Design the Tunable Wideband Filter for DDS+PLL Hybrid Frequency Synthesizer

In this paper, the tunable wideband bandpass filter is designed, which is used in hybrid frequency synthesizer of PLL+DDS mixing in the outside of the feedback loop. The channels of tunable wideband bandpass filter is chosen by two ADGM1304 single-pole, four-throw (SP4T) MEMS switch. And they are integrated on a high-frequency board with a substrate of Ro4350B.The central frequency of bandpass filter is 2.32 GHz, 2.38 GHz, 2.44 GHz and 2.5 GHz respectively. A wideband filter with adjustable center frequency is designed and the bandwidth is up to 240 MHz. Finally, physical tests show the spurious components and unwanted spectral components, especially near-end spurs at the center frequency are removed basically by the tunable broadband bandpass filter.