Abstract:

 A broadband monopole antenna working in UHF band is designed. A monopole antenna is cut
into two parts. They are connected in series. This step improves the horizontal gain in the upper part of the
operating band. A lossless LC ladder is then used to match the antenna impedance from 100 MHz to 400 MHz.
The truncating position and circuit element parameters in the matching network are obtained using CST2009
optimization. Reflection coefficients of the truncated antennas both with and without the matching network
are measured, showing good agreement with the simulation results. The following conclusions are drawn. The
gain in the horizontal direction of the antenna with matching network is more than 0 dBi between 100 MHz
and 350 MHz, and stays within ?7 ?0 dBi from 350 MHz to 400 MHz. The simulated reflection coefficient S11
of the antenna is below 10 dB within 100 MHz and 400 MHz. The efficiency is over 60% within the operating
band.

Key words:  truncation, broadband matching network, lossless, high horizontal gain, high efficiency