1. Introduction The optoelectronic oscillator (OEO) has received intense investigation for its outstanding phase noise performance and capability of generating high-frequency pure microwave signals [1]. It can find numerous applications in wireless communications, radar systems, signal processing, sensors, etc. For an OEO loop, a long optical fiber is usually employed to improve the quality of the output microwave signal [2], but it inevitably introduces a dense mode-spacing ranging from kilohertz to megahertz. To define the desired oscillating frequency and guarantee the spectrum purity, a high-Q electronic band-pass filter (EBPF) is required, but for high frequencies, it is not easy to find an EBPF with sufficiently narrow bandwidth and wide frequency tuning range.