Green, Roger G

English

In the beginning there was a spark. A spark that could magically create a second remote spark at some distance away without any interconnecting wires or visible medium. It is interesting to think what the early pioneers of radio; Hertz, Tesla, Marconi and Edison would make of the modern mobile phone that now sits comfortably in everyone’s pocket. The mobile phone and the cellular network have been truly life changing technologies. From the early analogue systems to the latest 4G LTE multi-band developments. Bandwidth is a limited resource and there are theoretical limits as to how much data can be accommodated within a finite allocated band. With the evolution of cellular radio, new use cases have been created which demand greater data capacity with faster download times and lower latency. LTE 4G for all its engineering improvements in areas such as modulation, error correction and diversity is not capable of meeting the future requirements of some of the emerging technologies such as vehicle to vehicle communications, internet of things, industrial automation and immersive virtual reality. The next generation of mobile, 5G - ‘new radio’ is expected to address these requirements with a step increase in channel capacity, up to 1000 times greater than 4G, with sub millisecond latency. A singular basestation antenna and a singular mobile antenna is not capable of providing such a quantum leap in performance, hence, 5G is designed to use antennas arrays in a multiple in, multiple out (MIMO) configuration. Antenna arrays are one of the key enablers of 5G new radio. Antenna arrays have been exploited for a number of years but they have a major drawback, cross coupling, which is known as mutual coupling. For MIMO, all the antenna elements need to be de-correlated (isolated) and high levels of mutual coupling can reduce the channel capacity.This thesis investigates mutual coupling in antenna arrays. It explains the load pull effect on power amplifiers and how the output vectors of an antenna array are influenced by neighbouring elements and their excitations. It shows how far field radiation patterns are distorted by the presence of mutual coupling using a bespoke custom designed 5 channel transmitter. There is detailed correlation analysis between elements in an array with different spacing and topologies.This research addresses the issue of mutual coupling at source with passive circuitry introduced into the antenna array to counter the element cross-talk by means of a radically novel analogue Vector Cancellation network that employs a bandpass filter and coupler/splitter. Cancellation of the mutual coupling is achieved by replicating the arrays coupling response in antiphase, thus destructively interfering with the inherent antenna mutual coupling. Several different configurations of network using both lumped components, and microstrips were analysed. In a coupled microstip design (measured), the coupling was reduced by greater than 23 dB over the whole antenna bandwidth with improved radiation efficiency and measured average reduction in load pull due to antenna coupling from over 50 Ω to 4 Ω. This can be scaled up to multidimensional antenna arrays which would reduce the load pull effects on the amplifiers, decrease spectral growth, increasing efficiency and improving beam steering

Explore Bristol Research

Mitigation of antenna mutual coupling for load pull reduction in MIMO and phased arrays

https://research-information.bris.ac.uk/files/354520528/Mitigation_of_Antenna_Mutual_Coupling_for_Load_Pull_Reduction_in_MIMO_and_Phased_Arrays.pdf

Mitigation of antenna mutual coupling for load pull reduction in MIMO and phased arrays

Abstract

Similar works

Full text

Available Versions

Explore Bristol Research