Design aspects of compact high power multiport unequal power dividers

Array antennas for radar require low sidelobe patterns to avoid jamming. Also, arrays used for airborne radar application are required to have very low sidelobes as the radar operates on a clutter limited mode rather than noise limited mode. In order to achieve low sidelobe antennas, the feeder network must be designed such that it should provide the required unequal power division. Corporate feeds are the preferred choice from the bandwidth point of view. But the feeder network will be very complex for larger arrays. Alternatively, a group of elements can be combined suitably and then they can be fed from a relatively simpler corporate feeder which may be a optimum solution. In either of the approaches, high power unequal power dividers are required. Waveguides can handle high powers and hence the high power dividers are to be designed using them. For equal power division, either E-plane tee, H-plane tee or Magic tee can be used. But, for unequal power division there are two ways, one is by slot couplers and the other is by the use of a septum. We discuss the design details of a septum based unequal power divider with multiple ports. We also cover the types of fabrication techniques adapted and their effect on the performance of the power dividers. Tables of results are included to bring out the close correlation between the design and measured results. Comments on the bandwidth performance of these power dividers are included with the results of studies on the effect of errors in these power dividers for low sidelobe antennas.