Research On Couplers For The Millimeter Wave Frequency Band Applications

In recent years,5G(the fifth-generation mobile communications)technology has become a research hotspot.With the frozen of the 3GPP Rel 15's first edition,the 5G spectrum was formally established as a combination of microwave and millimeter wave frequency bands.Millimeter-wave technology has become the key technology to realizing extremely high-speed and large-capacity wireless communications.However,at millimeter-wave frequency band,the traditional microstrip has serious electromagnetic leakage and the metallic waveguide devices suffer from the large size and difficulty to integrate with other planar circuits,so the circuits mentioned above are no longer designers' first choice.Therefore,people have to find other alternative technologies.Owing to its advantages of ease in fabrication,strong mechanical structure performance,low profile,low cost,high flexibility in design,patch element has been widely used to design different components.However,the circuit size becomes too small and the performance deteriorates significantly when the operating frequency climbs up to millimeter-wave frequency.Meanwhile,substrate integrated waveguide is a new type of waveguide structure which has the characteristics of low radiation,high Q factor,high power capacity.But the corresponding couplers generally occupy large size with complicate structure.Therefore it is desirable to combine the advantages of them to realize a compact millimeter-wave coupler with simplicity both in design and fabrication.In this thesis,the research status of millimeter-wave coupler had been introduced briefly together with the existing problems.The operating principle of substrate integrated waveguide technology and its application in design of coupler are described simultaneously.By combining the patch type circuits design method and substrate integrated waveguide technology,a series of millimeter-wave patch type coupler with arbitrary coupling coefficient and arbitrary phase difference are designed,fabricated and measured.The results of the measurement and simulation are highly consistent,which shows the simplicity and feasibility of the design.The disadvantages in bulky size and high complexity for traditional millimeter-wave couplers had been overcome.an ultra-compact millimeter-wave crossover with planar structure is proposed.It eliminates the defects of the traditional crossover's non-planar in structure and difficulties in the designation.