Propagation in discontinuous waveguides. Two parallel plate waveguides are connected as shown in Figure 17.24. The material between the plates is free space. Assume that both waveguides operate in TE modes only. The source on the left supplies power at all frequencies between 1 MHz and 100 GHz. What is the lowest frequency signal received at the receiver. Disregard reflections at the connection between the two waveguides.