| With the development of millimeter wave and terahertz technology,traditional transmission lines are further restricted in higher frequencies due to the disadvantages of large loss,processing difficulties,low power capacity,etc.Quasi-optical technology takes advantages of Gaussian beams to transfer millimeter waves in free space with low loss,which overcomes many defects of traditional transmission lines,and is widely used in millimeter wave and terahertz systems.In this paper,Quasi-optical spatial beam power combining and ultra-high temperature measurements of complex permittivity based on Quasi-optical technology are studied.The demand for high-power output device with high efficiency in millimeter-wave and terahertz frequencies has greatly increased in many applications such as detecting guidance and radar transmitter.Generally,owing to limitation by fundamental thermal and impedance problems,a single solid-state device cannot generate sufficient power for many applications in millimeter-wave and terahertz frequencies.Therefore,it is necessary to introduce an efficient power combining system to obtain adequate power output.Due to the loss of microstrip lines and waveguides,circuit-level power combining and waveguide power combining technology are difficult to directly generate power output matching with vacuum devices in high frequencies.Besides this,free space power combining is limited by efficiency.Therefore,the Quasi-optical space power combining system becomes an effective solution to achieve high power output in the short millimeter-wave and terahertz frequencies.In this paper,a Quasioptical spatial beam power combining system based on reflectarray is proposed.Utilizing the reflectarray to transform multiple beams to Gaussian beam can provide desirable power for several applications.In this paper,the full wave simulation of the proposed Quasi-optical spatial beam power combining system is carried out at 94 GHz and 220 GHz by CST software.The simulated results of eight channel system reveal that the beam combining efficiency is 83.3%,and the final power combining efficiency can reach 74.6% at 94 GHz,which can reach 61.2%by measurement.Dielectric materials are widely used in radomes and antenna windows of aerospace to protect the antenna and other equipment inside the aircraft.Particularly while aerospace fly at a very high speed in atmosphere,high-temperature and high-speed air flow will occur.The exterior surface of the space shuttle has to withstand extremely high temperatures,which can reach 1500 ? or above.Under the circumstances many nonlinear changes will occur in dielectric materials,which has a great impact on the stability of millimeter wave circuit devices inside the aerospace equipment.Therefore,it is of a great significance to obtain the accurate information of the complex permittivity of the dielectric materials in the case of rapid temperature rise condition.In the millimeter wave band,the closed resonators and systems based on transmission reflection method are difficult to be directly used in the ultra-high temperature measurement of the dielectric properties of materials for that it is generally need to use vacuum furnace with water-cooling equipment to avoid oxidation of devices in these systems,which results that the system is complex and difficult to operate.For this reason,a test system to measure the dielectric properties based on ellipsoid open cavity is built,in which the highest temperature can reach about 1550 ? in Ka band.In the system,the measured piece and the open cavity are separated in structure,but connected electrically to ensure that the piece is heated without affecting the open cavity.Through the direct flame impingement heating technology,the dielectric materials in the air environment can be rapidly increased to above1550 ?,which equals the actual environment of the aircraft.Finally,the proposed system based on ellipsoid open cavity finishes the test of many kinds of low loss dielectric material in the ultra-high temperature environment. |
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