Design of wide band-pass substrate integrated waveguide (SIW) filters based on stepped impedances

Abstract

A full-wave design technique of n-order Chebyshev stepped impedance band-pass filters in substrate integrated waveguide (SIW) is presented for the first time. The structure of the filter is based on including elliptic patterns etched on the SIW top surface to synthesize Chebyshev transfer functions. The band-pass response is obtained from the high-pass characteristic of the SIW line together with the behavior of the elliptic patterns, which implement the impedance inverters needed to control an upper cut-off frequency in the response of the filter. The synthesis technique is applied to the design of a sixth-order Chebyshev stepped impedance band-pass SIW filter. It is shown that the use of elliptic patterns instead of circular patterns can increase the spurious free range of the filter. In addition, when exponential microstrip-to-SIW transitions are integrated into the design process, a reduction in size and improvement in return loss are achieved, as compared to a base-line filter (sixth-order Chebyshev stepped impedance band-pass filter) designed with transitions separately. Electromagnetic (EM) simulation and measurements results have shown the effectiveness of the proposed design technique to carry out high-performance band-pass filters in SIW technology.