Researchers in Spain and the United Kingdom have developed a resonator element capable of simultaneously acting as both a filter and an antenna in a major step towards the development of programmable microwave function arrays (PROMFAs).
The so-called microwave circuit equivalent of an FPGA is a network of microwave hardware that can be reconfigured to take on different circuit functions as needed. The concept has been around since at least 1990, says James Kelly, PH.D., one of the authors of the paper reporting the accomplishment, published in this issue of Electronics Letters, but its development has been hard to track because the majority of PROMFA work has likely been hidden by the military.
“We assume only a small proportion of the results achieved have been openly published,” Kelly told the The Institution of Engineering and Technology. “However, it is likely that cost and complexity have been a major drawback. It is also challenging to devise a hardware block with a simple structure that can be reconfigured to assume a wide range of different circuit functions.”
Public use of such a technology could revolutionize the microwave industry by reducing system weight and manufacturing time while simultaneously increasing hardware flexibility, he added.
Typically, microwave hardware functionality is fixed during manufacturing. A PROMFA, however, could be reconfigured during operation, enabling the system to accommodate changes in operational requirements. To accomplish this, the array would consist of ‘building block’ elements much like the logic blocks in an FPGA, which would be capable of assuming different circuit functions on demand.
“This [ability] would be particularly valuable in applications where the hardware is difficult or impossible to access for maintenance and upgrades, such as space satellites,” Kelly said. “The technology will also reduce the cost and time associated with the hardware development cycle, because components will become off-the-shelf items that no longer require customization.”
In a proof-of-concept paper, “Hardware Block for Use in Programmable Microwave Function Arrays,” Kelly and Alejandro Borja, Ph.D., of Universidad de Castilla La Mancha, Spain describe the creation building block element required for “a true ‘microwave FPGA.’” Designed to operate within the industrial scientific and medical (ISM) band, the element consists of a microstrip square patch resonator connected to three external ports that provides different circuit functions on each port.
The achievement “is significant because it demonstrates that one can achieve two circuit functions at the same time with little or no performance trade-off,” Kelly said, adding that the hardest part “was to find a way to make a single resonator perform two functions without suffering a high degree of energy coupling between the two.”
“We achieved this by employing orthogonal eigenmodes within the resonator,” he explained. “Additional isolation is achieved by displacing the operating frequencies associated with the filter and antenna mode of operation.”
In the short term, the new approach could be used to reduce microwave circuit sizes by combining multiple functions within a single resonator. This ability could be of particular interest for system-on-chip designs and possibly waveguides as well, the researchers note, adding that they expect the first microwave IC analogous to an FPGA will be realized within four years.
“We believe PROMFAs have great potential,” Kelly and Borja said in their paper. ”Their cost, size and complexity will gradually reduce as the technology matures. This will enable more widespread use in areas such as next generation mobile technology and satellites. We hope to see entire microwave systems implemented on a single low cost PROMFA chip. These systems would be analogous to single board computers like Raspberry Pi, which have helped to democratize access to computing technology. We hope that PROMFAs will have a similar effect in the domain of microwave engineering.”
