Abstract: In this article, a compact fourth-order frequency tunable Bandpass Filter (BPF) with four Transmission Zeros (TZs) based on Varactor-Loaded Step-Impedance Resonators (VL-SIRs) is presented. With the utilization of VL-SIRs, the Tuning Range (TR) of the proposed fourth-order BPF is improved. Besides, by introducing cross coupling between VL-SIRs, a pair of TZs close to the passband are produced and the selectivity of the filter is enhanced significantly. Another pair of TZs are generated to improve the out-of-band rejection by using source-load coupling. Moreover, the Frequency-Dependent Coupling (FDC) structures based on VL-SIRs are employed to realize constant Absolute Bandwidth (ABW). The simulated and measured results are presented and show good agreement. The measured results exhibit a tuning range from 0.78 GHz to 1.15 GHz with a 3 dB constant ABW of about 55±3 MHz, the return loss of the filter is greater than 10 dB and the insertion loss is about 2.8 dB to 3.3 dB.