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 λ/2 element spacing required at the high-frequency band. To validate its performance, a proof-of-concept prototype — a 2×2 dual-band, shared-aperture, linear-polarized antenna array embedding the proposed NFP — was developed to operate within the 27–30 GHz and 37–41 GHz bands. S-parameter measurements confirmed the NFP’s ability to effectively couple signals in both frequency bands, meeting the required group delay and frequency response constraints. Specifically, the measured coupling over 1 GHz segments (corresponding to the linearization bandwidth for a 200 MHz signal), the coupling magnitude variation remains below 1 dB across 26.5–28.5 GHz and below 3 dB across 36–39 GHz. Furthermore, modulated signal measurements using two 200 MHz, 256-QAM OFDM signals demonstrated the NFP’s capability in training a dual-band, NF-based digital predistortion (DPD) function. The DPD significantly enhanced the array’s performance by compensating for non-linearities, achieving a 20 dB improvement in adjacent channel power ratio at 28 GHz and a 15 dB improvement at 38.5 GHz.