A microwave circuit comprises a printed circuit board (PCB) on which is fabricated a circuit including passive components such as filters (40) formed by printed conductive patterns. In order to enhance the performance of the circuit, selected components such as filters are made with a greater precision on substrate material (41), such as alumina, having a higher dielectric constant than that of the printed circuit board material. The finished component is mounted on the printed circuit board and the conductive pattern is connected by wire bonds (48, 50) to microstrip tracks (51) of the printed circuit board.