High selectivity balanced filter based on signal interference technology

Abstract

The invention discloses a novel high-selectivity balance filter comprising four pairs of open circuit / short circuit coupled lines, four pairs of open circuit coupled lines, two open circuit lines, seven microstrip transmission lines, and four metalized via holes. A horizontally-symmetric unbalance filter is connected though a half-wave microstrip transmission line to form a four-port balance filter. The coupling degree can be controlled effectively by adjusting parameters such as the distance and widths of the open circuit coupled lines such that a bandwidth can be controlled flexibly. By means of signal interference technology and the transmission characteristic of a loaded half-wavelength open circuit branch line, multiple transmission zero points can be generated. Thus, passband selectivity of a differential-mode signal and the inhibition degree of a common-mode signal are effectively increased. Under the effect of two transmission path signals, the balance filter achieves a good passband characteristic of the differential-mode signal and multiple zero points out of band. The inhibition frequency range of the common-mode signal achieves triple frequency multiplication. The novel high-selectivity balance filter is simple in structural design, good in electrical performance, and easy in circuit integration and system packaging.

Description

technical field [0001] The invention relates to the technical field of microwave balanced circuits, in particular to a high-selectivity balanced filter based on signal interference technology. Background technique [0002] The balance circuit plays a very important role in the wireless communication system. It can improve the signal-to-noise ratio of the receiver and improve the efficiency of the transmitter, thereby effectively suppressing the influence of environmental noise and device noise. Among various balanced circuit devices, balanced bandpass filters play a vital role. The purpose of a balanced bandpass filter is to maintain a good response to differential-mode signals while rejecting common-mode signals within a given frequency range. In order to better suppress common mode noise, the balanced bandpass filter should also have good out-of-band rejection and high frequency selectivity. In order to improve the frequency selectivity of the filter, cascading band-stop...

AI Technical Summary

Problems solved by technology

In order to improve the frequency selectivity of the filter, cascading band-stop filters is one of the commonly used methods. The disadvantage is that the volume of the overall filter is greatly increased; introducing transmission zeros by loading stubs is also a method to improve selectivity, but the filter’s The loss will inevitably increase. In recent years, many scholars have devoted themselves to the study of balanced filters with good common-mode rejection, high frequency selectivity and wide stopband, such as literature 1 (“X.H.Wang, Q.Xue, W.W. Choi, A Novel Ultra-Wideband Differential Filter Based on Double-Sided Parallel-Strip Line, IEEE Microw.Wireless Compon. Lett., vol.20, no.8, pp.471-473, Oct.2010"), and literature 2 ("L.L.Qiu, Q.X.Chu, Balanced bandpassfilter using stub-loaded ring resonator and loaded coupled feed-line, IEEE Microw. Wireless Compon. Lett., vol.25, no.10, pp.654-656, Oct.2015") The structure of several balanced filters is introduced in detail in the paper. The disadvantages of the balanced filter structure designed in the past are: (1) the circuit is complex and the volume is large; (2) the differential mode out-of-band performance is poor, and the common mode rejection Narrow bandwidth; (3) few out-of-band transmission zeros and low common-mode rejection

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