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The Way to a New Phased Array Radar Architecture (Beware of 5G technologies)

The Way to a New Phased Array Radar Architecture

15 January, 2018

Sponsored Article: Digital beamforming phased arrays are now common, and rapid proliferation is expected with a huge range of frequencies and architectures being developed from L-band through to W-band.

By Peter Delos, Analog Devices, Inc.
A large proliferation of digital beamforming phased array technology has emerged in recent years. The technology has been spawned by both military and commercial applications, along with the rapid advancements in RF integration at the component level. Although there is a lot of discussion of massive MIMO and automotive radar, it should not be forgotten that most of the recent radar development and beamforming R&D has been in the defense industry, and it is now being adapted for commercial applications.
While phased array and beamforming moved from R&D efforts to reality in the 2000s, a new wave of defense focused arrays are now expected, enabled by industrial technology offering solutions that were previously cost prohibitive. In classical phased arrays, the analog beamforming subsystem combines all the elements to centralized receiver channels. Every element in digital beamforming phased array has waveform generators and receivers behind every front-end module, and the analog beamforming layer is eliminated. In many systems today, some level of analog beamforming is common.
The waveform generator and receiver channels serve to convert digital data to the operating band RF frequencies. Digital beamforming is accomplished by first equalizing the channels, then applying phase shifts and amplitude weights to the ADC data, followed by a summation of the ADC data across the array. Many beams can be formed simultaneously, limited only by digital processing capability.
Analog Devices has solutions for every section of a beamforming system illustrated, and for both analog and digital beamforming architectures.

ANALOG VS. DIGITAL BEAMFORMING
The objective of a digital beamforming phased array is the simultaneous generation of many antenna patterns for a single set of receiver data. The Figure (right) shows the antenna patterns at an element, the combined elements in a subarray, and the beamformed data at the antenna level. The primary obstacle of the subarrayed approach is that beamformed data must be within the pattern of the subarray. With a single subarray, simultaneous patterns cannot be generated at widely different angles. It would be desirable to eliminate the analog beamformer and produce only digital beamforming system. With today’s technology, this is now possible at L- and S-band. At higher frequencies, size and power constraints often necessitate some level of analog beamforming.

Beamforming goes Digital

However, the quest remains to approach near elemental digital beamforming, which places significant demands on the waveform generators and receivers. While the beamforming challenges place demands on the waveform generators and receivers to reduce size and power, there is a simultaneous demand to increase bandwidth for most system applications.
These objectives work against each other, as increased bandwidth typically requires additional current and additional circuit complexity. Digital beamforming relies on the coherent addition of the distributed waveform generator and receiver channels. This places additional challenges on both synchronization of the many channels and system allocations of noise contributions.

New Technologies Needed

The superheterodyne approach, which has been around for a 100 years now, provides exceptional performance. Unfortunately, it is also the most complicated. It typically requires the most power and the largest physical footprint relative to the available bandwidth, and frequency planning can be quite challenging at large fractional bandwidths. The direct sampling approach has long been sought after, the obstacles being operating the converters at speeds commensurate with direct RF sampling and achieving large input bandwidth.
Today, converters are available for direct sampling in higher Nyquist bands at both L- and S-band. In addition, advances are continuing with C-band sampling soon to be practical, and X-band sampling to follow. Direct conversion architectures provide the most efficient use of the data converter bandwidth. The data converters operate in the first Nyquist, where performance is optimum and low-pass filtering is easier. The two data converters work together sampling I/Q signals, thus increasing the user bandwidth without the challenges of interleaving.
The dominant challenge that has plagued the direct conversion architecture for years has been to maintain I/Q balance for acceptable levels of image rejection, LO leakage, and DC offsets. In recent years, the advanced integration of the entire direct conversion signal chain, combined with digital calibrations, has overcome these challenges, and the direct conversion architecture is well positioned to be a very practical approach in many systems. The future will bring increased bandwidth and lower power, while maintaining high levels of performance, and integrating complete signal chains in system on chips (SoC), or system in packages (SiP) solutions.

Digital Data Converter

Data converter analog performance will continue to improve and these improvements at the analog level will include increased sampling rates for wider bandwidth, increased channel count, and maintaining the key performance metrics of noise, density, and linearity. These benefits will drive all of the RF signal chain solutions described, aiding new phased array solutions. An area of increased importance at the system level is the recent addition of many digital functions (as shown in the Figure below) that can be used to offload FPGA processing and help the overall system.


source:
[1]Delos, Peter. “The Way to a New Phased Array Radar Architecture.” TechTime: Electronics & Technology News. January 15, 2018. Accessed January 1, 2019. https://techtime.news/2018/01/ 15/analog-devices-phased-array-radar/. “Although there is a lot of discussion of massive MIMO and automotive radar, it should not be forgotten that most of the recent radar development and beamforming R&D has been in the defense industry, and it is now being adapted for commercial applications. While phased array and beamforming moved from R&D efforts to reality in the 2000s, a new wave of defense focused arrays are now expected, enabled by industrial technology offering solutions that were previously cost prohibitive.”
[2] “Electrosensitive Testimonials.” We Are The Evidence. 2018. Accessed January 1, 2019. https://wearetheevidence.org/adults-who-developed-electro-sensitivity/. “WATE intends to expose the suppressed epidemic of sickness, suffering and human rights crisis created by wireless technology radiation; elevate the voice of those injured; defend and secure their rights and compel society and governments to take corrective actions and inform the public of the harm.”

[3] Glaser, Lt. Z. “Cumulated Index to the Bibliography of Reported Biological Phenomena (‘effects’) and Clinical Manifestations Attributed to Microwave and Radio-frequency Radiation: Report, Supplements (no. 1-9).” BEMS Newsletter B-1 through B-464 (1984). Accessed January 1, 2019. https://www.cellphonetaskforce.org/wp-content/uploads/2018/06/Zory-Glasers-index.pdf. Lt. Zorach Glaser, PhD, catalogued 5,083 studies, books and conference reports for the US Navy through 1981.
[4] “Space Sustainability: A Practical Guide.” Secure World Foundation, 2014, 21. Accessed January 1, 2019. https://swfound.org/media/206289/swf_space_sustainability-a_practical_guide_2018__1.pdf.

“However, as more countries integrate space into their national military capabilities and rely on space-based information for national security, there is an increased chance that any interference (either actual or perceived) with satellites could spark or escalate tensions and conflict in space or on Earth. This is made all the more difficult by the challenge of determining the exact cause of a satellite malfunction: whether it was due to a space weather event, impact by space debris, unintentional interference, or deliberate act of aggression.”
[5] “Space Law: Liability for Space Debris.” Panish, Shea & Boyle LLP. 2018. Accessed January 1, 2019. https://www.aviationdisasterlaw.com/liability-for-space-debris/. “Filing a lawsuit against SpaceX for space debris is a little different than one against the commercial industry or state-sponsored launch. Since SpaceX is a private company, injured parties can file claims directly against the establishment in accord with the state’s personal injury laws. For the claim to be successful, the plaintiff will have to prove that SpaceX was negligent in some way that caused the space debris collision. Space law is notoriously complex, making it very difficult for injured parties to recover for [sic] their damages in California.”

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