When designing RF solution, RF filters play prominent roles in the system. If picking RF filter, the following parameters should be considered.
1. Center frequency: f0 is short for the center frequency of the passband of the RF filter, which is generally taken as f0 = (fL+ fH) /2, and fL and fH are the side frequency points of the relative 1dB or 3dB drop from the left and right of the band-pass or band-stop filter. The pass-band bandwidth of narrowband filters is usually calculated by taking the minimum insertion loss as the center frequency.
2. Cutoff Frequency: For the low-pass filter, it refers to the right frequency point of the passband, and for the high-pass filter, it refers to the left frequency point of the passband, which is usually defined in terms of 1dB or 3dB relative loss points. The reference for relative loss is as follows: for low pass filter, the insertion loss is based on DC, and for high pass filter, the insertion loss is based on the highest high-pass frequency without spurious stop-band.
3. BWxdB: Refers to the spectrum width to be crossed, BWxdB= (fH-FL). fH and fL are the corresponding left and right frequency points at X (dB) lowered based on insertion loss at center frequency f0. X=3, 1, 0.5, namely BW3dB, BW1dB, BW0.5dB, are usually used to characterize the pass-band bandwidth parameters of the filter. Fractional bandwidth =BW3dB/f0×100%, also commonly used to characterize the pass-band bandwidth of the filter.
Of course, except above factors, you may consider its working power, the measurement for the application, or for indoor or outdoor usage, as well as the connectors. However, the above parameters are most important to decide its performance.
As the designer of RF filters, Jingxin can help you out on the issue of RF filters, and customize the passive filter according to your solution. More detail can be consulted with us.