RF Transformer Types
| Type | Impedance Ratio | Frequency Range | Application |
|---|---|---|---|
| Transmission-line transformer | 1:1, 1:4, 1:9 | 1 MHz – 3 GHz | Wideband matching, balun |
| Wound ferrite transformer | 1:1 to 1:16 | DC – 500 MHz | HF, VHF matching, isolation |
| LTCC integrated transformer | 1:1 to 1:4 | 0.5 – 6 GHz | Differential IC interface |
4:1 Balun Transformer S-Parameters (Example)
4:1 impedance ratio (200Ω balanced → 50Ω unbalanced):
Port 1 = 50Ω unbalanced input
Port 2 = 100Ω (half of 200Ω balanced output, measured single-ended)
Ideal S-parameters (in 50Ω system, with 200Ω load):
After renormalization to 200Ω port 2:
S11 = 0 (matched input)
S21 = 0 dB (lossless)
S12 = 0 dB (reciprocal)
S22 = 0 (matched output at 200Ω)
Real transformer at 100 MHz:
IL = 0.2 dB (ferrite loss)
RL = 20 dB (port match)
Bandwidth: 1 MHz – 200 MHz (decade bandwidth)
Analyzing in RF View
- Load transformer .s2p file (measured with 50Ω VNA, terminated appropriately)
- S21 dB: verify insertion loss (<0.5 dB for good transformer)
- BW Marker: find −1 dB bandwidth (transformer bandwidth)
- S11 dB: check input port match at operating frequency
- Group Delay: flat group delay confirms wideband linearity
- Note: renormalization to transformer's characteristic impedances may be needed for accurate analysis
RF View: Load transformer .s2p, verify IL and BW with markers. For accurate impedance analysis, note the reference impedance used during VNA measurement — transformers require careful port normalization. Free on Android.