By using open ended parallel plate waveguides (often called TEM horn antennas) a new concept for an electronically steerable phased array antenna is shown. The concept allows a usable bandwidth of more than 100% and is suitable for full duplex communication systems. It provides orthogonal polarizations (both linear and circular) for both the transmit and receive paths. Configured as a two-dimensional (flat) array, scan angles of more than 55° can be achieved by good suppression of cross polarization. Easy integration of planar waveguides as well as rectangular waveguides provides a wide variety of system architectures. We present as examples arrays for X-band and for combined Ku- / Ka-band (17 ... 31 sGHz ) which can be scanned electronically above one axis. Receive path uses LHC, transmit path RHC, polarization.