Quasi-Elliptic Bandpass Filter With Controllable Multiple Transmission Zeros Using Coupled Lines

This paper presents RF design methodology for quasi-elliptic bandpass filter (BPF) with multiple transmission zeros (TZs). The proposed filter consists of a coupled line BPF section and TZ sections. Both sections comprised of coupled lines with short-circuit stubs. By generating multiple TZs at lower and upper sides of the passband, a quasi-elliptic BPF response can be achieved without affecting the passband response. For experimental proof of concept, a prototype of microstrip line quasi-elliptic BPF was designed and manufactured at center frequency of 3.5 GHz. The measured results demonstrate good agreement with EM simulations and theoretically predicted outcomes.