Research And Implementation Of Ka-Band I/Q Direct Modulator

Direct modulation technology has gradually become one of the most important development trends of the RF(Radio Frequency) front-end in modern communication system. As the requirements on the volume, cost and power consumption of the RF front-end increase, the direct modulation technology successfully attracts researches’ attention due to its simple structure and potentials in low cost and low power consumption system. Therefore, we choose the direct modulation technology as the main research content of this paper, which are listed as follows:First of all, detailed analyses about the key factors and causes of the direct modulation technology are finished in this paper. Summaries and comments about existed solutions are provided, on the base of which the system design scheme is proposed. According to the system design specifications, criterions on components like power dividers are determined, which acts as the design guide of the components used in the system.Secondly, detailed theoretical analyses about the PI-type single balanced mixer used in the direct modulator, which includes three possible phase states, are perfomed in this paper. Adequate structure is selected to design the mixer by comparing the ability of the three structures in rejecting those redundant frequencies generated in the mixing procedure. Furthermore, the signal across between base signal and RF in traditional PI-type single balanced mixer is avoided in this paper due to the public ground structure of the base signal and RF.Thirdly, according to the design specifications, several designs about passive components are completed, including three low pass filters, three quadrature couplers of two types and three 180? hybrid bridges of two types. Based on these designs, a Ka-band I/Q direct modulator is designed, fabricated and measured.Last, in view of the deviation between measured results and simulation data, detailed analyses and verifications are performed in this article. In consideration of the external factors in the test, good consistency is shown between measured result and simulation data, which proves the correctness of the design.