Wideband Slotted Array Antenna Based on Substrate Integrated Waveguide with Circular Aperture at Ka-Band

In this paper, a large wide band double layer substrate integrated waveguide (SIW) slotted array antenna is designed. The array is consisted of 12 radiating waveguides with the different number of longitudinal slots to form the circular aperture. The feed waveguide is placed perpendicularly underneath the branch waveguides for feeding them through the inclined coupling slots. To have accurate design and good agreement between design specification and simulated results not only external mutual coupling between slots but also internal mutual coupling between progressive mode and evanescent modes in the waveguide are taken into account in the design procedure. Also to increase the bandwidth, the overloading technique is used. In this technique, the admittance of each radiating waveguides is tuned correctly to design a wideband antenna. To have low side lobe level in radiation patterns, 25dB Taylor distribution has been chosen for slots voltage amplitudes. Radiation pattern and return loss are in very good agreement with design specifications. The sidelobe level at the center frequency is 23.9dB in the E-plane and 20.5dB in the H-plane. In addition, the gain of 25.7dB and 630MHz bandwidth for 10dB return loss is obtained. The relative bandwidth is 1.8% which is considered wideband for this large antenna by the size of about 6λ×6 λ where λ is the operating wavelength.