In this paper, a compact and low-profile dual beam slot antenna array operating at millimetre wave frequency is presented. A 6x4 C-shaped slot antenna array has been designed using Substrate Integrated Coaxial Line (SICL) technology. The feeding section of the array is SICL based one to four way power divider that feeds the four 6x1 antenna subarray. The placement of the slot disturbs the surface current in the outer conductor which excites it to radiate in free space. The width of the SICL is much less than \boldsymbol{\lambda}-{\mathbf{g}}/2, this makes SICL compact as compared to other feeding networks, low profile and suitable for broadside applications. The proposed 6x4 C-shaped slot antenna array operates at 25.16 GHz with 3 dB beamwidth of 46° and provides a gain of 9.87 dBi. This antenna is particularly suitable for cost effective solution for multi user communication at millimetre wave frequency. © 2019 IEEE.