Reduced-size, folded ground plane for use with low-profile, broadband monopole antennas

Monopole antennas are quite attractive to mobile and portable radio system designers primarily because of the inherent 2:1 size reduction over equivalent dipole designs. Further size reduction and bandwidth enhancement can be provided by any of several techniques. However, proper monopole operation requires an effective counterpoise or ground plane, hence the name ground plane antenna. Monopoles are generally used on vehicles or other electrically-large platforms which can serve as effectively infinite ground planes. Monopoles are sometimes used with handheld radios or other devices of moderate to small electrical size. In such applications the case of the radio itself (and to some extent the user) serves as the counterpoise. We present an alternative to the sleeve-type choke: the "folded" ground plane which provides a reduced-size ground plane with a highly effective choking action. This ground plane is adapted to a unique, broadband low-profile monopole which covers the frequency range of 1800-2500 MHz continuously. This allows utilization of the PCS bands, the 2450 MHz ISM band and the military 1750-1850 MHz band.