Research On Function Fusion Balanced Filter And Power Division Circuit

With the development of wireless communication technology,radio frequency?RF?circuits and integrated circuits have become more and more complex,and multi-function circuit modules are packaged in an integrated space.The mutual coupling of signals between circuits and the interference and crosstalk of free space put forward more severe requirements for the design of RF circuits.At the same time,increasingly crowded spectrum resources demand higher on the passband selectivity and out-of-band rejection of the circuit.The research of single-ended circuit is earlier than balanced circuit,but balanced circuit is superior in common mode noise suppression and circuit crosstalk reduction.Therefore,the study of balanced circuits is of great significance to modern communication systems.In this paper,from the perspective of increasing the integration of circuit functions,the passband selectivity of the differential mode signal and the suppression of the out-of-band harmonics and the common mode signal in the balanced circuit are improved by using the coupled line and the stepped coupled line.The main research work includes:1.Broadband balanced bandpass filter based on stepped coupled line:Firstly,the basic theory of the stepped coupled line and the mixed mode S parameters of the four-port network are introduced.Replacing the microstrip line in the traditional quarter-wavelength bandpass filter circuit with a coupled line can increase the order of the passband.Loading coupled line branches to generate two transmission zeros at both ends of the passband can improve the passband selectivity,which without affecting the transmission characteristics of the filter.Finally,two balanced filter circuits are designed by using stepped coupled line equivalents instead of traditional coupled lines.The circuit not only maintains a compact structure,but also achieves upper band rejection and common mode rejection in a wide frequency band.2.Balanced power divider based on coupled line:Firstly,the structure and characteristics of the coupled line and the mixed mode S parameters of the six port network are introduced.Two identical Wilkinson power divider circuits are connected together by a microstrip line.Adjusting the characteristic impedance connecting the two power divider transmission lines can change the bandwidth of the differential mode passband.In order to realize power divider with high unequal power division and high power consumption,a double-sided parallel strip line?DSPSL?is utilized to realize high characteristic impedance,and then a broadband balanced Gysel power divider with a power division ratio of 10:1 is designed.3.Multi-functional RF balanced filtering power dividers:Firstly,the structure and characteristics of balanced to single ended circuit are introduced.The proposed first circuit uses a traditional coupled line and single-wavelength ring resonator with wideband filter power splitting characteristics.Subsequently,two half-wavelength-long open stubs are introduced to generate two transmission zeros at 0.5 f₀ and 1.5 f₀,which improve the selectivity of differential mode to single-ended,and finally the stepped couple line further expands the suppression range of the upper stop band.The simulated and measured results of the four balanced filter power dividers are in good agreement.