Mixers and frequency converter testing

Mixer and frequency converter testing: Your challenges

Modern communication systems climb the frequency ladder, and direct RF is often not possible, so mixers are used to reach the target frequencies.

As active devices, mixers show various unwanted effects which need to be understood and minimized for the target application, as they significantly affect system performance.

Characterizing the performance of mixers and converters in RF systems is essential for understanding the full behavior of these devices and their impact on overall system performance. This process involves measuring their response to a range of operating conditions and input signals. Detailed analysis helps to identify performance limitations, optimize the design, and predict how the device will perform under various system requirements.

When looking at mixers, designers need to consider the following key parameters:

• Non-linearity is the core challenge. While mixers are intentionally designed to be non-linear to generate sum and difference frequencies from input signals, this same non-linearity also creates unwanted harmonics and intermodulation products. These effects degrade signal quality and introduce interference.
• Conversion loss is a crucial parameter in RF mixer testing. It represents the multi-dimensional gain or loss relationship that depends on the input power of both the IF and LO signals as well as their frequencies.
• Isolation measures the amount of unwanted crosstalk that leaks between the three key signal frequencies: RF, LO, and IF. Ideally, crosstalk between these frequencies should be minimized, and isolation is typically measured between the LO to RF or LO to IF ports. High isolation is essential to prevent unwanted interference signals. This parameter is critical for both mixer testing and understanding their impact at the system level, making it an important consideration when selecting mixers for system design.
• Noise figure (NF) quantifies the amount of unwanted noise introduced by an RF mixer during the frequency conversion process. Since mixers are active components, they inevitably add noise, and a lower noise figure indicates better performance.
• Phase translation, or group delay, refers to the phase relationship between the RF and IF signal, which is particularly important in beamforming applications and phased array antennas. Group delay examines the in-band phase linearity of the signal. Maintaining phase linearity is essential in digitally modulated systems, as it ensures low EVM, reduces bit error rates, and supports a good noise power ratio (NPR) with minimal intermodulation.

Our state-of-the-art solutions for mixer performance verification

Rohde & Schwarz is your trusted partner for comprehensive mixer performance verification with leading-edge testing solutions.

A vector network analyzer such as the R&S®ZNA is the tool of choice for comprehensive mixer validation. It supports a wide range of measurements and acts as a one-stop test setup for mixers. It supports much more than measuring accurate S parameters thanks to multiple LOs and sources with phase control:

• 2nd source for higher speed and for swept LO measurements
• 3rd and 4th LO for intermodulation on mixers and converters with multistage topologies
• Conversion loss, isolation, distortion and non-linearity
• Absolute and relative group delay
• Support for mixers with and without LO access
• Enhanced calibration methods for power and phase thanks to the phase reference Comb Generator R&S ZN-ZCG. This makes the traditional usage of a reference mixer superfluous.