Reply to thread

Message: <blockquote data-quote="dreamsat" data-source="post: 1165128" data-attributes="member: 412221">After calculating the waveguide irradiator with D = 18.3 mm, the average Ku length was found to be Lo = 25.8 mm Lc = 31.2 mm Lu = 23.9 mm Lg = 45.8 mm The height of the probe in the waveguide Lo / 4 = 6.4 mm Distance from the probe to the rear wall of the waveguide (short circuit or reflector) Lg / 4 = 11.4 mm So we have found that a pin of 6.4 mm length should be at a distance of 11.4 mm from the empty wall of the waveguide. The coefficient of reflection from it is -1, so the reflected wave returns to the probe in half a period and sums in phase with the wave incident on it. The signal at the output of the illuminator will be maximum. And now let's look into the real waveguide: The thickness of the probes is 1.2 mm, so from the axis of the lower probe to the deaf end of the waveguide is 6.5 mm, the minimum distance from the probe to the reflector is 5.9 mm, the maximum distance is 7.1 mm. At least one of these figures is close to 11.4 mm? These figures correspond to a quarter length and 26, 24.5 and 28.4 mm respectively or approximately middle, outer and upper Ku range. Let's see at what distance from the open end of the waveguide the receiving probe should be. Lg / 2 = 22.9 mm. And indeed - 13.3 + 0.6 = 13.9 mm, which corresponds to half the wavelength at a frequency of 10.8 GHz in free space. Contrary to the prevailing misconception, the height for the best adaptation of the receiving probe to the irradiation device of its (probe) must therefore be Lambda min / 4 The distance from the probe to the boundary of the irradiator / waveguide must be a multiple Lambda aver / 2 The distance from the probe to the electrical wall of the waveguide must be Lambda aver / 4 Where lambda aver is the average wavelength in free space The waveguide dimension is always different for different LNBs and must be included in the calculation!!</blockquote>

Verification