| The research is made with practical demand. Mobile communication antenna andshortwave antenna are studied.In the dissertation, the major research can be divided to two parts: firstly, a dual-bandYagi-Uda antenna with branch structure is designed due to problem of multi-antenna inmobile communication system. A compact Yagi-Uda vehicle antenna is designed toreduce the volume of the present antenna, and its volume is reduced30%. Secondly, tosolve the practical problems such as feedline modeling problem, the ground influenceproblem in project of shortwave, some related issues of shortwave antenna areresearched, including the influence of feederline modeling of the antenna on calculationresults, the effect of ground and conductor material on the antenna characteristics, andthe problems of HF propagation prediction and its simulation. The author’s maincontributions are as follows:1．A novel dual-band Yagi-Uda antenna is designed. The dual-band characteristic isrealized by the design of branch structure. The performance and size of the proposedantenna are corresponded to a sigle-band antenna. It can instead of two antennas for thedirectional and dual-band communication. The antenna is optimized by multi-objectivedifferential evolution algorithm and MOM. Both the measured and simulated resultsshow that the antenna reach gains5.6dBi and7.5dBi, FBRs8.8dB and9.8dB, in bands915-935MHz and1760-1805MHz respectively, and the VSWRs are less2in bothbands.2．A double-frame Yagi-Uda antenna is proposed, which make the Yagi-Uda antennafor vehicle directional communication of ultrashort wave (30-88MHz) scompacted andminiaturized. By the design, the mobilebility, flexiblity, and viability of the vehicle areimproved. The influence of vehicle on antenna is considerd in the design so as to itsaccuracy. To the traditional three element monopole Yagi-Uda antenna, the designedthree elements monopole double-frame compact Yagi-Uda antenna is reduced1.22m inaxial length and0.66m in height, and the gain and FBR are improve2.1dB and0.5dBrespectively.3. To insure the design accuracy, validity, the influence of feederline modelingmethod on the calculate results is researched, and the consistency of the antenna actualand simulate performance is improved. The two modeling methods, equivalent networkmethod and wire structure method, are used to analyze the fishbone antenna and LPDA antenna, using the MOM on the basis of the Pocklington equation and Sine interpolationbase function. Comparing the performance parameters calculated by the two methods,we present the proper method for each antenna, which is verified correct by the practicaldatas.4. To provide theory evidence for site selection and setting up antenna, the influenceof the ground on the antenna is researched. The fishbone antenna and LPDA antennawith different height on the ground with different electrical parameters are calculated byMOM and reflection coefficient approximation. The influence of the ground parameterand antenna height on the antenna that prallel and tilt with ground is presented, whichmay be a guide for engineering practice.5. The practicality of the stainless steel to be the shortwave antenna material isexpounded and proved. The present antenna material is costly, hard, and difficult tomaintain, while the stainless is not. The influence of the conductor on the shortwaveantenna performances is researched, by which it is proved that the stainless steel whichis cheaper and softer can take place of the copper line to make up of antenna in theengineering, when the gain can be accepted.6. A simulation module is designed, and a method of designing antenn according tothe propagatin prediction is proposed, which can provide guidance for buildingshortwave communication links and setting up antenna, with less actual data and priorknowledge. The practical proves that the communication link has good functions, whichprove the simulation module and antenna design method are valid. |
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