# Small scale lowpass and quad-band bandpass filter for 5G application

## TL;DR

This paper presents a compact filter design for 5G applications with low loss and high selectivity across multiple frequency bands.

## Contribution

A novel small-scale lowpass and quad-band bandpass filter is introduced for 5G communication systems.

## Key findings

- The proposed filter achieves low insertion loss and high selectivity with a compact size of 15.6 mm × 24.6 mm.
- The filter operates across four bands (1.39–2.78 GHz, 3.26–4.09 GHz, 4.42–5.24 GHz, and 5.64–5.89 GHz) suitable for 5G FR1.
- Experimental results confirm the design's performance aligns with simulations.

## Abstract

This work offers a new small-scaled lowpass and quad-band passband filter with low insertion loss and high selectivity. By integrating a shorted interdigital capacitor (IDC), closed ring resonator, meander line, and rectangular-shaped virtual ground plane, better impedance matching and transmission properties have been attained. Initially, the lowpass response structure comprises shorted IDC and closed ring resonators. Further utilizing pairs of meander lines and rectangular stubs on both sides of ring resonators, a quad bandpass along with a lowpass filter was constructed. Excluding the fifty-ohm feedline the proposed filter area measures only 0.04λg × 0.06λg (15.6 mm×24.6 mm) at the lowpass frequency of 3dB cutoff, 0.75 GHz. The fractional bandwidth at 3-dB of the proposed four passband zones are 63.76% (1.39–2.78 GHz), 22.55% (3.26–4.09 GHz), 17.15% (4.42–5.24 GHz), and 4.3% (5.64–5.89 GHz) at operating frequencies of 02.18, 3.68, 4.78 and 5.82 GHz, respectively. Moreover, the resonance frequencies of each band can be adjusted by altering the structural parameters of the intended filter, which results in modifications to their relative lumped parameters. By doing experimental measurements that correlate with simulated ones, the suggested filter is validated. The designed filter may be useful for 5G communication frequency range-1 (FR1), 0.45–6.0 GHz bands.