Miniaturization cross-coupled interdigital filter design using high permittivity substrate

A four-pole elliptic function bandpass filter is designed using compact miniaturized microstrip interdigital hairpin resonator. Miniaturization hairpin resonator is realized by using a interdigital capacitor. In addition, the bandpass filter was implemented with using high permittivity ceramic substrate. These effects result in the reduction of its size. The full-wave simulator IE3D is used to design the interdigital hairpin resonator, and to calculate the coupling coefficient of the basic coupling structures. The responses of the fabricated filters using Al
₂
O
₃
(ε
_r
= 9.7, Q × f = 350000 GHz) and ZnO-doped Nd(Co
_1/2
Ti
_1/2
)O
₃
(ε
_r
= 27, Q×f = 147000 GHz) ceramic substrates are designed at a center frequency of 2.4 GHz. The compact size and the performance of this class of filters have been demonstrated.