## THE THICK LINEAR ANTENNA

The thin linear antenna is frequency-sensitive. In practical communication scenarios, the transponders use wideband sig­nals to increase the channel capacity and therefore needs an­tennas that can handle a large band of frequencies. One way of increasing the bandwidth is to use electrically thick wires.

A thick cylindrical dipole (Fig. 16) is the inexpensive way to increase the bandwidth of linear antennas. The increase in thickness leads to circumferential component Ц of the other­wise linear current. This can be handled with the integral equation formulation. Figure 17(a) and Fig. 17(b), respec­tively, show the variation of input resistance and reactance of the dipole with l/2a ratios 25 (thick), 50, and 10,000 (thin), where 2a is the diameter of the wire.

10"

Near fields:

H<p component at z = 1^5 m Radiated power = 8J75 mW at f = 1 MHz

10"

E

<

33

о

ф

MININEC

. „ NEC

Antenna:

Height = h = 75 m Radius = a = 0^3 m 15-Segment model

100 200 300 400

500

MININEC compared to NEC

 4
 10c
 10-
 І10-
 >10-
 10-4
 Antenna: Height = h = 75 m Radius = a = 0.3 m 15-Segment model
 Antenna: z – Component at wire surface Radiated power = 8.775 mW at f = 1 MHz

Near fields:

 3

Vertical and radial components of E-fields z = 1.5 m

Power radiated = 8.775 mW f = 1 MHz

2

Antenna:

 ф CL

Height = h = 75 m Er Radius = a = 0.3 m

4 15-Segment model

Ez

0

50 100 150 200 250 300 350