# Design of Typhoon Detection Downcast Device Based on Four-Arm Helical Antenna Structure
## 4 Analysis and Improvement  
Although the performance indicators meet the initial design requirements, they were only obtained from a simulation result under ideal conditions. Through further analysis of the initially designed antenna structure, it was found that there are currently two main problems.  
1. The height of the four-arm helical antenna is much higher than the length of the sonde, which results in a large amount of redundant space and a large volume of the entire drop system, which is contrary to the original design preferences of a small size, integrated design, and light weight. In view of the extremely limited space and weight requirements of the airship in the typhoon detection scenario, further optimization is needed to ensure the performance of the antenna while reducing the volume and weight.
2. As shown in Figure 8, the four-arm helical antenna is in direct contact with the sounding instrument. During operation affected by high-altitude weather, the shaking sounding instrument can easily have a negative effect on the structural stability and performance of the four-arm helical antenna. If the antenna is subjected to external force impact and vibration from the sounding instrument, the antenna structure may be deformed or displaced, affecting the radiation performance of the antenna. Frequent collisions also accelerate the fatigue and damage of the antenna's structure material, which may lead to the formation and expansion of microcracks. In severe cases, the antenna breaks and fails to function. These various mechanical noises also introduce interference signals, increase the noise level of the system, and affect the signal reception quality of the antenna.  
Therefore, it is necessary to further reduce the size of the quadrifilar helical antenna while ensuring that the performance indicators meet the original design requirements. At the same time, it is imperative to ensure that the stability of the structure and performance of the quadrifilar helical antenna are not damaged by the radiosonde during operation. After consulting the literature, it was determined that the structure of the quadrifilar helical antenna can be printed with flexible materials, which has several advantages [18]. First, flexible materials are easy to process and can be conveniently used to produce complex antenna structures. Secondly, flexible materials can absorb mechanical stress and have better mechanical stability. In addition, they can still ensure RF performance under deformation conditions, solving some problems that may be caused by the collision between the radiosonde and the antenna. Thirdly, these flexible materials can further reduce the weight and size of our antenna, making it very suitable for the sensitive requirements of our typhoon detection project [19].  
The flexible material can be made of PTFE (polytetrafluoroethylene) composite materials, such as the [PERSON] RT/duroid series. This type of material has low loss and a  
Figure 11: Overall schematic diagram of the droppable sounding system.  
stable dielectric constant, making it very suitable for high-frequency antenna applications. RT/duroid 6002 was used in the simulation, and its dielectric constant is 2.94. In the original antenna scheme, the copper wire has high ductility and plasticity. Due to the large torque at the feeding point of the spiral antenna, it can be slowly deformed with ease via the impact of the radiosonde after long-term use. The PTFE tube has high hardness and deformation resistance and can withstand certain impacts in harsh weather environments without deformation. At the same time, it ensures the light weight of the antenna and heat preservation during the storage of the radiosonde.  
In summary, the use of flexible materials meets the improvement requirements. The overall schematic diagram of the sounding system after improvement is shown in Figure 12.