3.2 How RLSA antennas work

Figure 2 shows the wave propagation mechanism including TEM cavity mode and TEM coaxial mode. The feeder placed in the centre of the antenna cavity feeds the electromagnetic power (indicated by the arrows). The feeder is an ordinary SMA feeder, which is modified by adding a head disc. The head disc has a function to convert the electromagnetic power from a TEM coaxial mode into a TEM cavity mode (a radial mode), so that the electromagnetic power fed by the feeder will propagate in a TEM mode and in a radial direction within the antenna cavity.

When the power passes the slot pair, some amount of the power escapes through the slot pair and radiates as illustrated in Figure 3. Hence, the slot pair can be considered as one antenna element. Since there are many slot pairs (thousands in normal-size RLSA antennas), all the slot pairs will form an array antenna. Therefore, this is the reason why 'array' word is included in the name of RLSA.

#### Figure 1.

(a) The component of RLSA antennas. (b) The magnified view of the feeder [39].

Figure 2. Illustration of the TEM cavity mode and the TEM coaxial mode [39].
