Designing a miniaturized T-shaped non-orthogonal feed input/output dual-mode bandpass filter

Dual-mode filters with differently structured resonator were designed on Al₂O₃ substrate for pattern minimization and better properties. Al₂O₃ substrate with a permittivity of 9.8 is easily integrated with RF circuits. For the proposed filter, two open stubs, one perturbation patch, and one meandering loop ring were investigated to achieve the same purpose with smaller size. To improve the coupling effect, two additional stubs were used to form the T-shaped microstrip coupling lines. The proposed filter showed a size reduction compared with the published filters, and it also provided deep transmission zeros on both sides of the passband.