Scalar vs. Vector Mixers in RF Design: Key Differences

This article compares scalar mixers and vector mixers, highlighting the differences in their applications within RF and microwave circuit design. An RF mixer is a three-port device typically labeled as radio frequency (RF), intermediate frequency (IF), and local oscillator (LO). The RF and IF ports are bidirectional. With three ports, a mixer is described by nine S-parameters.

RF mixers are categorized in several ways:

• Scalar mixer and Vector mixer
• Single balanced mixer, Double balanced mixer, Triple balanced mixer
• Image reject mixer and Non-image reject mixer
• Diode mixer, Harmonic mixer

Scalar Mixer

• This type of mixer is used to measure RF parameters related to magnitude only. This is why it’s called a scalar mixer.
• Scalar Network Analyzers (SNAs) are used for scalar measurements with these mixers.
• Common parameters measured with scalar mixers include: Magnitude Conversion Loss, Isolation, Reflection, 1 dB Compression Point, Intermodulation, Noise Figure etc.

Vector Mixer

• This mixer is used to measure RF parameters related to both magnitude and phase. Hence the name, vector mixer.
• Vector Network Analyzers (VNAs) are used for vector measurements with these mixers.
• Common parameters measured with vector mixers include: Absolute and Relative Phase, Absolute and Relative Group Delay, Group Delay Ripple, Deviation from Linear Phase, Magnitude Ripple etc.

Challenges of Vector Mixers

Vector mixers present some challenges:

• RF and IF frequencies are typically different.
• All VNA receivers (reference & measurement) operate on identical frequencies.
• The LO phase directly affects the IF phase.
• Full system error correction requires a frequency conversion.