Dual-Band Near-Field Probing Antenna for Enhancing the Performance of Dual-Band Shared-Aperture Linear-Polarized Phased Antenna Arrays

This paper presents a novel dual-band, single-feed near-field probing antenna (NFP) designed to provide feedback signals for in-situ calibration and linearization of millimeter-wave dual-band, shared-aperture, linear-polarized phased antenna arrays. The NFP is designed to deliver flat coupling magnitudes and constant group delays to surrounding antenna elements across both frequency bands, while adhering to the tight lambda/2 element spacing required at the high-frequency band. A proof-of-concept prototype—a 2x2 dual-band, linear-polarized antenna array embedding the proposed NFP was developed to operate within the 27–30GHz and 37–41GHz bands. S-parameter measurements confirmed the NFP’s ability to effectively couple signals in both frequency bands, meeting flat frequency response and consistent group delay constraints. Furthermore, modulated signal measurements using 200 MHz, 256-QAM OFDM signals demonstrated the NFP’s capability in training a dual-band, NF-based digital predistortion (DPD) function, achieving a 20 dB improvement in adjacent channel power ratio at 28 GHz and 15 dB at 38.5 GHz.