A Novel Integrated Dielectric Rod Antennas With High Gain And Low Side Lobe Levels

The dielectric rod antennas(DRAs),known as "poly-rod," first appeared in 1929,are considered a special case of "surface wave" antennas.These antennas are usually of high gain over a broad bandwidth,making them attractive and useful for high radiation efficiency,high polarization purity and ultra-wideband applications,such as ground penetrating radars.There are two main disadvantages in conventional dielectric rod antennas one,its long length and other high side lobe levels.To develop such antennas which are able to achieve high gain with limited length as well as keeping the side lobe level within the acceptable limits is still challenging.In this dissertation,a novel integrated type of dielectric rod antennas is proposed.These antennas are useful for high gain and low side lobe levels with smaller length.Two design examples one for linear and the other for circular polarization are discussed in this dissertation.For linear polarization an integrated structure of the Yagi-Uda and the dielectric rod antenna is presented.The novel structure mainly consists of a tapered printed Yagi-Uda,a tapered dielectric cover and a periodic dielectric rod.Firstly,a tapered printed Yagi is designed as the primary feeder and embedded inside a tapered dielectric rod to improve the directive gain,radiation efficiency and side lobe levels.The influence of the dielectric cover to the Yagi is discussed.Then,a dielectric rod with triangular periodic surface is also loaded to the end the dielectric cover to obtain higher gain and better front-to-back ratio.Finally,a sample of the antenna working at 8.5-9.7 GHz with 18-dBi maximum gain and-23.37 dB side lobe level is designed.A prototype is fabricated and tested;the measured results meet well with the simulated.Compared with the traditional Yagi-Uda antenna and dielectric rod antenna with the same length,the presented integrated antenna has higher gain with lower sidelobe level.For circular polarization another integrated antenna with the advantages of Helix and dielectric rod antenna allows high gain with low aperture,especially high polarization purity and low side lobe levels are designed.The effective aperture improvement is achieved by embedded printed loops periodically in the dielectric rod.Low loss Teflon material with ? r = 2.1 is used as dielectric rod for high radiation efficiency.Finally,a sample of the embedded Helix dielectric rod antenna working at 8-9.7 GHz is designed,to enhance the gain of the whole structure,14 extra tapered printed loops are inserted perpendicularly into the dielectric rod with length of 3?.The influence of dielectric materials on the radiation patterns of Helix is studied in detail.Measurement results show that 18.85-dBi maximum gain,Side lobe level below-20dB,40dB front to back ratio(FBR)and Axial ratio(AR)below 3dB are successfully achieved.The fabricated antenna measured results meet well with the simulated one.Compared with the traditional Helix antenna and dielectric rod antenna with the same length,the presented Hybrid antenna has higher gain with lower sidelobe level and with good polarization purity.