Research Of The3mm Directional Coupler And Its Measuring System

Directional coupler is a four port device dividing power, a passive microwavedevice which is used widely in microwave systems. It takes a great role in electroniccountermeasure, communication system, radar system and measuring apparatus. It ismainly used in composing and dividing power, extending measuring range of power,monitoring power and frequency spectrum, etc. It also applies widely in othermicrowave measurement devices such as vector network analyzer and microwavereflectometer and so on.As it is easy to solve the structure of electromagnetic field, the research of thewaveguide directional coupler began early and the theory and process technology weredeveloped. The waveguide directional coupler performs well and has a big powercapacity. As the frequency of measuring apparatus and electronic countermeasurebecomes more and more higher, the frequency band becomes wider, it is essential toresearch for the directional coupler with high frequency and wide frequency band.The frequency band of the directional coupler researching in this dissertation is75~110GHz, and the coupling degree is3dB. In order to widening the frequency band,obtaining the required coupling degree and ensuring a satisfying directivity, double rankapertures is adopt. In order to simplify the design of directional coupler, we use equaldiameter and equally spaced apertures.The mainly works in this dissertation are as follows:First of all, presenting the basic principles, sorting technique and application ofdirectional coupler, the development status quo and the significance of researchingdirectional coupler are also mentioned. There are the derivation of the theory of couplethrough apertures, the principle of phase superimposing and the theory of the coupler ofsingle aperture and multi-apertures.Secondly, building the model of waveguide directional coupler with thethree-dimensional simulation software HFSS. We fix the thickness of the commonbroad wall between the host waveguide and the assistant waveguide and distancebetween apertures through synthesizing the target of the waveguide directional coupler, the existing dimension of the waveguide and the process precision. Then we change thedimension of aperture and the distance between the two rank apertures, and see analysishow the couple degree changes. Set variables on some dimensions and processoptimization, then analysis the optimization result of couple degree, then determiningthe dimensions of directional coupler. Finally we simulate on all target, achieving thesimulating curves.And then, base on the requirement of measuring this directional coupler, researchone most precise calibration method of the vector network analyzer–TRL calibrationmethod. Mainly analysis and derivate the error model of the TRL calibration method,and resolve the error term of the error box. Base on our requirement, we designed andproduced the TRL calibration kit. Then we append our own TRL calibration kit in thevector network analyzer and analysis the process of the calibration.Finally, we mainly present the process of measuring the directional coupler, andanalysis the measurement curves. Then we make a detailed analysis through comparingthe simulated curves with the measured curves.