6.5 Summary

The material in this chapter is a mix of physical design ideas and good modeling practice. We examined ways to get better bandwidth and lower matching loss with our small antennas. Of the methods presented, volume-loading is the most successful technique by far. It should be used whenever it s mechanically feasible. If the space allowed is so small compared to wavelength that resonance can t be achieved with volume-loading and a reasonable wire size, the next best thing to do is coil the radiating wire to get enough added inductance. Lumped coils of typical Q just have too much loss resistance.

We have made a start on examining antennas in their working environments. Antennas over the earth operating in the HF band have greatly reduced radiation efficiencies because of the waves penetrating the ground. On the other hand, VHF and UHF antennas can be helped greatly by the radio box on which they are mounted.

The modeling part of the design process has been illustrated many times. Whether a very simple model is written directly as a .nec file, or extensive code is written to translate a physical description into a wire list, the model must be examined and tested for validity. 4nec2 includes a geometry validation function, which is sometimes too conservative, that should be run. You should examine the drawing of the structure carefully from several perspectives to see that things are where you want them. Then run the model in free space and/or...