As MIMO radar research grows in popularity, it becomes important to understand that it doesn’t imply simply using multiple antennas at both the receiver and the transmitter. To differentiate MIMO from other multi-antenna radar technologies, such as phased-array radar, we will define these specific technologies and list their advantages and drawbacks.
Phased-array radar systems are well established and have been used since World War II for military and commercial aviation purposes. These systems use multiple antennas in a two-dimensional array to transmit the same phase-shifted waveform, using the principle of beamforming. Each antenna is equipped with a phase shifter to create constructive and destructive interference to steer the beam in the required direction.
Phased-array radar can be either active or passive. Passive arrays have a receiver antenna array that receives a common external RF source, whereas active arrays use a transmitter array coupled with the receivers. See our previous blog post for more information about active vs. passive radar.
The main advantages of phased-array radar are:
- Beamforming allows the radar to scan an area without any mechanical parts physically moving the antenna. It can also produce a pattern of multiple beams, each covering a cross section of the 360° plane.
- The array’s gain within the beam is very high, which leads to improved detection.
- The antenna array controls permit very fast jumps from one target to another (in the order of microseconds), which allows tracking of multiple targets.
The principle disadvantage of phased-array radar is that the area coverage is limited to a 120° cone; therefore multiple arrays are necessary if full coverage is needed.
MIMO radar’s main difference from phased-array radar is that it transmits different waveforms on all antennas. These waveforms can be either correlated or uncorrelated with each other. The MIMO radar waveform diversity allows significant gains to be made from the phased-array radar performance.
In “MIMO radar–diversity means superiority”
- ‘’Significantly improved parameter identifiably.’’ Simply put, MIMO radar improves the maximum number of identifiable targets. Li and Stoica state that the ratio is of ‘’up to Mt times that of its phased-array counterpart where Mt is the number of transmit antennas.’’
- ‘’Direct applicability of adaptive arrays for target detection and parameter estimation.’’ Since MIMO radar transmits different waveforms on all antennas, the differently located target’s reflections can be linearly independent of each other. Li and Stoica state that this “allows the direct application of many adaptive techniques to achieve high resolution and excellent interference rejection capability.’’
- ‘’A much enhanced flexibility for transmit beampattern design.’’ Allowing each antenna to transmit an independent waveform adds flexibility to the beampattern design which can be optimized to increase performance.
The main disadvantage of MIMO radar is that it requires an increased complexity in its design compared to phased-array radar. The system size and component costs are therefore high. p>
The enhanced processing requirements of MIMO radar technology over phased-array radar is the main challenge faced by researchers and developers. Nutaq’s uDigitizer, which allies a high channel density (up to 128 channels) to a large processing capability (two Xilinx® Virtex®-6 SX475 FPGAs), can provide a relatively low cost solution for MIMO radar algorithms and waveform design. https://www.nutaq.com/products/udigitizer
1. Li, Jian, and Petre Stoica. 2009.”MIMO radar–diversity means superiority.” Proceedings of the 14th Adaptive Sensor Array Processing Workshop (ASAP’06) 1-6. http://www.ll.mit.edu/asap/asap_06/pdf/Papers/03_Li_Pa.pdf