Design of electromagnetic shield based on voltage-controlled conduction (Part 2)

3 Experimental studies

The horn antenna is used as the protection object, and the BAP63 PIN diode, FR4 copper-clad substrate, and 1 mm wide metal lead are selected to make protective cover A (3 mm spacing) and protective cover B (5 mm spacing). The actual photo of the protective cover and the experimental configuration are shown in Figure 7. The protective cover is placed close to the horn mouth, and the horn antenna is vertically polarized.

A transmit and receive antenna test solution based on a vector network analyzer is used.

An external DC bias voltage is applied to control the on/off of the PIN diode, simulating the state of the protective cover when a strong electromagnetic pulse is applied, and measuring its insertion loss IL and isolation I. The experimental setup is shown in Figure 8. When the DC power supply is disconnected, the PIN diode is not turned on, the protective cover is in a high-resistance state, and the insertion loss IL is measured; when the DC power supply is connected, the PIN diode is turned on, the protective cover is in a low-resistance mode, and the isolation I is measured.

The test results are shown in Figures 9 and 10. The figure shows the change of the ratio of the antenna transmission and reception power with the frequency f under different conditions. When f<1.6 GHz, the insertion loss of the protective cover meets ILB18 dB, where IB>46 dB (f=1.55 GHz); when f>2 GHz, the protection performance of protective covers A and B tends to be consistent, and the corresponding frequency points of the curve fluctuations are basically the same, with only slight differences in amplitude.

The package capacitance and inductance of a PIN diode affect its impedance characteristics.

When shielding, the PIN diode array conducts and resonates, and the reflection and absorption of strong electromagnetic pulses exist simultaneously. The mesh size of shield B is larger, but IB>IA (f<2 GHz). When shield B transmits waves, parasitic capacitance and inductance exist, which eliminates the large resonance of pure capacitance. The wave transmission performance of the shield is improved, and only some frequency points have small resonances.

After applying a DC bias, the forward voltage drop of the diode is 0.8 V and the conduction current is 20 mA. Since the high-level microwave signal is not as effective as the DC in modulating the conductivity of the diode I region, the power density of the strong electromagnetic pulse irradiation will be greater than the above data. By adjusting the size of the metal grid, reducing the PIN diode limiting threshold, and increasing the PIN power capacity, protective covers for different protection needs can be made.

4 Conclusion

This paper analyzes the voltage-controlled conductive characteristics of PIN diodes and combines the metal grid shielding theory to propose a design scheme for an electromagnetic environment adaptive protective cover. After that, a simulation study of the ideal protective cover was conducted to analyze the influence of various factors on the protective performance of the protective cover; an experimental study of the protective cover was conducted to analyze its performance from the perspective of transmission characteristics, achieving an insertion loss of less than 2 dB for the frequency band below 1.6 GHz; and an isolation greater than 18 dB for the frequency band below 2 GHz. The electromagnetic protective cover has the advantages of adaptability and ultra-wideband. By improving the processing technology, adjusting the grid structure and selecting ideal devices, strong electromagnetic pulse protection can be achieved for equipment and systems with different frequency bands and different protection requirements.