Spectral and reflection characteristics of PIN diode based tunable grating
Chi-Chun Lin1, Cheng-Chung Lin1*, Ching-Wen Chang2, Li-Wei Tu2, Quark Yung-Sung Chen2, Hong-Zhe Wei1
1Chemical Systems Research Division, National Chung-Shan Institute of Science and Technology, Longtan, Taiwan
2Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
* presenting author:林承忠, email:dannycclin@gmail.com
In the previous paper [1], we proposed an alternative method of dynamically tuning the transparency of a grating wafer in the microwave regime. The tuning was realized via fabricating an array of metallic stripes in cooperation with PIN diodes (SMP 1321-005). The estimation was implemented via far-field free space measurement. A similar result has also been found by some other authors via testing in parallel plate waveguide. These wafers, termed active frequency selective surface, were claimed to be desirable in both the microwave shutter and the time-varying stealth design of antennas (or agile radome) [2-4]. In this paper, spectral characteristics are further investigated. Here, we deploy a diode between each pair of metallic stripes. It is found that transmission spectral dip (with in excess of 20 dB isolation) drifts to lower frequency (from 8.42GHz to 5.73GHz) as diodes are turned ON. The result is consistent with Munir and Fusco, 2009 [4]. As shown by the result, our postulation that the change of conductivity of the diodes changes the current distribution upon the stripes as well as an equivalent length of the tuned stripes should be true. However, more accurate model needs to be found further. Nevertheless, we found that reflection change of the grating can be enhanced by deploying a metal ground plane beneath the tuned grating. It is believed that the enhanced reflection change is associated with the wave interference between the ground and the tuned grating. A similar postulation was proposed by Munir and Fusco, 2009 [4]. As also depicted by some other authors, the combination can be exploited in reconfigured reflector or backscatter device with agile radar cross-section [3-4].

References
1. Lin, C. C., et al., Tunable microwave grating based on RF diode array, 2014 AM PSROC, paper # P2-OE-002 (2014).
2. Bao, Z., et al, A novel active frequency selective surface based on complementary structures, IEEE MTT-S International Microwave Workshop Series on Millimeter Wave Wireless Technology and Applications (IMWS). p.1(2012).
3. Munir, A. and V. Fusco, Dual band switchable substrateless frequency selective surfaces, 2009 International Conference on Electrical Engineering and Informatics, paper # EE-21 (2009).
4. Munir, A. and V. Fusco, Frequency selective surface with dual band switchable reflection and transmission characteristics, Microwave and optical technology letters, 51, 2059 (2009).


Keywords: Tunable grating, Active frequency selective surface, Microwave