Emerging Trends in Radar: Harmonic Radar Systems With mmWaves

In pest management research, harmonic radar systems have been largely used to study insect movement across open or vegetation-poor areas because the microwave signal is attenuated by the high water content of vegetation. This study evaluated whether the efficacy of this technology is sufficient to track insects in vegetative landscapes. Field efficacy data were collected using portable harmonic microwave radar and electronic dipole tags mounted on adults of three economically important pests: Leptinotarsa decemlineata (Say), Diabrotica virgifera virgifera (LeConte) [corrected] and Conotrachelus nenuphar Herbst. Detection and recovery of tagged Colorado potato beetles, plum curculios and western corn rootworms was high within and among potato plants, moderate within apple trees and high within, but not between, corn plants respectively. The efficacy of the radar depends on the ability of the operator to move around the host, scanning for a signal 'sightline' with the tagged insect among plant structures. The detection rate of tagged insects by harmonic radar systems is high enough to track the walking path of pests through low row crops such as potato, tall row crops such as corn or tall but well-separated trees of orchard-type crops by adapting the scanning procedure to the vegetative architecture.

Harmonic radar is a promising radar technique for the detection of electronic devices in security related applications. In contrast to established and commercially available systems, where the radar works in conjunction with a known and cooperative transponder responding at a harmonic frequency, the goal here is to detect and localize noncooperative targets such as mobile phones. In this work, a combination of classic and harmonic radar in one system is presented. The system layout together with the design strategies and experiences gained is described in detail. Measurement results indicate how an inverse synthetic aperture radar (ISAR) setup could be beneficial in a real world scenario.

Harmonic radar technology has been researched and developed for studying the foraging behaviour of honey bees. This work presents the development of a working prototype of a narrow-band harmonic radar system, at 2.5/5GHz, using off-the-shelf components to detect the presence of Indian honey bees. Based on empirical tests on the tag, we estimate the radar probability of detection and probability of false alarms as 88% and 0.3% respectively. The maximum detectable range for a monostatic configuration of the radar is 3.84 m.

Monitoring technologies are needed to track insects and gain a better understanding of their behavior, population, migration, and movement. A portable microwave harmonic-radar tracking system that utilizes antenna miniaturization techniques was investigated to achieve this goal. The system mainly consists of a compact radar unit, a hand-held transmitter/receiver (Tx/Rx) patch antenna array panel, and a passive radio frequency (RF) transponder. The system transmits a signal at 5.882 GHz and receives returned signals in the 11.764 GHz band. The RF transponder to be mounted on insects is a 9.63 mm 9.63 mm flat plane weighing 6 mg. Tests were conducted to optimize the horizontal and vertical tracking ranges of the system by measurement of radio frequency signal strength from the transponder in open terrain, inside tree canopies, and underground at different tracking angles. In open terrain, a directional tracking range of over 60 m was achieved. However, obstructions from tree canopies and the high water content of leaves severely weakened the microwave signal strength and restricted the tracking range to below 20 m. To obtain maximum signal strength, the Tx/Rx antenna panel and the transponder must be in a mutually clear line of sight and their angles must be maintained within a 10 range. However, the use of harmonic radar technology to develop a portable tracking system with a small insect-borne transponder currently poses insurmountable challenges for antenna design due to the very stringent requirements to accommodate the tracking range, the transponder size and mass, and the methods used to attach the transponders to insects.

A Doppler radar system was built to detect the motion of modulated backscatter data from a passive tag, while rejecting the unmodulated backscatter from other elements. A harmonic tag was designed and fabricated to show the feasibility of sensing cardiopulmonary related Doppler shift in the received second harmonic signal. A fundamental frequency of 2.45 GHz was transmitted at a target and a quadrature homodyne receiver was used to sense the received second harmonic signal. The setup was used to first successfully isolate periodic motion from a tag on a programmable mechanical target in close proximity to other moving objects and to sense respiratory motion of a human subject. Respiratory data obtained from the tag was compared to a reference. The harmonic radar setup was then successfully used to isolate the respiration of a tagged human subject from an untagged large scattering object. The response of the harmonic radar was also compared to a 2.45 GHz Doppler radar for some experiment scenarios that clearly indicate the utility and potential for such systems.

The baseband system serves as the core component responsible for signal processing in harmonic radar systems. However, designing a baseband system that meets requirements poses several challenges. In this study, we addressed the design and simulation of a baseband system for a 3.6GHz harmonic radar. A fundamental signal at a frequency of 3.3MHz was selected, with 90° phase-shift binary phase shift keying (BPSK) modulation employed as the modulation scheme for the baseband system. MATLAB was utilized for program development to simulate the reception of nonlinear target-reflected harmonic signals. Results of signal processing for the second and third harmonics were provided. Furthermore, an FPGA-based hardware circuit for the harmonic radar was designed, followed by hardware testing and target data collection. The practical feasibility of the design approach was validated. Comparative analysis between measured and simulated data revealed the system's proficiency in identifying harmonic signals during signal processing.

Contrary to claims made Multiple Input and Multiple Output (MIMO) radars do not provide an order of magnitude better angle resolution, accuracy and identifiability over conventional radars. What is claimed: MIMO array radar system consisting of a full transmit array and thinned receive array (or vice versa; called here a full/thin array) provides an order of magnitude or more of accuracy, resolution and identifiability, the ability to resolve and identify targets than a conventional array. This claim for MIMO results from making the wrong comparison to a full conventional array rather than to a conventional full/thin array. It is shown here that a conventional full/thin array radar can have the same angle accuracy, resolution and identifiability as a MIMO full/thin array. Moreover the conventional full/thin array example given here can have a better search energy efficiency. Where does the MIMO radar provide a better angle accuracy than a conventional radar? A monostatic MIMO array radar does provide a better angle accuracy than its conventional monostatic equivalent, but it is only about a factor of 1/ √2 (29 percent) better and its resolution is the same. Alternately, a monostatic MIMO array radar can offer the advantage of the same accuracy as a conventional monostatic array radar with a smaller aperture size, one that is 1/ √2 = 0.707 smaller, or equivalently 29 percent smaller. This improved accuracy comes at a heavy computation cost. For a MIMO monostatic linear array of N elements ≥ N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> matched filters (MFs) are needed versus just N for its conventional equivalent. The factor ≥ results from the need for a bank of F ≥ 1 MFs being needed for the MIMO array. A bank of F MFs are need because the MF for an orthogonal waveform is usually Doppler intolerant. In contrast a conventional array would use a linear FM waveform (chirp waveform) which is Doppler tolerant. An alternate approach for achieving this factor of √2 advantage is to simply increase the radiated power of a conventional radar by a factor of 2. This latter approach to getting the √2 advantage has to be traded off against the cost resulting from the throughput increase required when using MIMO. MIMO radar is best for search not for track, unless track-while-scan. For track, conventional array processing should be used for maximum energy efficiency and to reduce the signal processing requirements. When a MIMO array is used to search a large scan angle, it is best for maximum search energy efficiency to use subarrays of the array as the elements of the MIMO array to form what we call a subarray-MIMO (SA-MIMO). When searching a small scan angle, the subarrays should be sized so that the volume of space illuminated by the subarrays of the SA-MIMO array matches, or is smaller than, the volume of space to be searched. Using SA-MIMO reduces the processing throughput requirements. MIMO radar in the near term will be useful for coherent and incoherent combining of existing radars to achieve about a 9 dB better power-aperture-gain (PAG).

Nonlinear radar exploits the difference in frequency between radar waves that illuminate and are reflected from electromagnetically nonlinear targets. Harmonic radar is a special type of nonlinear radar that transmits one or multiple frequencies and listens for frequencies at or near their harmonics. Nonlinear radar differs from traditional linear radar by offering high clutter rejection and is particularly suited to the detection of devices containing metals and semiconductors. Examples include tags for tracking insects, tags worn by humans for avoiding collisions with vehicles, or for monitoring vital signs. Such tags contain a radio-frequency (RF) nonlinearity, often a Schottky diode, connected to a suitable antenna. Targets with inherent nonlinearities, such as metal contacts, semiconductors, transmission lines, antennas, filters, and ferroelectrics, also respond to nonlinear radar. In this paper, the successful exploitation of harmonic radar for moving target imaging and synthetic aperture imaging of targets, while suppressing clutter signals from linear targets, are presented. Our results demonstrate some unique advantages of harmonic radar over its traditional linear counterpart.

This paper considers the most simple tag of a harmonic radar system at millimeter wave frequencies which consists of an antenna for reception and transmission and a Schottky diode as a nonlinear element. A fundamental performance limit assuming perfect matching between diode and antenna is calculated and the optimum biasing point of the Schottky diode is found. Except of the necessary battery all elements are passive.

A compact rectenna suitable for the tracking harmonic radar dedicated for small-sized creatures is designed and implemented. To efficiently harvest the RF power and radiate the doubled harmonic frequency for the tag of the harmonic radar system, the dualband 4-/8-GHz antenna is designed and implemented. The average gains at the two bands are −1.03 dBi and −2.37 dBi, respectively. Moreover, a two-stage Dickson rectifier at 4 GHz of a compact size 8.5×8.5 mm2 has the dc output voltage larger than 1 V as the input RF power higher than −5.5 dBm. The rectenna featuring a miniaturized size of 18×17 mm2 has been examined by a test system equipped with 3 identical CW transmitters.

Harmonic radar technology can be used to track the dispersal of tagged insects. The tag consists of a wire antenna attached to a Schottky diode, which uses the original radar signal as an energy source, re-emitting a harmonic of the transmitted wavelength. Two forms of harmonic radar use this basic technology to study insect movement. The more sophisticated form consists of a ground-based scanning radar station that tracks the movement of a tagged insect on a circular radar display. A simpler, "off-the-shelf" form of harmonic radar is a commercially available, light-weight, handheld transmitter/receiver from RECCO Rescue Systems. We briefly review both of these forms and describe our experience monitoring the movement of carabid beetles in agricultural habitats with the handheld transmitter/receiver. We identified a commercial source of diodes compatible with the RECCO transmitter/receiver and tested several diode and wire combinations. We found that a tag built with a diode attached to a single section of 8-cm wire (monopole) was more appropriate for marking carabids. Tags built from flexible Teflon-coated wires were an improvement on tags built with stiff, aluminum wire, but beetle movement was still hindered. In corn and soybean fields, large carabids ( Scarites quadriceps Chaudoir and Harpalus pennsylvanicus , (DeG.) Coleoptera: Carabidae) could be recaptured even when they burrowed out of sight 3 to 9 cm below the soil surface. We discuss the trade-offs between tag detection and durability that occur when designing a tag for a given organism. Although the technique shows promise, producing a tag that does not hinder movement of the target insect in the field will require further development.

In order to fulfil real time signal processing tasks such as clutter rejection, moving target detection (MTD) and constant false alarm rate (CFAR) control in airborne radar, an airborne radar parallel signal processing system (ARPS2) is proposed with DSP chips as its kernel processing nodes. The DSP chips are used with parallel architecture. Each node has its private input and output memory. It adopts several parallel techniques, such as parallel storage, parallel processing, parallel code loading and parallel data organization to achieve high efficiency. It has a simple structure, excellent flexibility and easiness in developing. ARPS2 is going to be applied to an airborne radar. It can also be applied to perform high-speed real time signal processing algorithms in other kinds of radar.

This study presents a time division multiplexing (TDM) multiple-input–multiple-output (MIMO) digital beamforming (DBF) radar concept based on a single transceiver (one transmitter and one receiver). Compared with a conventional MIMO DBF radar system with M-element transmitting array and N-element receiving array, the proposed concept can reduce the number of transmitter/receivers from M + N to 2 for a drastic cost reduction. In addition to theoretical analysis and numerical simulation, an experimental TDM MIMO DBF radar demonstrator is realised and tested for verification using real data. Numerical analysis and experimental results show that the proposed concept can achieve considerable higher angular resolution at lower cost compared to conventional DBF radar concepts using the same antenna array with one-way or two-way beamforming.

A multiple input multiple output (MIMO) radar system is an emerging research field which has attracted many studies in recent years. This type of radar, unlike conventional phased array radar, can transmit different probing signals via its antennas, that may be correlated or uncorrelated with each other. This waveform diversity offered by MIMO radar systems enable superior capabilities compared to conventional phased array radar. Many papers have introduced different ways for beamforming of MIMO radar. In this paper it is desirable to analysis some methods for beamforming of MIMO radars with planar arrays constellation and examine their 3D result beam-pattern of such constellations for covariance based MIMO radar waveforming method. MATLAB software is being employed for simulations.

The Networked Over-the-Horizon Radar (NOTHR) is a flexible and scalable high-frequency (HF) radar system for wide-area surveillance and target detection over oceans and remote regions.It is based on a bistatic configuration with a large transmitter and multiple small, mobile receivers, offering a cost-effective and easily deployable solution [1].The system employs Multiple-Input Multiple-Output (MIMO) radar signal processing techniques to enhance signal detection, angular estimation, and clutter rejection [2].Designing a large MIMO radar transmitter presents several engineering challenges, such as selecting waveforms for a high number of transmitted signals while preserving their orthogonality.