Compact lowpass filter with flat group delay using lattice‐shaped resonator

Abstract

A compact lowpass filter (LPF) using a lattice-shaped resonator is presented with a wide rejection band and sharp roll-off. The designed LPF has −3 dB cutoff frequency at 4.34 GHz. The fabricated LPF is simulated and tested; there is a good agreement between the simulation and experimental results. Experimental results show that the maximum variation of flat group delay is only 0.3 ns in the passband. Also, the measured return-loss and insertion loss are more than 19 dB and <0.1 dB in 88% of the passband region, respectively. The size of the designed filter is only 22.5 × 8.65 mm 2 .

Design of Compact Planar Lowpass Filters by Using Fragment-Type Structure With Multi-Bit Scheme

“…Finally, we use a compact design area to achieve higher performance. Compared with [3], [7], [8], [9], [14], and [15], we achieve better performance of passband, transition band and stopband with a smaller design size. Compare with [10], [11], [13] and [17], 2-bit LPF in IV has higher RSB and higher RL in passband with a smaller design area.…”

“…This 2-bit cell LPF challenges a large roll-off rate by setting ξ0=120 and an ultra-wide stopband ranging from 2.5 GHz to 20 GHz. We set n=7 and divide the stopband into 4 sub-bands, which in GHz are [2.5, 5], [5,10], [10,15], and [15,20], respectively.…”

“…Several other planar resonators have also been proposed in planar LPF designs. The tapper resonator cell is proposed in [14], a lattice-shaped resonator is presented in [15]. In [16], three multimode resonators are considered.…”

“…In [16], three multimode resonators are considered. The designs report highest roll-off rate  of 100 in [15] and a highest RSB of 1.58 in [16]. In addition, complicated structures including vias, defected ground plan, and multilayer PCB are considered in LPF design as well.…”