Conical Conformal Shaped-Beam Substrate-Integrated Waveguide Slot Array Antenna With Conical-to-Cylindrical Transition

The analysis and design of a millimeter-wave conical conformal shaped-beam substrate-integrated waveguide (SIW) array antenna is demonstrated in this paper. After investigating the influence of the conical surface on the propagation characteristics of a conformal SIW, a modification for the width of a conical conformal SIW is proposed to obtain the same propagation characteristic along the longitudinal direction. This feature is indispensable to employ the classic equivalent circuit of a planar slot array antenna in the design of a conical conformal antenna. In this case, the design process of the conformal antenna can be simplified. An efficient and accurate model method of the conical conformal SIW antenna is presented as well. Then, a design process of the conical conformal SIW slot array antenna is introduced. Furthermore, to implement the transition between a conical surface and a cylindrical surface, a flexible SIWtransition is designed with a good impedance matching. Finally, two low sidelobe level (SLL) SIW conical conformal antennas with and without the flexible transitions are designed. Both of them have -28 dB SLLs in H-plane at the center frequency of 35 GHz.