試題詳解

23. Consider a parallel-plate waveguide (plates at y=0and y=b planes), with wave propagating in the +z direction. For the lowest-order TM mode, if the instantaneous field expression for the z-component of the clectric field at (x, y, z) = (x, b/4. 0) is Ez(t) = E₀cos wt, what is the corresponding expression for E_z(t) at (x, y, z) = (x. b/2, d)?
(A)2E₀cos(wt-βd)
(B)
(C)2E₀sin(wt-βd)
(D) sin(wt-βd)