Radar School

Most Counter-UAS tech sheets open with a sensor list. Radar. Camera. RF. Acoustic. Maybe a glossy spec table. The implicit promise is that with enough boxes on the diagram, the drone problem is solved. It is not. The honest question is this. Given the sensors you actually have, with the noise and detection probabilities they actually have, what is the best position accuracy and classification reliability any algorithm in the world could possibly deliver? And does that ceiling clear your mission requirement? Almost nobody in the commercial C-UAS space has a clean answer to that. Gordon Ariho and I wrote up how we think about it, starting from what we learned in EECS 965 Detection and Estimation Theory at the University of Kansas under Prof. Jim Stiles. Some Cramér-Rao Bound, some Fisher information, one A-Team reference, one Minions detour. Homer Simpson too, Prof. Stiles would insist on it. The formal paper is in the works. This is the version you read over coffee. Gordon Ariho Hara Madhav Talasila, PhD #CounterUAS #RadarSystems #SensorFusion #EstimationTheory #4cThreat #EECS #SignalProcessing

Vote in the poll first, see more to reveal answer! Higher frequencies are absorbed too quickly by the Earth. In any conductive medium like soil or wet sand, electromagnetic waves suffer from "skin effect" and attenuation. While GHz frequencies give great resolution, they would only penetrate an inch or two. To see buried pipes or archaeological ruins several meters deep, we must use longer wavelengths that can survive the trip through the dirt. Citation: Jol, H. M. (2008). Ground Penetrating Radar Theory and Applications. Elsevier. Today in Science History: May 22, 1906: The Wright brothers were granted their patent for a "Flying Machine." The birth of controlled flight created the very problem that radar was eventually invented to solve: detecting objects in the sky that the human eye cannot yet see. #RadarSchool #GPR #CivilEngineering #Geology #PhysicsInAction #RadarHistory

Vote in the poll first, see more to reveal answer! It creates grating lobes. This is essentially spatial aliasing. When the elements are spaced too far apart, the electromagnetic waves interfere constructively in directions you didn't intend. This creates "ghost" beams that can lead to false target detections and wasted energy. Maintaining half-wavelength (lambda/2) spacing is the golden rule for clean electronic steering. Citation: Mailloux, R. J. (2017). Phased Array Antenna Handbook. Artech House. Today in Science History: May 21, 1927: Charles Lindbergh landed in Paris. His flight highlighted the desperate need for long range navigation and detection systems, fueling the rapid development of the radio based systems that became radar. #RadarSchool #PhasedArray #AESA #ElectricalEngineering #WavePhysics #TechTips

Vote in the poll first, see more to reveal answer! You must make the antenna larger. Beamwidth is inversely proportional to the size of the aperture. A physically larger antenna (or a larger array) can "focus" the electromagnetic energy more tightly. This is why high resolution mapping radars often have massive dishes or use SAR to "fake" a larger antenna through motion. Citation: Balanis, C. A. (2016). Antenna Theory: Analysis and Design. Wiley. Today in Science History: May 20, 1990: The Hubble Space Telescope sent its first image back to Earth. While optical, the precision pointing and telemetry systems used are the direct descendants of high precision tracking radar developed during the Cold War. #RadarSchool #Antennas #HardwareDesign #Focus #EngineeringDaily #ScienceHistory

The previous article left a quiet elephant in the room. Stealth. This is the elephant. Stealth is not a property of an object. It is a condition. From the anechoic chamber to the open sky, an electromagnetics view of what monostatic RCS, RAM, and bistatic geometry actually mean, across airframes, missiles, and ships. #Radar #RadarSchool #Stealth #RCS #LowObservable #PassiveRadar #BistaticRadar #MultistaticRadar #ElectromagneticTheory #Maxwell #Electromagnetics #SignalProcessing #RFEngineering #AESA #PhasedArray #DefenseTech #Aerospace #Avionics #Fighter #Missile #CruiseMissile #Naval #Drone #CUAS

Vote in the poll first, see more to reveal answer! Circular polarization. Raindrops are roughly spherical. When a circularly polarized wave hits a sphere, it reverses its "handedness" (example - Left Hand to Right Hand). Most radars are built to reject the opposite handedness. However, a complex target like an aircraft has irregular surfaces that scramble the polarization, allowing its signal to pass through the filter while the rain is canceled out. Citation: Bringi, V. N., & Chandrasekar, V. (2001). Polarimetric Doppler Weather Radar. Cambridge University Press. Today in Science History: May 19, 1906: The Federated Wireless Telegraph Company was formed. This early push into large scale radio infrastructure helped establish the high power transmitters eventually used in the first generation of early warning radars. #RadarSchool #WeatherRadar #RemoteSensing #AntennaDesign #PhysicsFacts #RFEngineering

A radar system looks at a busy highway backed by a massive mountain range. How does the processor filter out the stationary mountain to only display the moving vehicles? It relies on Moving Target Indication (MTI) filters. The radar transmits consecutive pulses and compares the phase of the returning signals. Stationary objects, like mountains, return the exact same phase from pulse to pulse. Moving cars alter the phase due to the Doppler shift. By mathematically subtracting consecutive pulses, the stationary clutter is canceled out entirely, leaving only the targets currently in motion. Ref: Barton, D. K. (2004). Radar System Analysis and Modeling. Artech House. Today's History: May 18, 1969: Apollo 10 launched from Kennedy Space Center. Its lunar module utilized a highly sophisticated rendezvous radar system to accurately measure range and range rate during critical lunar orbit maneuvers. #RadarSchool #SignalProcessing #MTI #RadarEngineering #DopplerEffect #STEM

Vote in the poll first, see more to reveal answer! The maximum unambiguous range decreases. In radar design, you face the "Radar Dilemma." A high PRF (pulse repetition frequency) is great for measuring high velocities without Doppler ambiguity, but you must wait for a pulse to return before sending the next one to know the distance. If you fire too fast, a return from a far away target might be mistaken for a return from the most recent pulse, confusing your distance math. Citation: Sullivan, R. J. (2004). Radar Foundations for Imaging and Advanced Concepts. SciTech Publishing. Today in Science History: May 18, 1969: Apollo 10 launched. It carried the first rendezvous radar used in lunar orbit, a critical piece of hardware that allowed the lunar module to find the command module for a safe return home. #RadarSchool #Aerospace #RadarDesign #EngineeringProblems #SignalProcessing #SpaceHistory

Over The Horizon (OTH) radars can detect aircraft thousands of miles away, well beyond the physical curve of the Earth. How do they bend their signals around the planet? They bounce signals off the Earth's ionosphere. High Frequency (HF) radio waves naturally refract through the highly ionized layers of the upper atmosphere, eventually reflecting back down to the surface. This creates a skip zone, allowing the radar to illuminate targets completely hidden from conventional line of sight systems. Variations in solar activity directly impact how well this atmospheric mirror functions. Ref: Headrick, J. M., & Thomason, J. F. (1998). Applications of High-Frequency Radar. IEEE Antennas and Propagation Magazine, 40(3), 11-12. Today's History: May 17, 1865: The International Telegraph Union was founded in Paris. It later evolved into the International Telecommunication Union (ITU), the global entity responsible for allocating the critical radio frequencies that all radar systems rely on today. #RadarSchool #Ionosphere #ElectromagneticWaves #RadarSystems #RadioFrequency #TechEducation

Vote in the poll first, see more to reveal answer! The power drops by a factor of 16. This is the "cruel" reality of the monostatic radar equation. Because the signal must travel to the target (inverse square law) and then travel back again (another inverse square law), the received power is inversely proportional to the range to the fourth power (1/R^4). Doubling the distance (2^4) results in a 16-fold decrease in signal strength. Citation: Skolnik, M. I. (2001). Introduction to Radar Systems. McGraw-Hill. Today in Science History: May 17, 1865: The International Telegraph Union was established. This global cooperation paved the way for international radio frequency allocations, ensuring your radar doesn't interfere with your neighbor's communications. #RadarSchool #RF #EngineeringLife #Electromagnetics #Math #RadarLogic