Modeling of High Roll-off SIW Coax Filter with Novel Coupling Structures
and Stopband Transmission Reduction Methods
Abstract
Proposed dual-mode substrate integrated waveguide (SIW) short-circuited
coax filter demonstrates a passband that has transmission zeros on both
upper and lower stopbands; in addition, such a filter is also inherent
with good out-of-band rejection up to three times of the center
frequency (fc). There are four signal paths from input port to output
port. The signal routings are done by conductor-backed coplanar
waveguide (CBCPW) and the slotlines on the top metal. In addition to
signal routings, frequency control capacitors (CFreq), and electric
coupling capacitors (CE) are on the bottom metal. The center frequency
of the passband can be determined by CFreq, and the transmission zero on
the lower-end can be tuned by CE respectively. The phase delay of the
signal routings are investigated individually as a way to explain the
generation of the transmission zero below the passband. Furthermore,
capacitors’ touchstone files from the vendor are implemented in the
schematic such that simulation results including all the parasitic
components can be emulated to real-world measurements. In the best
scenario, presented filter shows a prescribed passband centered at 4.84
GHz, and with insertion loss (IL) of 2.11 dB as well as 3-dB bandwidth
of 0.46 GHz.