Miniaturized Bandpass Filter Design Utilizing Substrate-Integrated Metasurface in Coupled Dipole-Antenna Array With Harmonic Suppression

This communication presents a novel filter design methodology using a coupled dual-dipole array to create a thin microstrip bandpass filter (BPF) developed by a substrate-integrated metasurface middle layer (MML). Current engineering on MML, utilizing dipole near fields, excites two new electrically long resonances, improving transmission impedance and inducing countercurrents that reduce total radiation in the well-matched, miniaturized filter. An array factor (AF) analysis with MML-linked current explores radiation suppression tactics through MML adjustments. An MML-based closed-form expression for the filter’s pole and a study on dipole dimension for matching/poles control are reported for systematic design. By uniting the stub pair shorted on MML and low-pass filter pair, high selectivity and harmonic suppression (up to 4 f₀) can be succeeded, significantly. Some evolving symmetric circuit models are derived to assess the filter behavior and harmonic suppression. The prototype with a thickness of just 0.78 mm ( $0.006\lambda _{0}$ at 2.5 GHz) and an area of $0.1\lambda _{0}^{2}$ exhibits a 12% bandwidth with over 25-dB matching, insertion loss below 1 dB, and over 26-dB roll-off under 360 MHz. It shows significant radiation reduction, reaching Max-U below 10 mW/sr. Experimental results align with theoretical models, validated by ADS full-wave analyses.