Minimizing gain roll-off in rotman lens antenna using phase gradient transmission lines

We present a simple method to minimize the gain roll-off of the Rotman lens antenna with wide scans. Phase gradient transmission lines are used to neutralize a precipitous drop in the power efficiency of Rotman lens when the scan angle increases. To validate the proposed method, a Rotman lens antenna at X band with 8 beam ports and 9 array ports are designed and simulated. The results show that the gain roll-off of Rotman lens antenna can be improved from 5.5 dB to 2 dB over a 90-degree beam coverage.