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 \({\varepsilon }_{r}=3\) and thickness of 0.508 mm, the prototype occupies \(4.27{\lambda }_{g}\times 2.14{\lambda }_{g}\) , 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 ( \({S}_{21}\) ). The filter exhibits sharp roll-off with a measured 40-dB rejection within ± (0.8–1.2) GHz from \({f}_{0}\) , 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.
