Research On Mixer And Key Technology At Q-band

With the approaching of the 5G mobile communication era,spectrum resources in the low frequency band are becoming increasingly tight,and millimeter wave systems with small bandwidth,small size and compact structure are receiving more and more attention in the industry.As an important part of RF transceiver,the performance of mixer will directly affect the key indicators such as the dynamic range and transmission rate of the entire system.Therefore,in order to meet the actual demands of millimeter wave system,the Q-band single-balanced and double-balanced mixer has been designed by Substrate Integrated Waveguide?SIW?structure and applied to the Doppler receiver front-end.The works and results are as follows:Firstly,a cruciform 3dB directional coupler with small-hole coupling based on SIW structure is designed.The amplitude balance between through port and coupling port is enhanced by introducing a coplanar waveguide?CPW?structure in the upper metal.The measured results indicate that in the 31GHz-37GHz frequency bandwidth,the return loss is more than 17dB,the coupling port average output is-4.1dB,only 0.2dB different with through port,and the isolation is higher than 20dB.Then,the cruciform 3dB directional coupler with small-hole coupling of SIW structure is used as the feeding network of mixer,three different configurations of mixer,including single-balance,circular double-balance,and star double-balanced mixers are designed.The test results show that the single-balanced structure has the highest conversion gain?-9.4dB?and the circuit diagram is compact.The ring double-balanced structure improves the isolation between the local oscillator and the RF port?up to 16dB?,increases the RF bandwidth?up to 3.7GHz?and linearity(IIP_1dB is 8dBm),and in-band fluctuation is very small?0.8dB?.The star double-balanced structure reorganizes the placement of four diodes,enabling easy layout on a single-layer double-sided board.Two additional baluns are introduced to further improve port isolation?up to 20dB?and the RF bandwidth?up to 5.5GHz?,the highest gain is-10.6dB,and the IIP_1dBdB is 8dBm.Finally,the single-balanced mixer is selected,a Q-band Doppler receiver front-end of SIW structure is designed in combination with the research of Dielectric Resonator Oscillator?DRO?and SIW filter.The test results show that the IF output of the system is stable,IIP_1dB is 6dBm,the down conversion gain is about-11dB,the second harmonic suppression is greater than27dBc,the local oscillator signal power of the DRO output is greater than 16dBm,and the amplitude error of I/Q IF output signals is 1.5dB,the phase error is 4.4°.