With today’s accelerating popularity of wireless communications, one busy area of research in Hong Kong is smart antennas.
At The Hong Kong University of Science & Technology (HKUST), two research projects are looking at how to optimise performance of multiple-input multiple-output (MIMO) technology which promises big increases in performance without the need for more radio spectrum or power.

Prof Murch with a prototype of the compact two antennas in one design

While one project has computed how to reduce signal interference (seeAlgorithm leads to boost in performance), the other has devised a compact MIMO antenna by combining two antennas into one.
Principal Investigator of the antenna design project, Prof Ross Murch, explained that using multiple antennas increases the number of transmitting channels and therefore allows greater speeds of data.
“In radio communications, there are two key items: bandwidth and power. With the MIMO antennas you don’t need any more bandwidth or power so it seems you get something for nothing.”
He added: “That’s good news for mobile phone operators who get a limited spectrum from the government. With multiple antennas and the same spectrum, they can send more data which means more users or getting people to use additional services like video-telephones.”
Multiple antennas, however, need to be spaced apart so they do not interfere with each other. Traditional thinking says they should be spaced apart by half the wavelength they are being used for. For a mobile phone using a frequency of 900 Mhz, two antennas would need to be 15cm apart.
Said Prof Murch: “This means that multiple antennas are quite impractical for compact devices. As antenna designers, we needed to ask if we can do anything clever to make the design smaller.”
His research came up with an answer. As radio waves come in different orientations, he used a polarisation technique of placing two antennas perpendicular to each other. They then became “fairly independent” and interference dropped off significantly.
He combined this with two “diversity” ideas which increase the likelihood of catching good signals and came up with the compact design. Prof Murch’s research also looked at the safety aspect of using a mobile phone with a design of the MIMO antenna and found that electro-magnetic radiation was reduced by 25 to 50 per cent.
“Although radiation from a mobile phone has never been scientifically proved to be harmful to health, it’s good to be able to control it,” said Prof Murch.

Principal Investigator
Prof Ross Murch : eermurch@ee.ust.hk