The phenomenal growth of mobile devices, including smart phones and tablet computers, has resulted in a huge demand in wireless networks. Particularly, Wi-Fi networks, which are based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards, are becoming increasingly ubiquitous. In a typical Wi-Fi network, an end-user device (end device) can move freely within the range of an access point's (AP's) radio transceiver while maintaining high-speed data connectivity.
In a large-scale network, such as an enterprise or campus network, provisioning such a Wi-Fi network is non-trivial. One challenge is how to increase the coverage of an AP to cover a large area with a few APs, while providing a user with the desired performance from the Wi-Fi network. An end device can wirelessly communicate with an AP within the coverage are of the AP. An AP's coverage depends on its antenna(e). An AP can have one or more omni-directional and/or directional antennae that provide coverage to the surrounding area of the AP. An omni-directional antenna radiates radio waves (i.e., electromagnetic wave) in all directions, and a directional antenna radiates radio waves to a specific direction.
Typically, a directional antenna radiates with higher power than an omni-directional antenna in the direction associated with the antenna. This allows the antenna to increase its performance on transmission and reception. Because the antenna operates in a specific direction, communication by the directional antenna faces interference only from devices operating in its directional radiation. This facilitates reduced interference than an omni-directional antenna.
Currently, to facilitate a large-scale Wi-Fi coverage and increased performance, an AP can be equipped with a plurality of directional antenna. This approach to construct an AP requires a respective directional antenna to be individually configured and managed. Furthermore, end device in the coverage of a respective antenna usually contend among each other for airtime with the AP (i.e., transmission time between the AP and an end device), leading to a low-utilization of the wireless bandwidth provided by the antenna.
Phased array antennas are one type of directional antenna that may help address these problems. A phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions. Thus, the antenna may be considered “directional” as the beam from the antenna may be directed (formed) in a desired direction. Beamforming may be particularly useful when preserving power, signal strength and operating time in communicating between devices, both from an AP to one or more client devices as well as to/from an AP and another AP, base station, etc.
Existing beamforming lenses for phased array antennas, such as the well-known Rotman lenses, are well described for use in microwave systems, and may be used for RF systems. Unfortunately, such lenses must be relatively large and expensive, particularly in the RF frequency range (e.g., between 2 GHz and 50 GHz). Although various improvements in Rotman lenses have been proposed, such improvements typically reduce the efficacy of the lens, and require somewhat expensive and complicated arrangements of features, including multiple dielectric materials. See, for example, U.S. Pat. No. 8,736,503 to Zaghloul et al., which requires a strip of negative refractive index medium bisecting a positive refractive index medium. Thus, a compact and efficient electronic lens that is inexpensive to operate and manufacture would be very useful.
An antenna array may be a group of multiple active antennas coupled to a common source or load to produce a directive radiation pattern. The spatial relationship of the individual antennas may also contribute to the directivity of the antenna array. Use of the term “active antennas” may be used to describe elements whose energy output is modified due to the presence of a source of energy in the element (other than the mere signal energy which passes through the circuit) or an element in which the energy output from a source of energy is controlled by the signal input. One common application of this is with a standard multiband television antenna, which has multiple elements coupled together.
Described herein are phased array antennas that enhance base station gain by focusing the signal transmission and reception in a narrower beam that, in turn, reduces transmission interference and increases range. For example, the array antennas described herein may be used in base station applications to solve key limitations of traditional wide and narrow beam technologies. In wide beam communication, a signal is transmitted and received over a wide angle to overcome physical obstructions and uneven terrain. Unfortunately, this form of transmission can be inefficient and noisy. Narrow beam communication requires many antennas and frequency channels to provide the broad coverage associated with wide beam communication. The phased array antennas described herein may combine narrow beam technology and time based multiplexing of transmissions and receptions to overcome both challenges.
The phased array devices described herein may provide base station design that delivers high antenna gain and broad coverage by using a combination of narrow beams in various directions. This design may allow frequencies to be re-used by having beam transmissions and receptions in different directions take place at different times. This increases the efficiency of spectrum usage by allowing re-use of frequency bands, which enables the use of more radios on the same tower and the deployment of our products in environments where limited frequency bands are available in the unlicensed spectrum.