Vertically Stacked Circular SIW Filter with Controllable Transmission Zeros and Higher-Order Mode Suppression

Abstract

A novel high-performance 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> -order bandpass filter is developed by stacking four circular substrate-integrated waveguide (SIW) cavities vertically. The fundamental TM010 resonance mode of each SIW cavity is utilized to form the filtering response and they are vertically coupled by etching both electric and magnetic coupling apertures on the copper layers in-between. Higher-order passbands produced by two orthogonal TM110 resonance modes are suppressed by weakening the related coupling strength. Controllable transmission zeros are generated to enhance the selectivity by introducing cross couplings between the nonadjacent resonators. The SIW cavity structure of the four vertically stacked layers is first investigated and verified. The coupling matrix based, simulated and experimental results are all provided, showing good agreement. This filter demonstrates advantages in terms of compact size, high selectivity and wide stopband.