Techniques for Increasing Bandwidth A higher profile antenna has a reduced separation between the TM’101 and TM’102 mode and this can usefully increase S11 the bandwidth of the TM’101 as illustrated in Fig. 4(a) at 1800 MHz.
The antenna was optimized for the widest bandwidth at a -10 dB level by adjusting the monopole length. The -10 dB bandwidth has increased from a maximum of 7.9% to 12.9% for tanδε,μ=0.01 and from 13.6% to 25.87% for tanδε,μ=0.03. The dimensions of the antennas are: i) low profile block size was 30 X 30 X 30 mm, dipole length = 11 mm, ε’ ~ 9, μ’ ~ 3.3, and ii) higher profile block size was 20 X 20 X 40 mm, dipole length = 8.5 mm, ε’ ~ 6.5, μ’ ~ 6.4. In Fig. 4(b) it is seen that the higher profile antenna has a 3.7% increase in and a 28% increase in SAR when the dipole source of both antennas is 30 mm from the surface of the phantom. The perpendicular orientation again ensures a very low SAR value. 

Fig. 4. Simulated results showing the effect of increasing the height profile of a 30 X 30 X 30 mm rectangular material coated antenna with central dipole excitation to 20 X 20 X 40 mm showing variation with relative permittivity; dipole radius = 0.5 mm; tanδε = tanδμ = tand. (a) bandwidth BW (b) efficiency η and SAR (perpendicular orientation).