analysis approach and design guideline are obtained for CCMRC. CCMRC features compact size and transmission zeros (TZs) at the lower and upper edges of the passband. It is shown that the TZs are produced by the cross-couplings between non-adjacent resonators. By adjusting the length-width ratio of the cell, the locations of the TZs can be adjusted for different selectivity of the filter. The size of CCMRC can be further reduced by removing lower or upper half of the cell, resulting in a half-CCMRC. The performance of half-CCMRC is as good as that of CCMRC. Moreover, two different half-CCMRCs are combined into an asymmetric CCMRC (ACCMRC), which has dual-band response. The center frequency and bandwidth of each passband can be separately adjusted to desired values. To verify the design methodology, different types of filters are implemented on the standard printed circuit board process. The measured results agree well with the simulated results.