A tuneable elevated microstrip antenna for cellular handhelds

Whip antennas can provide good performance for RF communications, such as cellular telephony, especially when mounted on top of vehicles. Unfortunately, they are not easily integrated into a small handheld chassis. As handheld radios become smaller and more ergonomic, the whip antenna represents a growing inconvenience to the user. This paper describes one member of a new family of antennas under development at NovAtel: Elevated Microstrip Antennas (EMAs). These can provide significant size and performance advantages yet are cost effective and readily manufactured. They combine high efficiency and controlled radiation characteristics in a compact and convenient geometry. Separation of the transmit and receive elements replaces much of the normal duplexer filtering function as well as reducing spurious interference. A significant advance is the capability of separately and actively tuning both the receive and transmit sections of EMAs. As in any radiating structure there are fundamental limitations constraining the practical size and performance of EMAs [1]. A specific implementation is presented along with a distributed passive element analysis, measured results, a discussion of compromises, and a 3D radiation plot from an automated antenna test range developed at NovAtel. It is concluded that EMAs are capable of providing performance equal to or better than a typical whip antenna but have several significant advantages.