16 Wire Conical Feed Monopole Antenna

Dipole and monopole antennas are resonant structures which are inherently narrowband.  Various methods have been proposed to increase the bandwidth of these antennas, one of which is to increase the antenna radius.  In order to feed the antenna where the wire radius is large a cone shaped feed is used.  Figure 1 shows such an antenna designed for the high MHz and low GHz frequency range.

Figure 1:  Thick monopole antenna with conical feed

It is also possible to approximate this antenna by using a set of wires conforming to the outer boundary of the solid, as shown in Figure 2.  The advantages thereof are a lighter antenna, simpler manufacturing and better wind resistance.

Figure 2:  16 wire antenna used to approximate a solid thick monopole with conical feed.

When building such an antenna the designer is faced with few design parameters, e.g. monopole radius and cone half angle.  The effects of varying these parameters have been investigated [1].  An antenna consisting of 16 (Figure 2) wires was designed and simulated to determine the wideband performance of the antenna.  Figure 3 shows the VSWR for the 16 wire antenna compared to that of a solid monopole antenna (Figure 1).

Figure 3:  VSWR for the wire antenna compared to that of the solid thick monopole.

From Figure 3 it is seen that the antenna is matched across a very wide band and VSWR<2 relative bandwidth is more than 5:1.

References