الفهرس 
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Abstract
In this thesis, low frequency antennas for Ground Penetrating Radar (GPR) systems operating at frequency below 200 MHz are developed. The thesis presents design, analysis, fabrication and measurements of all proposed designs. Measurements include reflection coefficient (S11), input impedance (Z) as well as radiation patterns using a homemade setup in the VHF band.
First, printed Meander dipole antenna operating at 73 MHz and 145.75 MHz is presented. The dual band dipole antenna is composed of meander line terminated with a stub. The proposed antenna is implemented on FR4 substrate with an overall size of 61.3 X6.45 cm2 (0.15o x 0.015o). A 70% reduction in length is realized with the proposed antenna design compared to a regular dipole operating at the lower band (73 MHz). The reflection coefficient for the measured antenna is -15 dB and -18.5 dB at 73 MHz and 145.75 MHz with bandwidth of 2 MHz and 6.6 MHz, respectively. The antenna exhibits omnidirectional radiation characteristics at both bands with simulated radiation
efficiency up to 87%.
Second, the printed meander dipole antenna acquires enhanced -10 dB bandwidth of 20 MHz (13%) compared 6.6 MHz (4.5 %) in the VHF band. Bandwidth enhancement is realized through two techniques; 1) resistive loading to the meander line, and 2) metal strips at the back side acting as capacitive loading. A parametric study is implemented for the position, values of the resistors and the dimensions of the metal strips to realize maximum bandwidth. Using resistive loading, the bandwidth is increased from 6.6 MHz to 12 MHz with efficiency 42 %. On the other hand, adding two metal strips further increases the bandwidth to 20 MHz with efficiency up to 56%. The antenna exhibits omnidirectional radiation characteristics over the operating frequency 140-160 MHz.
Finally, all proposed structures are fabricated, measured and compared to simulated results Measurements are in good agreement with simulation results. Moreover, measurements and simulations for the proposed antennas in proximity to soil as well as with buried objects are also presented
.