A Parallel Open Circuit Ladder Impedance Low Pass Filter

Abstract

The invention discloses a parallel open-circuit stepped impedance low-pass filter which is suitable for low waveband signal filtering in a broadband frequency sweeping super-heterodyne spectrum analyzer. Firstly, a fifteen-order parallel open-circuit stepped impedance strip line elliptic function low-pass filtering unit is constructed based on a microwave sheet material and used for meeting the requirement for filtering a low-frequency signal; secondly, a eleven-order parallel open-circuit stepped impedance strip line elliptic function low-pass filtering unit is constructed based on the microwave sheet material and used for meeting the requirement for filtering a high-frequency signal; thirdly, the fifteen-order parallel open-circuit stepped impedance strip line elliptic function filtering unit and the eleven-order parallel open-circuit stepped impedance strip line elliptic function filtering unit are cascaded to form a twenty-six-order strip line low-pass filtering module. The twenty-six-order strip line low-pass filtering module is used for meeting the requirements for filtering the high-frequency signal and the low-frequency signal. The defects that a coaxial cavity low-pass filter is large in size, and port matching is not prone to being improved are overcome, besides, high-quality signal output is achieved, the product size is shrunk and power consumption is reduced.

Description

technical field [0001] The invention relates to the field of broadband sweeping superheterodyne spectrum analyzers, in particular to a parallel open-circuit ladder impedance low-pass filter. Background technique [0002] In a typical wideband swept superheterodyne spectrum analyzer, the wideband RF signal is divided into high and low frequency bands. The radio frequency signals of different bands are transformed into low-intermediate frequency signals after different frequency conversions respectively, so that the analog-to-digital converter can sample them. The frequency of low-band radio frequency signals generally covers the S-band, that is, 0Hz-4GHz. When the low-band radio frequency signal enters the spectrum analyzer, it first passes through a 4GHz low-pass filter, and then performs frequency conversion with the first local oscillator signal working in the frequency sweep mode in the first frequency converter to obtain the first intermediate frequency signal, that is,...

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Problems solved by technology

However, the stopband suppression of the microstrip low-pass filter is not ideal. It can be seen that the stopband suppression at 5GHz-14GHz is only about 60dB. This is because the microstrip line has a parasitic passband due to space radiation, which is difficult to meet the requirements of the instrument.

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