Abstract-Improving the isolation between antenna elements in compact arrays has been a major focus of recent research. In this paper, we present ideas to improve the wideband isolation between closely spaced antennas. We do this by connecting lumped lossy (resistive) elements between the antenna feeds. A simple analytical expression is provided to compute the impact of resistive elements on efficiency to analyse the power lost in the resistive element. Three configurations of decoupling circuits are designed and fabricated for two closely spaced monopoles operating at 2.4 GHz. The decoupling circuit contains transmission lines of different lengths at the antenna inputs such that the mutual admittance between the antenna elements is 1) resistive, 2) resistive and inductive, or 3) resistive and capacitive. Lumped elements are then connected between the transmission lines followed by matching circuit. The paper shows that with configurations 2) and 3) we can improve the wideband isolation compared to 1), as well as compared to using only lossless elements. The wideband isolation was improved by 17.6 dB across a 200 MHz band at 2.4 GHz, with a final isolation level of 20 dB over that band. Better than 30 dB isolation was achieved across a narrower band of 55 MHz. The proposed technique provides wideband isolation improvement for multiple-input multipleoutput (MIMO) as well as narrowband performance with large isolation suitable for in-band full-duplex (FDX) applications. The impact on efficiency is investigated to verify that the advantages from the improved wideband isolation outweighs the possible reduction in overall efficiency.
Abstract-In an in-band full-duplex system, radios transmit and receive simultaneously in the same frequency band at the same time, providing a radical improvement in spectral efficiency over a half-duplex system. However, in order to design such a system, it is necessary to mitigate the self-interference due to simultaneous transmission and reception, which seriously limits the maximum transmit power of the full-duplex device. Especially, large differences in power levels in the receiver frontend sets stringent requirements for the linearity of the transceiver electronics. We present an advanced architecture for a compact full-duplex multiantenna transceiver combining antenna design with analog and digital cancellation, including both linear and nonlinear signal processing.
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Abstract-In-band full-duplex relaying has been of recent interest as it can potentially double spectral efficiency and decrease latency, thus improving throughput to the end user. The bottleneck in enabling full-duplex operation is the selfinterference (SI) due to the relay's own transmission, which must be mitigated at the antenna, radio frequency and digital domains. In the case of compact back-to-back relays which are proposed for outdoor-to-indoor relaying, the SI comprises direct coupling and multipath components. This paper models the SI channel across 300 MHz bandwidth at 2.6 GHz in two indoor environments with a back-to-back relay antenna. The power delay profile of the SI channel is modelled as a single decaying exponential function with specular components represented by delta functions. The fading characteristics of each tap are modelled by a normal distribution based on the measurements. The proposed model can be used to generate a tapped-delay model of the SI channel between compact back-to-back antennas for use in link-level simulations and hardware in the loop emulation.
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