Microstrip/slotline transitions: modeling and experimental investigation

An analysis of microstrip/slotline transitions is given using a network description through transmission-line models. Different transitions, such as transitions containing uniform and nonuniform lines as well as soldered and virtually shorted microstrip lines, are treated. Although a transition with a soldered microstrip short offers the largest bandwidth, optimal combinations of different microstrip and slot stub diameters can be found by modeling. In the case of a virtual short through an optimally chosen circular microstrip stub, the bandwidth is typically about 10% below the maximum achievable value of a soldered short. The validity of the modeling results is verified experimentally by measuring the transmission coefficient of a cascade of two transitions separated by a slotline in the frequency range from 1 to 16 GHz. For practical applications, design curves are given for 0.635-mm-thick alumina substrates