Please explain me What is 3dB frequency . And its importance?
I assume you are asking about the 3dB point with respect to filters?
The 3dB point, or 3dB frequency, is the point at which the signal has been attenuated by 3dB (in a bandpass filter). This is generally considered the point for determining the filter’s bandwidth. The bandwidth is defined as the difference between the upper and lower 3dB points.
For example, if you have a filter which has a lower 3dB point of 720 MHz, and an upper 3dB point of 730 MHz, you have a bandwidth of 10 MHz.