SUMMARY
Simple analytical relations for calculating parameters of microstrip directional couplers are obtained. It is shown that depending on the power splitting ratio k in the output ports of the circuit the technological restrictions of couplers are changed. At k =1 for double-stab four-port directional coupler, unlike three- and four-stab couplers, the range of characteristic impedance satisfies the technological restrictions. However, at k <1 three- and four-stab directional couplers become more technological. Analytical formulas for high precision calculation of the dispersion of effective permittivity and losses in the substrate valid for the main microstrip T-wave in a wide frequency range are also presented.