Compact dual-band LTCC UWB bandpass filter using independent transmission zeros technology

In this paper, a compact dual-band ultra-wideband (UWB) filter has been newly designed and fabricated by embedding all the passive lumped elements into low temperature co-fired ceramic (LTCC) substrate for 3.1 to 4.75 GHz and 6.0 to 8.5 GHz UWB system applications. In order to reduce its size/volume and prevent parasitic electromagnetic (EM) coupling between the embedded filter circuit elements, it was newly designed by using a modified 3^rd order Chebyshev circuit topology and J-inverter transformation technology. Moreover, in order to highly reject the WLAN bands of 2.4 to 2.48 GHz and 5.15 to 5.5 GHz, independent transmission zeros technology was applied. Moreover, for formation of higher sub-band, lowpass filter was applied with two LC resonant circuits for millimeter-wave applications by using roll-off characteristics of the independent transmission zeros. The measured insertion losses in the lower and upper band were better than 2.5 dB and 2.3 dB, respectively. Return loss and group delay were better than 8 dB and 0.61 ns in all passbands. Independent transmission zeros occurred at 5.17 and 5.42 GHz provided the suppression of 22 dB at the WLAN band. In addition, the resonant frequencies of the lowpass filters formed at 13 and 14.5 GHz provided the attenuation of 30 dB for millimeter-wave frequency band ranged from 12 to 14 GHz. The size/volume of the fabricated LTCC dual-band UWB filter was 3.65 × 2.35 × 0.65 (H) mm³ which was much smaller than the previously reported ones.