Changed d to delta.

docs/source/examples_antennas.rst

@@ -17,7 +17,7 @@ This example demonstrates a model of a half-wavelength wire dipole antenna in fr
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-The wire is modelled using the ``#edge`` command which specifies properties of the edge of the Yee cell. The antenna is fed using the ``#transmission_line`` command. The one-dimensional transmission line model virtually attaches to the dipole at the gap between the arms. The antenna has an input impedance (:math:`Z_0`) of 73 Ohms specified in the ``#transmission_line`` command, and uses a Gaussian waveform with a centre frequency of 1GHz. A time window of 60ns is used: firstly, to give enough time for the response to settle to a steady state; and secondly, to allow a reasonable (17MHz) spacing for the frequency bins when calculating FFTs, as :math:`\Delta f=1/T` where :math:`\Delta f' is the frequency bin spacing and :math:`T' is the time window.
+The wire is modelled using the ``#edge`` command which specifies properties of the edge of the Yee cell. The antenna is fed using the ``#transmission_line`` command. The one-dimensional transmission line model virtually attaches to the dipole at the gap between the arms. The antenna has an input resistance :math:`Z_{in} = 73~\Omega` specified in the ``#transmission_line`` command, and uses a Gaussian waveform with a centre frequency of 1GHz. A time window of 60ns is used: firstly, to give enough time for the response to settle to a steady state; and secondly, to allow a reasonable (17MHz) spacing for the frequency bins when calculating FFTs, as :math:`\Delta f=1/T` where :math:`\Delta f` is the frequency bin spacing and :math:`T` is the time window.
 
 Time histories of voltage and current values in the transmission line are saved to the output file. These are documented in the :ref:`output file section <output>`. These parameters are useful for calculating characteristics of the antenna such as the input impedance or S-parameters. gprMax includes a Python module (in the ``tools`` package) to help you view the input impedance and admittance and s11 parameter from an antenna model fed using a transmission line. Details of how to use this module is given in the :ref:`tools section <plotting>`.