Microwave Direct Rf Modulation Technology Studies

Direct modulator converts baseband signal to RF signal without upconvertion. The system design is relatively simple compared to upconversion. So direct modulator provides adventages of compact size, low cost and low spurious response. Error Vector Magnitude (EVM) is important consideration of direct modulation.In this paper, direct modulation technology working at Microwave band is researched. The carrier wave is modulated directly by the baseband signal at several frequency point in L band and S band. Firstly, this paper clarifies the theory of I/Q modulation, elaborates EVM and ACPL, and analyzes the effect of amplitude and phase unbalance and DC offset on EVM. Secondly we review the basic principle of phase locked loop and it's composing parts, including the basic conception and design method of PLL frequency synthesizer , especially introduce the charge pump PLL frequency synthesizer in detail. We present the designing result of passive loop filter . Thirdly, the research of the RF frontend for simulating the signal of secondary planet with the direct modulation technology is introduced. Finally, we provide the real test results of the direct modulation. The results probably reach the requirement.