This paper presents optimal shape design of planar array antennas for microwave energy harvesters. The topology optimization of the C4-symmetric array antenna is conducted to maximize their isotropic gain and minimize the return losses in a frequency band ranging from 1.5 to 3.5 GHz. Then, we design the rectifier by varying the circuit parameter based on measurement results to realize the impedance matching between the optimized antenna and rectifier. It is shown by experiment that the harvester composed of the optimized array antenna and rectifier has higher receiving voltage in comparison with the single one. Moreover, the resultant harvester is found to start operating when the arrival electric field is greater than 0.1 V/m.
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