Novel balanced BPF design using half-mode substrate integrated waveguide with common-mode suppression

The contribution of this letter is to propose a novel balanced bandpass filter (BPF) design of the half-mode substrate integrated waveguide (HMSIW) using open-stubs for the common-mode (CM) suppression. The HMSIW is a half-mode waveguide alike structure, which is composed of a substrate sided with a thru-via array emulating the shorted side-wall of the half-mode waveguide. As compared with some other planar structures, such as microstrip line, coplanar waveguide, and slotline, the HMSIW possesses a relatively high quality factor and is immune of the waveguide's notorious bulkiness and high fabrication cost. The insertion losses of the proposed balanced BPF are extremely low in differential mode (DM) and the CM rejection levels are over 30 dB in the DM's passband. The thru-via array that existed in the HMSIW is eliminated in this balanced BPF design, greatly decreasing the fabrication complexity. Prototype of the proposed balanced BPF is fabricated and measured. Agreements between measured and simulated data are observed, validating the circuit performance.