RESULT AND DISCUSSION

A parametric study of the planar structure varies the air gap between the two layers (see Table 1). The simulated optimal value of insertion loss is about 0.3 dB for the 7.6 mm air gap. Hence, further study is done using 7.6 mm. The transmission characteristic of dual-layer planar structure with that air gap is shown in Figure 6.

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Table 1
Figure 6

Figure 6 Planar FSS |S21|.

Good bandpass performance is demonstrated experimentally for the planar FSS in the frequency range of 6.7 to 10.7 GHz. Insertion loss is low with a -10 dB bandwidth of 4 GHz (45.96 percent). The planar structure exhibits a sharp roll-off of 45 dB/GHz (left) and 73.33 dB/GHz (right). The experimental result is in good agreement with the simulation. A comparison of the planar structure’s performance with other reported work is shown in Table 2. It exhibits a wider bandwidth and sharper roll-offs on both band edges.

Table 2
Figure 6

Figure 7 Curved FSS |S21|.

Table 3

Results for the dual-layer semi-cylindrical finite curve structure are shown in Figure 7. The two layers of semi-cylindrical curved FSSs are assembled with an air gap of 7.6 mm. Measurements of the structure demonstrate a wide passband of 4.2 GHz for a 45.16 percent bandwidth. It has a good bandpass property with a low insertion loss. Roll-off at the lower band edge is 16.66 dB/GHz and roll-off at the higher band edge is 32.09 dB/GHz. The sharp roll-off achieved by the curved structure increases its selectivity. Good agreement between simulated and measured results is observed. A comparison with recent results reported for curved FSSs is shown in Table 3, demonstrating the highest percentage bandwidth and the sharpest roll-offs.

CONCLUSION

Performance of the dual-layer semi-cylindrical aperture-type curved FSS described here is shown to be better than other recent work, while also being nearly the same as the planar structure.9,12,13 Achieving a wideband performance with low passband insertion loss and sharp roll-offs in a curved structure is the key accomplishment of this work. Because its conformal structure is easily integrated onto complex surfaces, such as ogives, it is suitable for use in the design of sub-reflectors and radomes.

References

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