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The configuration modelled in this study is a monopole on an infinite ground plane with a coaxial feed. In this model the objective is to calculate the reflection from the drive point of the monopole within the feed co-axial cable. Validation is carried out against measured data from a study by Maloney et. al.[1]
In this study case the transmission line feed is used to calculate the reflection of a Gaussian pulse from the drive point of a monopole antenna mounted on an infinite ground plane. This example is taken from Maloney and the results generated using Celia are compared to those measured and published by Maloney. A 50W coax is used to excite the monopole. The model represents a monopole of 20cm length and radius 6.1mm, which is mounted on an infinite ground plane. The Celia calculation uses a 6 cell PML located 10 cells from the wire in each direction.
The figure shows the comparison between results achieved using Celia and those from Maloney. The graph shows the shape of the pulse reflected from the antenna drive point, measured within the feed transmission line. The time is shown normalised to the transit time of the antenna, which in this case is 0.66ns. As can be seen there is excellent agreement between model and measured results.
The configuration for this case is a monopole on an infinite ground plane with a nearby flat perfectly conducting reflector. In this case, as above, the drive point reflection is calculated. It is very similar to the above case while extending the verification of the feed operation in receive mode. This is validated against measurements published by Maloney et. Al.[1]. Results for this case are shown below.
The graph shows the shape of the pulse reflected from the antenna drive point, measured within the feed transmission line. The time is shown normalised to the transit time of the antenna, identical to the above case at 0.66ns. Again there is excellent agreement between model and measured results. The difference in the form of the reflected voltage waveform compared to the isolated monopole is caused by the transmitted wave that is reflected from the nearby plate and subsequently received by the monopole some time later.
1 Maloney J G, Shlager K L, Smith G S
"A Simple FDTD Model for Transient Excitation of Antennas by Transmission
Lines"
IEEE Transactions on Antennas and Propagation
Vol42, No. 2, Feb 1994, pp 289-292