Antenna Array Design with Suppressed Sidelobes

Short-range car radar systems can provide safety and comfort features such as parking aid, pre-crash warning, change lane assistant, etc. These radar systems create a safety belt around the car using transmission of ultra wideband (UWB) 24 GHz signals. Regulations limit the level of radiation at certain elevation angles to avoid interference or disturbance in the 24 GHz band. The specific goal of this research was: ”Design a broadband antenna array at 24 GHz that exhibits side lobe suppression of 35 dB at angles > 30 and has enough forward gain.” c © Koninklijke Philips Electronics N.V. 2006 iii TN-2006-00539 Unclassified Conclusions: The effects of tapering methods on the side lobe suppression are investigated. It is shown that by just using multiple antenna elements, the specifications can not be met. Space tapering and amplitude tapering of the antenna elements are explored. Amplitude tapering turned out to be the best choice for the design of the array. However, transmission lines to feed the array increases the side lobe level, with a minimum level of about -23 dB. The Chebyshev family of amplitude tapering functions is introduced. Using this function and by exploiting aliasing of side lobes, specifications can be met with only 6 antenna elements. The actual tapering is done by exploiting the relatively high substrate losses of the transmission lines. For large amplitude ratios it is convenient to fold the feed lines into a meander structure. To minimize the spurious radiation of the feed network, the feed lines are moved to the third metal layer (Signal3) and are shielded by a metal plane in the second metal layer (Signal2). The final design achieves a side lobe level suppression of -33.1 dB for the nominal frequency of 24.7 GHz. This meets the specifications until Jan 1st , 2014. iv c © Koninklijke Philips Electronics N.V. 2006 Unclassified TN-2006-00539