This paper presents a reconfigurable bandpass filter (BPF) with constant absolute bandwidth (ABW). The structure is composed of a pair of novel half wavelength (λ/2) resonators with two center-tapped var actors. Frequency tuning is made possible by modifying the electrical length of the resonators with four varactors. Following the traditional synthesis approach, the internal coupling is analyzed and designed properly to meet the requirement of constant ABW. At last, the proposed filter exhibits a 49% fractional tuning range from 500 to 825 MHz, and a near constant 3-dB bandwidth of 56 ± 5 MHz. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1401–1404, 2016