A tunable RF notch filter, also called a programmable notch filter, is a filter used to remove a specific radio frequency. It can set the center frequency of the notch at different values, either mechanically or electronically. Here’s what a typical test setup with a tunable RF notch filter may look like:

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Source: Ranatec

The signaling units emulate the radio access network base station/access points in both downlink and uplink. To be able to calibrate the various signal paths and perform some of the measurements, a set of standard lab instruments are required, typically including power meters, a spectrum analyzer, and a signal generator. These parts are generally supplied by tier 1 players within the wireless test equipment industry, for example, Anritsu, Keysight, or Rohde & Schwarz.

At the center of this typical test setup for testing mobile devices, you find:

  1. Signaling selection and MIMO multiplexing using programmable switches, couplers, and attenuates to accommodate the adequate signal constellation ー in both uplink and downlink. 
  2. Signal routing by means of programmable switches, couplers, and attenuators. It enables high levels of test automation and provides flexible routing and level setting across the test system.
  3. Frequency extension by the means of switchable high- and low-pass filters to enable spurious emission measurement over the entire frequency range.
  4. Tunable (programmable) RF notch filter to remove specific frequencies. 
  5. DUT and MIMO multiplexing is the correspondence of the signaling selection and MIMO multiplexing. It provides an adequate signal constellation in both uplink and downlink to/from the mobile devices under testing.

However, an actual test setup will depend on the overall ambition in terms of:

  • coverage of standards
  • frequency bands
  • type and number of DUT:s used
  • selection of signaling units
  • selection of lab instrumentations
  • the ambition level in terms of automation.

The above example of a typical test setup is exactly an example, nothing more, nothing less. If you need help setting up your test setup, we highly recommend contacting Ranatec for assistance as they can provide you with everything you need for all your RF testing needs.

Low-pass filter vs. High-pass filter vs. Notch filter vs. Bandpass filter

There are four main types of filters:

  • A low-pass filter attenuates frequencies higher than the set cutoff frequency, allowing all frequencies lower than that to pass.
  • A high-pass filter does the opposite of a low-pass filter, it attenuates frequencies below a certain cutoff frequency and allows frequencies that are higher to pass.
  • A bandpass filter combines the properties of the low- and high-pass filters. Bandpass filters allow a certain range of signals with certain frequencies to pass and attenuate all the others in its stopband. 
  • A Notch filter is inverse to a bandpass filter. Similar to bandpass filters, they attenuate frequencies within a certain range only and allow other frequencies surrounding it to pass in its passband. The main difference is that a bandpass filter allows signals within a specific frequency range to pass, while a notch filter filters those signals out in that one frequency range.