An　ultra-wideband　microwave　photonic　frequency　downconverter　is　proposed　based　on　carrier-suppressed　singlesideband　(CS-SSB)　modulation.　A　radio　frequency　(RF)　signal　and　a　local　oscillator　(LO)　signal　are　combined　to　drive　a　dual-parallel　Mach-Zehnder　modulator　(DPMZM)　through　the　electrical　90.　hybrid　coupler.　To　break　through　the　bandwidth　limit,　an　optical　bandpass　filter　(OBPF)　is　applied　simultaneously.　Then　a　photodetector　(PD)　after　OBPF　is　used　to　obtain　intermediate　frequency　(IF)　signal.　Experimental　results　demonstrate　that　the　proposed　frequency　downconverter　can　generate　the　CS-SSB　modulation　signal　from　2　to　40　GHz　in　optical　spectrum.　All　the　mixing　spurs　are　completely　suppressed　under　the　noise　floor　in　electrical　spectrum,　and　the　output　IF　signal　possesses　high　purity　with　a　suppression　ratio　of　the　undesired　signals　(＞=　40　dB).　Furthermore,　the　multi-octave　downconversion　can　also　be　implemented　to　satisfy　the　bandwidth　requirement　of　multi-channel　communication.　The　proposed　frequency　downconverter　supplies　an　ultra-wideband　and　high-purity　alternative　for　the　signal　processing　in　microwave　photonic　applications.　(C)　2017　Elsevier　B.V.　All　rights　reserved.