**3.1 PD with high isolation**

Wilkinson PD is used to achieve a high degree of isolation between output ports. An architecture of Wilkinson PD is based on fixed-width SIW lines with isolation resistors as shown in **Figure 20** [25]. The resistors are formed of various surfacemounted parallel resistors to reduce the effect of SIW-resistance discontinuity. The present topology shows enhanced isolation and adaptation in a wide bandwidth.

Another SIW PD with high output isolation is shown in **Figure 21** [26]. The power divider is constructed by using two substrate layers and three metal layers. Five microstrip lines are placed on the top metal layer and coupled with the SIW through three-slot lines located on the middle metal layer (common ground). Three resistors are used to improve the output isolation. This device has input return loss and

**Figure 20.** *The novel Wilkinson PD.*

**Figure 21.** *Structure of proposed PD (a) 3D view. (b) Top view [26].*

insertion loss greater than 17 dB and 1.6 dB, respectively. However, this structure increases the complexity of the process.
