Conformal antennas are both antennas and structures at the same time. Having the ability
of using the surface of a structure allows the design of conformal high performance
antennas. Examples include conformal Log-Periodic Dipole Arrays, Log-Periodic slot
Arrays, cavity backed spirals, waveguide slot arrays, microstrip patch phased arrays,
and distributed array of dipole radiators to name a few. Applications include cognitive
radio, geological survey, and wireless internet to remote areas.
Electromagnetic Bandgap (EBG) materials are engineered structures. Many applications
need directional dipole, spiral antennas that can be flush mounted on the surface
of a structure. But the presence of the ground plane below the antenna poses a challenging
environment to develop very thin conformal antennas. Typically the antenna height
can very well exceed 3-5 inches at UHF (Ultra High Frequency) frequencies. Recently
we demonstrated that by designing and using a Non-Uniform Aperiodic (NUA) meatsurface
a dipole can be placed less than 1 inch from the ground for operation from 570-1100
Pixelated antennas present a unique opportunity to ideally reconfigure infinite number
of antenna shapes and sizes. However, the feeding constraints, materials, and device
availability, integration, and biasing present the challenges to attain the highly
desired properties e.g. high gain, broad bandwidth, and large Forward to Backward
Ratio (F/B). In our research broad bandwdith is achieved using by reconfiguirng a
pixelated antenna in an aperture coupled patch concept.
Conformal Reconfigurable Antennas
Antennas that can be reconfigured with respect to frequency, pattern, polarization
etc. have gained notice from engineers and researchers for the advantages they provide.
Of particular interest are pixelated antennas which make use of individual conducting
pixels to form changeable aperture geometry. This makes broadband or multiband operation
feasible using a single antenna.
Low Cost Phased Arrays for Portables/Wearables
These arrays are designed using the parasitic antenna arrays concept where the parasitic
elements are controlled using RF switches. Unlike traditional phased arrays where
elements are placed half wavelength apart and are controlled using expensive phase
shifters our proposed array consists of parasitic elements that are placed 1/30th
of the wavelength from each other. By controlling the distances between the driven
and the parasitic elements and the feed-point impedances of the parasitic elements
the array beam can be steered in space. For the first time, beam steering (Ali) approaches
at the mobile are being combined with time-frequency utilization considering enhanced
partially overlapped domains (Arslan).
Wireless Power Transfer and Wireless Sensing
Historically wireless power transfer has adopted one of two principles, near-field
and far-field power transfers. The former applies to very short distance power transfer
where power is transferred through magnetic fields that are coupled between the transmit
and receive sides. Examples include RFID systems, wireless cell phone battery charging,
vehicle battery charging using below the pavement magnetic coils. In most cases these
are achieved at frequencies below 100 MHz and at distances of at most several feet.
Cases where wireless power needs to be transmitted over large distances the method
of transmission is called far-field where the transmit and receive antennas are no
longer coupled to each other. Power transfer is governed by the Frii’s transmission
formula. USC researchers in Prof. Ali’s lab have done considerable amount of work
on wireless power transfer and rectifying antennas. A rectifying antenna or rectenna
is an antenna and a rectifier integrated together that receives RF power and converts
that to DC. A photograph of a rectenna built and tested at USC is shown on the right.
Challenge the conventional. Create the exceptional. No Limits.