Research On Small Antennas Based On Composite Right/Left-Handed Transmission Lines

Composite right/left-handed (CRLH) transmission line is the transmission line form of themetamaterials. CRLH TL have many unusual electromagnetic properties, which have been theforeland and hotspot ifeld of the microwave engineering. CRLH TLs are composed ofpeirodical unit cells, can be regarded as1-D metamaterials. They have the effectivepermittivity8and permeability [i determined by their micro-structures. Moreover, due to theirfantastic controllable dispersion characteristic which cannot be achieved by the uniformtransmission lines, the CRLH TLs can pave the way for a novel generation of microwavedevices and circuits. Especially, the backwave and zeroth/negative-order resonant propertiesof the CRLH structures have been widely used in antenna design.In this thesis, the attention is paid to the composite right/left-handed transmission lines andtheir applications in the small antennas. The control method of the dispersion characteristicthe permittivity s and permeability [i of the CRLH TLs have been discussed. Emphatically,the zeroth/negative-order resonant properties of the CRLH structures have been analyzed.Several small antenna based on zeroth/negative-order resonant structures have been proposed.The main contents and contributions are listed as follows:1.Floquet theorem and Bloch impedance analysis have been discussed which are the basicmethods of analyzing the periodical CRLH TL structures. The zeroth/negative-order resonantproperties of the CRLH structures have been analyzed.2.Amonopole antenna with zeroth-order resonator loaded is proposed, which comprises asingle unit cell of the epsilon negative (ENG) transmission line. It works on multi-band due tothe multi resonance.3.Apirnted broadband planar inverted-F antenna (PIFA) with zeroth-order resonator loaded isproposed whose shorting strip of the PIFA is replaced by an inter-digital capacitor and thininductive strip in series. The loaded inter-digital capacitor and thin inductive strip act as ashorting strip at the upper band, which allows the antenna to maintain its regular performance.Around lower band, the antenna with the inter-digital capacitor and thin inductive strip workson the zeroth-order resonance mode, which makes the physical size be independent of the wavelength. By merging the two modes, a broadband performance can be achieved. Moreoverthe antenna has same direction of the radiation patterns in the broadband.4.The shortcoming like low radiation efficiency and non-omnidirectional pattern of the ifrstnegative-order resonance on antenna application was analyzed, and a method to improve theradiation efficiency and pattern was proposed. By this method a compact first-negative-orderresonance-based small loop antenna was designed, which consists of two unit cells ofcomposite right-left hand transmission line (CRLH TL). By folding one of the unit cells to thebottom layer, higher radiation efficiency and omnidirectional radiation property can beachieved5.Alow profile multi-polarization patch antenna was proposed，which was comprise of themushroom type zor antennas and microtrip patch antenna. The multi-polarization antenna hasvertical polarization with the same thickness of the conventional microtrip patch antennas.The performance of antenna coverage is good in the upper half space.