Design And Realization Of If Broadband Satellite Transmitter

In modern wireless communication technology,microwave communication plays a very important role.The original digital baseband signal is moved to a higher frequency microwave frequency band through the transmitter for transmission.The design of the transmitter will have an important impact on the performance of the entire communication system.Common transmitter structures include superheterodyne structure and zero-IF structure.The zero-IF structure has the advantages of high integration and simple structure,but this structure has the problem of amplitude and phase imbalance between I/Q channels,which leads to useless edges.The generation of the band causes the performance of the communication system to deteriorate.In this paper,an IF transmitter system with a working frequency of 950-2150 MHz is designed,which is the intermediate frequency subsystem of the Ku-band satellite transmitter,and a corresponding calibration scheme is proposed for the I/Q imbalance problem of zero-IF structure.First,the link design scheme of the intermediate frequency transmitter system is determined.This system is the intermediate frequency subsystem of the Ku-band satellite transmitter system.The FPGA generates a digital baseband signal,which is modulated to the intermediate frequency by the intermediate frequency transmitter.The design of each module of the system is introduced in detail,including FPGA module,digital-to-analog conversion module,LC low-pass filter circuit,quadrature modulation circuit,and phase-locked loop module.In addition,this paper also designs a one point sixteen microstrip Wilkinson power divider with a working frequency of 950-2150 MHz,which enables multiple IF transmitter systems to synthesize one output.The test results of the power splitter show that in the working frequency band,its transmission coefficient is about0 dB,the maximum input port reflection coefficient is about-18.4dB,and the isolation between ports is less than-28 dB,which meets the design requirements.Next,the I/Q imbalance calibration scheme for the zero-IF transmission structure is proposed.The I/Q imbalance model is established,and the principle of sideband suppression is derived.On the basis of the narrowband signal I/Q imbalance calibration scheme,this paper introduces the wideband signal I/Q imbalance calibration method,and innovatively proposes a transmitter and receiver I/Q imbalance joint calibration scheme.This joint calibration scheme does not require external instruments and has strong practicability.Finally,test the IF transmitter system and verify the feasibility of the calibration scheme proposed in this article.The test results show that when the local oscillator frequency is 2GHz,the QPSK signal symbol rate is 30 Msps,and the carrier offset zero frequency is 15 MHz,the upper and lower sideband power ratio of the modulated signal before calibration is 49.94 dB,and the upper and lower sideband power ratio after calibration is 55.08 dB.The feasibility of the wideband signal I/Q imbalance calibration scheme is verified.When the local oscillator frequency is 1GHz,the 30 Msps symbol rate QPSK signal EVM can reach 1.87%,and when the single tone signal is offset by 1MHz from the carrier frequency,the carrier suppression is-61.25 dBm,which meets the design requirements.