“…The common coupler types are Parallel-line coupler, Branch-line coupler [55][56][57][58][59], Ratrace coupler [56,57,[60][61][62], Lange coupler, Directional coupler [63][64][65], Lumped-Element coupler [66], and Hybrid coupler [67,68]. The design can be achieved by various structures such as Coplanar waveguide (CPW), Substrate-integrated waveguide (SIW), Microstrip line, etc.…”