As shown in Figure 7(a), the BPF for WLAN application consists of two coupling QWRs, denoted by the length [l.sub.1] +[1.sub.2] + [l.sub.3] and width [w.sub.1], and short microstrip feedlines ([k.sub.1] + [k.sub.2], [w.sub.1]).
As discussed in Section 2.1, the QWRs in coupling short tapped stub and coupling open tapped stub can generate new transmission zeros [T.sub.z7] and [T.sub.z4], respectively.
The broadband BPF is designed by using symmetric three-coupled-line structure composed of a QWR side-coupled to two open stubs.