This paper presents a study of two longitudinal slots of same electrical lengths milled on two waveguides for series and shunt slot array planar antenna. Initially single longitudinal slot element is milled on waveguide which is called single element waveguide slot antenna (WSA). Two same or different structures of single element WSA are kept either in series or shunt for making of two element longitudinal waveguide series slot array orologi falsi omega and shunt slot array planar antenna respectively. Theoretical data for the reflection coefficient and transmission coefficient due to mutual impedance have been obtained for two element series and shunt planar WSA. The theoretical data have been compared with simulated data for validation the proposed design structures. The almost outstanding agreement obtained between the results validates the investigation of proposed design structure. After the reflection and transmission coefficients validation, the total gain of the proposed design structures is simulated. The result found in series slot array planar antenna behaves as a multi band within in X-band for the application of the multi frequency selective device for communication and shunt slot array planar antenna behaves as in single band entire coverage of X-band for the application of long distance data communication.