Catheters are presented herein having planar end effectors of various configurations, generally providing a two-sided and multi-layered platform for electrodes and sensors. In some examples, the end effector has a support frame (e.g. nitinol) between a pair of flexible circuits. The end effector can also include a polymer (e.g. silicone, LCP, etc.) between the flexible circuits and encapsulating the support frame. This platform facilitates positioning of electrodes on either side (including both sides) of the end effector in a variety of spacings and facilitates ultra-tight electrode spacing and/or a large area electrode. Sensors (ultrasound transducers, navigation coils, etc.) can be layered within the end effector between outer surfaces of the flexible circuits in a variety of configurations.