A Compact Dual-Band mm-Wave Bandstop Filter Using Multilayer Structures

In this paper, a compact dual-band millimeter-wave (mm-wave) bandstop filter is proposed based on multilayer structures. The circuit schematic is presented and analyzed, which can generate four transmission zeros to form two stopbands with controllable frequencies. The proposed filter can be used for 5 G mm-wave applications, where the passband can meet the 5 G mm-wave bands, such as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{n} 257 / \mathrm{n} 258$</tex> bands, while the stopbands can be set to reject the unwanted signals, such as the image frequency in the down-conversion receiver. The transition bands between the passbands and the stopbands show sharp roll-off characteristics. For verification, the proposed dual-band bandstop filter is realized in a multilayer structure, showing a compact size with good performance.