An improved design for the uniform substrate integrated waveguide (SIW) long slot leaky wave antenna (LWA) is presented in this paper. To achieve the desired sidelobe level (SLL), beamwidth and beam direction, proper distributions for leakage constant and phase constant should be created along the slot. An accurate calculation of leakage and phase constants is performed by considering an unwanted mode, in addition to the leaky mode, along the uniform LWA structure. Considering this unwanted mode in the design procedure results in good consistency between the desired and designed radiation patterns. The presented leaky wave antenna realizes a Taylor distribution with predefined SLL of -25 dB at 17 GHz. The radiation pattern, amplitude distribution and phase distribution of the designed antenna are compared with the desired ones. This comparison shows the high accuracy of the proposed design procedure. Measurement results are also presented at 16.5, 17 and 17.5 GHz for validation of the design procedure.

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