Low pass filter and design method thereof

Abstract

The invention relates to a low pass filter and a design method thereof. The design method comprises the following steps: S0, the index is determined according to the design input condition of the low pass filter; S1, the normalized value of out-of-band specified frequency of the low pass filter is calculated; S2, the section number is determined according to an equal-ripple filter stop-band attenuation characteristic diagram; S3, a model diagram of the low pass filter is created according to the section number; S4, normalized values of all elements are determined according to a normalized element numerical table of an equal-ripple low pass prototype filter; S5, actual values of all elements are calculated according to the normalized values. According to the low pass filter designed with the design method, both input impedance and output impedance are 50 omega, the low pass filter can be matched with a front end antenna and rear end receiving equipment conveniently, about no more than 1 dB of effect is caused to sensitivity of downstream equipment, and the typical value is no more than 0.5 dB. At the same time, the low pass filter adopts a symmetric circuit, input and output can be exchanged, and the use is convenient.

Description

technical field [0001] The invention relates to the technical field of radio high-frequency circuits, in particular to a low-pass filter and a design method thereof. Background technique [0002] In circuits and electronic systems, filters are an important part of automatic control, signal processing, and radio communication. According to their attenuation characteristics, they selectively pass frequencies, select required signals, and suppress unwanted signals. [0003] The existing short-wave receiving equipment has a fourth-order elliptic low-pass filter composed of inductance and capacitance elements in its antenna input circuit, which attenuates signals other than the receiving frequency to a certain extent to improve the image frequency and other indicators. . However, in actual use, due to the attenuation characteristics of the elliptic low-pass filter, its attenuation curve will fluctuate with the increase of frequency outside the passband, especially for high-frequ...

AI Technical Summary

Problems solved by technology

However, in actual use, due to the attenuation characteristics of the elliptic low-pass filter, its attenuation curve will fluctuate with the increase of frequency outside the passband, especially for high-frequency interference signals above hundreds of megahertz to one gigahertz. It is effectively suppressed, and the attenuation of the fourth-order elliptic low-pass filter is only 30 to 40 decibels

Images