Spectrum Management Media ArticleTSC has developed the ability to design rapid custom Radio Frequency (RF) waveforms which result in clean spectral notching to meet strict spectral requirements. TSC also has developed the ability to design rapid mis-matched filters which allow suppression of large radar reflectors in order to forensically detect extremely small objects in very close proximity to the large reflector. These products have been tested on UAV systems with excellent results.
The radio frequency spectrum continues to become an increasingly scarce resource. A major factor affecting spectral availability is that military systems are being challenged to provide increasingly high resolution data. In order to achieve better resolution, radars require larger sections of the spectrum. For this reason, these radars operate using broad waveform (WF) bandwidths that often overlap spectral regions occupied by other systems. The same spectral constraints also apply to secure communication systems. Spectral sideband containment and in-band notching of these waveforms are therefore becoming frequent requirements.
To further complicate spectrum usage, each country, and, often, different locations within the same country, have unique spectral requirements and allocations. Available spectrum space in one location will likely be denied in others. Additional challenges include dynamic requirements derived from electronic attack and unaccounted for radio frequency (RF) interference. These dynamic requirements require a quick turn around on spectral management during mission execution.
“Brute force notching” is used by some systems. These systems switch their transmitter amplifier on and off as the waveform sweeps over a denied spectral region. This approach can result in high VSWR (Voltage Standing Wave Ratio) values, excessive sidelobes and a reduction in the effective radiated power. High VSWR values generate reflected waves in the transmitting system, that can result in increased RF transmit power losses, increased heat production, and, possibly, damage to the transmitter. The energy spillover from the power amplifier chain generally raises the bottom of the notch, often forcing the system to switch off the transmitter over a much broader time interval than desired. This increases losses and range resolution even further. Other available techniques require undesirable variations in the transmitted power.
Dr. Carroll Nunn of TSC has developed algorithms to rapidly find solutions to address this very issue. Custom, phase coded, waveforms that meet dynamic requirements can be generated in a matter of a minutes. This is a TSC accomplishment met by no one else to date. These waveforms are continuous – i.e., they do not require transmitter switch-off, and have constant amplitude, thereby obviating all of the above issues. Spectral compliance is achieved with excellent results. The spectrum which becomes fragmented due to the in-band notching is maximized. This is achieved due to the absence of spill over, consequently enhancing range resolution.
The figure represents an example of a 210 Mhz bandwidth waveform with a variety of spectral notches implemented to meet strictly specified spectral compliance profile. The figure shows that the notches and sidebands are controlled as stated by requirement. This particular waveform has been successfully tested on existing systems for feasibility and produced outstanding results.
In addition to custom waveform generation algorithms, Dr. Nunn also created rapid algorithms to create carefully controlled mismatched filtering. Using banks of mismatched filters with staggered sidelobe notches, the capability was demonstrated to generate forensic search capabilities that result in the unmasking of extremely small objects buried deep within the time sidelobes of strong clutter discrete returns. In every day terms, it makes it possible to detect the proverbial ‘needle in the haystack’.
The US Army has utilized TSC developed waveforms and mismatched filters in a UAV mounted radar system during actual demonstrations. The Army has been so impressed with the product that they have purchased licensed copies of the software to rapidly develop custom spectral complaint waveforms and mismatched filters in the field.
Contact information:
Dr. Carroll Nunn
(301) 576-2393