Research Of Microwave Broadband Low Spurious Response Down Converter

Microwave receiver front-end is the equipment which is used to pick up the useful frequency signal from the spatial signal, microwave frequency down converter is one of the core components.Wide broadband and highly spurious response inhibition ability are the key to the microwave frequency down converter equipment performance indicators.This thesis mainly research direction is microwave frequency down converter,and emphasis on the study of the receiver system planning, the primary channel frequency division, down converter spurious response under interference suppression and so on, and the one of the most important components, primary filter and second harmonic mixers, do the detailed design and implementation.The input frequency range of the receive front-end is 0.2-18 GHz, the output frequency is 70 MHz.This article adopts the structure of multi-channel superheterodyne receiver, the frequency is divided into three frequency bands.0.2-4GHz frequencies which adopts the second frequency conversion method, 4-10.5GHz spectrum using the local oscillator frequency conversion method, 10.5-18 GHz frequency using second harmonic mixers method.Three ways of frequency conversion transformed to the Shared medium frequency at 1.8GHz, then the secondary inverter was used to for RF front-end of intermediate frequency required.According to the frequency distribution of the stray, 4-10.5GHz and 10.5-18 GHz frequency bands refine respectively.In order to prevent the adjacent channel interference, the microwave switch circuit was used to choose the path.Using the Link Budget Simulation to conclude the different channel device requirements for the design of the indicators.According to the demand of various frequencies of restraint outside the band,based on the analysis comparison of different types of band-pass filter performance difference, this paper uses the Evanescent Mode Microwave Bandpass Filter to design the primary channel filter.The structure of this kind of filter can meet the miniaturization, good ability to restraint outside the band, low insertion loss and the characteristics of rapid the rolling down, This paper enumerates several typical frequencies band-pass filter simulation and test results, it satisfied the natural frequency of vibration suppression is more than 30 dB, mirror frequency suppression and important spurious frequency suppression is greater than 75 dB.This paper designs a new type of second harmonic mixer.This mixer adopts that the Microstrip Barron which connect diode pairs with the Balun’s balance terminations to do the reverse phase mixing. Using the new type Spiral Compact Microstrip Resonant Cell(SCMRC) structure to adjustment the characteristics of phase within the mixer. Using Chebyshev Low-Pass Filter Prototype design of intermediate frequency filter. Through the simulation optimization of different components, respectively, to design a second harmonic mixer.Actual measurement of frequency conversion loss between 10.5-18 GHz typical values can be less than 13 dB.Finally, this paper will put the down converter into the microwave receiver front-end and test.Within 0.2-18 GHz frequency band, the gain of receive front-end system greater than 30 dB, the mirror frequency suppression is greater than 65 dB, the local oscillator leakage is less than 80 dBm, unrelated stray inhibition is greater than 65 dB.This down converter can basically meet the design needs of microwave receiver front-end system.