UHF RFID Read Range — Impinj R420 + Alien Higgs-3

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Laboratory · Read Range Calculation

Engineering calculation using Friis free-space model. Three substrate scenarios. ETSI EN 302 208 compliant. Theoretical upper bounds and practical field margins.

Reader

Impinj R420

EU · 30 dBm · 4-port

Antenna

Times-7 Far-Field

9 dBi · RHCP

Tag / Chip

Alien Higgs-3

−18 dBm · 93×19 mm

Standard

ETSI EN 302 208

865 MHz · ERP 2 W

01 · Link Budget 

Input Parameters

Parameter	Value	Source / Notes
Frequency	865 MHz	ETSI EU band centre
Wavelength (λ)	0.347 m	λ = c / f
TX Power (ERP)	33 dBm (2 W)	ETSI EN 302 208 maximum
Reader antenna gain	9 dBi	Times-7 Far-Field typical
Tag chip sensitivity	−18 dBm	Alien Higgs-3 datasheet
Tag antenna gain	~2 dBi	Dipole inlay, 93×19 mm
Polarisation loss (RHCP→Linear)	3 dB	Fixed, circular→linear
Cable / connector loss	~0.5 dB	Typical short run
Total link budget (air)	~52 dB	Before substrate losses

02 · R_max Results 

Read Range by Substrate — Three Scenarios

Scenario 1 · Air / Foam

~11^m

Practical indoor: ~3–4 m

Mismatch loss: 0 dB
Link budget: ~52 dB

Scenario 2 · Wood (dry)

~6^m

Practical indoor: ~~2 m

Mismatch loss: ~5 dB
Link budget: ~47 dB

Scenario 3 · Plastic

~8^m

Practical indoor: ~~2.5 m

Mismatch loss: ~3 dB
Link budget: ~49 dB

⚡ Key finding: The manufacturer's 6–7 m reflects the Friis theoretical value for near-ideal conditions. Indoor with multipath fading and random tag orientation converges to 3–4 m for reliable system design.

Model limitationFriis assumes far-field, isotropic radiation and a single path. Multipath fading (±10–20 dB), tag orientation loss (up to 20 dB) and backscatter sensitivity are not captured. All values are theoretical upper bounds. On-site measurement required.

03 · Mismatch Loss 

Substrate Effect on Read Range

Material	ε_r	Mismatch Loss	R_max (theoretical)	Primary mechanism
Air / foam spacer	1.0	0 dB	~11 m	—
Plastic (ABS, PP)	2.5–3.5	~3 dB	~8 m	Dielectric loading
Wood (dry)	2–4	~3–6 dB	~6 m	Dielectric + moisture
Glass	6–8	~4–7 dB	~4–5 m	High ε, strong detuning
Metal (no ferrite)	—	+10–20 dB	< 0.5 m	Eddy currents, interference
Liquid / wet surface	~80	+15–25 dB	< 0.3 m	High dielectric absorption

04 · Conditions 

When Is the Manufacturer's 6–7 m Achievable?

✓ Achievable when all conditions met:

✓ Line-of-sight (LOS), no obstacles
✓ Tag on air gap or foam spacer (≥10 mm)
✓ Tag orientation optimised — face parallel to antenna
✓ RH < 50%, temperature +15–25°C
✓ Single reader, no WiFi / RFID interference
✓ VSWR < 1.5, calibrated connectors
✓ Fading margin ≤ 3 dB (controlled environment)

✗ Not achievable in these conditions:

✗ Tag on bare metal — eddy currents eliminate range
✗ Random tag orientation (bulk / conveyor)
✗ Dense indoor with multipath reflections
✗ RH > 60% or condensation on tag
✗ Multiple readers active in same zone

05 · Model Limitations 

What Friis Does Not Account For

#	Factor	Typical Impact	Relevance
1	Multipath fading (indoor)	±10–20 dB	Dominant indoor factor
2	Tag orientation (random)	up to 20 dB	Uncontrolled placement
3	Antenna detuning (substrate)	5–15 dB	Metal / liquid proximity
4	Backscatter sensitivity	limiting	Reader RX sensitivity
5	Cable / connector VSWR	1–3 dB	Installation quality
6	Chip-to-chip variation	±3 dB	Higgs-3 production spread
7	Temperature / humidity	2–5 dB	Outdoor / cold chain
8	Adjacent interference	5–10 dB	Dense reader environments

Friis Assumes

· Isotropic antennas

· Free-space LOS

· Static channel

· Single path

· Forward link only

· Perfect impedance match

Real RFID Deployment

· Directional + polarisation

· Multipath + reflections

· Dynamic environment

· Multipath fading dominant

· Backscatter limits system

· Substrate-dependent detuning

06 · Recommendation 

Engineering Summary

Parameter	Design Value	Notes
Reliable read range (indoor)	3–4 m	With 10 dB fading margin
Theoretical max (air, LOS)	~11 m	Friis, ideal conditions only
Manufacturer claim (6–7 m)	achievable	Controlled environment only
Minimum power margin	15 dB	Fading + orientation
Recommended design range	3–4 m	Plan worst case, test on site
Improvement option	+3 dB	Switch to linear polarisation antenna

Final recommendationDesign for 3–4 m reliable read range. Treat 6–7 m as theoretical ceiling, not planning baseline. Always conduct site survey with real tags and substrate before finalising antenna positions.

07 · FAQ

Frequently Asked Questions

What is the real-world read range of Impinj R420 with Alien Higgs-3?

In typical indoor conditions practical read range is approximately 3–4 m with a 10 dB fading margin. The manufacturer's 6–7 m is achievable only at line-of-sight, foam spacer, optimal orientation and RH below 50%.

How does substrate material affect RFID read range?

Substrate permittivity causes antenna detuning. Air: 0 dB. Plastic (ε_r 2.5–3.5): ~3 dB. Wood (ε_r 2–4): ~5 dB. Metal without ferrite: 10–20 dB, range under 0.5 m.

Why does the Friis equation overestimate RFID read range?

Friis assumes free-space and a single propagation path. Real deployments add multipath fading (±10–20 dB), tag orientation loss (up to 20 dB) and backscatter sensitivity limits.

rfid.org.ua · Laboratory · 2026-02-27Model: Friis · ETSI EN 302 208

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