Carrier aggregation systems and methods are disclosed. In some embodiments, a radio-frequency circuit can include a first signal path configured to present an approximately zero impedance to a first out-of-band signal that is out of a first frequency band. The radio-frequency circuit can further include a coupling circuit coupled to the first signal path and configured such that the approximately zero impedance presented by the first signal path to the first out-of-band signal results in the first out-of-band signal being substantially excluded from the first signal path. The radio-frequency circuit can further include a second signal path configured to present an approximately zero impedance to a second out-of-band signal that is out of a second frequency band.