This overview article compares fundamental rectenna architectures and their variants including single and multiband rectennas, rectennas making use of polarization or harmonics, rectennas offering scalability, and feed-arranged rectennas making use of multiple ports and rectenna geometry. Key capabilities and advantages of each architecture are determined, and example applications that may heavily rely on the architecture's attributes are identified. Findings and capabilities of contemporary prior art are summarized for each architecture for the WPT-EH researcher, and several outstanding implementation examples are presented.