01 Direct Effects of Lightning

The direct effects of lightning refer to the physical damage caused when lightning directly strikes a radome or antenna housing. These effects primarily include lightning impulse shock, electrical breakdown, heating, and electromagnetic forces.

02 Lightning Strike Zones on Aircraft

Based on the probability of lightning attachment to different parts of an aircraft, the lightning strike zones are divided into three main categories, further subdivided into six sub‑zones. Zones 1A, 1B and 1C are first return stroke zones; Zones 2A and 2B are swept lightning channel zones; Zone 3 is the current conduction zone.

In protection design, priority should be given to placing radomes and antenna housings in zones with a lower probability of lightning attachment, such as Zone 3.

03 Lightning Protection Techniques for Radomes and Antenna Housings

Protection against direct lightning effects mainly relies on the material properties of the housing, structural design, and protective devices. On the one hand, selecting materials with a high dielectric constant can increase the breakdown voltage of the radome, thereby enhancing its ability to withstand lightning strikes. On the other hand, properly designing the thickness and shape of the radome can optimize the electric field distribution and reduce lightning damage. Additionally, devices such as diverter strips can be used to guide lightning currents to safe areas, thus protecting the radome and antenna housing from damage.

1. Protection through Housing Characteristics and Structural Design:

a. Relationship between housing material and electric field distribution: For conventional dielectrics, as the relative permittivity (εr) of the housing increases within the range of 0 to 50, the lightning protection effect becomes more pronounced.

b. Relationship between housing thickness and electric field distribution: As the thickness of the housing increases, the electric field near the internal antenna gradually decreases, and the trend becomes less steep.

2. Protection using Segmented (Gapped) Diverter Strips:

Segmented diverter strips (or gapped diverter strips) are devices used for lightning protection. They offer good radome transparency and have minimal impact on antenna performance. Their working principle is as follows:

Construction: A segmented diverter strip consists of a series of thin conductive metal segments connected by resistive material and mounted on a composite backing tape.

Normal condition: Under normal conditions, the gaps between the metal segments keep the conductive path open, so the entire diverter strip acts as an insulator.

During a lightning strike: When a lightning strike occurs, large amounts of charge accumulate at the ends of adjacent metal segments, producing a feather‑like arc. When the voltage reaches a certain level, the metal segments break down the air above them, forming an ionized channel.

Lightning current conduction: The lightning current is conducted through this ionized channel to the down conductor, bypassing the diverter strip itself. This prevents damage to the diverter strip and also avoids high‑current damage to the blade surface.

a. Relationship between diverter strip gap and electric field distribution
   The gap between diverter strip segments has a significant impact on electric field distribution. Currently, the gap is generally around 0.2 mm. Compared to gaps of 0.6 mm or 1.0 mm, the 0.2 mm gap produces a higher electric field strength, making it easier to attract lightning.    

b. Relationship between diverter strip shape and electric field distribution
   The shape of the diverter strip significantly affects electric field distribution. Different shapes produce different field distribution characteristics during a lightning strike. For example, elliptical and circular strips have higher electric field intensities during the initial stage; diamond‑shaped strips may erode at the tip at the moment of breakdown, making the tip rounder; while square strips offer better continuity after conduction, allowing the lightning arc to persist. Therefore, the choice of diverter strip shape should consider the specific application scenario and protection requirements.    

c. Influence of diverter strip dimensions and substrate dielectric constant
   The dimensions of the diverter strip are also an important factor affecting its protection performance. If the strip dimensions exceed 1/8 of the wavelength, its radome transparency is degraded. Generally, strip dimensions between 1 mm and 2.5 mm are suitable. In addition, the dielectric constant of the backing material affects electric field distribution – a lower dielectric constant leads to a stronger electric field. Therefore, when selecting backing material, its dielectric constant must be considered.    

d. Distribution design of diverter strips

e. Diverter strip length calculation

The length should be calculated based on the voltage breakdown effect. Generally, a length about 30% to 50% longer than the antenna is most suitable. In the model shown below, a 350 mm diverter strip already provides lightning protection, while a 450 mm strip offers very good protection.

f. Number of diverter strips required

04 Test Verification and Simulation Analysis

In the development of lightning protection techniques, test verification and simulation analysis are indispensable. By building test equipment, the damage process of direct lightning effects on radomes and antenna housings can be simulated, and the actual performance of protective devices can be observed. Simultaneously, simulation software can be used to model and analyze electric field distribution, further optimizing the design parameters and structural forms of protective devices.

1. Initial leader attachment test: Lightning can come from any direction, so tests must be conducted from multiple directions and angles. An actual antenna or a representative mock‑up should be placed during testing to ensure validity and accuracy.

2. Swept channel test: If the test object is larger than 0.25 m, it must be tested in sections.

3. High‑current physical damage test: After identifying the lightning attachment point on the housing, high‑current testing should be performed to verify the current‑carrying capability of the protective device, while monitoring induced voltage and current at the antenna port to ensure they remain within design thresholds.

Conclusion

In practical applications, protection can be enhanced through the following approaches:

1. Strengthen material research to find new materials with higher dielectric constant and better radome transparency;

2. Optimize structural design by adjusting parameters such as the shape and thickness of the radome to improve electric field distribution;

3. Conduct in‑depth research on the protection mechanisms and performance characteristics of diverter strips and other devices to develop more efficient and reliable protection solutions;

4. Strengthen test verification and simulation analysis to continuously improve the reliability and practicality of lightning protection techniques.