k is the wave number of the incident wave, and /3m, hn, and ymn are propagation constants of the (/»,«)th space harmonic wave along x, y, and z respectively. These higher waves correspond to grating lobes. When all higher waves are evanescent, the active conductance is expressed using Eq. (2) as follows: where p = ka sinfl. The absorption efficiency of the infinite rectenna array is defined as a ratio of the maximum receiving power of one element to the incident power per an element (4). Then the absorption efficiency is represented by Here, the numerator denotes the absorption cross section. And the denominator denotes the cross section of the cell. The absorption cross section Ae is given by where Grad and D are the radiation conductance and the directivity of a singh element respectively, and G the active conductance. Therefore, Ae is rearranged a: follows: Here, we consider the case of no grating lobes. The substitution of Eq. (3) into Eq. (7) shows that the absorption efficiency r) is 100%. This means that the infinite rectenna array of CMSA’s can absorb the incident power perfectly under the condition of no grating lobes. This result is identical to that on the dipole antenna with ground plane. Figure 3 shows the absorption efficiency vs. element spacing in the case of a square lattice (Lx = Ly = L). When the grating lobe generates, the efficiency be-
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