12.7.3 Long Range (>1,500)

The sloping-V can be used for long ranges up to about 3,500 km. However, for greater ranges than 1,500 km, low radiation angles of 10˚ or less are required, and high-gain directional antennas are essential. There are various complicated arrays available, all very large, static and time-consuming and beyond the scope of this book. The rhombic antenna is a travelling wave antenna that has been popular for some time and is about the simplest of these antennas.

Figure 12.23 shows a rhombic antenna, which is again a variation of the end-fed antennas. The primary purpose of the rhombic is to provide high gain at low angles and to suppress unwanted sidelobes. As shown by Figure 12.23, lobes A, B, C, and D add and all the rest cancel. Gain from this antenna can be 15 dB or more with respect to a dipole. The rhombic design procedure is complicated and the antenna occupies an area of 5–15 acres. It is a difficult field antenna and is principally for long-range static links.