The stability of dual channel filters (such as dual band filters, differential filters, etc.) may be affected in practical applications due to environmental interference, changes in component characteristics, design defects, and other factors, resulting in a decrease in filtering performance (such as frequency band offset, increased insertion loss, decreased isolation, etc.). Here are some specific examples of stability being affected in practical applications:
1、 Dual channel filters in communication systems
RF base station dual band filter (such as 4G/5G coexistence scenario)
The dual channel filter used in base stations to separate signals from different frequency bands (such as 3.5GHz and 2.6GHz in Sub-6GHz), if operated in a high-temperature environment for a long time (temperature fluctuations in the base station room or outdoor exposure), will cause thermal expansion and contraction of the metal material in the resonant cavity of the filter, or the dielectric constant of the dielectric substrate (such as ceramics, PCB) to change with temperature, resulting in a center frequency shift.
For example, the decrease in dielectric constant of ceramic media at high temperatures may cause the filtering curves of two frequency bands to shift towards higher frequencies, resulting in signal crosstalk in the originally isolated frequency bands and affecting communication quality.
Dual polarization filter for satellite communication
The dual channel filter in satellite payloads needs to process both horizontal and vertical polarization signals simultaneously. If it is affected by space radiation (such as high-energy particles), the metal coating (such as silver coating) inside the filter will oxidize or corrode, resulting in increased insertion loss and a greater difference in loss between the two polarization channels, which will damage polarization isolation and cause signal demodulation errors.
2、 Dual channel filter in radar system
Dual channel filter for transmitting and receiving pulse Doppler radar
A dual channel filter used in radar to separate transmission signals (high-frequency high-power) and reception signals (weak echoes). If it is subjected to high-power signal impact for a long time, it will cause saturation of the inductor core, breakdown of the capacitor medium, or exacerbation of the skin effect of PCB wiring in the filtering circuit, resulting in impedance matching imbalance between the two channels.
For example, the high-power signal from the transmitting channel leaks into the receiving channel, causing the noise base at the receiving end to rise, the sensitivity of the radar to detect distant targets to decrease, and the stability to be disrupted.
Dual band filter for vehicle mounted millimeter wave radar (such as 77GHz/24GHz)
A dual channel filter used in vehicle mounted radar to distinguish between different frequency bands (long-range detection 77GHz and short-range blind spot 24GHz). If the welding points inside the filter become loose due to engine vibration or road bumps (such as virtual soldering of surface mount components), it will cause the resonance frequencies of the two channels to be unstable, resulting in frequency band overlap and radar misjudgment (such as identifying static obstacles as dynamic targets).
3、 Dual channel filters in power systems
Harmonic suppression dual channel filter for high-voltage power grid
A dual channel filter used to suppress the 3rd and 5th harmonics in the power grid. If the power grid voltage fluctuates (such as instantaneous overvoltage caused by lightning strikes) or the load suddenly changes (such as motor start stop), the capacitor and inductor components in the filter will be subjected to excess voltage/current, resulting in component parameter drift (such as a decrease in capacitor capacity and a change in inductor permeability).
For example, the capacity of the filtering capacitor in the 3rd harmonic channel decreases after aging, and the filtering frequency band shifts towards higher frequencies, which cannot effectively suppress the 3rd harmonic and leads to increased waveform distortion in the power grid, affecting the operation of precision equipment.
Dual channel filter for new energy grid connected inverters
A dual channel filter used in inverters to separate fundamental waves (50Hz/60Hz) from high-frequency switching noise. If the inverter operates at full load for a long time, the heat dissipation of the filter circuit is insufficient, resulting in an increase in the temperature of the resistance element (positive temperature coefficient resistor) or an increase in the loss of magnetic core material (such as ferrite) with temperature, causing an imbalance in the attenuation characteristics of the two channels and high-frequency noise leakage to the power grid, interfering with adjacent communication equipment.
4、 Dual channel filter in instruments and meters
Dual band pre selection filter for spectrum analyzer
The dual channel filter used in spectrometers to suppress spurious signals (such as covering frequencies below 1GHz and 1-18GHz), if the mechanical tuning structure (such as the tuning screw of a cavity filter) wears out after long-term use, resulting in a decrease in tuning accuracy and overlapping or concave transition bands between the two frequency bands, cannot effectively filter out spurious signals and reduce the signal-to-noise ratio of the measurement results.