Figure 3(a) shows the fabricated antenna having dimensions obtained from simulation. Return loss of the fabricated antenna is measured using Keysight N9912A network analyzer. Retrun loss of better than 39 dB is achieved for the operating frequency range of 400-407 MHz.
(a) (b)
Figure 3:(a) Fabricated Quarter-wave antnnea and (b) measured S11 parameter
Designed monopole antenna provides maximum gain in the lower elevation region. At higher elevation angles between 45° to 90° its gain varies from 0 dBi to -30 dBi. This creates no coverage region or gap region overhead the antenna. Therefore another antenna was designed to provide the coverage in the overhead gap region of the fabricated quarter-wave monopole antenna.
Qurter-wave monopole AntennaQuadrifilar Helix Antenna [10] is a good choice to provide the coverage in gap region of designed quarter-wave monopole antenna. Beam-width of greater than 100° was required in the vertical plane. Optimizer functionality of 4NEC2 was used to achieve beam pattern and reflection coefficient as shown in Figure 4. Final dimensions of the antenna obtained from the 4NEC2 are tabulated in Table 3.