## 7 Conclusions  
Cage armour systems are an interesting way to increase the protection of armoured vehicles (especially lighter vehicles) to offer protection against a number of highly proliferated antitank rocket projectiles, especially from the RPG-7 family. This level of protection cannot be obtained using passive armour only. Different technical solutions, including slat, bar, net and inertial distributed weight systems, have been developed for cage armour applications. As was shown, the efficiency of such a cage armour system can as a first approximation be deduced from geometrical analysis only. This approach was validated based on an extensive number of tests done with different cage armour systems against different RPG-7 antitank rocket projectiles.  
Although most evaluate the ballistic efficiency of cage armour systems only against the impact angle in the vertical plane, it was shown that the performance of especially the net solutions is also highly dependent on the impact angle in the horizontal plane. An analysis based on the compound impact angle shows that the perceived ballistic inefficiency of the simpler slat and bar armour systems as a function of the vertical impact angle is more than compensated for by their insensitivity to the horizontal impact angle. Furthermore, a trajectory model for the PG-7 projectile showed that the actual vertical impact angles should be lower than 11\({}^{\circ}\) for most practical cases, further accentuating the performance  
Figure 30: Mass efficiency of the different considered cage armour systems for a maximum vertical impact angle of 15\({}^{\circ}\) as a function of the considered horizontal impact angle range.  
difference between slat and bar armour on the one hand and net solutions on the other hand. It was also shown that the inertial distributed weight armour has the highest ballistic efficiency of all considered cage armour systems.  
Although the net solutions have an obvious disadvantage regarding ballistic efficiency, they do, however, come with the highest mass efficiency, especially the polymer fibre-base solutions. The latter is by far the most weight-efficient solution, and if the weight constraints for adding a cage armour solution to an armoured vehicle are severe, net systems offer the best practical solution.  
Major drawbacks of the polymer fibre-based net armour and the inertial distributed weight armour are, however, their increased complexity and limited shelf and in-service life due to the use of polymers. Slat, bar and steel net solutions do not have the drawback of a limited shelf and in-service life, and especially bar and aluminium slat solutions give low-cost, low-complexity, high-performance cage armour systems.  
Last but not least, it is important to point out the limitations of this analysis. Firstly, the geometrical analysis is approximate and does not take into account all intricacies of the interaction between a cage armour system and an incoming projectile. Secondly, the analysis only considered the active components of the cage armour system. The influence on the ballistic and mass efficiencies of all components, attachments, supports, etc., necessary to mount the cage armour onto the vehicle has been omitted from this analysis. Finally, most of the analysis was based on a specific threat, being the PG-7 projectile. Depending on the actual threat scenario, different threats might have to be considered leading to differences in efficiency.  
This research received no external funding.  
The author declare no conflict of interest.  
Appendix A Theoretical ballistic efficiencies of the different cage armour systems can be calculated based on their specific geometry and dimensions, and the dimensions and the trajectory of the incoming projectile. The main dimensional properties of the projectile affecting the efficiency and mathematical models to calculate this efficiency based on the specific cage armour design will be introduced in the following sections.