2. Briefly explain the operating principles of a two-opening superimposed- waveguide directional coupler. 3. Briefly explain what are the main parameters used to compare directional couplers: the coupling factor and the directivity. 4. What would be the directivity of an ideal directional coupler? 5. (Refer to Figure 48.) Determine the power at arms 2, 3 and 4 (P2, P3, and P) if the incident power at arm 1 (P) is 1 mW, given a coupling factor C of 20 dB, and a directivity D of 20 dB