Updated reference attributions for antenna models.

docs/source/user_libs_antennas.rst

@@ -22,8 +22,8 @@ GSSI 400MHz              300x300x170mm 0.5, 1, 2mm   Sam Stadler (Sam.Stadler@li
 **Attributions/citations**:
 
 1. Warren, C., Giannopoulos, A. (2011). Creating finite-difference time-domain models of commercial ground-penetrating radar antennas using Taguchi's optimization method. *Geophysics*, 76(2), G37-G47. (http://dx.doi.org/10.1190/1.3548506)
-2. Giannakis, I., Giannopoulos, A., & Warren, C. (2018). Realistic FDTD GPR antenna models optimised using a novel linear/non-linear Full Waveform Inversion. *IEEE Transactions on Geoscience and Remote Sensing*, . ()
-3. Stadler, S. (2017). A Forward Modeling Study for the Investigation of the Vertical Water-Content Distribution of Using Guided GPR Waves (Master's Thesis, Freiberg University of Mining and Technology, Germany). (https://tinyurl.com/y6vdab22)
+2. Giannakis, I., Giannopoulos, A., & Warren, C. (2019). Realistic FDTD GPR antenna models optimised using a novel linear/non-linear Full Waveform Inversion. *IEEE Transactions on Geoscience and Remote Sensing*, 57(3), 1768-1778. (https://doi.org/10.1109/TGRS.2018.2869027)
+3. Stadler. S., Igel J. (2018). A Numerical Study on Using Guided GPR Waves Along Metallic Cylinders in Boreholes for Permittivity Sounding. 17th International Conference on GPR. (https://tinyurl.com/y6vdab22)
 
 Module overview
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