Breaking the Transmitter–Receiver Isolation Barrier in Mobile Handsets With Spatial Duplexing

Abstract

In full-duplex radio communication systems like e-UTRAN, CDMA-2000, the radio transmitter (Tx) is active at the same time as the radio receiver (Rx). The Tx and the Rx will be using separate dedicated frequency bands and the Tx-Rx isolation is ensured by duplex filters. However, agile duplexers required for multiband operation are almost nonexistent while dedicating a bank of narrowband filters is bulky and incurs considerable switching losses. In this paper, we propose an approach that dramatically reduces the complexity of the RF frontend, first by replacing the duplex filter with a spatial filter and second, by codesigning the filtering antennas and the RF frontend. The spatial filter is synthesized by equipping the Tx with redundant antennas. By properly weighting the Tx antennas, the Tx signal is selectively attenuated in the Rx direction. The spatial filter can be tuned to different frequency bands as long as the antennas are made tunable. Moreover, the spatial filter may directly benefit from the balanced architecture of the power amplifiers (PAs) thus reducing the total system complexity and insertion loss. Finally, simulation and initial measurement results are provided in a challenging low-frequency band, serving as a proof-of-concept.

Novel Architecture for LTE World-Phones

“…The proposed architecture was first conceptualized in 2003 [22]. Initial investigations were published in [23] and [24]. The concept was demonstrated at the high bands (1.85 GHz -2.17 GHz) in [14].…”

Addressing carrier aggregation with narrow-band tunable antennas

“…Several solutions have been proposed to address this issue. A comprehensive overview is given in [1]. The main approaches are:…”

“…Furthermore, the antennas being narrow-band, they exhibit a very low profile. This concept has been more extensively described in [1], [4], [5].…”

Self‐matched high‐ Q reconfigurable antenna concept for mobile terminals

“…Such an approach is proposed to have separate transmitter (Tx) and receiver (Rx) path throughout the FE [8][9][10], thus requiring separate Tx and Rx antennas. Since these two antennas need to cover only the transmit and receive channels in a band, they can be quite narrow band.…”

“…Some papers have mainly addressed the isolation issue between the Tx and Rx antennas. In [8,13] it is proposed to improve the isolation by introducing a spatial filter, where the spatial filter is synthesised by equipping the Tx with at least one more antenna than the Rx, resulting in a balanced Tx antenna and unbalanced Rx antenna. Isolation study of wide-band, medium-band and narrow-band antennas is conducted in [9,14] to show the advantage of narrow-band antennas in terms of isolation.…”