A double-layered self-diplexing antenna using ring patch antenna and its feed circuits

A circularly polarized self-diplexing antenna (SDA) for mobile satellite communications is analyzed from the viewpoint of internal isolation. The mutual coupling between transmitting and receiving of the SDA greatly depends on the output amplitude and phase imbalance of the feed circuits. The feed circuits give an isolation of more than -50 dB for two- and four-feed points of the SDA. Simulation of the output amplitude and phase errors for four-feed circuits shows the theoretical limit of the suppression of the isolation. To obtain an isolation loss of less than -50 dB, it is necessary that the output power imbalance of the feed circuits be less than 0.5 dB of amplitude error and less than 0.5 degrees of phase error.<>