Low-Cost Phased-Array Antennas for ISM Bands
Omar Mohammed Bakr, Kevin Jones and Ali Niknejad
King Abdullah University of Science and Technology
Phased-array antennas can have a considerable impact on how we design wireless systems in the future. Most of the current wireless systems (e.g., WiFi) are based on broadcast. Broadcast reduces range and increases interference levels in wireless systems. Both of these factors significantly increase the overall cost of network deployment. These short comings can be addressed by using phased-arrays, which enable electronic beam-steering or beamforming. However, building scalable, low-cost and low-power phased-arrays is a challenging problem. The complexity, power, and requirements grow with the size of the array. In addition, good layout is required to minimize pattern distortion and cross-coupling between elements of the array. Finally, network protocols must be redesigned in order to take advantage of the beamforming capabilities of these antennas.
In this project, we address some of those challenges. We have built a phased-array prototype on a printed circuit board (PCB) using discrete passive and active RF components at the 2.4 GHz band in order to demonstrate the feasibility of low-cost phased-arrays for WiFi systems. A photo of our first prototype, a 16-element planar array, is shown in Figure 1. We have implemented the phase-shifting and signal combining/splitting functionalities at the RF level. Using this architecture, the output and input signals to the array are in RF, so that it can interface directly with an existing WiFi card. The next phase, after testing the board in the lab, will involve conducting outdoor tests on our long distance Bay Area testbed.
Figure 1: 16-element array prototype