Cambridge Consultants has adopted novel RF power technology for a military radio software-defined radio (SDR) architecture.
Called ModStar, the architecture relies on Coolteq from Nujira, also Cambridge-based, which is a super-fast tracking switching PSU technique that can modulate the supply rail of an RF power amplifier (PA) to follow the RF amplitude profile.
The result of Coolteq, which Nujira sells as modules for base stations and chips for phones, is a PA that wastes less heat because it always operates with just enough headroom to keep it linear, and no more.
Software defined radio copes with arbitrary modulation schemes at arbitrary frequencies by using broadband RF hardware, fast ADCs and DACs, and copious amounts of digital signal processing.
"In recent years, defence organisations around the world have invested in a variety of custom radio systems, using many different air interfaces, to perform specific tasks," said Cambridge Consultants (CCL). "A key challenge for operations today is ensuring that all of these different air interfaces can be interoperable in the field, and that seamless communications can be conducted on any of the legacy systems. SDR can provide exactly this capability, delivering support for multiple air interfaces within a single, flexible implementation."
However, SDR radios can be bulky and less power efficient than radios dedicated to particular bands and modulation.
"The ModStar architecture has been designed to enable implementation of SDR modules that can link multiple communication platforms in a lightweight device that would be far more portable for troops," claimed CCL. "Portability is enhanced by Nujira's efficient envelope tracking technology for power amplifiers, that can extract double the power output from a given power transistor. Equipment and battery size are minimised by reducing filtering and power consumption requirements, allowing smaller form factors or wider bandwidths to be achieved."
CCL is making extra use of the fast PA power supply.
"Nujira's component tracks the envelop, and we are also doing something else with it," CCL business development manager Tim Phipps told Electronics Weekly.
ModStar uses an open loop polar modulator with non-continuous time feedback and software pre-distortion.
Non-continuous time feedback compensates for changes in frequency, temperature and power without the need for a complicated continuous time polar loop, said CCL. The resulting design is an efficient power amplifier with multi-band, multi-mode operation.
"The polar loop modulator we have incorporated into the ModStar architecture is an extremely robust technique, that has been used in millions of mobile phones, that can deliver exceptional performance with extremely high reliability for military applications," said Phipps.
A proprietary Cartesian to polar conversion, ensures continual phase lock is achieved within the radio and, according to CCL, zero crossings are handled with a novel DSP technique.
"The advantage of this architecture is that the radio design is simplified; with the most significant design challenges being moved into the digital domain, where they can be resolved with an integrated and scalable solution. A digital, fractional N synthesiser provides a clean reference clock signal with an inherently low phase noise," said the firm.