At Drexel University, engineering students are required to undertake a 9-month design project during their senior year to serve as one final graduation requirement. To fulfill this requirement, I'm currently working with three other Electrical Engineering students to design a 28 GHz beam steerable antenna system that is capable of transmitting information to a dynamic handset within an area outlined below a grid of SDRs within Drexel's Wireless Systems Laboratory. The project consists of a plethora of deliverables including:
1. The design of a reconfigurable, conformal antenna to serve as both the base station and handset in our system.
2. The design of a beam steering control circuit for the conformal antenna.
3. The selection and implementation of an algorithm to steer the handset antenna's radiation pattern toward a base station featuring both a static position and radiation pattern.
The following figures display the current status of the project. In addition, below is a link to a more in-depth written proposal of the project.
The picture above is our current conformal antenna model. This antenna features a 2x16 matrix of patch antennas fed from a transmission line utilizing T-junction power dividers and PIN diodes to control which patches receive current and radiate. To achieve beam steering, the cylindrical geometry is exploited in which only 4 patches (a single 2x2 patch matrix) radiate at a time. The resulting beam steering range is 360 degrees with a resolution of 45 degrees. Ansys HFSS was used to simulate the antenna characteristics.
At the junction of each power division, quarter wavelength transformers are used to match the impedance of the incoming and outgoing transmission lines. To mitigate grating lobes in the radiation pattern, the horizontal and vertical patch spacing is fixed at 5.357mm (1/2 of the wavelength at 28 GHz). As a result of this constraint, it was necessary to arc the bottommost quarter wavelength transformer and meander the ensuing transmission line to minimize reflections.
A planar 2x16 was first created to iterate and verify the applicability of the design. The substrate used for this planar model is Rogers 4003C with a thickness of .305mm. A 1.85mm connector from Hirose Electric was modeled to achieve more accurate simulation results.
The image above is one of a few variable description diagrams created to serve as a legend for the variables created in our HFSS project.
Initial demonstration of a 'random selection' algorithm in which a handset (red dot) travels within a random linear path within our testbed grid while a base station (bottom BS) randomly selects one of its radiation patterns. Three final selection algorithms are currently being implemented including Multi-Armed Bandit, Adaptive Pursuit, and UCB. This animation was created using Python.
Test antenna modeled in HFSS based on an aperture-fed leaky-wave antenna resonant at 28 GHz.
