RF Filter Design

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ELEC 412 RF Microwave Engineering
Fall 2004 Lecture 12 Low and High Pass Filter
Examples
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Low-Pass Filter Design Example

• Design a Low-Pass Filter with cut-off frequency
  of 900 MHz and a stop band attenuation of 18 dB
  _at_1.8 GHz.
• From the Butterworth Nomograph, Amax 1 and Amin
  18. Amax 1 since unity gain. And the order
  of the filter is N 3.
• From Butterworth Tables, g1 g31.0 and g2
  2.

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Transformation From Low-Pass Filter

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Normalized Lumped Parameter values

• What to do with the gk s

and
Where fc is the cutoff frequency and Lk_norm and
Ck_norm are normalized element values
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P5.7 Low-Pass Filter Design

• The normalized lumped element values
• g01
• g10.7654/(2?fc )
• g21.8478/(2?fc )
• g31.8478/(2?fc )
• g40.7654/(2?fc )
• g51.

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Denormalized Lumped Parameter Values
and
For all filter configurations
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Low-Pass Filter Design Example

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Low- To High-Pass Transformation

• Transform the Low-Pass Filter Normalized
  Component Values to the Normalized High-Pass
  Values
• Inductors in Low-Pass Configuration Become
  Capacitors in High-Pass.
• Capacitors in Low-Pass Configuration Become
  Inductors in High-Pass

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Denormalized Lumped Parameter Values
and
Same as that for the Low-Pass Filter
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De-Normalizing Filter Component Values

• All Normalized Component Values Are De-Normalized
  Using the Following
• and