MICROWAVE BANDPASS FILTER : filter Types

FILTER

Filter is an electrical network that can transmit signals within a specified frequency range . This frequency range is called pass band and other frequency band where the signal are suppressed is called stop band .The frequency that separates the pass and stop band is known as cut off frequency .

TYPES OF FILTER : Filters are of four types . These are as follows -

1. Low pass filter : In low pass filter the transfer function is

aо

H(s) = ----------------------- where s = jw H(jw) = gain

b2s² +b1s + bо

here increase of frequency makes the gain extremely low .

2. High pass filter : In high pass filter transfer function is

a2s²

H(s) = ---------------------- s=jw H(jw) = gain

b2s² + b1s + b0

Here at low frequency gain is low but at high frequency gain become constant.

3. Band pass filter : In band pass filter transfer function is

aıs

H(s) = -------------------------

b2s² + b1s +bo

here at a middle frequency range H(s) remains constant.

4. Band stop(or rejected) filter : In band stop filter transfer function is

a2s²+ aо

H(s) = ------------------------------

b2s² +b1s+bo

Their characteristic is shown in the figure