Enhancing antenna performance in RF devices

#This invention relates generally to the field of radio frequency (RF) devices and antennas, and more particularly to incorporating other platform elements such as a battery within the main RF antenna circuitry to enhance overall RF performance while minimizing spurious RF emissions.

#Cellular devices typically include one or more processors for general and specialized computing tasks, and one or more radios for communication tasks. Other sub-systems may include displays, input/output devices, sensors and GPS. A key constraint of such devices is the small form factor desired by users that complicates specifically the design of the RF subsystems. Antennas need a certain physical size related to the wavelengths they receive or transmit to be effective. Close proximity of other platform elements such as circuit boards, batteries, shielding, and the like can severely impair RF performance. In addition, such proximity also increases undesired RF coupling from the antenna back into the device which can lead to unacceptable spurious radio emissions outside the desired operational frequency bands.

#Traditionally, antennas are designed with their surroundings in mind, specifically preexisting passive ground planes. The antenna should be tuned to the presence of such ground planes to operate effectively. Thus, antenna designs that include other non-RF platform components, such as batteries, can be desirable to accommodate surrounding components confined within restricted volumes of handheld and portable devices.

#FIG. 1a is a simplified block diagram of the physical layout of circuit components within a typical handheld device.

#FIGS. 1b, c are modified block diagrams of the circuit components of FIG. 1a in accordance with embodiments of the present invention.

#FIG. 2 is a simplified schematic circuit illustrating antenna, battery and ground plane connections with respect to DC.

#In one embodiment of the present invention, non-RF components such as a battery serve as secondary radiators (and receivers) of RF signal in conjunction with one or more primary RF antennas. For example, the lithium-ion battery that powers a handheld device is utilized as a secondary RF component.

#Typically, especially in cellular handset-type designs, the battery takes up a significant portion of the device's overall volume. Positioning the active RF antenna in relation to the battery position is problematic because the battery tends to attenuate a significant amount of RF energy, thus diminishing the effectiveness of the antenna. This can be detrimental to cellular device certifications that require an efficient antenna design to meet minimum over-the-air performance criteria.

#In accordance with one embodiment of the present invention, the battery is co-located with the main RF antenna, as usually required in handset designs because of space constraints, and is designed to act as a secondary radiator of RF signal. In this embodiment, the battery is connected to the system's ground plane for DC circuitry but is isolated from the ground plane for RF circuitry. This can be accomplished using various types of conventional RF filters and transmission-line segments as RF isolators. Furthermore, a dedicated wire loop in the main battery power path accomplishes both RF coupling with the main antenna and also RF decoupling from the ground plane. Thus, the battery, that reduces antenna effectiveness in conventional circuit designs, is an active component that increases antenna performance in accordance with the present invention.