Design Of Ultra-small Directional Coupler Based On LTCC Technology

Microwave passive component is one of the key passive components in wireless communication and radar system, which has a development trend of miniaturizing and integrating. To achieve microwave MCM (Multi-Chip Module), LTCC (Low Temperature Co-fired Ceramics) technology based process is most readily available in the current. Directional coupler is one of the most commonly adopted microwave passive components, whose function is to divide and distribute signals according to the direction set by the designer. Notably, its performance is directly related to the parameters of the entire RF circuit system.Based on multilayer structure LTCC technology, the design methodology of ultra-small directional couplers is examined in a systematic manner in this thesis. Thereby, two types of ultra-small 3-dB directional coupler designs (chip device and integrated module) are presented as well.Feedback network with odd and even mode characteristics of stripline is used as the main method of analyzing coupled stripline. The effects of various structural parameters on performance parameters are examined and quantified through the simulation and analysis. In addition, the methods of optimizing the directional coupler are proposed.According to single-section stripline directional coupler theory, an ultra-small 3-dB directional coupler in the form of chip device is designed by Ansoft HFSS software whose central frequency is 2.4GHz. Simulation results shows that with frequency range of 1.8GHz to 3.0GHz, isolation more than 24dB, VSWR less than 1.2, phase unbalance less than 2 degrees, all of these results match our design requirements well. The dimension of the directional coupler is only 3.20mm×1.60mm×1.24mm, close to the state of the art. Eligible adaptability of the structure with LTCC technology is shown in tolerance analysis. Another ultra-small 3-dB directional coupler is designed in the form of integrated module to suffice the integrated design applicability, it can be seen that better performance parameters are achieved by reducing port crosstalk.