Abstract
The use of metasurfaces to increase the number of modes, lower the operating frequency, and improve the field uniformity in reverberation chambers (RCs) is investigated in this paper. The method used to improve the field uniformity and decrease the resonance frequencies is based on increasing the number of modes by using the concept of subwavelength cavities. The resonance frequencies of a RC with metasurface wall are derived and expressed analytically in terms of macroscopic characteristics. Simulation of the reflection phase of the unit cell is then given as a guideline to choose the required microscopic parameters of the designed metasurface. The mode density in such subwavelength RCs is then obtained using a numerical eigenmode solver. Compared to traditional RCs, a much higher modal density is obtained at low frequencies. The standard deviation of the field uniformity in the test volume of the RC corresponding to different types of metasurface walls is finally compared. It is shown that by increasing the number of modes in the RC at the lower band, the operating frequency decreases and the field uniformity of the RC is improved.
Highlights
Current use of the reverberation chamber (RC) is based on a number of commonly accepted rules.It is a multi-mode cavity with its smallest dimension much larger than the operating wavelength at which it provides an electromagnetic compatibility (EMC) test environment exhibiting statistically homogeneous, isotropic, incoherent, uniform, and randomly polarized cavity field within acceptable limits
For traditional RCs, with walls consisting of metallic reflectors, the phase conditions are φ L = φ L0 = φW = φW 0 = φ H = φ H 0 = π, and, using (1), we can calculate the lowest usable frequency (LUF), which is the first frequency from which the test volume can be considered to be homogeneous and isotropic
For which concern the metasurface type, it can be inferred from the results of Figure 6 that the best option, i.e., the one providing the larger number of modes as a function of frequency, is the one corresponding to the two unit cells (#1 and #2) arranged alternatively (Figure 4)
Summary
Current use of the reverberation chamber (RC) is based on a number of commonly accepted rules. [8], this method was applied in order to reduce the LUF and to increase the mode density in RCs. The physical phenomenon exploited to increase the number of modes is the subwavelength cavity effect, which means that the first resonances occur at frequencies much lower than for a metallic cavity. An analytical model was proposed to fully characterize the modal structure of 3D metamaterial cavities which can be used to improve the properties of RCs [9] This analytical method provides the mechanisms underlying the improvements in the number of modes and mode density, related to the reflection coefficients of the modified walls, different to those of the classic case of perfect electric conductor (PEC). The simulation results show that when the number of modes increases, the field uniformity is effectively improved
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