In this paper a multi-functional metasurface is proposed which can work as a narrowband transmissive/reflective frequency selective surface (FSS) and an on-air frequency mixer based on its switching response. The metasurface is made up of unit cells with square and circular metallic loops connected by PIN diodes that are controlled by a biasing source. In contrast to typical wideband FSSs, the structure provides 0.55 GHz of narrow stopband (a fractional bandwidth of 22\%) at 2 GHz in the OFF state bias. The bandstop response can be adjusted by varying the reverse bias voltage. The metasurface alternates between its functionalities when in forward bias by providing a passband at the operational frequency. The structure is compact and operates as a transmissive/reflective surface under two different bias conditions (ON and OFF). The design is angularly stable and polarization-insensitive for both TE and TM polarisation. A prototype of the designed structure is developed and the measured results correlate well with the simulated responses. On-air frequency mixing for a wave propagating through the metasurface is experimentally demonstrated and effects of different parameters affecting the mixing are parametrically studied.

In this paper, MATLAB based computational approaches for the design and analysis of time-varying capacitors using the finite-difference time-domain (FDTD) technique and the Simulink design environment are presented. The FDTD formulation for multiple lumped capacitors loaded in series on a transmission line is discussed and extended to include time variation of capacitance. The design methodology for the same is also discussed using MATLAB’s Simulink using the RF Blockset Library. The developed FDTD formulation and the Simulink method are then used to design a mixer with time-varying capacitors loaded transmission line.