§ 73.160   Vertical plane radiation characteristics, f(θ).

   (a) The vertical plane radiation characteristics show the relative field
   being radiated at a given vertical angle, with respect to the horizontal
   plane. The vertical angle, represented as θ, is 0 degrees in the horizontal
   plane,  and 90 degrees when perpendicular to the horizontal plane. The
   vertical plane radiation characteristic is referred to as f(θ). The generic
   formula for f(θ) is:

   f(θ) = E(θ)/E(O)

   where:

   E(θ) is the radiation from the tower at angle θ.

   E(O) is the radiation from the tower in the horizontal plane.

   (b) Listed below are formulas for f(θ) for several common towers.

   (1) For a typical tower, which is not top-loaded or sectionalized, the
   following formula shall be used:
   eCFR graphic ec13no91.015.gif

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   where:

   G is the electrical height of the tower, not including the base insulator
   and pier. (In the case of a folded unipole tower, the entire radiating
   structure's electrical height is used.)

   (2) For a top-loaded tower, the following formula shall be used:
   eCFR graphic ec13no91.016.gif

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   where:

   A is the physical height of the tower, in electrical degrees, and

   B is the difference, in electrical degrees, between the apparent electrical
   height (G, based on current distribution) and the actual physical height.

   G is the apparent electrical height: the sum of A and B; A + B.

   See Figure 1 of this section.
   eCFR graphic ec01mr91.066.gif

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   (3) For a sectionalized tower, the following formula shall be used:
   eCFR graphic ec13no91.017.gif

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   where:

   A is the physical height, in electrical degrees, of the lower section of the
   tower.

   B is the difference between the apparent electrical height (based on current
   distribution) of the lower section of the tower and the physical height of
   the lower section of the tower.

   C is the physical height of the entire tower, in electrical degrees.

   D is the difference between the apparent electrical height of the tower
   (based on current distribution of the upper section) and the physical height
   of  the entire tower. D will be zero if the sectionalized tower is not
   top-loaded.

   G is the sum of A and B; A + B.

   H is the sum of C and D; C + D.

   Δ is the difference between H and A; H−A.

   See Figure 2 of this section.
   eCFR graphic ec01mr91.067.gif

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   (c) One of the above f(θ) formulas must be used in computing radiation in
   the vertical plane, unless the applicant submits a special formula for a
   particular type of antenna. If a special formula is submitted, it must be
   accompanied by a complete derivation and sample calculations. Submission of
   values for f(θ) only in a tabular or graphical format (i.e., without a
   formula) is not acceptable.

   (d) Following are sample calculations. (The number of significant figures
   shown  here should not be interpreted as a limitation on the number of
   significant figures used in actual calculations.)

   (1) For a typical tower, as described in paragraph (b)(1) of this section,
   assume that G = 120 electrical degrees:
   θ   f(θ)
   0  1.0000
   30 0.7698
   60 0.3458

   (2)  For  a top-loaded tower, as described in paragraph (b)(2) of this
   section, assume A = 120 electrical degrees, B = 20 electrical degrees, and G
   = 140 electrical degrees, (120 + 20):
   θ   f(θ)
   0  1.0000
   30 0.7364
   60 0.2960

   (3) For a sectionalized tower, as described in paragraph (b)(3) of this
   section, assume A = 120 electrical degrees, B = 20 electrical degrees, C =
   220  electrical degrees, D = 15 electrical degrees, G = 140 electrical
   degrees (120 + 20), H = 235 electrical degrees (220 + 15), and Δ = 115
   electrical degrees (235−120):
   θ   f(θ)
   0  1.0000
   30 0.5930
   60 0.1423

   [ 46 FR 11993 , Feb. 12, 1981]

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