Design of a Miniaturized On-Chip Bandpass Filter Using Edge-Coupled Resonators for Millimeter-Wave Applications

A unique miniaturization technique for on-chip passive device implemented in gallium arsenide (GaAs)-based technology is presented, which is based on edge-coupled cells (ECCs). The principle of an ECC is first studied by means of the equivalent LC circuits. Then, using the ECC as a baseline, a combination of different shorting-ground and tapping methods is fully investigated in terms of their impact on frequency responses. By directly shorting the specific edge-coupled fingers to the ground, an ECC can be converted into a resonator without increasing any physical size. To further demonstrate the feasibility of using this technique for miniaturized monolithic microwave integrated circuit design, an on-chip bandpass filter (BPF) is implemented and fabricated in a commercial 0.1-μm GaAs technology. The measurement results show that the 3-dB bandwidth of the filter is from 21.2 to 26.5 GHz, while the insertion loss is less than 2.9 dB at 23 GHz. In addition, more than 30 dB of suppression is achieved from 0 to 15 GHz and from 44 to 54 GHz. The size of the BPF is only 640 x 280 μm², excluding the pads, which is equivalent to 0.17 × 0.08λ_g². (λ_g is the guided wavelength at 23.5 GHz.).