A design of Q-band noise injector

This paper presents a well performance noise injector that is used in the Q-Band (35-50GHz) dual beam cryogenically cooled receiver of Shanghai 65m Radio Telescope. A good flatness of coupling over a wider frequency spectrum is required in the noise injector. The design is based on the traditional circular waveguide directional coupler. The noise injector exhibits a -31.5dB mean coupling, flatness below 3dB, and an excellent cross-polarization below -45dB. The simulated results by using finite-element analysis (Ansys HFSS) are presented.