Design of a Compact Distributed-Lumped Ka-Band BPF with Wide Stopband in IPD Technology

This work presents a bandpass filter (BPF), centered at 27.6 GHz and a fractional bandwidth of 22% with a wide stopband using integrated passive device (IPD) technology. The filter is implemented by incorporating both distributed and lumped elements. The central component of the architecture is a $3^{\text {rd }}$ order Chebyshyev’s folded hairpin line tapped filter, which is followed by two lumped element based transmission zero networks(TZN) that enhances the rejection at $2 f_{0}$. Inter-digital capacitors and spiral inductors are used to realize the capacitors and inductors respectively in the TZNs. To the best knowledge of the authors lumped element based TZ have been realized for the first time in hairpin resonator based filter in Ka Band with a miniaturized configuration. Wide stopband rejection of more than 20 dB upto 60 GHz, with an insertion loss (IL) of 1.5 dB and return loss (RL) better than $\mathbf{- 1 9. 5} \mathbf{d B}$ across the band in a size of $0.93 \times 0.99 \times 0.1 \mathrm{~mm}^{3}$ is achieved.