For optimal LTE MIMO performance, cellular Main and Aux antennas should be positioned at least 20 inches (50 cm) apart. This specific spacing is crucial for maximizing the benefits of Multiple-Input, Multiple-Output (MIMO) technology.
Optimal Spacing for LTE MIMO Performance
To achieve the best possible performance from your LTE MIMO setup, a minimum separation of 20 inches (50 cm) between the cellular Main and Aux antennas is recommended. This distance allows the antennas to experience sufficiently decorrelated signal paths, which is fundamental for MIMO to operate effectively.
At the lowest LTE frequency of 617 MHz, this 20-inch separation corresponds to approximately one wavelength (1λ). Spacing antennas by at least a full wavelength is often considered ideal for maximizing spatial diversity and MIMO gain.
Achieving Good MIMO Performance
While 20 inches (50 cm) provides optimal results, good MIMO performance can still be achieved with a slightly closer spacing. A separation of 10 inches (25 cm) between antennas is generally sufficient to deliver good performance. At 617 MHz, this 10-inch distance represents about half a wavelength (0.5λ).
Half-wavelength spacing is a common guideline in antenna theory for achieving good isolation and diversity, offering a balance between performance and practical installation constraints.
Why Antenna Spacing Matters for MIMO
MIMO technology leverages multiple antennas at both the transmitter and receiver to improve wireless communication performance. Its core benefit lies in utilizing spatial diversity and spatial multiplexing.
- Spatial Diversity: By placing antennas apart, they experience slightly different signal paths and environmental conditions. This means if one antenna receives a weak or faded signal, another might receive a stronger one. Proper spacing ensures these signal paths are sufficiently decorrelated, leading to:
- Improved signal reliability: Reduced likelihood of a complete signal drop.
- Enhanced signal quality: Stronger and more stable connections.
- Reduced errors: Fewer retransmissions, leading to more efficient data transfer.
- Spatial Multiplexing: MIMO can also send multiple independent data streams over the same frequency, effectively increasing data throughput. Adequate antenna separation is essential for the receiver to distinguish these separate streams accurately.
Without proper spacing, the signals received by each antenna would be too similar (highly correlated), negating the benefits of MIMO and potentially leading to performance no better than a single-antenna system.
Key LTE MIMO Antenna Spacing Recommendations
Here’s a summary of the recommended antenna spacing for LTE MIMO, based on performance goals:
| Performance Level | Antenna Spacing (Inches) | Antenna Spacing (Centimeters) | Wavelength Equivalence (at 617 MHz) |
|---|---|---|---|
| Optimal | At least 20 | At least 50 | 1 wavelength |
| Good | 10 | 25 | 0.5 wavelength |
Practical Installation Considerations
When installing LTE MIMO antennas, consider the following practical insights:
- Minimums are Key: The recommended distances are minimums. Exceeding them, within practical limits, generally does not harm performance and can sometimes offer additional benefits by further increasing decorrelation.
- Frequency Dependence: The physical distance for a given wavelength changes with frequency. The provided measurements (20 inches/50 cm and 10 inches/25 cm) are specifically tied to the lowest LTE frequency of 617 MHz. At higher LTE frequencies (e.g., 2.5 GHz or 3.5 GHz), the physical distance corresponding to a full or half wavelength will be significantly smaller. Always refer to specific installation guidelines for your equipment and operating frequencies.
- Obstructions and Environment: Ensure a clear line of sight between the cellular tower and the antennas if possible. Obstructions can impact signal quality and the effectiveness of MIMO.
- Mounting Type: Whether mounting on a pole, wall, or inside an enclosure, ensure the chosen location allows for the necessary separation between the Main and Aux antennas without compromising their performance or physical integrity.
Adhering to these spacing guidelines is a fundamental step in ensuring your LTE MIMO system delivers its full potential in terms of speed, reliability, and coverage.
