Design and packaging of antennas for wireless systems

Mobile RF systems may consist of single or multiple links between stationary base units, and mobile remote units. The stationary base and mobile remote antennas are almost always mounted on the chassis which contains the radio and/or other electronics. The remote tends to be compact in size, and aside from form factor constraints for the remote antenna, one of the key specifications is that it radiate omnidirectionally in the horizontal plane, so that a stable communication link can be established with a base unit in any direction. An omnidirectional pattern may or may not be a requirement for the base antenna, depending on how base station "cells" are structured. EMC and EMI considerations require that packaging for the remote and base have adequate shielding, for inner electronics and prevent radiation leakage outside the chassis. Consequently the chassis are coated with a conductive paint, and/or conductive shields are present. The external packaging can cause "shadowing", in which the radiation pattern to becomes directive or has deep nulls, or call "detune" the antenna, in which the impedance seen at the antenna input terminals is altered, or can significantly effect antenna gain. Simultaneously meeting antenna and package goals presents an interesting challenge from an antenna and package design point of view. In this paper, antenna design is discussed with a focus on the impact of packaging on radiation characteristics, and physical design of antennas in order to best meet specifications.