Design And Research Of A Equal Ripple Directional Coupler

Nowadays,with the rapid development of wireless communication technology,microwave devices are developing towards broa d Band and miniaturization,which also puts forward higher requirements for directional couplers,which play an important role in microwave systems.There are many kinds of directional couplers.According to the classification of transmission lines,the most common are microstrip line couplers and stripline couplers.Due to its own structural characteristics,microstrip line and stripline have different working modes,that is,microstrip line works in quasi TEM mode and stripline works in TEM mode.Therefore,the stripline directional coupler is easier to obtain better directivity.In the design theory of multi section symmetrical parallel coupling line coupler,each coupling line has the same electrical length,and the complete design table is used as a reference.The couplers studied in this thesis are multisection stripline 3d B directional couplers.The main contents are as follows:1.For multi section parallel coupled line couplers,an ideal transmission line is used to build a model,and the advantages and disadvantages of symmetrical and asymmetric directional couplers are studied and compared.The simulation results show that when the number of coupling lines is the same,the phase difference between the two output ports of the former is 90 degrees,and the phase difference of the latter changes quasi linearly;When the phase difference is not limited to 90 degrees,the latter can use a size nearly half smaller than the former to achieve the same working bandwidth.2.A broadband Tandem coupler operating in the range of 2-14 GHz is designed.The structure of this directional coupler is composed of two identical,multi section symmetrical 8.34 d B directional couplers in cross cascade.The simulation results of the coupler are excellent,the reflection coefficient and isolation are less than-19 d B,the output amplitude of the two output ports is(-3±0.4)d B,and the phase difference of the output ports is(90±1.5)degrees.3.A broadband directional coupler which can work normally at low temperature(24K)is designed and fabricated.This directional coupler has symmetrical structure,working frequency range of 2-14 GHz,coupling degree of 3 d B,and phase difference between two output ports of 90 degrees.Through repeated iterative optimization,a directional coupler with excellent performance is obtained.Low temperature resistant materials were selected for processing,and tested at room temperature and low temperature.The test results show that the coupler works well at two temperatures.The maximum amplitude imbalance of the two output ports is 0.8 d B and the maximum phase imbalance of the two output ports is 3.5 degrees.