Developements in next-generation advanced communication systems and devices have triggered multi-antenna systems for improved data throughput and transmission reliability. According to Shannon's theorem, to improve the channel capacity of a communication system, one method is to broaden the system bandwidth. Another method is to use the multiple-input-multiple-output (MIMO) technology. This technology uses multiple antennas at both transmitter and receiver to improve the channel capacity by several folds. Therefore, compact and broadband multi-antenna systems are very promising for future high-capacity wireless communication systems.
In parallel to advances in MIMO technologies, there is an irreversible trend that more and more communication protocols together with their respective antennas and radio transceivers are integrated into one compact unit. The radio systems of different protocols may work in very closely adjacent frequency bands or even overlapped bands. The coexistence of these multiple antennas has also become a concern from both industry and academic communities
However, since the number of antenna elements is increasing in more and more compact devices, the physical limitation on inter-element spacing cannot be easily transcended, which will lead to destructive mutual coupling interference as well as pattern/spatial dependent correlation. In a multi-antenna system, the signals at all antenna ports are coded differently either to increase the packet rate or simply because that they belong to different radio transceivers. If unwanted signals are coupled to the ports, the signal-to-noise ratio will be deteriorated. Furthermore, the far-field patterns of closely spaced antennas are highly correlated and the signal envelope correlation will become significantly large. All these negative impacts will greatly diminish the channel capacity and the data throughput. Such drawbacks restrain the use of multiple antenna systems. It is therefore vital to develop a simple, broadband and effective decoupling technique for compact multiple antenna systems/arrays in advanced communication systems.
The major objectives of this thesis are (1) to innovate a new antenna decoupling technique called shunt type of coupled resonator decoupling networks (S-CRDNs) for wireless mobile terminal antennas; (2) to develop the synthesis theory and the design methodologies of the shunt type of CRDNs (S-CRDN) for various of antenna arrays; (3) to extend the theory and the design concept to dual band S-CRDNs, three port S-CRDNs and a LTCC S-CRDN module for mobile terminal applications; (4) to develop a cascaded type of coupled resonator decoupling networks (C-CRDN) for base station and wireless routers antennas; (5) to innovate a novel decoupling technique for multiple element antenna arrays with dummy antennas arrays; and more importantly, (6) to explore innovative applications with experimentally verified superiority.
Based on the characteristics of the coupled antennas, the synthesis theory of S-CRDNs starts from a set of required admittance polynomials, the targeted coupling matrix can be obtained from the polynomials analytically for a second-order S-CRDN. Possible coupling topologies of S-CRDNs include, but not limited to, a second-order all pole S-CRDN, a second-order S-CRDN with source-load coupling, a high-order S-CRDN network for dual band applications and a three port S-CRDN for three-element antenna arrays. Moreover, the concept of a “one-fit-all” S-CRDN module base on LTCC technology is also proposed and investigated, which makes an integrated S-CRDN module antenna independent as long as the frequency range matches.
The general theory of C-CRDN is developed in this thesis based on the circuit model of a 4-port coupled resonators network, which is proposed to solve the antenna decoupling problem between two base station antennas, to which a high level of isolation between two adjacent frequency bands is required, for the first time. This type of CRDN is particularly useful when one antenna transmitting very high power energy in a vicinity to a receiver antenna that works in an adjacent frequency band with very high sensitivity.
A decoupling technique with appropriately designed dummy elements and their passive complex loading is also proposed in this thesis. The technique employs the characteristics of non-radiating antenna elements (dummy elements). Multiple dummy elements can be introduced to alter the mutual coupling characteristic the radiating antennas in the original compact array. Therefore, this technique is more suitable for decoupling problem of an array with multiple elements. It is demonstrated that for a four-element compact array, four dummy elements are sufficient to decouple the four radiating elements in a broadband sense. Additionally, each radiating element can be independently matched. This decoupling technique can be extended to antenna arrays with a high number of radiating elements.
Finally, necessary and important figures of merit for benchmarking a multiple element antenna array are introduced. Prototypes of multi-antenna systems with and without using proposed decoupling techniques are fabricated, measured and compared. A large number of experimental results have demonstrated the superiority and the significance of the proposed decoupling techniques for compact antenna arrays of advanced wireless communication systems.
|School:||The Chinese University of Hong Kong (Hong Kong)|
|School Location:||Hong Kong|
|Source:||DAI-B 76/08(E), Dissertation Abstracts International|
|Keywords:||Antenna decoupling, Decoupling network, Interference supression, MIMO, Mutual coupling, Network synthesis|
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