High-Order Quasi-Elliptic-Type Single-Ended and Balanced Wideband Bandpass Filters Using Microstrip-to-Microstrip Vertical Transitions

• Published in: IEEE transactions on circuits and systems. II, Express briefs Vol. 70; no. 4; pp. 1425 - 1429
• Main Authors: Yang, Li, Gomez-Garcia, Roberto
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-04-2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Balanced filter; Band-pass filters; bandpass filter (BPF); Bandpass filters; Broadband; differential-mode filter; Equivalent circuits; high selectivity; high-order filter; Microstrip; microstrip filter; Microstrip filters; multilayer circuit; quasi-elliptic-type (QET) filter; Resonator filters; Slot lines; Transmission lines; transmission zero (TZ); Transversal filters; vertical transition; Wideband; wideband filter
• ISSN: 1549-7747; 1558-3791
• DOI: 10.1109/TCSII.2022.3223949

High-order single-ended and balanced wideband bandpass filters (BPFs) with quasi-elliptic-type (QET) responses are reported. Firstly, a fifth-order wideband BPF based on a two-layer microstrip-to-microstrip vertical transition with two shunt open-circuit-ended two-section microstrip stubs at the input and output ports, respectively, is designed. Compared to a typical third-order vertical transition, two more transmission poles (TPs) along with a pair of close-to-passband transmission zeros (TZs) are attained. Next, an application to design a ninth-order QET balanced wideband BPF using a vertical transition is carried out. Owing to the used slotline resonator, an intrinsic common-mode (CM) suppression capability is obtained for it. The RF operational and design principles of these BPF devices are detailed by means of their relevant transmission-line-(TL)-based equivalent circuits. For experimental-validation purposes, two microstrip prototypes corresponding to a 3-GHz fifth-order wideband BPF and a 2-GHz ninth-order balanced wideband BPF are developed and tested. The measured single-ended and balanced BPF circuits feature sharp-rejection QET responses with two close-to-passband TZs and stopband-power-attenuation levels above 27.3 dB and 43.66 dB, respectively. The measured CM suppression levels for the balanced BPF device are higher than 34.59 dB from DC to 5 GHz.