| For a high frequency especially a millimeter-wave system, developing an oscillator that has both high frequency and stable performance remains a great challenge. One of ways to develop a high performance system is to use sub-harmonic mixer. This kind of scheme has been widely used in practical engineering due to its high effectiveness. However, as compared to the fundamental frequency mixer, its conversion loss is generally high. The conversion loss and other parameters such as image frequency rejection, noise factor would deteriorate the performance of a system. Thus researches on mixers have a great significance.This thesis mainly contains the following sections:1) Research on mixing scheme, determining the layout of the whole mixing circuit and mixing components which will be used in this design.2) In order to make the LO and RF mixing sufficiently in the mixing diode and maintain a relatively high isolation, a 3-port 0-d B coupler is designed to realize this specific function.3) For a fourth sub-harmonic mixer, its idle frequency should be adequately utilized to improve the conversion loss.4) In IF output port, an IF filter is designed to filter the IF frequency well. At the same time, it can reflect the idle frequency back to the diodes. To make the mixer work well, two grounds for LO and RF signal are indispensable.5) Circulations on LO and RF as well as the input matching networks are analyzed. Based on the layout, the whole schematic circuit is optimized to find the best result. It turns out that the lowest conversion loss of the 4th sub-harmonic is merely about 6.3 d B and the band width of the conversion loss below 10 d B is more than 1 GHz.6) As a further research of this project, a λ/4@4f LO open stub and two bias networks are added in the 0-d B coupler. In this way, a sub-harmonic mixer which can provide many working conditions is realized. |
