Principle of Longbo lens antenna and its application in 5G communication system

The Luneburg Lens is a spherical dielectric lens with a gradual refractive index gradient, proposed by Rudolf Karl Luneburg in 1944.

Core structure and refractive index profile

• Shape: It is a perfect sphere, with structural/material parameters being completely symmetrical around the center of the sphere.

• Refractive index: Radial gradient, gradually decreasing from the center to the surface of the sphere.

Ideal formula: n(r) = \√(2−(r/R)²)

◦ r: Distance from the center of the sphere; R: Radius of the sphere; n(R)=1 (matched with air).

• Equivalent structure: resembling an onion, with multiple dielectric rings, each layer having a different dielectric constant, achieving gradient refraction.

Working principle (reversible optical path)

Transmission mode: A spherical wave is emitted from a feed source at a certain point on the sphere, and is refracted by a lens into a parallel plane wave (high-gain narrow beam).

Receiving mode: Incident plane waves from any direction are refracted by a lens and precisely focused onto corresponding points on the spherical surface.

Key features: omnidirectional focusing, multi-beam independence, interference-free, high gain, low sidelobe.

II. Application in 5G communication system

5G requires high gain, multi-beam, wide coverage, large capacity, low interference, cost reduction, and efficiency improvement, and the Longbo lens antenna perfectly fits these requirements.

5G macro/micro base station coverage

• High-gain narrow beam: It boasts higher gain, longer coverage, and stronger penetration compared to traditional panel antennas.

• Simultaneous multi-beam coverage: Multiple feed sources are arranged on the spherical surface to form independent multi-beams, which do not interfere with each other, doubling the capacity.

• Roof resource reuse: Single antenna supports multiple frequency bands/multiple standards (2G/3G/4G/5G), reducing the number of antennas and saving space.

Typical 5G scenario applications

• High-speed rail/expressway/tunnel/bridge (narrow and long coverage)

◦ Narrow beam + high gain, continuous coverage over long distances, reducing the number of base stations.

◦ Case: The Mudanjiang-Jiamusi High-Speed Railway achieves full 5G coverage, reducing 195 base stations and saving approximately 92 million yuan in costs over 10 years.

• High-density scenarios (campus/venue/residential area)

◦ Multi-beam precise coverage reduces co-channel interference and enhances capacity and user experience.

◦ Supports Massive MIMO and works in synergy with 5G air interface technology.

• Millimeter-wave 5G (24G/28G/39G, etc.)

◦ Due to the significant path loss of millimeter waves, the Longbo lens offers ultra-high gain to compensate for the loss and enhance coverage.

◦ Supports wide-angle beam scanning (up to 146°), adapting to the flexible coverage requirements of millimeter wave.

• Ultra-long-range coverage in oceanic/remote areas

◦ With a maximum coverage of 75km, it solves the coverage challenge in maritime areas/remote regions.

• Emergency communication/temporary hotspot

◦ Rapid deployment, multi-beam high-capacity, meeting the needs of high concurrency scenarios such as music festivals and events.

Core value (solving 5G pain points)

• Cost reduction and efficiency enhancement: Reduce the number of base stations and lower deployment/maintenance costs.

• Capacity enhancement: With multi-beam parallelism, the capacity is enhanced by several times.

• Coverage enhancement: Longer range, deeper penetration, and more continuous coverage.

• Interference suppression: narrow beam + high isolation, reducing co-channel/adjacent channel interference.

• Multi-frequency compatibility: Supports Sub-6G + mmWave, adapts to 5G full-band.

III. Summary

The Longbo lens antenna, which achieves omnidirectional focusing, multi-beam, and high gain through spherical gradient refractive index, is a key technology for 5G coverage/capacity/cost optimization and has been widely used in multiple scenarios on a large scale.