Features of the coupling coefficients of planar stepped-impedance resonators at higher resonance frequencies and application of such resonators for suppression of spurious passbands

Features of the electromagnetic coupling coefficients between stepped-impedance resonators made of the sections of symmetric strip and microstrip transmission lines at higher resonance frequencies are investigated. It is found that, in stripline resonators, these coefficients are equal to zero at some coordinates of the jump of the characteristic impedance. A new method of expansion of the stopband of bandpass filters, which is based on suppression of the first spurious bandpass and frequency diversity of the main band and the second spurious bandpass is proposed. A Chebyshev bandpass filter with a center frequency of 2.45 Hz and a spurious band at 6.06 f ₀ is manufactured and tested to demonstrate the proposed method.