Three-Dimensional Integrated Circularly Polarized Filtering Antenna Array With High-Efficiency Hybrid Feeding Network

A 3-D integrated antenna array is proposed with the low-temperature co-fired ceramic (LTCC) technology in this article, which has the characteristics of circular polarization (CP), good filtering response, and high efficiency simultaneously. To guarantee both the transmission efficiency and the routing flexibility, a hybrid feeding network is constructed with a 16-way air-filled gap waveguide (AFGWG) power divider and
$4\times 4$
stripline (SL) two-stage sequentially rotated feeding networks, to excite
$16\times 16$
radiating elements of stacked patch etched with cross-shaped slots, operating in K-/Ka-bands. The AFGWG feeding structure is very suitable for large-scale integrated arrays. A substrate integrated waveguide (SIW) filter is introduced with the passband of 23–27.5 GHz to further improve the bandedge frequency selectivity. All the components and their transitions are designed collaboratively and co-implemented vertically, enabling high-density multifunctional integration. The proposed antenna array shows the peak realized gain of 25.2 dBi, the in-band antenna efficiency of 38%–48.6%, and the axial ratio (AR) below 1.98 dB. By combining the responses of all parts, such as the quasi-bandpass stacked patches, the quasi-bandpass AFGWG-to-SL transitions, the quasi-highpass AFGWG structure, and the bandpass SIW filter, the out-of-band suppression is achieved better than 32.5 dB in 28.5–40 GHz and 41 dB in 18–22 GHz. Our idea has been demonstrated by the good agreement obtained between the simulated and measured results.