Self-packaged wideband balanced filtering quadrature coupler with high selectivity based on SISL

A self-packaged balanced filtering quadrature coupler (BFQC) based on substrate integrated suspended line (SISL) is designed in this article, achieving wide differential-mode (DM) bandwidth and high selectivity. The wideband filtering function benefits from the application of an unequal-width three-coupled line structure. Moreover, an asymmetric configuration is introduced into the unequal-width three-coupled-line structure to generate a DM transmission zero (TZ) on the right side of the passband. To further enhance selectivity, an open-circuited stepped impedance resonator is incorporated, generating a pair of TZs on both sides of the passband. Quadrature coupling is realized by using a branch-line hybrid network. A wideband common-mode (CM) suppression performance is achieved by the balanced feed structure. Moreover, the SISL structure allows the BFQC to be embedded in a metallic shielding enclosure, enhancing the anti-interference capability. To demonstrate the theoretical design, the proposed BFQC was implemented and its performance was measured. A good match is achieved between the measurement and simulation. The DM 3-dB fractional bandwidth of the BFQC is 52.2%, the rectangle coefficient achieves 1.22, isolation is better than 14 dB, and CM suppression is better than 20 dB.