VHF adaptive antenna using a rear defogger

摘要

This thesis presented the design of an adaptive bearnforming antenna using arear defogger. The main purpose of this project is to develop the vehicular adaptiveantenna for VHF band, which does not require the installation space, does not spoil theindustrial design, has low cost and low power consumption. In land communication,there is no clear line of sight between transmitter and receiver. The transmitted signalmight be reflected, refracted because of the building or terrain. The receiver mightreceive a delayed, or reflected signal instead of the original signal. Adaptive antenna isthe best candidate to mitigate the multipath fading effects. However, for VHF band,conventional adaptive antenna has a drawback of a large aperture size. Therefore, in thispaper a rear defogger is proposed as an aperture to overcome the size problem of using aconventional adaptive antenna. A rear defogger of a vehicle can be used as an aperture,' 7 - 3and in order to make it compatible with ESPAR antenna, several ports have been1 1,provided. One port is used as an active port or output port, while other ports areconnected to the variable reactor. Downhill simplex method is used as an algorithm toform the adaptive beam for the proposed antenna. This algorithm is maximized thecorrelation coefficients. Simplex method has been chosen because it has severaladvantages. Simplex method has a fast convergence time, robust beamforming, and itcan be used for multi-dimensional optimization. There are several steps in simplexmethod for optimization; reflection, expansion, contraction, and multiple contractions.IE3D software is used to model the defogger with the car and from the IE3D results itshows that the defogger can be used as an adaptive antenna because it has low voltagestanding wave ratio (VSWR) to make it operate as an antenna, low spatial crosscorrelation (SCC) for better diversity and has high coupling between port (CBP) forbetter capability of beamforming. In the analysis, the VSWR is lower than 3, SCC islower than 0.5, and the CBP is between -6 dB to -10 dB. For numerical simulation,MATLAB is used to make a program for simplex method. From the simulation results,it shows that almost 80 % of the signals have signal to interference noise ratio (SINR)greater than 20 dB. Besides that, null is performed for incoming interference andremained high gain for the desired signal. A Rear defogger is made from heating wire,therefore it is necessary to confirm the effects of the resistivity to the antenna'sperformance. The effects of the resistivity has been confirm through IE3D simulator andMATLAB programming by comparing it to the copper wire. From IE3D simulator,comparison has been made for VSWR, SCC, and CBP for both resistive and copper wire. The results show that the values of VSWR, SCC, and CBP for copper and resistivewires are nearly same. A statistical analysis has been carried out for copper and resistivewire, and the analysis show that the performance of the resistive wire is slightlydecrease compared to copper wire. However, the different is very small, plus theresistive wire has more than 80% of the signal has SINR greater than 20 dB. The beampattern is controlled by a varactor circuit. The varactor circuit is connected to the threepassive elements. The reactance range is limited from - j300Q to j3000 in thesimulation, consider manufacturing. It is difficult to manufacture a large range ofreactance. The reactance value is different for each incoming DOAs. Measurement hasbeen conducted in anechoic chambers for adaptive beamforming. It shows that afterperform beamfonning, null is performed for incoming interference, improved VSWR,BER and SINR over the bandwidth. The proposed antenna has a fast convergence times,the convergence time is less than 50 ms and the iteration number is less than 70.Measurement in Rayleigh fading environment also been conducted, it shows that byapplying the beamforming the BER is improved. The experiment was conducted for 473 ' * ', xiMHz and 900 MHz for horizontal (co-polarization) and vertical (cross-polarization). Forboth co-polarization and cross-polarization, BER show an improvement.