.. _sphx_glr_api_gallery_communications_antennas:

Antennas
--------

Gain and effective aperture, and the half-wave dipole.


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    <div class="sphx-glr-thumbcontainer" tooltip="Friis first wrote his transmission formula not with gains but with the antennas&#x27; effective areas: P_r/P_t = A_t A_r/(d\lambda)^2. A receiving antenna collects the power falling on its effective area A_e, and reciprocity ties that area to its gain, A_e = G\lambda^2/4\pi (~engineeringkit.communications.effective_aperture). For a dish of physical area A and aperture efficiency \eta_a, G = 4\pi\eta_a A/\lambda^2 (~engineeringkit.communications.aperture_gain). A dish of fixed size gains 6 dB at every doubling of frequency, while an antenna of fixed gain collects less and less power.">

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  .. image:: /api/gallery/communications/antennas/images/thumb/sphx_glr_plot_01_friis_effective_aperture_thumb.png
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  :doc:`/api/gallery/communications/antennas/plot_01_friis_effective_aperture`

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      <div class="sphx-glr-thumbnail-title">Friis's effective aperture: gain and area (1946)</div>
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    <div class="sphx-glr-thumbcontainer" tooltip="The half-wave dipole is the reference antenna of radio engineering. With the sinusoidal current a thin wire carries, its far field varies as \cos(\tfrac\pi2\cos\theta)/\sin\theta (~engineeringkit.communications.half_wave_dipole_pattern), a little narrower than the \sin\theta of a short dipole. Integrating the radiated power gives a directivity of 1.64, or 2.15 dBi (~engineeringkit.communications.half_wave_dipole_directivity), and a radiation resistance of 73 ohms (~engineeringkit.communications.half_wave_dipole_resistance). Philip Carter of RCA put such calculations in circuit form in 1932: his induced-EMF method gave the self- and mutual impedances of dipoles, the basis of every array design that followed.">

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  .. image:: /api/gallery/communications/antennas/images/thumb/sphx_glr_plot_02_carter_half_wave_dipole_thumb.png
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  :doc:`/api/gallery/communications/antennas/plot_02_carter_half_wave_dipole`

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      <div class="sphx-glr-thumbnail-title">Carter's half-wave dipole (1932)</div>
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.. toctree::
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   /api/gallery/communications/antennas/plot_01_friis_effective_aperture
   /api/gallery/communications/antennas/plot_02_carter_half_wave_dipole