---
title: "Hazardous and safe zone for 2600 MHz BTS"
subject: "RF and Microwave Engineering"
chapter: 7
key: "semester_7/rf_and_microwave_engineering:bts-2600mhz-safe-zone"
source: https://www.bctengineer.com/q/semester_7/rf_and_microwave_engineering/bts-2600mhz-safe-zone
site: BCT Engineering
---

# Hazardous and safe zone for 2600 MHz BTS

RF and Microwave Engineering · Chapter 7: Microwave Antennas and Propagation

- Asked in: 2081 Bhadra, 4+4 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/rf_and_microwave_engineering/bts-2600mhz-safe-zone
- Whole chapter: https://www.bctengineer.com/md/semester_7/rf_and_microwave_engineering/chapter-7

## Question

Approximate the hazardous and safe zone for BTS tower operating at 2600MHz with antenna size of 0.5 m. Explain, how non-radiating radiation is hazardous to the human body?

## Short answer

For 2.6 GHz, D=0.5 m: λ=0.1154 m, R1=0.62√(D³/λ)=0.645 m, R2=2D²/λ=4.33 m. Hazardous zone is within about 4.3 m; far-field public zone is beyond 4.3 m if S=EIRP/(4πr²) is below 10 W/m². Non-ionising radiation heats tissue (SAR=σE²/ρ), causing cataract and burns above limits.

## Answer

#### Hazardous and safe zones at 2600 MHz, D = 0.5 m

```text
λ  = c/f = 3×10⁸ / 2.6×10⁹ = 0.1154 m
R1 = 0.62√(D³/λ) = 0.62√(0.125/0.1154)
   = 0.62 × 1.0408 = 0.645 m
R2 = 2D²/λ = 2×0.25/0.1154 = 4.33 m
```

| Zone | Distance from antenna | Status |
|---|---|---|
| Reactive near field | 0 – 0.65 m | Hazardous: very high, non-uniform E and H; no entry while transmitting |
| Radiating near field | 0.65 – 4.33 m | Hazardous in main beam: restricted to trained workers |
| Far field | > 4.33 m | Generally safe; S = EIRP/(4πr²) falls with r² |

```text
 [ant]|--0.65 m--|-------4.33 m-------|----->
      | reactive |  radiating near    | far field
      | DANGER   |  CAUTION (beam)    | SAFE (public)
```

So the hazardous zone is within about **4.3 m** of the antenna (mainly in front of it), and the public safe zone is beyond about **4.3 m**, provided the far-field power density there is below the ICNIRP public limit of 10 W/m² (2–300 GHz). The exact compliance distance depends on EIRP; for example, an EIRP of 1 kW gives S = 1000/(4π × 4.33²) = 4.2 W/m² at 4.33 m, which is already below 10 W/m².

#### How non-ionising radiation is hazardous

(The "non-radiating radiation" in the question is read as **non-ionising radiation**.)

- RF photons cannot ionise atoms, but the fields make polar molecules (water) rotate and ions move; this energy turns into **heat**.
- The absorption is the SAR = σE²/ρ (W/kg). Above about 4 W/kg the core temperature rises by about 1 °C, giving heat stress.
- At 2.6 GHz penetration is a few centimetres, so the skin, eyes and testes are heated most. The eye lens has poor blood flow and can develop **cataract**; burns occur at high power density.
- Long-term, possible non-thermal effects (headache, sleep disturbance, IARC Group 2B "possibly carcinogenic") are still being studied.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. For D = 0.5 m at 2600 MHz (lambda = 0.1154 m), what is the reactive near-field boundary R1 = 0.62 sqrt(D^3/lambda)?
   A. About 0.65 m
   B. About 4.33 m
   C. About 6.5 m
   D. About 0.115 m
   Answer: A. R1 = 0.62 x sqrt(0.125/0.1154) = 0.62 x 1.0408 = 0.645 m. (Key point: Reactive boundary calculation)

2. Where does the far field begin and why does it define the approximate safe zone?
   A. At 2D^2/lambda = 4.33 m; beyond this the power density falls as 1/r^2 and is usually below the public limit
   B. At 0.65 m; everything beyond is automatically safe
   C. At 43.3 m
   D. At lambda = 0.115 m
   Answer: A. R2 = 2 x 0.25/0.1154 = 4.33 m. Beyond it, the public is generally safe provided power density is under the ICNIRP limit. (Key point: Far-field start)

3. For an EIRP of 1 kW, what is the power density at 4.33 m and is it within the 10 W/m^2 public limit?
   A. About 4.2 W/m^2, which is below 10 W/m^2
   B. About 42 W/m^2, which exceeds the limit
   C. About 0.4 W/m^2 but the limit is 1 W/m^2
   D. About 1000 W/m^2
   Answer: A. S = 1000/(4 pi x 4.33^2) = 4.2 W/m^2, below 10 W/m^2. (Key point: Compliance check)

4. How does non-ionising radiation harm the body?
   A. Photons ionise atoms and damage DNA directly
   B. Fields rotate water molecules and move ions, and the energy becomes heat; the eye lens (poor blood flow) can develop cataract
   C. It causes radioactive decay in bones
   D. It has no effect at 2.6 GHz
   Answer: B. The harm is thermal; SAR above about 4 W/kg raises core temperature, and poorly cooled organs like the eye lens are damaged first. (Key point: Non-ionising hazard)

## Related in RF and Microwave Engineering

- [BTS radiation fields at 900 and 1800 MHz](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Abts-900-1800-radiation-fields) — RF and Microwave Engineering, chapter 7
- [GSM BTS propagation fields and non-ionizing SAR](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Agsm-bts-fields-sar) — RF and Microwave Engineering, chapter 7
- [Hazards and device to map BTS radiation zones](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Ahazards-bts-radiation-zone-device) — RF and Microwave Engineering, chapter 7
- [Short note: Microwave radiation hazards](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Amicrowave-radiation-hazards-note) — RF and Microwave Engineering, chapter 7, asked 3×
- [Microwave radiation hazards based on radiation fields](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Aradiation-fields-hazards) — RF and Microwave Engineering, chapter 7, asked 2×

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