Initial models that I used to explore the question all used wire diameters that were relatively large for the wavelength involved. For example, I used 0.1" (3 mm) elements for a VHF (225 MHz) antenna. For a 3-element beam showed only about 0.17 dB less gain for a stainless steel model relative to an aluminum model.
Material Gain dBi F-B dB Source Z R ± jX Ohms 6061-T6 Aluminum 8.25 24.80 24.4 - j 0.8 Stainless Steel Type 302 8.08 23.65 25.0 + j 0.1
If we use only such large wire diameters relative to wavelength, the large surface area can mislead us into thinking that perhaps phosphor bronze and stainless steel are satisfactory for all antenna applications.
Of course, the question here is the electrical properties of the material, not the physical and chemical properties. Weight, corrosion, and other such factors must be considered in addition to these notes on the electrical properties of certain kinds of wire in antenna applications.
Proper tests of antenna wire types should press them toward levels of thinness relative to a wavelength that begin to show their limitations. Hence, the low HF wire dipole become a better test vehicle. It can show to some degree at what point one is better off leaving some materials alone, even if they offer some good physical and chemical properties. Materials that offer good performance when fat often reach their limits of application when thinned down.
All runs were made with NEC-Win Pro a version of NEC-2. Exact numbers may vary in the last decimal place with other programs--or if you simply choose a different level of segmentation. 21 segments per dipole was the segmentation density used for these simple tests.
Conductivity Material Gain Source Z Efficiency S/m dBi R ± jX Ohms % Perfect (lossless) 2.13 72.2 + j 0.1 100.00 6.2893E7 Silver 2.04 73.7 + j 1.4 98.09 5.8001E7 Copper 2.04 73.7 + j 1.5 98.01 3.7665E7 Pure Al. 2.02 74.1 + j 1.8 97.54 3.0769E7 6063-T832 2.01 74.3 + j 1.9 97.28 2.4938E7 6061-T6 2.00 74.6 + j 2.2 96.98 1.5625E7 Brass 1.96 75.2 + j 2.7 96.19 9.0909E6 Phosphor Bronze 1.91 76.2 + j 3.6 95.02 1.3889E6 Stnlss Stl 302 1.55 83.0 + j 8.8 87.53
Note that even silver (untarnished) shows a 2% efficiency loss and a 0.1 dB gain loss relative to perfection. Even if silver were cheap, I would not waste it on a wire antenna of this kind, given the performance of copper. Also note the larger step drops as you move below pure aluminum on the list.
Material Source Z Effici- Gain dBi Length AWG Wire R ± jX Ohms ency % Meters Size Stls. Steel 78.3 + j 0.1 91.64 1.75 36.36 # 8 Ph. Bronze 78.3 - j 0.4 91.75 1.75 36.46 #16 Brass 78.1 + j 0.1 92.06 1.77 36.50 #18 6061-T6 78.1 - j 0.0 92.08 1.77 36.52 #20 6063-T832 77.5 - j 0.6 92.85 1.81 36.52 #20 Pure Alum. 78.3 - j 0.5 91.88 1.76 36.53 #22 Copper 78.4 - j 0.5 91.76 1.75 36.55 #24 Silver 78.2 + j 0.4 92.08 1.77 36.57 #24
First, the gain numbers are not exactly 1.75 dBi, but the value closest to it on the high side yielded by the smallest wire size that would yield at least 1.75 dBi.
Second, within those limits, notice that there is an equality of source impedance and efficiency for a specific gain level. What differs among the antennas is the length necessary for resonance and the wire size.
Third, notice the wide range of antenna sizes in the list. As the wire grows thin for a given wavelength, the material losses play an increasing role in performance. If we use a conservative minimum gain of 1.75 dBi free space as the limit of acceptability, stainless steel--the strongest of the wires--would require a #8 AWG size to meet the standard. The electrical performance is at odds with its physical advantages.
Phosphor bronze is marginal under this test, requiring a minimum size of #16 AWG. If we set the gain standard higher, perhaps at 2.0 dBi free space, then phosphor bronze might fail to meet the electrical standard at an acceptable diameter.
Whether phosphor bronze will meet a given standard or whether the gain level obtainable with an available diameter of phosphor bronze wire is acceptable to a user is not a decision that can be made here. Instead, this note and the tests reported in it yield the advice not to misapply test results, not even these.
The selection of wire material requires that you set standards of
performance for a given application. Then, model (or build) your antenna
using the range of possible materials to see if each material meets the
standard. When the diameter of the wire becomes thin enough relative to a
wavelength, you may encounter a threshold situation in which some materials
simply fail the electrical test.
Updated 8-8-98. © L. B. Cebik, W4RNL. Data may be used for
personal purposes, but may not be reproduced for publication in print or
any other medium without permission of the author.