Research And Design Of End-Fire Antenna

In tunnel communication and radar detection systems,both the receiving and transmitting antenna arrays are required to conform to the geometry of the carrier as much as possible to reduce the air resistance.This implies that the receiving/transmitting antenna needs to have good aerodynamic characteristics.Because of its unique pattern characteristics,the end-fire antenna can not only solve the "blind area" problem of radar,but also plays a role in suppressing the multipath effect in tunnel communication.The end-fire antennas,which is known for its high gain,low cost and end-fire radiation,has widely applications in both wireless local area networks(WLAN)or military equipment fields,even in the medical field,such as some microwave hyperthermia and tumor surgery,which have become a hot research topic in the field of antennas.Two design methods based on end-fire antenna types is presented in this paper.The first one is design method of Yagi-Uda antenna with multiple driven elements,which based on the method of maximum power transmission efficiency.This novel design method for end-fire antennas which are similar to conventional Yagi-Uda antennas but have more than one driven elements.The method of maximum power transmission efficiency is used to optimize the excitation of multiple driven elements,so that the antenna end-fire gain can be further improved while the size of the antenna is fixed.In other words,when the desired end-fire gain of antenna is determined,the antenna size will be significantly reduced by using this design method.To demonstrate the feasibility of this method,two designs of the Yagi-Uda antenna with multiple driven elements are presented.1.The first design works at 2.45 GHz for Wi-Fi applications and makes use of printed half-wavelength dipole as radiating element.It has four driven elements,one reflector and three directors.The measurements and simulations indicate that the end-fire gain is 1.8 dB higher than the traditional printed dipole Yagi-Uda antenna with the same number of elements and size.2.The second design is based on the SRR elements,working at 5.5 GHz for wireless local area network(WLAN),and includes five-driven elements.Compared to the Yagi-Uda antenna based on the same elements previously reported,the longitudinal dimension is significantly reduced by 46% while maintaining the same lateral dimension and end-fire gain.The second one is design method of bidirectional antenna array with adjustable end-fire gains,which based on the weighted method of maximum power transmission efficiency.The weighted diagonal matrix is introducing into the method of maximum power transmission efficiency for the first time in this design method,the optimized excitations for the antenna elements can be obtained to realize the desired distribution for the end-fire gains by adjusting the weight ratio of the received power of the receiving antennas.To demonstrate the feasibility of the method,a bidirectional dipole array working at 2.45 GHz and consists of four printed half-wavelength dipoles driven by the optimized distribution of excitations,obtained from the weighed method of maximum power transmission efficiency and then realized by a continuously adjustable feeding circuit board.It is shown that the end-fire gain of the dipole array in one direction varies from 1.5 to 10.2 dBi as the ratio of weights changes from 0 to 1,and the end-fire gain reaches 9.3 dBi when the identical bidirectional beams are realized with equal weights.