## 4 Conclusions  
This study presents the development of tungsten electrodes with high-curvature-radius spiked structures, replacing traditional iron-nickel alloy electrodes in plasma elements. The new electrodes achieved an ultra-high-density, low-pressure cold plasma with a density of 1.15 \(\times\) 10\({}^{12}\) cm\({}^{-3}\), surpassing similar studies by an order of magnitude. Lightweight and cost-effective tubular and annular cold plasma elements were also developed, showing an 88.2% increase in plasma density under the same conditions. These elements have the potential to serve as plasma countermeasure antennas and can form large-area, high-density plasma by combining multiple element arrays, demonstrating excellent performance in electromagnetic wave absorption.  
The tungsten electrodes, treated hydrothermally to form spiked structures, enhanced field emission characteristics and reliability compared to conventional iron-nickel alloy electrodes. At 100 mA, the tungsten electrodes achieved a plasma density of 7.79 \(\times\) 10\({}^{11}\) cm\({}^{-3}\) (88.2% improvement), and at 150 mA, a density of 9.47 \(\times\) 10\({}^{11}\) cm\({}^{-3}\) (15.3% improvement). Even at 200 mA, the tungsten electrodes maintained a high plasma density of 1.15 \(\times\) 10\({}^{12}\) cm\({}^{-3}\), while the iron-nickel electrodes showed damage and a drop in plasma density.  
The study also investigated the impact of plasma on radar electromagnetic waves. The experimental results showed that both tubular and annular plasma elements exhibit excellent radar countermeasure performance. For HH-polarized radar signals in the S and C bands, the RCS value decreased with increasing plasma density, indicating that these high-density plasma elements have excellent potential as radar countermeasure antennas. The experimental data of the RCS values of high-density cold plasma element arrays and their underlying metal films demonstrated that large-area, ultra-high-density cold plasma is highly effective in reducing radar detection capability in the S and C bands. For instance, for a 3.1 GHz radar signal, the RCS value was reduced from 25.18 m\({}^{2}\) to 8.41 m\({}^{2}\). Attenuation was also observed in the X band, proving the superior characteristics of plasma technology in electronic countermeasures.  
This research lays a foundation for further defense applications, showcasing the superior characteristics of high-density cold plasma technology in electronic warf  
Figure 10: RCS results of Plasma tube array. (**a**) S-band HH polarization; (**b**) S-band VV polarization; (**c**) C-band HH polarization; (**d**) C-band VV polarization; (**e**) X-band HH polarization; (**f**) X-band VV polarization.  
**Author Contributions:** Conceptualization, Y.Z. ([PERSON]) and Y.Z. ([PERSON]); Methodology, X.H. and Y.Z. ([PERSON]); Software, H.Y.; Validation, H.W.; Formal analysis, H.W. and K.L.; Resources, Y.X., Y.T. and Y.Z. ([PERSON]); Writing--original draft, H.W.; Writing--review & editing, H.W.; Supervision, Y.Z. ([PERSON]); Project administration, Y.Z. ([PERSON]). All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding authors.  
**Conflicts of Interest:** The authors declare no conflict of interest.