RF Filter Calculator: Microstrip Low Pass & Bandpass

This RF filter calculator is designed for microstrip filter calculations. It covers both low pass and bandpass RF filter calculations commonly used in microstrip designs. Both pi filter and T filter section filter topologies are supported.

Microstrip Low Pass Filter Calculator

This is a simple LC-based RF lowpass filter calculator of order N equal to 3.

Example:

• INPUTS: Fc = 1182.5 MHz, Z0 = 50 Ohm
• OUTPUTS: L = 1.34e-8 Henries, C = 5.38e-12 farads

Microstrip Low Pass Filter Formula

The following equations are used in the RF lowpass filter calculator of order N equal to 3. Figure 1 depicts lowpass pi filter and T filter section topologies.

This simple RF filter calculator, made of L and C components, can be very handy.

Figure 1: Lowpass Pi and T Filter Topologies

Microstrip Bandpass Filter Calculator

This is a simple LC-based RF bandpass filter calculator of order N equal to 3.

Example:

• INPUTS: f1 = 1024.5 MHz, f2 = 1060.5 MHz, Z01 = 50 Ohm
• OUTPUTS: L1 = 4.42e-7 Henries, L2 = 1.319e-10 Henries, C1 = 5.276e-14 farads, C2 = 1.76e-10 Farads

Microstrip Bandpass Filter Formula

Figure 2 depicts bandpass pi filter and T filter section topologies. Following are the equations for the RF bandpass filter topologies mentioned above.

Figure 2: Bandpass Pi and T Filter Topologies

• L1 = [ Z0/ (Pi*(f2-f1)) ] … Henries
• L2 = [ Z0*(f2-f1) / (4*Pi*f2*f1) ] … Henries
• C1 = [ (f2-f1) / (4*Pi*f2*f1*Z0) ] … Farads
• C2 = [ 1 / (Pi*Z0*(f2-f1) ] … Farads

To further understand the concepts behind the Microstrip filter calculator, you can refer to a step-by-step RF filter design example. This design article covers a microstrip-based RF/Microwave Low Pass Filter design example, along with Kudora’s identities, Richard’s transformation, and a filter coefficients table for Chebysev LPF.