A one-dimensional cavity is approximately simulated by placing two perfect electric conductor (PEC) metal plates parallel to each other such that the distance they are apart is very small compared to their length and width. This way, the only dimension that matters is the z-direction. This chapter presents equations for the case of a standing wave that is elliptically polarized. A source wave splits into three modes when an unbounded plasma medium is created. Two of the modes are propagating modes with upshifted frequencies. The third mode is a wiggler magnetic field, which is a space-varying dc (zero frequency) magnetic field. The wiggler wavelength is the same as the wavelength of the source whistler standing wave, as is to be expected since the wavelength is conserved over a temporal discontinuity in the properties of the medium. However, the strength and the direction of the wiggler field are controlled by the switching angle.