The　power　spectral　densities　of　UWB　impulse　radio　systems　with　pulse　position　modulation　(PPM)　consist　of　both　continuous　spectra　and　discrete　frequency　spikes.　These　discrete　spikes　cause　interferences　to　narrowband　systems　and　deny　the　harmless　coexistence　of　PPM　UWB　systems　and　narrowband　systems.　To　suppress　these　discrete　spikes,　in　this　paper,　a　random　pulse　carrier　phase　jitter　(PCPJ)　technique　is　presented　and　applied　to　PPM　UWB　signals.　Both　theoretical　analyses　and　simulations　are　carried　out　and　the　obtained　results　show　that　the　proposed　technique　can　effectively　suppress　the　frequency　spikes,　increase　the　transmitted　power,　and　thus　improve　the　performance　of　PPM　UWB　systems.　©　2010　IEEE.