A fixing apparatus for fixing a waveguide plate includes a number of conductive fixing members fixed to corresponding sides of the waveguide plate, and a bracket. Each fixing member includes a fixing portion having an identical length to the corresponding sidewall and a resilient abutting portion extending from a side of the fixing portion. Each fixing portion is in tight contact with the corresponding side of the waveguide plate. The waveguide plate is received in the bracket. The resilient abutting portions resiliently abut against an inner surface of the bracket.