A dispersive delay line is a structure that causes signals of different frequencies to suffer different time delays. It is found that excessive group delay occurs in an induced pass‐band of filter using asymmetric, parallel stubs in transmission lines. The maximum group delay of the dispersive delay line is determined by characteristic impedances, physical lengths of parallel stubs and the bandwidth of the induced pass‐band. The induced, band‐limited pass‐band is transformed into an all‐pass band by introducing non‐coplanar slot‐lines, while the negative group delay time of original, asymmetric, parallel stubs structure at transmission zeros are compensated to further increase the group‐delay‐time bandwidth. The theoretical results are validated by experiment using compact microstrip lines.