Millimetre-wave low-temperature co-fired ceramic bandpass filter with independently controllable dual passbands

摘要： This study presents a detailed investigation on the frequency properties of the stub-loaded stepped-impedance resonator (SIR). For the first time, the frequency controllability of the third and fifth harmonic resonant frequencies (f3 and f5) of the SIR under different ratios of impedance and electric length is subjected to a complete theoretical analysis. It can be found that there is a length ratio which makes f3 and the voltage-null point at f3 never be affected by the change of the impedance ratio. Furthermore, the stub loaded at this voltage-null point also has no effect on f3. These features are successfully applicable to realise independent frequency control for dual-band bandpass filters (BPFs). In this situation, a new coupling path through the loaded stub can be constructed only for f5, and the coupling coefficients for the two bands can be individually varied. Accordingly, both the operational frequencies and bandwidths of the two bands can be separately adjusted. For demonstration, an independently controllable dual-band BPF operating at 27.5/33?GHz is designed and fabricated for millimetre-wave wireless applications. Good accordance is achieved between the simulated and measured results.