ABSTRACT
The most common designs for the microwave frequency range employ a branch-line, Lange, or “rat-race” hybrid structure. Armstrong was the first to use a vacuum tube as a frequency converter (mixer) to shift the frequency of an incoming signal to an intermediate frequency, where it could be amplified and detected with good selectivity. At the beginning of the 20th century, radio frequency detectors were crude, consisting of a semiconductor crystal contacted by a fine wire which had to be adjusted periodically so that the detector would keep functioning. The concept of the switching mixer model can also be applied to field-effect transistors used as voltage-controlled resistors. Mixers can be divided into several classes: single ended, single balanced, or double balanced. The design of single-diode mixers can be approached in the same manner as multi-port network design. Balanced mixers offer some unique advantages over single-ended designs such as local oscillator noise suppression and rejection of some spurious products.
