Narrowband and Wideband Bandpass Filters Based on Empty Substrate Integrated Waveguide Loaded With Dielectric Elements

Although several bandpass filters have been designed in the recently proposed empty substrate integrated waveguide (ESIW) technology to improve the quality factor and reduce losses with respect to those in SIW and planar technologies, all structures exhibit narrowband properties and none uses the design concept applied in this paper. The idea has been to insert a dielectric element in an ESIW section (DE-ESIW), which can work as a dielectric resonator or impedance inverter depending on the propagation nature of the fundamental mode. Thus, two novel Chebyshev bandpass filters for narrow and wide bandwidths based on this design concept have been designed in this paper in ESIW technology. The narrow bandpass filter has been realized by inserting four dielectric resonators in an evanescent ESIW section and using a coupling matrix synthesis method, whereas the wideband bandpass filter has been implemented by including six dielectric line sections in an ESIW line propagating the fundamental mode and applying a stepped impedance synthesis approach. A novel wideband microstrip to ESIW transition using cubic Bézier curves has also been designed for the successful integration of both narrow and wideband filters with other microstrip components. EM simulation and measurement frequency responses on manufactured prototypes have shown the versatility of the dielectric elements to efficiently implement narrowband and wideband ESIW bandpass filters, using the proposed design techniques based on coupling matrix and stepped impedances, respectively.