Research On Millimeter Wave Quasi-optical Beam Power Combining Technology

With the development of sub-millimeter wave and Terahertz technology,the techniques for increasing the output power to satisfy the system requirements are required.So far,it is very difficult to produce the demanded output power of the system in terahertz band,whether it is the vaccum technology,the optical technology or the solid state electronic technology.As the output power of a single transmitter is difficult to meet the demand,the power combining technique which is widely used in microwave and millimeter wave band is an efficient method to enhance the output power.The conventional circuit-level combining uses transmission lines for combining the active devices,which is limited by the dimensional tolerances and power output.In the meanwhile,the high transmission losses lead to a reduction in combining efficiency.And due to the complexity of the circuit,it is difficult to apply in high frequency.Compared with the circuit power combiner,although the physical structure of the waveguide spatial power combining is much simpler than the circuit,the size of the waveguide is getting smaller and smaller with the increase of the operating frequency.The output power tends to be very low and transmission loss increases.Therefore,the waveguide power combining technology is also difficult to achieve in the terahertz band.Quasi-optical beam power combining technology combines several beams into one big propagating beam in the space to realize the power combining.Since all the elements are operating in parallel,the loss is roughly independent of the number of amplifier,which avoids the defects of limited number and high loss caused by circuit or waveguide combining technology in high frequency domain.This technique is suitable for the power combining of high millimeter wave band and terahertz band.And if the wave is coherent,no matter the eletromagnethic wave is produced by the electroic vaccum technology,the optical technology or the solid state electronic technology,it can aslo be used in the system.A completely symmetric structure of quasi-optical beam power combining system,which can combine N beams into 1 beam by one stage is designed in this paper.Hyperbolic and ellipsoidal mirrors is utilized in the power combining system,which can transform several coherent Gaussian beams into one propagating beam.In order to obtain the Gaussian beam,corrugated beam converter and shaped structure beam converter are designed in this paper.By using the beam converter,the high mode of Gaussian beam can be transformed to Gaussian beam.When the combined beam transformed by the shaped beam converter,the combining efficiency can reach 74.75%,the Gaussian coupling efficiency is up to 96.58%.Finally,a power combining network based on dual-ellipsoidal reflector structure is designed.A conical part is used to reduce the radius of the combined beams.The dual-ellipsoidal reflector channel is added at the back of the transformed beam.The beams can converge in the space by using the reflector channel.The energy is converged in the center part and combining efficiency can reach to 87.65%.