RF Filter Measurements and Testing Methods

This page details various RF filter measurements performed during RF filter testing methods or procedures.

RF Filter Testing and RF Filter Measurements

RF filters can be constructed using either analog components or RF transmission line concepts, such as microstrip, cavity, or stripline. Before designing a filter, appropriate L, C, and R components are chosen with high precision. This ensures the desired characteristics and frequency response with minimal deviation from the expected results. An LCR bridge is used to measure the values of L, C, and R. Resistance and capacitance can also be measured using a digital multimeter.

The following are the RF filter specifications, representing the RF filter measurements that need to be evaluated:

• Frequency Range
• Insertion Loss
• Out-of-Band Rejection
• Bandwidth
• Return Loss or VSWR
• Shape Factor
• Ripple

RF Filter test setup

The following test equipment or tools are used for RF filter testing:

• LCR Bridge
• Spectrum Analyzer
• Vector Network Analyzer (VNA) or Scalar Network Analyzer (SNA)
• Oscilloscope

The figure above depicts a test setup using a spectrum analyzer. Here’s how the testing process goes:

• First, perform calibration, taking into account the RF cables and RF connectors required to connect the Device Under Test (DUT), which could be an LPF or BPF, etc.
• After the thru calibration is complete, connect the DUT in between and view the frequency response on the screen.
• This will provide the insertion loss at different frequencies of interest.
• Set the frequency range/BW/Span according to the technical specifications of the RF filter.
• Perform other measurements after setting up the test accordingly.