*3.3.4 Tapered transmission for improved matching*

As a way to solve the problem of mismatch between the low impedance of the NWSIW and 50 Ω reference impedance, tapered transitions can be inserted between accesses of the NWSIW and microstrip or coplanar waveguides lines used for the connection with other devices. A schematic view of the microstripto-NWSIW transition is shown in **Figure 8**. The taper allows a smooth progressive change of characteristic impedance along taper length, which favors the matching.

**Figure 9** shows simulated performances of microstripline -to - NWSIW transition for various values of taper length L = Ltaper (left) and taper width Wtaper (right).

Adequate values for maximizing transmission S21 and minimizing reflection S11 are Ltaper = λ/4 where λ is the wavelength at the operating frequency assumed here equal to 10 GHz, and Wtaper = 0.6 x W = 3.6 mm.
