6.0 Introduction

This chapter presents some ideas and performance results for antennas that are variations on the monopole. Some will contain coils, and so will look like loop variations, but they have an open end at which the current must be zero. Loop variations are presented in the next chapter. The things that can be done to improve a monopole performance for a given space and operating wavelength are:

1. Make it thicker.

2. Increase its capacitance by top loading.

   1. Disc or radial wires.

   2. Volume loading.

1. Make it resonant

   1. by adding an inductor at the base or higher up,

   2. by making it with enough wire wound in the available space to make it ?/4,

   3. by making the radiating element a coil and top-loading it with enough C.

Method 3(b) is wave resonance, whereas 3(a) is circuit resonance by adding a nonradiating inductor, and 3(c) is circuit resonance by making the radiating element also an inductor. Examples of each method are examined with respect to efficiency, impedance matching, and bandwidth. All designs for monopoles on a PEC plane are scalable with wavelength, but antennas on a radio box are a different story. The radio box is part of the antenna, but its dimensions are usually not determined by this fact; rather, they are made as small as will accommodate the electronics. Sometimes the box is a significant fraction of a wavelength, and sometimes it isn t.

Most of the antennas discussed in this chapter...