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kpcheah
Joined: 07 May 2008
Posts: 23
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 10 Feb 2009 14:00 how to get length of the input&output matching line? |
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how to determine the length of the input and output matching line of the bandpass filter?izzit 1 wavelength?half wavelength? 1/4 wavelength? or others? for example, i need to design a bandpass filter with specification as below:
Center frequency: 2.4GHz
3dB bandwidth: 200MHz
dielectric constants: 4.5
dielectric thickness: 0.406mm
please refer to the picture below:
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vfone
Joined: 10 Oct 2001
Posts: 2328
Helped: 327
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10 Feb 2009 14:54 Re: how to get length of the input&output matching line? |
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| Theoretically, if are perfect 50 ohms, the length of these in/out transmission lines will not affect the characteristics of the filter.
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biff44
Joined: 24 Dec 2004
Posts: 1836
Helped: 244
Location: New England, USA
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10 Feb 2009 16:20 Re: how to get length of the input&output matching line? |
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When you design this filter, the widths and gaps of the resonators depend on what the input/output impedance is specified to be. IF you designed the filter impedance to be 50 ohms, then the above post is correct, the input and output 50 ohm lines can be any length you want.
In some cases you might deliberately design the coupled line filter for an impedance other than 50 ohms (for example if the gaps would be too small for a 50 ohm design). In those few cases, you would make the input and output lines quarterwave long, and their impedance would be Zm = √(50*Filter Impedance)
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