is it necessary to use 50om-port when designing a filter

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hakunamatata

Joined: 26 Feb 2003
Posts: 33

17 Jun 2003 10:44 is it necessary to use 50om-port when designing a filter

hello!everyone !i am desiging a harpin microstrip filter with SONNET now!
generally the port of the filter must be 50om but i have designed a 8poles harpin filter with very good performance using the ports which is about 20om,that means the port is wider than 50om-port!all the work i have done is completed by SONNET,i want to know whether it is right ?
is it necessary to use 50om-port when designing a microstrip filter?
can the filter i designed in the SONNET really behave a good performance in the practice?
thanks in advace!!!!!!

goxy

Joined: 25 Jul 2002
Posts: 268
Helped: 1

27 Jun 2003 20:29

Yes, it's extremly important!!

50ohm is standard impedance so all devices must be matched on 50ohm.
For example all fabricated LNA, filters, mixers ... are matched on 50ohm so it's easy to make combinaton with different manufactures with different caracteristics.
You can see changes whan you replaced output port with 50 or 20 ohm resistor.

If you attach your filter on some standard 50 ohm system, amplifier, spliter, analyzer... your filter will not have same caracteristics because your system is 50ohm but you'r matched input/output impedance is 20ohm.

How do you know that you are matched ports on 20ohm, are you changed standard settings from 50 to 20ohm?
If you are than turn back on 50ohm and simulate again.

eladg

Joined: 13 Jan 2002
Posts: 208
Helped: 4

29 Jun 2003 12:40 Re: is it necessary to use 50om-port when designing a filter

hakunamatata wrote:

yes u need 50 ohm
your results will be defrent when u use diffrent impedance, and olmost all the measure equvipment is 50 ohm

junction_crosstalk

Joined: 03 Dec 2002
Posts: 24

02 Jul 2003 12:07

Although 50 ohm impedance is usually used, you do not necessarily need to define 50 ohm port. The best is to define the port impedance with value of your load impedance, in this case your filter.

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burton

Joined: 12 Dec 2003
Posts: 198
Helped: 9

19 Dec 2003 3:09 Re: is it necessary to use 50om-port when designing a filter

I think the impedance of port is not very important when designing a filter, while whether the impedance of the network which consists of filter and input and output ports is 50 Ohm is very important.