Simple and Easily Connetable Transition from Empty Substrate-Integrated Waveguide to a 3D Printed Rectangular Waveguide  
[PERSON]  
1 Departamento de Ingenieria Electrica, Electronica, Automatica y Comunicaciones, Escuela Politecnica de Cuenca, Universidad de Castilla-La Mancha, Campus Universitario, 16071 Cuenca, Spain; [EMAIL_ADDRESS] (A.B. ); [EMAIL_ADDRESS] (M.F)  
2 Instituto de Telecomunicaciones 'Aplicaciones Multimedia, Universitat Politecnica de Valencia, 46022 Valencia, Spain; [EMAIL_ADDRESS] (S.C.); [EMAIL_ADDRESS] (H.E. ); [EMAIL_ADDRESS] (V.E.B.) 3D printing is one of the most promising manufacturing methods in the most developed technological fields, including microwave hardware fabrication. On the other hand, the well-known manufacturing methods of planar substrate integrated circuits allow high-quality prototypes to be made at low cost and with mass production capabilities. The combination of both manufacturing methods, 2D or 2.5D (substrate integrated circuits) and 3D (3D printed structures), will allow us to take advantage of the main strengths of each technology and minimise disadvantages. In this article, for the first time, a transition structure between the Empty Substrate-Integrated Waveguide (ESIW) technology--a planar waveguide integrated on a printed circuit board--and a standard rectangular waveguide manufactured by 3D printing is proposed. This transition will make it possible to combine planar circuits with 3D structures, thus taking advantage of the benefits of both types of technologies. The fabricated prototype presents low losses (0.6 dB for the transmission coefficient and 15 dB for reflection coefficient), good electrical response (very flat), and simultaneously good mechanical stability and robustness to manufacturing and assembly errors. The proposed design for this transition piece is easily realisable for a wide range of affordable 3D printers. Repeatability is guaranteed and the proposed transition allows us to combine different SIC structures to 3D printed circuits. Hence, this transition will enable advancements in the fabrication of microwave devices, particularly with regard to satellite communications. Received: 6 October 2023  
20 October 2023  
24 October 2023  
20 October 2023  
(Fused Deposition Modeling), SLA (Stereolithography), and SLS (Selective Laser Sintering), among many others [3]. So far, the main applications of 3D printing in microwaves have been focused on implementing flanges and launchers, with very stringent manufacturing requirements [4; 5]. Also, there have been some research studies on 3D manufacturing components for SIWs [6; 7; 8], but not for ESIW or transitions that connect them to other technologies, although this type of transition exists for other technologies [9]. Several previous attempts at approximating planar-to-3D transitions, as documented in references [10; 11], have shown very limited versatility, very low bandwidth, and often exhibit complexity and high manufacturing costs. As both SICs and 3D printing techniques continue to advance and mature, a method for merging both of them and assembling devices of both types will be necessary to take advantage of the benefits of both technologies. In this article, the first transition from ESIW to a rectangular waveguide manufactured with 3D printing is presented. Therefore, it is for this reason that this transition will ease improvements in the interconnectivity and interoperability among microwave satellite circuits, with a specific emphasis on satellite communications, as elucidated in this article. As discussed in [12], ESIW circuits are waveguides with discrete heights. Therefore, the transition between the ESIW lines and printed 3D waveguide does not require any type of adaptation circuit. In this particular case, the ESIW and the printed 3D waveguide are exactly the same waveguide (\(a\) and \(b\) are identical), and both of them are empty, so \(\varepsilon_{R}\) is the same.