A method is described for calculating the frequency-dependent properties of symmetrical microstrip Y-junctions and 120° bends. The Y-junction includes angles of 120° and may have two different line impedances. Using a waveguide model with frequency dependent parameters, a field-matching technique proposed by Kuhn is employed to compute the scattering matrix of a Y-junction with three equal line impedances. The generalised telegraphist's equations are used to extend the calculations to Y-junctions with two different line impedances. The transmission properties of 120° bends are derived from the Y-junction by a symmetry consideration. The theoretical results are compared with measurements, and theory and experiment are found to correspond closely.