Slot antennas fed by the wiggly ridge wave?guides are difficult to construct using a typical milling machine. Therefore, a special type of the double ridge waveguides is introduced here to feed the center line longi?tudinal slot antennas. Furthermore, in the proposed slot antennas, all the slots are placed along the waveguide center line. So, employing the proposed slot antennas leads to the elimination of the butterfly lobes that are attributed to the alternating offsets of the successive slots with respect to the centerline. In the proposed slot antennas, the ridges are placed on the lower broad walls of the waveguides while the slots are cut into the upper broad walls of the waveguides. The height of the ridges is changed gradually at the slot positions in several steps, i.e., the height of one of the ridges is increased upward while the height of the other ridges is decreased downward. It is shown that in-creasing the step heights leads to stronger radiation of the electromagnetic energy by the slots. To verify the effective?ness of the proposed slot antenna, a linear array antenna consisting of five slots with side-lobe level of –20 dB is designed and constructed. The simulation and the measurement results show that the designing goals are achieved which verifies the effectiveness of the proposed slot antennas.
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