Progress In Electromagnetics Research Letters, Vol. 69, 23–28, 2017
Second-Order Mixed Coupling Filter with One Controllable
Transmission Zero Using Multilayer Substrate Integrated Waveguide
Tao Zhang, Hong-Wei Deng
*
, Fei Liu, and Tao Xu
Abstract—In this letter, a compact second-order mixed coupling bandpass filter (BPF) with one
controllable transmission zero (TZ) near the passband edge is presented using multilayer substrate
integrated waveguide (SIW). Two arranged circular SIW resonators can be vertically coupled via the
circular apertures etched on the middle metal layer while preserving a compact physical size compared
with the conventional horizontally coupled filter made of the single layer. The mixed electric and
magnetic coupling can be introduced by two etched circular apertures. And one controllable TZ can
be created in the lower stopband for the magnetic-dominant or in the upper stopband for the electric-
dominant. To demonstrate the proposed design method, a multilayer SIW BPF for WLAN application
has been designed and fabricated, and the measured results show good agreement with the simulated
ones.
1. INTRODUCTION
SIW filters, which are generally synthesized in a planar substrate with arrays of metallic vias and
widely used in various communication systems, can provide a low-profile, easy integration and low-cost
solution while maintaining high-quality factor, high power capability performance as conventional metal
waveguide filters [1, 2]. SIW filters with multiple TZs are required to meet the increasing demands of
modern communication systems with regard to compact size and high selectivity [3, 4]. Therefore, they
have been extensively investigated and various design approaches using the printed circuit board (PCB)
or low-temperature co-fired ceramic (LTCC) processes have been proposed. In [5, 6], the implementation
of the mixed electric and magnetic coupling SIW filters with TZs for high selectivity have been reported,
in which an inductive window between two SIW resonators introduces the magnetic coupling, and an
embedded short-ended strip is employed to create the electric coupling, however, this filter is relatively
large not only because of its planar arranging structure, but also due to suffering from the structure
complexity and lack of flexibility, and there will be radiation loss if it operated in millimeter-wave bands.
The application of SIW technology makes the realization of filters with the multilayer structure and
compact size possible in [7–12]. The coupling between the vertically stacked SIW resonators can be
introduced by etching the apertures with different sizes, positions and number on the middle metal
layer. And the vertically oriented coupling also plays a role in achieving the cross coupling. The mixed
coupling is realized by embedding apertures on the inductive window between the horizontally oriented
cascade SIW resonators of the single layer. Hence, the high selectivity for the multilayer SIW filters are
achieved in [11, 12]. However, the filter which directly introduces mixed coupling by etching appropriate
aperture structures between two vertically stacked SIW resonators has rarely been reported.
In this letter, a compact SIW filter is developed with two circular SIW resonators which are fed by
50 Ω microstrip line and two slotlines, and allocated integration in the vertical direction, as illustrated
Received 3 May 2017, Accepted 14 June 2017, Scheduled 30 June 2017
* Corresponding author: Hong-Wei Deng (hwdeng@nuaa.edu.cn).
The authors are with the College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics,
Nanjing 210016, China.