Concepts¶
A quick refresher on the RF measurement vocabulary RFlect uses.
Active vs passive measurements¶
| Type | What you control | What you measure |
|---|---|---|
| Active | The DUT transmits at a known conducted power | Radiated power per angle → TRP |
| Passive | The chamber transmits, DUT receives passively | Gain per angle (relative to a calibrated reference) |
Active TRP needs a known conducted-power level so you can compute efficiency:
$$\eta = \frac{\text{TRP}{\text{radiated}}}{P$$}}
Passive gain is already in dBi relative to isotropic.
Polarization¶
Antennas radiate in two orthogonal polarizations (Ludwig-3 convention used here):
| Component | RFlect calls it | Maps to |
|---|---|---|
| $E_\phi$ | HPOL | Azimuthal / "horizontal" |
| $E_\theta$ | VPOL | Elevation / "vertical" |
Combined into total gain = $10 \log_{10}(|E_\theta|^2 + |E_\phi|^2)$ relative to isotropic.
Derived metrics:
- Axial Ratio (AR): major/minor axis ratio of the polarization ellipse
- Tilt Angle: orientation of the polarization ellipse
- XPD: Cross-Polarization Discrimination, $20 \log_{10}(\text{co-pol field}/\text{cross-pol field})$
- Sense: RHCP vs LHCP (right- vs left-hand circular polarization)
TRP: Total Radiated Power¶
IEEE-149 / CTIA discrete solid-angle integration with $\sin\theta$ Jacobian:
$$\text{TRP} = \frac{1}{4\pi} \int_0^{2\pi}!\int_0^{\pi} P(\theta,\phi)\,\sin\theta\,d\theta\,d\phi$$
RFlect implements that convention on EIRP-per-angle chamber data. Golden-reference tests lock the isotropic oracle (constant EIRP integrates back to itself). That is a math check, not laboratory accreditation or a certified measurement report.
Efficiency vs directivity¶
- Efficiency $\eta$: radiated power / accepted power. Includes ohmic and mismatch losses.
- Directivity $D$: peak gain divided by average gain over the sphere (the "shape" of the pattern).
- Gain = $\eta \cdot D$
Beamwidth¶
- HPBW (Half-Power Beamwidth, aka -3 dB beamwidth): angular width where gain drops to half-peak
RFlect computes HPBW with proper boundary wrapping at 0/360°.
Cal-drift epochs¶
A "setup_group" tags a calibration run with its methodology epoch (e.g. pre-2024-cable-change, 2026-v2-mount). Two runs in different groups are flagged on the cross-epoch consistency tab as not apples-to-apples. See Cal Drift.
UWB / SFF¶
For ultra-wideband antennas, gain isn't enough. You also care about preserving pulse shape across angles. System Fidelity Factor (SFF) = normalized cross-correlation between transmitted and received pulse. 1.0 = perfect; 0.95+ is typically good.