# A high-selectivity 24-GHz SIW–DGS–CPW bandpass filter with wide stopband rejection for automotive radar and ADAS

## TL;DR

This paper presents a compact, high-performance 24-GHz bandpass filter for automotive radar and ADAS, combining design elements to achieve strong signal selectivity and wide stopband rejection.

## Contribution

The novel contribution is a single-layer SIW–DGS–CPW co-design that improves selectivity and stopband suppression in a compact form.

## Key findings

- The filter achieves a 450-MHz 3-dB bandwidth with a return loss better than 24 dB.
- It provides 40-dB rejection within ±(0.8–1.2) GHz from the center frequency and 30–35 dB suppression across 20–30 GHz.
- Thermal analysis shows minimal performance degradation from 25–105°C, ensuring reliability in automotive applications.

## Abstract

A performance-efficient compact, highly selective 24 GHz SIW-based bandpass filter (BPF) is proposed for automotive radar and advanced driver-assistance systems (ADAS). The key contribution is a single-layer SIW–DGS–CPW co-design in which SIW cavities provide a high-Q passband, an open-rectangular DGS introduces transmission zeros to steepen the skirts and reinforce the stopband, and a CPW feeding transition improves matching and practical integration. Implemented on a substrate of Rogers RO4003C with \documentclass[12pt]{minimal}
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\begin{document}$${\varepsilon }_{r}=3$$\end{document} and thickness of 0.508 mm, the prototype occupies \documentclass[12pt]{minimal}
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\begin{document}$$4.27{\lambda }_{g}\times 2.14{\lambda }_{g}$$\end{document}, achieving a pronounced miniaturization while maintaining strong spectral selectivity. Full-wave simulations and measurements confirm a center frequency of 23.97 GHz and a 450-MHz 3-dB bandwidth, with return loss better than 24 dB and an in-band insertion loss of 1.6–2.0 dB (\documentclass[12pt]{minimal}
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\begin{document}$${S}_{21}$$\end{document}). The filter exhibits sharp roll-off with a measured 40-dB rejection within ± (0.8–1.2) GHz from \documentclass[12pt]{minimal}
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\begin{document}$${f}_{0}$$\end{document}, and 30–35 dB suppression across 20–30 GHz. A compact equivalent-circuit model captures the passband behavior and transmission zeros. Thermal analysis (25–105 °C) shows only a slight downshift (~ 30 MHz) with minimal performance degradation, supporting automotive reliability. Compared with prior 24-GHz BPFs, the proposed co-integration simultaneously improves skirt selectivity and wide stopband suppression within a compact footprint.