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The Pseudo-Brewster Angle Revisited - L. B. Cebik, W4RNL
Recentemente un OM ha affermato che i Social ci hanno rimbambito, nello stesso periodo su uno di essi un OM ha decantato la importanza di questo datato post di W4RNL (e dico poco!), avvevo voglia di riprendere la mia attivita' di elmer (se il CRER si muove, faremo a breve alcuni veri e propri corsi a livello qualitativamente alto); questi i motivi che mi hanno spinto a condividere lo sharing critico sulla iniziale affermazione che in detto documento ha fatto Cebik. Spero non vi arrabbierete se lo scrivo in inglese... si sa mai che chi lo ha decantato volesse anche leggere le mie riflessioni. Ogni intervento ed ogni richiesta di chiarimento sono oltremodo graditi!
The "The Pseudo-Brewster Angle Revisited - L. B. Cebik, W4RNL" Revisited
Eng. M. Filippi, I4MFA W4MFA
Absolutely NO!
What goes to 1 (ONE) when the take-off considered angle, that is the incident (and reflected by) angle with the ground goes to 0, is the Reflection Coefficient, that lowers in a vertical polarized wave FASTER THAN in an horizontal polarized wave when such take-off considered angle rises [Propagation Handouts]; that is true up to degrees lower than the one a PBA value for a vertical is.
Keep in mind that Fresnel equations for the wave polarization in which the electric field is parallel to the boundary are different to the Fresnel equations for the wave polarization in which the magnetic field is parallel to the boundary (This implies that the coefficients of reflection and transmission for these two wave polarizations are, in general, different).
The vertical component of the electric field reflects without changing "sign".
We have a sign inversion (180deg) on the horizontal component of the electric field.
As we may consider ground attenuation by land as a knife-edge attenuation,[*] at very low angles its value is very high, so the far-field on ANY-polarization antenna goes to zero at zero-degrees elevation.
But if we consider ground attenuation by sea, at very low angles its value is negligible:
THAT IS THE REASON we have higher "terrain gain" in the case of a sea-mounted vertical antenna.
As Reflection Coefficient drops faster to zero for vertical polarized waves with respect to horizontal, THAT is the reason for the height of an horizontal antenna has a greater impact with respect to a vertical if we consider take-off angles approaching the one giving a 180deg delay on the reflected component.[*] In knife-edge path calculation, there is no difference between considering the antenna at 0 height and an edge hill at H height or the antenna at H height and an edge at 0 height, the latter being the real situation in a spherical earth world.
Or not
?
Recentemente un OM ha affermato che i Social ci hanno rimbambito, nello stesso periodo su uno di essi un OM ha decantato la importanza di questo datato post di W4RNL (e dico poco!), avvevo voglia di riprendere la mia attivita' di elmer (se il CRER si muove, faremo a breve alcuni veri e propri corsi a livello qualitativamente alto); questi i motivi che mi hanno spinto a condividere lo sharing critico sulla iniziale affermazione che in detto documento ha fatto Cebik. Spero non vi arrabbierete se lo scrivo in inglese... si sa mai che chi lo ha decantato volesse anche leggere le mie riflessioni. Ogni intervento ed ogni richiesta di chiarimento sono oltremodo graditi!
The "The Pseudo-Brewster Angle Revisited - L. B. Cebik, W4RNL" Revisited
Eng. M. Filippi, I4MFA W4MFA
Michaels, W7XC [SK], on The ARRL Antenna Book Chapter 3, devoted to "The Effects of Ground", simply notes that below the PBA angle, the radiation of a ground-mounted vertical decreases rapidly, falling toward zero at the horizon.
In a pattern taken over perfect ground, maximum gain would be at the horizon.
In one sense, then, the PBA does some explanatory work in the overall account of why the far field of a vertical antenna goes to zero at zero-degrees elevation.
In a pattern taken over perfect ground, maximum gain would be at the horizon.
In one sense, then, the PBA does some explanatory work in the overall account of why the far field of a vertical antenna goes to zero at zero-degrees elevation.
What goes to 1 (ONE) when the take-off considered angle, that is the incident (and reflected by) angle with the ground goes to 0, is the Reflection Coefficient, that lowers in a vertical polarized wave FASTER THAN in an horizontal polarized wave when such take-off considered angle rises [Propagation Handouts]; that is true up to degrees lower than the one a PBA value for a vertical is.
Keep in mind that Fresnel equations for the wave polarization in which the electric field is parallel to the boundary are different to the Fresnel equations for the wave polarization in which the magnetic field is parallel to the boundary (This implies that the coefficients of reflection and transmission for these two wave polarizations are, in general, different).
The vertical component of the electric field reflects without changing "sign".
We have a sign inversion (180deg) on the horizontal component of the electric field.
As we may consider ground attenuation by land as a knife-edge attenuation,[*] at very low angles its value is very high, so the far-field on ANY-polarization antenna goes to zero at zero-degrees elevation.
But if we consider ground attenuation by sea, at very low angles its value is negligible:
THAT IS THE REASON we have higher "terrain gain" in the case of a sea-mounted vertical antenna.
As Reflection Coefficient drops faster to zero for vertical polarized waves with respect to horizontal, THAT is the reason for the height of an horizontal antenna has a greater impact with respect to a vertical if we consider take-off angles approaching the one giving a 180deg delay on the reflected component.[*] In knife-edge path calculation, there is no difference between considering the antenna at 0 height and an edge hill at H height or the antenna at H height and an edge at 0 height, the latter being the real situation in a spherical earth world.
Or not
?