B
billcalley
- Jan 1, 1970
- 0
Something has me really stumped: Since cascading two 50 ohm BP
filters can lead to big trouble*, wouldn't similar problems occur when
connecting a 50 ohm filter to the input of, let's say, a narrowband
LNA? Or to the output of a PA? Would the narrowband LNA (or PA)
disrupt the filter's response, since the filter will now no longer see
a wideband 50 ohm termination at one of its ports? I know I'm missing
something here, but I just can't figure out what...
Thanks,
Bill
* Since the BP filters themselves are expecting to see only a very
wideband 50 ohm termination at both in/out ports in order to function
as designed -- but when two filters are cascaded the passbands of these
50 ohm filters are the *only* frequencies that actually and truly see
50 ohms; the stopbands of each filter will now not see 50 ohms at all,
as these stopbands are now each looking at the very low return losses
inherent each other filter's reflective stopbands.
filters can lead to big trouble*, wouldn't similar problems occur when
connecting a 50 ohm filter to the input of, let's say, a narrowband
LNA? Or to the output of a PA? Would the narrowband LNA (or PA)
disrupt the filter's response, since the filter will now no longer see
a wideband 50 ohm termination at one of its ports? I know I'm missing
something here, but I just can't figure out what...
Thanks,
Bill
* Since the BP filters themselves are expecting to see only a very
wideband 50 ohm termination at both in/out ports in order to function
as designed -- but when two filters are cascaded the passbands of these
50 ohm filters are the *only* frequencies that actually and truly see
50 ohms; the stopbands of each filter will now not see 50 ohms at all,
as these stopbands are now each looking at the very low return losses
inherent each other filter's reflective stopbands.