A 45$^\circ$ Linearly Polarized Slot Array Antenna With Substrate Integrated Coaxial Line Technique

The growing interest in collision avoidance automotive radar systems in Ka-band necessitates the development of dedicated antenna systems with a 45 $^\circ$ inclined linear polarization (LP). In this letter, a 45 $^\circ$ inclined LP slot array antenna with the substrate integrated coaxial line (SICL) technique is presented. The proposed antenna is composed of an amplitude-tapering corporate-feed structure and a 5  $\times$  6 inclined-slot array that radiates the 45 $^\circ$ linear polarization. In addition, a blind via bridging the inner conductor and the ground of the SICL is adopted beneath each radiating slot for impedance matching. The proposed planar slot array antenna occupies an aperture area of 33.24 mm $ \times$ 41.13 mm. Measured results indicate that the holistic sidelobe levels in $\boldsymbol{xoz}$ plane and $\boldsymbol{yoz}$ plane are $-$ 19.6 and $-$ 18.0 dB, and the corresponding cross-polarization levels are $-$ 29.5 and $-$ 26.8 dB, respectively. A measured peak gain of 17.09 dBi is observed at 34.5 GHz with a $-$ 10 dB impedance bandwidth of 910 MHz. The measured results are in good agreement with the theoretical calculations and have demonstrated the validity of the design methodology for the proposed antenna.