Why Resampling Is Needed
S-parameter files from different VNAs, different sweep setups, or different EM simulators often have different frequency grids. Direct overlay comparison requires the same frequencies. Cascade simulation is most accurate when components share the same grid. Resampling aligns files to a common set of frequency points.
Correct Interpolation Method
CRITICAL: Interpolate in RI (real + imaginary) domain, NOT in dB!
Why: Near a null (S21 minimum), dB changes rapidly:
S21 changes from −40 dB to −60 dB over 1 MHz
But |S21| changes from 0.010 to 0.001 — a small linear change
Interpolating dB gives wrong results; interpolating RI gives correct results
Steps for each S-parameter pair (e.g., S21):
1. Convert (dB, angle) → (re, im)
2. Linear interpolate re(f) and im(f) at new frequency points
3. Convert (re, im) → (dB, angle) for output file
Step-by-Step in RF View
- Open RF View → SNP Converter → Frequency Change tab
- Load source file (e.g., filter_VNA_A.s2p: 800–3000 MHz, 221 points)
- Set target grid: Start=900 MHz, Stop=1000 MHz, Points=101, Spacing=Linear
- Tap Apply → resampled file saved to output folder
- Load original + resampled together → traces should be identical (resampling is lossless for smooth data)
Batch Resampling Multiple Files
Use case: 20 filter .s2p files from different VNA sweeps All must be aligned to: 1800–1900 MHz, 101 points, 1 MHz step 1. Select all 20 files in RF View Batch Converter 2. Set common target grid (same for all) 3. Apply → 20 resampled files created in output folder 4. Load all 20 → same frequency axis → valid comparison
Resampling Limitations
- Cannot add resolution beyond source data — if source has 5 MHz steps, don't resample to 1 MHz steps (false precision)
- Sharp filter edges: interpolation may slightly smooth the edge — use ≤2× upsampling
- Extrapolation beyond source range: RF View extrapolates using last available data — use with caution
RF View Frequency Change: Batch resample any number of SNP files to a common grid in one operation. Uses correct RI-domain interpolation for accurate results near filter edges. Free on Android.