Research On VHF Miniature Broadband Loaded Antenna

Antenna is an integral part of communications systems. In modern military communication, to fulfill secure and confidential communications and minimize the enemy’s interference, frequency modulation and spread spectrum communication techniques have found wide use in communication equipment such as HF and VHF radio. Since a multitude of antennas are used in tanks and naval ships and don’t carry easily, it is necessary for multiple radios to share one antenna, stricter requirements made for the broadband of antennas. Antennas operating at HVF bands are usually large in physical size and liable to be exposed, and therefore much research in recent years has focused on the realization of the broadband and miniaturization of antennas while maintaining their good performance.The paper mainly discusses the design and implementation of broadband miniature antennas, describes in detail the analysis and computation of wire antenna by the moment method and relevant theories concerning circular array, and explains the techniques for the broadband and miniaturization of antennas. Combining theoretical analysis with the research, the paper adopts the feko simulation software and designs two antennas.The paper consists mainly of the following parts:1. The paper designs a 225-512 MHz broadband cage-type antenna with a desirable voltage standing wave ratio and pattern bandwidth. In the antenna structure design, the traditional column-type symmetrical dipole structure is converted into a grid patter consisting of eight static wires, forming a cage-type symmetrical dipole antenna, on the basis of which by exploring methods such as applying a capacitance at the feeding point the symmetrical dipole bandwidth can be effectively expanded. An analysis of the parameters which affects the performance of the antenna is made, thus summarizing the best values for each parameter. Simulation results show that the standing wave ratio of the antenna is smaller than 2.5 within the whole frequency band and that the gain is greater than 2d B, meeting its specifications.2. An eight-unit circular array antenna is designed, and a detailed analysis is made of the radiation pattern of all the array elements while excited with equal amplitude and phase, scanning at azimuth planes while excited with equal amplitude and different phase, and variation of side-lobe level scanning at different frequency spots while excited with equal amplitude and different phase.