Integrated single balanced mixer/oscillator with slot and hybrid coupler

摘要

In an RF receiver, the unsymmetric RF input to a single balanced mixer is provided from the preceding portion of the receiver by means of a hybrid coupler to provide DC decoupling and impedance transformation at the RF and image frequencies. The hybrid coupler includes first and second microstrip conductors on the first side of a circuit board, each respectively coupled to the preceding portion of the receiver such as to a preamplifier and to the mixer and mutually electromagnetically coupled. On a second side of the circuit board is located a slot etched in the circuit board's conductive ground plane providing the single balanced mixer with a symmetric oscillator frequency source. The ground plane in which the slot is located forms one wall of a cavity in which a dielectric resonator is contained which, coupled to either end of the slot and in combination with an active device, forms the oscillator frequency source. Optimum performance of the oscillator and the mixer requires choosing the proper length of the slot, proper positioning of the mixer and active device connections along the slot and providing the active device itself with proper feedback elements (transmission line stubs) on all of its ports. The integrated mixer/oscillator of the present invention thus forms an inexpensive, compact and efficient frequency downconverter particularly adapted for use in the front end of a microwave satellite television receiver.