This letter presents an approach to design a linear phase substrate integrated waveguide (SIW) bandpass filter with good selectivity. The topology of the proposed filter is implemented based on cross and bypass coupling schemes, which simultaneously introduce a linear phase response and good selectivity, respectively. According to the proposed topology, a multilayer SIW filter is presented to realize the two kinds of couplings and preserve a compact size. Then, the defected ground structure is adopted to further improve the out-of-band rejection. To demonstrate the proposed design method, one double-layered SIW bandpass filter is fabricated and measured. Measured results show that the proposed filter has a linear phase response and good out-of-band rejection, as well as a good agreement between simulated and measured results.
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