Consumers are demanding smaller and feature-rich wireless communication devices, such as cellular (cell) telephones. A smaller cell phone with more functions and features can be produced with two housing portions. One such multipart configuration is a flip phone. A flip phone opens up like a clamshell. Other configurations are sliding phones and swivel phones. In a sliding phone, one portion of the cell phone housing slides relative to the other portion. In a swivel phone, one portion of the cell phone swivels open, relative to the other portion. A sliding phone is shown in application Ser. No. 10/931,712, filed on Sep. 1, 2004, assigned to the assignee of the present application, the disclosure of which is hereby incorporated herein by reference. Generally, a wireless device case with multiple-part housing portions, including the examples described above, is referred to herein as a multipart case or multipart housing.
Typically, one arrangement of the two housing portions has an overall smaller form factor than the other arrangement. The smaller arrangement is often called the closed configuration, and the larger arrangement is called the open configuration. The cell phone user can keep the cell phone in the closed configuration when carrying the cell phone, or for storage. In use, the cell phone is put in the open configuration. Some phones can be used in both configurations.
In some configurable cell phones, both housing portions have a ground plane. Ground planes often act as the counterpoise for proximate antennas and almost always affect antenna performance. An antenna might perform optimally with the cell phone in one (i.e., open) configuration, but sub-optimally with the cell phone in the other (i.e., closed) configuration. The sub-optimal performance may be due to the positional change of one of the ground planes relative to the antenna. An antenna that depends heavily on the ground plane, such as a patch antenna, planar inverted-F antenna (PIFA), or folded monopole, may perform poorly when a grounded metal is near the antenna in some configurations.
One measure of poor antenna performance is the amount of current unintentionally generated through a transceiving device, typically as surface currents, as opposed to amount of energy radiated into the intended transmission medium (i.e., air). From the point of view of a transmitter, poor antenna performance can be measured as less radiated power, or less power in an intended direction. From the receiver perspective, poor antenna performance is associated with degraded sensitivity due to noisy grounds. From either point of view, poor performance can be associated with radio frequency (RF) ground currents.
The above-mentioned ground issues are compounded with the use of multipart type cell phone cases. Many cell phones use so-called flex films to carry signals between the two casing halves, for example, between a liquid crystal display (LCD) module and the main printed circuit board (PCB). These flex films are typically multi-layered planes of grounds and signal lines formed on, and separated by flexible sheets of dielectric insulator materials. These long thin signal wires may unintentionally act as antennas, interfering with the intended antennas and degrading the receiver performance. At the cost of connector flexibility, silver ink shielding (ground) layers can be used to cover the connector, or even added as internal layers. While this brute-force approach does shield the connector signal lines, other problems may be introduced. Since the shielded connector is located proximate to the antenna, the intended radiation patterns can be altered. Using a cell phone as an example, the shielded flex connector may cause a desired upward-pointing radiation pattern in the PCS band to point in an alternate, less desirable direction.