The authors justify the use of combined longitudinal-coaxial connectors — waveguide-coaxial or waveguide-microstrip type — in new modern antenna-feeder microwave paths. Using the example of a basic coaxial waveguide-coaxial connector based on a section of a regular rectangular waveguide, the study considers the process of converting an electromagnetic wave of a regular waveguide of the main waveguide type H10 into a transverse electromagnetic wave of a coaxial line with a wave resistance (impedance) Z0 = 50 Ohm. Such a connector allows implementing good electrical parameters — matching (standing wave ratio, SWR) and linear losses — but its design is difficult to configure and cannot be reliably reproduced. However, the basic operation principles of this connector make it possible to use it as a prototype when creating modern coaxial waveguide-coaxial or waveguide-microstrip connectors. One example of such a modern connector is the sealed longitudinal-coaxial waveguide-microstrip connector based on a segment of H-shaped waveguide, shorted by an end wall on one end. Correcting the reactive component of both inductive and capacitive nature will allow achieving the required parameters of the wave impedance of the connector. With this in mind, the author has built an inductive-capacitive system consisting of a matching element in the form of a staggered fin and a corrective element in the form of a rectangular parallelepiped. To ensure the air tightness of the connector design, the segment of the coaxial line was replaced by a sealed coaxial insert, which is a serial electronic component. Particular attention was paid to the layout and design of this sealed waveguide-microstrip connector, as well as to the calculation of the overall dimensions of its elements. The article proposes an original technique for measuring the main parameters of both waveguide-coaxial and waveguide-microstrip connectors. The author forms a mathematical model of combined type connectors based on the scattering wave matrix and presents the parameters of real hermetically sealed longitudinally coaxial waveguide-microstrip connectors based on waveguide segments of various standard sizes and measured at various frequencies.