In many communication and radar applications it is needed to have antennas that create multiple beams in several directions or scan a beam spatially. Phased array antenna is an alternative approach for such applications.Phased arrays can be fed via several ways. One of the simplest methods for feeding them is embedding a microwave lens between transceiver and array. The microwave lens is one of the low cost, low profile and light instrument for feeding phased arrays. Many different types of lenses are available; but “Rotman” lens is the best among them; because it has compact size and easily attached to a linear array.Rotman lens is a multi-input, multi-output network. The input and output ports are called “beam port” and “array port” and the array ports are connected to the array elements through transmission lines. If one of the beam ports is excited, the electromagnetic wave will be emitted in the cavity space and reaches to array ports. The shape of contour that array ports have laid on it and the length of transmission lines are determined so that, a progressive phase taper is created on array elements, and thus a beam is formed at a particular direction in the space. If another beam port is excited, the phase taper on the array elements will be changed and the beam will be created at another direction.Rotman lens is used in situations that small and lightweight antenna with beam scanning ability is required. Some practical applications of the Rotman lens antenna are: Mounting on aircraft's nose for Electronic Counter Measure (ECM), using as Unmanned Aerial Vehicle (UAV) antenna and also for artificial vision of vehicles, etc. Up to now, different kinds of Rotman lenses such as metallic waveguide lens and microstrip lens have been introduced. Recently, one kind of transmission line, called Substrate Integrated Waveguide (SIW) was introduced. SIW structures combine the advantages of lightweight and low cost fabrication of printed circuit and the low loss characteristic of closed structures. In addition, SIW can easily be integrated with all the planar circuits. In this thesis, the design equations of SIW Rotman lens antenna are completely presented. After explanation the structure of Substrate integrated waveguide (SIW), a prototype SIW Rotman lens is designed to create 7 beams at angles of 0°, ±10°, ±20° and ±30°. This Rotman lens operates at center frequency of 16 GHz and frequency bandwidth of 1 GHz. Then three linear arrays of patch, Vivaldi and slot antennas are connected to the lens to realize the Rotman lens antenna. Keywords: Beam steering; microwave le Rotman lens antenna; substrate integrated waveguide