Design And Implementation Of Wideband Satelite If Receiver

With the rapid increase of the communication data amount nowadays,broadband transmission has great significance in satellite communications.As an important part of the wireless communication system,the high rate reception and I/Q amplitude and phase imbalance correction of the IF receiver are of much concern.On account of the temper situation,this paper develops a 25Msps symbol rate IF receiver with operating bandwidth between 950MHz and 2150MHz,and carries out the study of I/Q amplitude-phase imbalance correction.First,the IF receiving link is designed and tested.The IF modulated signal passes through the power divider module,the quadrature demodulation down-conversion module and the ADC module in sequence,and is sampled as I/Q digital baseband and then transmitted to the FPGA through the adapter board.A three-step Wilkinson power divider is designed to resonate at three frequency points to achieve the wideband matching between950MHz and 2150MHz,and the tested S₁₁<-11.5dB,which meets the design requirements.The down-conversion link adopts the form of amplifier-attenuator-amplifier to increase the dynamic range,and applies the switch selecting filters for broadband filtering.The test phase noise of the local oscillator PLL is-96.91(dBc/Hz)@1kHz,and the isolation between the local oscillator and the intermediate frequency is-47.63dBm and-77.89dBc respectively.The differential I/Q signal generated by the demodulator is filtered and driven,sampled by the ADC and transmitted to the FPGA development board through the FMC connector.Using low-IF receiving mode,when the receiving local oscillator frequency is1.3GHz and QPSK modulation symbol rate is 25Msps,EVM=2.72%,EVM equals 1.47%at10Msps,at 5Msps EVM can reach 0.94%.At the local oscillator frequency of 1.9GHz,when the modulation bandwidth is 20MHz EVM=2.81%,the demodulation accuracy of the IF receiver satiefies the design requirements.Broadband correction on the amplitude and phase of the I/Q channels in the digital domain is applied in this design,thereby suppressing the image frequency of the intermediate frequency receiver.The IRR of 25MHz single tone signal after correction is75.00 dBc,with a 43.22 dBc significant decrease.For 45 MHz single tone signal,the IRR is restrained from 26.18 dBc to 77.21 dBc.The look-up table of modulated signal can be obtained through the interpolation of the tone signal correction matrix,then the correction is done in the frequency domain.The 25Msps symbol rate QPSK modulated signal has an IRR of 37.0dBc,and that goes to 43.2dBc for 10Msps signal.Whenever in single tone or modulated signal conditions,the image frequency after suppression is drowned out by noise floor,therefore the algorithm works well.Finally,a method of suppressing the image frequency of the transceiver joint modulation is proposed,which can correct the I/Q amplitude and phase imbalance of the receiver and the transmitter under the simple conditions without the aid of a signal source and a spectrum analyzer.The IRR of the single-tone signals of the receivers tested in the joint modulation test are all above 60dBc,and both of the transmitting and receiving image frequencies are submerged in the bottom noise.In the case of 25Msps symbol rate QPSK signals,the receiving EVM=3.81%,and the demodulation accuracy meets the requirements,which verifies the feasibility of the I/Q imbalance correction method for the joint modulation of the transceiver.