1. Field of the Invention
Embodiments of the invention relate generally to radio antennas for wireless communication systems. More particularly, the embodiments of the invention relate to low cost compact printed circuit board (PCB) antennas for subscriber units of wireless broadband communication systems and cellular wireless communication systems.
2. Description of Related Art
It is widely known that antennas can be used to transmit and receive electromagnetic radiation of certain frequencies to carry signals. That is, an antenna is typically designed to transmit and receive signals over a range of carrier frequencies. The antenna is a critical part of all wireless communications devices. Typically, antennas should meet very stringent requirements regarding size, efficiency, wide bandwidth of operation, ability to function efficiently when space is at premium and a low manufacturing cost. Small space, usually available for an antenna, dictates antenna choice, which may be a printed monopole antenna, an L-shaped antenna, a planar inverted-F antenna, a printed disc antenna or a patch antenna.
Small size of printed antennas, usually a quarter of operation wavelength, is the result of a ground plate effect utilized in the antenna design. Induced currents form a mirror image of a radiating element on the ground plate. Eventually the effective size of the antenna should include a part of the ground plate which includes significant part of induced currents. On the other hand, induced currents are very susceptible to any conducting elements placed in the neighborhood of the antenna. The commonly used approach to improve the performance of the printed antenna is to keep the antenna away from any conducting components of the device. The minimum distance between antenna and RF components, considered safe in the 3 GHz frequency band is equal to about of 1 cm. Violation of this rule results in a significant impedance mismatch between an antenna and a transmission line, efficiency loss and a resonant frequency shift.
Another factor, which significantly effects antenna performance, is the communications device plastic casing. Plastic casing significantly effects radiation efficiency of the antenna. Nevertheless, in an attempt to miniaturize a device, designers, practically, do not leave much space between a PCB and a plastic cover.
All factors, described above, make antenna design procedure extremely complicated and difficult. In each particular case, not only a PCB size and position of radio frequency (RF) components should be taken into account, but also devices plastic body shape and material dielectric constant. Other design criteria of an antenna may need to be considered, such as costs, portability, and possibly aesthetics. These design criteria are particularly relevant to portable wireless communication devices that are to be marketed to the general public. Moreover, the size or form factor of portable wireless communication devices poses particular challenges in antenna design. Additionally, consumers are demanding greater portability, higher data bandwidth, and better signal quality in wireless communication devices and systems.
Like reference numbers and designations in the drawings indicate like elements providing similar functionality. Additionally, it is understood that all the drawings of figures provided herein are for illustrative purposes only and do not necessarily reflect the actual shape, size, or dimensions of the elements.