An X-band electrical balance duplexer for in band full duplex communications

Memioğlu, Onur
In Band Full Duplex systems are getting popular to meet the increasing demand of consumers and stringent requirements of developing 5G systems. In this type of communication, receiver and transmitter frequencies are at the same carrier frequency and occurs simultaneously, increasing both data rates and spectral efficiency. Its advantage over time division duplexing and frequency division duplexing have been theoretically proven and practically demonstrated in a number of recent studies. One major bottleneck of this type of duplexing is the echo created by the leakage from the transmitter to the receiver due to the same carrier frequency of the receiver and the transmitter. A typical design challenge is to suppress this leakage so that the transmitted signal does not appear as a blocker, reducing receiver’s sensitivity. A novel method is to use an electrical balance duplexer which provides an isolation in a single antenna receiver if the antenna impedance is equal to a balancing impedance connected to the other side of the duplexer. However, antenna impedance varies considerably due to environmental factors, reducing the suppression. In order to achieve adequate suppression in practical implementations, a varying matching load, tuned to the varying antenna impedance is required. Typical way of creating a matching load is to construct a digitally configurable load which can be externally switched to desired impedance. However, discrete number of switches limit the performance and hence isolation in some cases. In the context of this thesis, a new balancing architecture for electrical balance duplexer is proposed and analyzed. Unlike other works in the literature, the proposed architecture has the capability to suppress in a continuous range of impedances rather than discrete steps. This system offers flexibility to the designers as the system can respond even to the slightest change in the antenna impedance maintaining maximum available isolation. In order to evaluate the effectiveness of the proposed technique, it is implemented in a fully integrated system along with a power amplifier able to provide 1W of power and a differential LNA. The MMIC is tuned to work in the X-band and fabricated in a commercial 0.25 um GaN on SiC technology. The measurement results show that the proposed system achieves a self interference cancellation level of more than 40 dB within a 100 MHz bandwidth for antenna impedance values up to 2.0:1 VSWR.
Citation Formats
O. Memioğlu, “An X-band electrical balance duplexer for in band full duplex communications,” M.S. - Master of Science, Middle East Technical University, 2018.