# Study on Electromagnetic Radiation Interference Caused by Rocket Fuel
## 2 Methods  
### Experimental Setup  
Figure 2 shows that an electromagnetic radiation measurement system based on an ultrawideband omnidirectional antenna and a shortwave omnidirectional antenna was designed to measure the characteristics of electromagnetic radiation generated by rocket fuel [14]. The time-domain characteristics, spectrum distribution, and intensity of electromagnetic radiation were analysed as the experimental ends. In this paper, a shortwave antenna and ultrawideband antenna were cooperatively adopted to measure electromagnetic radiation, covering the frequency band up to 3 GHz, and a high-speed acquisition card was used to record data with a time-domain signal accuracy of \(10^{-9}\) s and a recording time as long as 1000 ms. As shown in Figure 2, the test point consisted of a shortwave passive omnidirectional antenna, an ultrawideband passive omnidirectional antenna and a signal conditioner. The sampling bandwidth of the shortwave passive omnidirectional antenna was 1.5 MHz\(\sim\)30 MHz, and it adopted a vertical polarization mode with a standing-wave ratio (SWR) of less than 2.5 and a gain greater than \(-35\) dBi. The ultrawideband omnidirectional antenna used a double-cone loading structure with a vertical polarization method, the sampling bandwidth was 30 MHz\(\sim\)3 GHz, the gain was greater than \(-15\) dBi, and the output impedance of both the shortwave antenna and ultrawideband antenna was 50 \(\Omega\). The signal conditioner possessed multiple functions, including a combiner, signal amplifier and limiter, which could combine two electromagnetic signals of different frequencies and amplify the signal at the same time with a range of amplification factors of 10\(\sim\)30 dB. The function of the limiter with limiting power greater than 10 W was to prevent the signal power from being excessively high and damaging the acquisition card [15; 16; 17; 18].  
Additionally, the process of analysing the electromagnetic signal can be clearly seen in Figure 2. In the sampling period, the delay time, peak arrival time and duration time of the electromagnetic signal were important parameters of the time-domain analysis. Through the Shench data processing program, various parameters of an electromagnetic signal could be obtained very accurately. The frequency spectrum distribution of an electromagnetic signal could be obtained by performing a fast Fourier transform on the time-domain signal of the electromagnetic radiation, but a simple fast Fourier transform could cover sampling points with smaller amplitudes. Since the electromagnetic radiation generated by fuel deflagration was a random unknown signal, using a Fourier transform with a Hanning window made it possible to extract the maximum effective electromagnetic spectrum. Electromagnetic radiation intensity is the most important type of data for preventing electromagnetic hazards. Since the fuel used in aerospace missions is of very high mass and has a strong deflagration energy, it is particularly necessary to consider the electromagnetic wave propagation loss when analysing the electromagnetic field intensity [19; 20].