Abstract-This paper investigates electrical balance (EB) in hybrid junctions as a method of achieving transmitter-receiver (TX-RX) isolation in single antenna full duplex wireless systems. A novel technique for maximizing isolation in EB duplexers is presented, and we show that the maximum achievable isolation is proportional to the variance of the antenna reflection coefficient with respect to frequency. Consequently, antenna characteristics can have a significant detrimental impact on the isolation bandwidth. Simulations which include embedded antenna measurements show a mean isolation of 62dB over a 20MHz bandwidth at 1.9GHz, but relatively poor performance at wider bandwidths. Furthermore, the operational environment can have a significant impact on isolation performance. We present a novel method of characterizing radio reflections being returned to a single antenna. Results show as little as 39dB of attenuation in the radio echo for a highly reflective indoor environment at 1.9GHz, and that the mean isolation of an EB duplexer is reduced by 7dB in this environment. A full duplex architecture exploiting electrical balance is proposed.

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