Radiotelephones generally refer to communications terminals which provide a wireless communications link to one or more other communications terminals. Radiotelephones may be used in a variety of different applications, including cellular telephone, land-mobile (e.g., police and fire departments), and satellite communications systems. Radiotelephones typically include an antenna for transmitting and/or receiving wireless communications signals. Historically, monopole and dipole antennas have been widely employed in various radiotelephone applications, due to their simplicity, wideband response, broad radiation pattern, and low cost.
However, radiotelephones and other wireless communications devices are undergoing miniaturization. Indeed, many contemporary radiotelephones are less than 11-12 centimeters in length. As a result, there is increasing interest in antennas smaller than conventional monopole and dipole antennas that can be utilized internally within radiotelephones.
In addition, it is becoming desirable for radiotelephones to be able to operate within multiple frequency bands in order to utilize more than one communications system. For example, GSM (Global System for Mobile communication) is a digital mobile telephone system that typically operates at a low frequency band, such as between 880 MHz and 960 MHz. DCS (Digital Communications System) is a digital mobile telephone system that typically operates at high frequency bands, such as between 1710 MHz and 1880 MHz. The frequency bands allocated in North America are 824-894 MHz for Advanced Mobile Phone Service (AMPS) and 1850-1990 MHz for Personal Communication Services (PCS). Since there are two different frequency bands, radiotelephone service subscribers who travel over service areas employing different frequency bands may need two separate antennas unless a dual-frequency antenna is used.
Inverted-F antennas may be designed to fit within the confines of radiotelephones, particularly radiotelephones undergoing miniaturization. Unfortunately, conventional inverted-F antennas are typically narrow band and occupy more volume as compared with other types of antennas, such as helices, monopoles and dipoles. As such, a need exists for small, internal radiotelephone antennas that can operate within multiple frequency bands, including low frequency bands.