Three-dimensional (3D) printed rectangular waveguide T-junction is presented with in-phase and equal power division by means of iris and septum at 10-15 GHz frequency range to use the waveguide feed network for array antenna. The proposed T-junction structure is designed and fabricated with 3D printing, as novelty, that is a good alternative to traditional methods in terms of reduced-weight, cost, flexible applicability, and being monolithic for complex geometry. After making the skeleton of T-junction from acrylonitrile butadiene styrene, metal plating process is applied over the all surfaces with copper. Transmission and reflection characteristics and electric-field distribution of the structure are obtained with CST Microwave Studio software. Qualitative agreement is obtained between measurement and simulation with approximate to 7 dB shift and that shift is because of high precision and low surface roughness on 3D printed junctions. Unlike studies in the literature, the proposed study provides two points, as a novelty: First is that the fabrication of rectangular waveguide T-junction with 3D printing is made. Second is that the return loss of T-junction is improved by changing the geometry of iris and septum.