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Re: Signal Waveform Sent Out on Channel 0

 

Hi, Jim,

Schelkunoff and Friis define "end effect" as being due to the non-zero current flow into the capacitance of the end cap of a finite radius conductor (Section 8.23).? The ARRL Antenna Books and Handbooks define end effect as being due to the increased capacitance of the loop of wire through the end insulator.? Some of the Antenna Books mention the dielectric constant of the end insulator as being a factor.? The 1952 Handbook (my first brand new one) makes a clear distinction between the shortening of the resonant length as a function of the length to diameter ratio and the end loop/insulator effect, which it terms "end effect."

In discussing current expansion on wires, the NEC-2 description acknowledges that current may flow into the end cap when the free end is a wire of finite radius.? Separate expressions are provided for a free end and a junction, although the term "end effect" is not used.

These seem to be the same effect, but with the ARRL description describing the larger contribution of the end loop and insulator that Schelkunoff and Friis and the NEC-2 description ignore.

Chapters 24 and 25 of Orfanidis seem to assume zero current at a free end, but I'll have to go back and read them in more detail. Fortunately, I can run a lot of Matlab code under GNU Octave, which is easier on my budget.

73,

Maynard
W6PAP

On 9/3/21 9:58 AM, Jim Lux wrote:
On 9/3/21 9:23 AM, Maynard Wright, P. E., W6PAP wrote:
Texts and references on antennas such as Schelkunoff and Friis, "Antennas - Theory and Practice," Bell Telephone Laboratories, 1952 (printed by Wiley) also discuss "end effect" and "fringing effect" as being characteristic of an antenna element that has a finite radius.
yeah, but later works (Kraus, Balanis) abandon that terminology - because it implies that there's some sort of lumped phenomenon going on, and there isn't.

What it really comes from is if you integrate the Electric Field Integral Equation (EFIE) the solution is a combination of the cosine integral and the sine integral (not the integral of cosine and sin). The real part of the feedpoint impedance is related to the Cosine integral, and the imaginary part is the Sine integral. it doesn't go through zero at lambda/2, but slightly different.

Check out Kraus, chapter 5 (where the cosine and sine integrals are defined) or chapter 10 section 3 (where the self impedance is rigorously developed).? Chapter 9 on the Moment Method is also good (esp since it's what NEC is based on) - (Chapter in 2nd ed, probably the same).

Orfanidis, chapter 24 and 25 - Chap 24 gives all the popular ways (and some not so popular) ways to approximately solve the equation with comparisons among them. Chap 25, section 3 looks at self and mutual impedance, and derives the solution using the Ci() and Si() functions.




I find Kraus more "readable" but Orfanidis, since he's updating it all the time, and it's online, is better for more modern approaches. Orfanidis is substantially more math intensive, but on the other hand, he gives you matlab examples for computation.
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