A Series Slot Array Antenna for 45 $^{\circ}$-Inclined Linear Polarization With SIW Technology

The design method for a standing-wave series slot array antenna with 45°-inclined linear polarization in the Ka-band is presented. The proposed 16 × 8 planar slot array antenna consisted of arrays with alternating reactance slot pairs that could achieve impedance matching and uniform field ex- citation, simultaneously. Furthermore, the grating lobes were effectively suppressed with the help of these radiating units due to the one-half guided wavelength slot spacing. An equivalent circuit analysis was done to evaluate the input impedances of the radiating and feeding lines with the impedance recursive formulas as well as the mode voltages of the radiating slot elements. In addition, a wideband transition with a 30.13% bandwidth under the criteria of less than VSWR 1.5:1 was presented to provide the necessary power with the minimal reflection and to prevent the distortion of the radiation patterns. The proposed planar slot array antenna occupied an aperture area of 57.4× 51.6 mm. The measured bandwidth, gain, and efficiency were 990 MHz (2.88%), 24.3 dBi, and 53.7%, respectively. Furthermore, the side lobe levels (SLLs) were verified for each cutting plane with -13.57 dB and -13.17 dB, respectively. The proposed antenna structure was achieved with a substrate integrated waveguide (SIW) with the low costs and lightweight features.