Figure 6 shows the measured and simulated VSWR characteristic
for the TEM horn antenna, displayed in Fig. 5. The simulated
performance was obtained using CST microwave studio simulator [22],
and measurements are accomplished using Agilent 8722ES network
analyzer. As shown, the measured and simulated VSWRs are similar to
each other. The measured results present that the proposed TEM horn
antenna has the frequency band of 1.45 to 14.20 GHz for VSWR ≤ 2.0.
The antenna gain and radiation pattern are measured in a fully
anechoic chamber. Fig. 7 shows measured E- and H-plane radiation
patterns at three different frequencies. As shown, at higher frequencies,
there is a fluctuation in radiation pattern; therefore the single main
lobe is split into two large side lobes that grow in an equally spaced
fashion around the 0◦
center axis while the main lobe appears to be
strongly indented. This can be due to the field distribution over the
aperture plane that has a destructive effect in the far field at the
broadside direction. The presence of these side lobes is particularly
problematic for EMC applications such as testing in an anechoic
chamber, which usually depend on a well-defined radiation pattern
with only a single main lobe. In the following section, a new method is
proposed to remove this drawback For frequencies below 10 GHz, the
radiation pattern looks as expected for a typical horn antenna, i.e., it
has one dominant main lobe.