Microstrip Vertical Transition Design With Ultra-Broadband Passband

Two broadband microstrip-to-microstrip vertical transitions are presented in this letter. The basic structure of the two proposed microstrip vertical transitions is based on the broadside coupling of the upper and lower wide strips. A wide bandwidth with two transmission poles in the passband is easily realized by the slot-coupling method. To expand the bandwidth of the slot-coupling structure, a shunt short-circuited stub is chosen to connect with the upper microstrip line to realize a three poles transition. To further expand the bandwidth, another shunt short-circuited stub is chosen to connect with the lower microstrip line to realize a four poles transition. A four poles sample transition is processed and measured. Experimental results indicate a wide frequency range of 1.25–7.35 GHz with return loss better than 10 dB can be obtained. This proposed transition has the advantages of wide bandwidth, low insertion loss, compact size, and easy implementation.