**3. SIW power divider**

Power divider (PD) can be used in phased array antennas, multiplexers, power amplifiers, and so on. Substrate-integrated waveguides have attracted attention in the design of power dividers due to their strong anti-interference, smaller radiation loss, and higher quality factor (Q value). There are three main research directions on SIW power dividers in recent years. Firstly, SIW PDs are developed with higher isolation and lower insertion loss. The main isolation networks include one or more resistors and the microstrip-based network [25, 26]. Secondly, the filtering power dividers (FPD) are proposed to combine the power divider and filter to realize the miniaturization of the circuit [27–29]. Thirdly, ultra-wideband and wideband isolation PDs are fabricated [30, 31]. The main technical parameters of the power divider include insertion loss, return loss, isolation between ports, amplitude balance and phase balance, etc.
