K-/Ka-/Q-Band Switched Filter Bank With Wideband Low-Loss SP4T Switch in 0.1 μm GaAs pHEMT Technology

This letter presents a four-channel fully integrated switched filter bank (SFB) for K-/Ka-/Q-band applications in a 0.1-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>m GaAs p-HEMT process. The proposed SFB consists of two octave-band single-pole four-throw (SP4T) switches and four bandpass filters (BPFs), using a switch-filter co-design approach. The SP4T switch is a two-stage structure, consisting of single-pole double-throw (SPDT) switches, covering 18–45 GHz. Through a fully symmetric design, it ensures consistency among the signals of each channel. The topology of the lumped <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filters introduces a hybrid structure of Chebyshev and elliptic designs, featuring flat passbands and steep transition bands, which also reduces the filter area to 0.21/0.26/0.13/0.12 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. The four-channel SFB, with passband frequencies of 18–20, 20–23, 34–36.5, and 40–45GHz, has a passband insertion loss (IL) below 16.5 dB, with a flatness better than 3 dB, a return loss (RL) better than 7.1dB, and out-of-band suppression exceeding 32 dB. To the best of our knowledge, this is the highest out-of-band suppression among on-chip SFBs with the octave-band SP4T switches in the K-/Ka-/Q-band.