W-Band LTCC Circularly Polarized Antenna Array With Mixed U-Type Substrate Integrated Waveguide and Ridge Gap Waveguide Feeding Networks

In this letter, a low-temperature co-fired ceramic (LTCC) substrate integrated 8 x 8 circularly polarized (CP) antenna array is proposed for the wideband and high-gain W-band antenna-in-package application. By introducing the planar L-probe together with the original coupling probe, the E-fields in the substrate-integrated-waveguide (SIW) cavity are changed, and additional E-field components with a 90 degrees phase difference are produced. Then, a CP antenna array is obtained. To reduce the losses in the feeding network, the gap waveguide technology is utilized with the SIW technology, as a mixed feeding network. To validate the proposed CP antenna array design, an 8x8 CP antenna array is fabricated by the LTCC technology and measured. Measured results show that the LTCC CP antenna array obtains a gain of 22.3 dBi, and its axial-ratio (AR) bandwidth is from89 to 98.5 GHz for AR< 3 dB. Besides, good agreements of the radiation patterns between the simulations andmeasurements are achieved within the operational frequency range.