Fundamentals of Terahertz Devices and Applications. Группа авторов

Fundamentals of Terahertz Devices and Applications - Группа авторов


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2.5a. The power transmitted by the ellipse Pa and propagating in parallel to the z‐axis through the aperture area of dAa = ρ, is equal to the transmitted power, Pt, by the ellipse through the area images; where ri is the distances between the first focus and the lens surface (see Figure 2.5b). Moreover, the transmitted power is related to the power incident, on the lens surface, Pi (i.e. neglecting the reflected power):

      The amplitude of the aperture and incident Poynting vectors can be expressed as:

      (2.40)equation

      (2.41)equation

      where |Ea| is the amplitude of the electric field on the equivalent aperture of the lens, and |Ei| is the amplitude of the far‐field pattern of the incident electric field. Moreover, the term images can be simplified as:

      where images. The term images can be calculated as:

      (2.44)equation

      (2.48)equation

      Therefore, the spreading factor can be defined as:

      (2.49)equation

      This is because, in the considered geometry (feed at the focus), the output GO phase front is planar and consequently has no power spreading.

      2.2.2.3 Equivalent Current Distribution and Far‐field Calculation

      (2.50)equation

      (2.51)equation

      where r ′ (θ′) is given by (2.5) and tan θ′ = ρ′/z′ where images. The vectorial components of these equivalent current distributions can be also expressed in Cartesian coordinates using images and images.

      (2.52)equation

Schematic illustration of reference system for the evaluation of the far fields radiated by the elliptical lens antenna.

      (2.53)equation

      where images and images; and η0 is


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