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Synthetic-aperture-radar (SAR) imaging is an expensive endeavor. It can be difficult for universities, small business, or individuals to experiment with SAR imaging and algorithm development on a low budget. For this reason, a uniquely inexpensive solution to frequency-modulated continuous-wave (FMCW) radar was developed and then utilized as an ult...
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... objective of this article is to prove that synthetic aperture radar (SAR) imaging on an extremely low budget is possible. This research was conducted by the Michigan State University Electromagnetics Research Group in an effort to expand our research opportunities at a minimum financial risk. A unique approach to frequency-modulated continuous-wave (FMCW) radar design was developed and utilized as an ultra low cost SAR imaging system. This system was then used successfully to develop four different SAR imaging algorithms which have been used in a number of subsequent research projects. The unique approach to FMCW was previously introduced in [ 1], [2], and [3]. Section 2 is an explanation of the MA87127-1 Gunn oscillator based transceiver module known as a ‘Gunnplexer.’ An explanation of the unique approach to FMCW radar is presented in section 3. Range profile results are presented in section 4. Section 5 will explain the SAR system implementation. Section 6 will present imaging results using a range stacking SAR algorithm. Section 7 will present imaging results using two versions of the polar format algorithm (PFA). Section 8 will present imaging results using the range migration algorithm (RMA). Conclusions and future work will be discussed in section 9. The unique approach to FMCW radar design depends on the use of two inexpensive microwave transceiver modules. These modules are Gunn diode based, and are more commonly known as ‘Gunnplexers.’ The particular microwave transceiver module used for this system is the M/A-Com model MA87127-1 X-band microwave transceiver module. In practice almost any X-band varactor tuned ‘Gunnplexer’ could be used to implement this system. The MA87127-1 is composed of three major components, a voltage controlled oscillator (VCO), mixer, and circulator (see figure 1). The VCO is fed into port 1 of the circulator. Port 2 of the circulator is connected to the WR-90 waveguide flange input/output port of the transceiver. Port 3 of the circulator is connected to the RF input of the mixer. Some power is coupled off the VCO and fed into the Local Oscillator (LO) port of the mixer. The IF output of the mixer is connected to a small solder terminal on the outer case of the transceiver. VCO1 is a varactor controlled Gunn diode oscillator. A varactor diode is placed inside of a cavity Gunn oscillator as shown in figure 2. A bias voltage on the varactor diode between, roughly, 0 and 20 V controls the frequency of the Gunn oscillator. A second bias voltage of approximately 10 V causes the Gunn diode to oscillate at the frequency of the cavity that it is placed in. Looking at figure 1, CPLR1 is a symbolic representation of the coupling action that occurs between the Gunn oscillator diode and the Schottky mixer diode placed within close proximity as shown in figure 2. MXR1 is created by the coupled power from the Gunn diode oscillator. This coupled power causes the Schottky mixer diode to switch on and off. This switching action causes the Schottky mixer diode to operate as a single balanced mixer. CIRC1 is a ferrite circulator placed inside of the WR90 waveguide that contains MXR1 and that is weakly coupled to the resonant cavity where the Gunn oscillator is located. CIRC1 is basically a large magnet precisely placed inside of the WR90 waveguide section. CIRC1 causes RF power from VCO1 to exit the input/output port, and causes RF power coming into the input/output port to be transferred into MXR1. When looking at figure 1, it appears as though just one transceiver module alone can be utilized as an FMCW radar system. However, it was found in lab tests that the pass band of the IF port on MXR1 starts to roll off around 1 MHz, causing little to no response at audio frequency, which is were most beats from a short range FMCW radar system will be located. The transceiver module’s receiver worked most efficiently at IF frequencies above 30 MHz, where the loss due to the mixer was found to be the least. The lack of an acceptable low frequency to near DC response from MXR1 renders one individual transceiver module useless for most short range FMCW radar applications. Regardless of its shortcomings, when two MA87127-1 (or similar) transceiver modules are used together, the unique FMCW radar design solution can be obtained. In order to fully understand the unique approach to FMCW radar, the reader must be well versed in the theoretical operation of FMCW radar systems. A good explanation of FMCW radar can be found in [4]. The unique approach to FMCW radar was implemented using two low cost MA87127-1 Gunn diode based transceiver modules. All schematics and further explanation of this design can be found in [1]. A picture of the system is shown in figure 3. Figure 4 shows a simplified block diagram of the FMCW radar system. The following is a mathematical explanation of the unique approach to FMCW radar. The MA87127-1 transceiver module XCVR1 is centered at frequency f and ...
Context 2
... objective of this article is to prove that synthetic aperture radar (SAR) imaging on an extremely low budget is possible. This research was conducted by the Michigan State University Electromagnetics Research Group in an effort to expand our research opportunities at a minimum financial risk. A unique approach to frequency-modulated continuous-wave (FMCW) radar design was developed and utilized as an ultra low cost SAR imaging system. This system was then used successfully to develop four different SAR imaging algorithms which have been used in a number of subsequent research projects. The unique approach to FMCW was previously introduced in [ 1], [2], and [3]. Section 2 is an explanation of the MA87127-1 Gunn oscillator based transceiver module known as a ‘Gunnplexer.’ An explanation of the unique approach to FMCW radar is presented in section 3. Range profile results are presented in section 4. Section 5 will explain the SAR system implementation. Section 6 will present imaging results using a range stacking SAR algorithm. Section 7 will present imaging results using two versions of the polar format algorithm (PFA). Section 8 will present imaging results using the range migration algorithm (RMA). Conclusions and future work will be discussed in section 9. The unique approach to FMCW radar design depends on the use of two inexpensive microwave transceiver modules. These modules are Gunn diode based, and are more commonly known as ‘Gunnplexers.’ The particular microwave transceiver module used for this system is the M/A-Com model MA87127-1 X-band microwave transceiver module. In practice almost any X-band varactor tuned ‘Gunnplexer’ could be used to implement this system. The MA87127-1 is composed of three major components, a voltage controlled oscillator (VCO), mixer, and circulator (see figure 1). The VCO is fed into port 1 of the circulator. Port 2 of the circulator is connected to the WR-90 waveguide flange input/output port of the transceiver. Port 3 of the circulator is connected to the RF input of the mixer. Some power is coupled off the VCO and fed into the Local Oscillator (LO) port of the mixer. The IF output of the mixer is connected to a small solder terminal on the outer case of the transceiver. VCO1 is a varactor controlled Gunn diode oscillator. A varactor diode is placed inside of a cavity Gunn oscillator as shown in figure 2. A bias voltage on the varactor diode between, roughly, 0 and 20 V controls the frequency of the Gunn oscillator. A second bias voltage of approximately 10 V causes the Gunn diode to oscillate at the frequency of the cavity that it is placed in. Looking at figure 1, CPLR1 is a symbolic representation of the coupling action that occurs between the Gunn oscillator diode and the Schottky mixer diode placed within close proximity as shown in figure 2. MXR1 is created by the coupled power from the Gunn diode oscillator. This coupled power causes the Schottky mixer diode to switch on and off. This switching action causes the Schottky mixer diode to operate as a single balanced mixer. CIRC1 is a ferrite circulator placed inside of the WR90 waveguide that contains MXR1 and that is weakly coupled to the resonant cavity where the Gunn oscillator is located. CIRC1 is basically a large magnet precisely placed inside of the WR90 waveguide section. CIRC1 causes RF power from VCO1 to exit the input/output port, and causes RF power coming into the input/output port to be transferred into MXR1. When looking at figure 1, it appears as though just one transceiver module alone can be utilized as an FMCW radar system. However, it was found in lab tests that the pass band of the IF port on MXR1 starts to roll off around 1 MHz, causing little to no response at audio frequency, which is were most beats from a short range FMCW radar system will be located. The transceiver module’s receiver worked most efficiently at IF frequencies above 30 MHz, where the loss due to the mixer was found to be the least. The lack of an acceptable low frequency to near DC response from MXR1 renders one individual transceiver module useless for most short range FMCW radar applications. Regardless of its shortcomings, when two MA87127-1 (or similar) transceiver modules are used together, the unique FMCW radar design solution can be obtained. In order to fully understand the unique approach to FMCW radar, the reader must be well versed in the theoretical operation of FMCW radar systems. A good explanation of FMCW radar can be found in [4]. The unique approach to FMCW radar was implemented using two low cost MA87127-1 Gunn diode based transceiver modules. All schematics and further explanation of this design can be found in [1]. A picture of the system is shown in figure 3. Figure 4 shows a simplified block diagram of the FMCW radar system. The following is a mathematical explanation of the unique approach to FMCW radar. The MA87127-1 transceiver module XCVR1 is centered at frequency f and ...
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Citations
... S YNTHETIC aperture radar (SAR) plays an increasingly significant role in civil topographic mapping due to its all-weather and all-time capabilities [1]- [2]. With the rapid development of SAR technology, the SAR system has been widely applied to high-speed maneuvering platforms, such as airplanes, missiles, and unmanned aerial vehicles [3]- [13], for airplane navigation, terminal guidance, and autonomous landing of interesting areas. However, with the increasing demand for civil surveying and mapping fields, the SAR system requires compact size, lightweight, and low cost [14], which is suitable for frequency-modulation continuous-wave (FMCW) SAR. ...
Three-dimension acceleration, azimuth dependence, and real-time processing are the main issues to be solved in highly-squinted frequency-modulation continuous-wave (FMCW) SAR with a curved trajectory. To overcome these issues, a modified wavenumber-domain algorithm is developed in this paper. The proposed modified wavenumber-domain algorithm mainly includes the following six aspects. Firstly, a modified range model considering three-dimension acceleration for a curved trajectory is established. Then, the spectrum compression and rotation operations are performed to guarantee further processing. Afterward, residual phase terms introduced by acceleration are bulk compensated for. Moreover, the azimuth dependence is eliminated by the azimuth resampling to achieve uniform focusing. Subsequently, the range-azimuth coupling is removed by the modified Stolt interpolation. Finally, to avoid image aliasing, the azimuth wavenumber domain is selected to focus final image. The experimental results of both numerical and raw-measured FMCW-SAR data demonstrate the superiority of the proposed method.
... have investigated several FMCW-SAR architectures: (Charvat and Kempel, 2006) Developed an ultralow-cost FMCW GB-SAR imaging system, operating on an automatic rail. (Charvat et al., 2010) developed an ultrawideband (UWB) rail-SAR system with 2 GHz of bandwidth (1.926-4.069 ...
... (Reigber et al., 2013) Reviewed signal processing and imaging algorithms for very high-resolution SAR systems including time-domain algorithms, frequency-domain algorithms, and error correction methods. (Charvat and Kempel, 2006) Implemented four imaging algorithms in frequency-domain (PFA, simplified PFA, RMA, and RSA) to create a focused image of FMCW rail-SAR system. ...
Synthetic aperture radar (SAR) system based on frequency modulated continuous wave (FM-CW) transmission is a viable option for producing high-resolution ground-based imaging radars. Compared with pulsed SAR systems, the combination of FM-CW technology and SAR processing techniques have the advantages of small cubage, lightweight, cost-effectiveness, and high resolution in the SAR image. These characteristics make FM-CW SAR suitable to be deployed as payload on ground Based SARs (GB-SARs) for environmental and civilian applications. In this paper, the Range Migration Algorithm (RMA) is used in the processing chain of a Ground-Based SAR (GB-SAR) sensor. The mentioned sensor has been developed in Microwave Remote Sensing Laboratory (MReSL) at the School of Surveying and Geospatial Engineering, the University of Tehran for the generation of a complex image from the raw signal. The raw signal is acquired with that sensor working at S-band, frequency modulating from 2.26 GHz to 2.59 GHz.
... Also, a highrange resolution can be obtained, even though it has a low sampling rate [11,12]. The developed FMCW radar only measures real components; nevertheless, it can obtain complex data by using the Hilbert transform [13][14][15][16]. ...
... Through the Hilbert transformation, a quadratic component (imaginary part) can be generated. The Hilbert transformation is a method for generating a signal that has the same magnitude but is orthogonal to the original signal [15]. As shown in Eq. (10), the Hilbert transformation is used to obtain an in-phase/quadratic (I/Q) signal. ...
... Similar attempts has been made in [1] by same authors but using Vector Network Analyzer (VNA). In [2] an X-band lab model of SAR is designed but most of the components used are not commercially available. ...
Hands-on experience and instructions are required in the fields of Synthetic Aperture Radar (SAR) and Radars for fully understanding and developing complex radar systems. Unfortunately, Engineering institutions especially in developing countries cannot afford expensive Radar trainers required for imparting necessary skills to students. In this work a low cost X-band FMCW based lab model of SAR is developed using COTS hardware. This lab model can be utilized by students for understanding working of SAR and can also be used as part of their research activities.
... Two common approaches to the formation of a coherent aperture include a single antenna (or pair of transmit/receive antennas) physically scanned over an area, and the use of a dense array of sources and receivers positioned over an area. In the former approach, often termed synthetic aperture, the radiation pattern from the antenna can be modeled as a dipole or similarly simple analytic expression, with the set of distinct measurements indexed by the set of locations of the antenna [1,2]. In the latter approach, the collection of antennas distributed over the aperture can be modeled as a set of dipole radiators, with the phase and amplitude of each element assumed to be variable. ...
Recently, a frequency-diverse, metamaterial-based aperture has been introduced in the context of microwave and millimeter wave imaging. The generic form of the aperture is that of a parallel plate waveguide, in which complementary metamaterial elements patterned into the upper plate couple energy from the waveguide mode to the scene. To reliably predict the imaging performance of such an aperture prior to fabrication and experiments, it is necessary to have an accurate forward model that predicts radiation from the aperture, a model for scattering from an arbitrary target in the scene, and a set of image reconstruction approaches that allow scene estimation from an arbitrary set of measurements. Here, we introduce a forward model in which the metamaterial elements are approximated as polarizable magnetic dipoles, excited by the fields propagating within the waveguide. The dipoles used in the model can have arbitrarily assigned polarizability characteristics. Alternatively, fields measured from actual metamaterial samples can be decomposed into a set of effective dipole radiators, allowing the performance of actual samples to be quantitatively modeled and compared with simulated apertures. To confirm the validity of our model, we simulate measurements and scene reconstructions with a virtual multiaperture imaging system operating in the K-band spectrum (18–26.5 GHz) and compare its performance with an experimental system.
... Imaging of objects using microwaves has been the subject of much research in the literature. In view of this, traditional microwave imaging techniques, such as synthetic aperture radar (SAR) [1,2] and microwave holographic imaging [3,4], have been studied extensively with promising results. Both of these techniques involve the use of a mechanical scan, in which an antenna is moved across a synthesized aperture and transmits and receives the field at each sampling point, to perform imaging. ...
We investigate the performance of various image reconstruction algorithms for the design of metamaterial
aperture based imaging system. The metamaterial imaging system consists of a transmitting metamaterial aperture panel and a receiving low-gain probe antenna. The imaging of a 3 cm resolution target is performed using a number of reconstruction algorithms, including pseudo-inverse, matched filter, conjugate gradient squares (CGS), and two-step iterative shrinkage/thresholding (TwIST) methods. The differing quality of the resulting reconstructed images is shown as a function of these reconstruction techniques.
... It was found that a GDD commercial neon indicator lamp can be an effective detector in a 0.2 THz imaging system. 3D Imaging systems based on conventional FMCW radars in the MMW regime were demonstrated previously [11,12]. ...
... Those systems are based on scanning mechanisms and thus they are slow [12]. Furthermore, those systems employ very expensive MMW components such as detectors, mixers, antennas, and quasioptics [12,13]. ...
... Those systems are based on scanning mechanisms and thus they are slow [12]. Furthermore, those systems employ very expensive MMW components such as detectors, mixers, antennas, and quasioptics [12,13]. ...
Millimeter wave (MMW)-based imaging systems are required for applications in medicine, homeland security, concealed weapon detection, and space technology. The lack of inexpensive room temperature imaging sensors makes it difficult to provide a suitable MMW system for many of the above applications. A 3D MMW imaging system based on chirp radar was studied previously using a scanning imaging system of a single detector. The radar system requires that the millimeter wave detector will be able to operate as a heterodyne detector. Since the source of radiation is a frequency modulated continuous wave (FMCW), the detected signal as a result of heterodyne detection gives the object’s depth information according to value of difference frequency, in addition to the reflectance of the 2D image. New experiments show the capability of long distance FMCW detection by using a large scale Cassegrain projection system, described first (to our knowledge) in this paper. The system presents the capability to employ a long distance of at least 20 m with a low-cost plasma-based glow discharge detector (GDD) focal plane array (FPA). Each point on the object corresponds to a point in the image and includes the distance information. This will enable relatively inexpensive 3D MMW imaging.
... Those systems are based on scanning mechanisms and thus they are slow. It takes a long time to create an image (perhaps tens of seconds) [8]. Furthermore those systems employ very expensive MMW components such as detectors, mixers, LNA's, antennas and quasi-optics [3]. ...
Imaging systems in millimeter waves are required for applications in medicine, communications, homeland security, and space technology. This is because there is no known ionization hazard for biological tissue, and atmospheric attenuation in this range of the spectrum is low compared to that of infrared and optical rays. The lack of an inexpensive room temperature detector makes it difficult to give a suitable real time implement for the above applications. A 3D MMW imaging system based on chirp radar was studied previously using a scanning imaging system of a single detector. The system presented here proposes to employ a chirp radar method with Glow Discharge Detector (GDD) Focal Plane Array (FPA of plasma based detectors) using heterodyne detection. The intensity at each pixel in the GDD FPA yields the usual 2D image. The value of the I-F frequency yields the range information at each pixel. This will enable 3D MMW imaging. In this work we experimentally demonstrate the feasibility of implementing an imaging system based on radar principles and FPA of inexpensive detectors. This imaging system is shown to be capable of imaging objects from distances of at least 10 meters.
... It was indicated that a GDD commercial neon indicator lamp can be an effective detector in a imaging system. 3D Imaging systems based on conventional FMCW radars in the MMW regime were demonstrated and published [10,11]. Those systems are based on scanning mechanisms and thus they are slow. ...
... Those systems are based on scanning mechanisms and thus they are slow. It takes a long time to create an image (perhaps tens of seconds) [11]. Furthermore those systems employ very expensive MMW components such as detectors, mixers, LNA's, antennas and quasi-optics [11,12]. ...
... It takes a long time to create an image (perhaps tens of seconds) [11]. Furthermore those systems employ very expensive MMW components such as detectors, mixers, LNA's, antennas and quasi-optics [11,12]. System based GDD focal plane arrays can be very efficient in real time 3D radar imaging. ...
Millimeter wave (MMW) imaging systems are required for applications in medicine, communications, homeland security, and space technology. This is because there is no known ionization hazard for biological tissue, and atmospheric attenuation in this range of the spectrum is relatively low. The lack of inexpensive room temperature imaging systems makes it difficult to give a suitable MMW system for many of the above applications. 3D MMW imaging system based on chirp radar was studied previously using a scanning imaging system of a single detector. The system presented here proposes to employ a chirp radar method with a Glow Discharge Detector (GDD) Focal Plane Array (FPA) of plasma based detectors. Each point on the object corresponds to a point in the image and includes the distance information. This will enable 3D MMW imaging. The radar system requires that the millimeter wave detector (GDD) will be able to operate as a heterodyne detector. Since the source of radiation is a frequency modulated continuous wave (FMCW), the detected signal as a result of heterodyne detection gives the object's depth information according to value of difference frequency, in addition to the reflectance of the image. In this work we experimentally demonstrate the feasibility of implementing an imaging system based on radar principles and FPA of GDD devices. This imaging system is shown to be capable of imaging objects from distances of at least 10 meters.
... 3D millimeter wave imaging using RADAR principles and GDD is a new concept which has diverse application in home land security, medicine, and industry. 3D Imaging systems based on conventional FMCW radars in MMW regime were demonstrated and published in [1,2]. Those systems are based on scanning mechanisms and thus it takes a long time to obtain an image [1,2]. ...
... 3D Imaging systems based on conventional FMCW radars in MMW regime were demonstrated and published in [1,2]. Those systems are based on scanning mechanisms and thus it takes a long time to obtain an image [1,2]. Furthermore those systems employ very expensive MMW components such as detectors, mixers, LNA's, antennas and quasi-optics [3]. ...
Demonstration of Millimeter Wave (MMW) imaging system using chirp radar method and Glow Discharge Detector (GDD) Focal Plane Array (FPA) is presented. A unique quasi optical set up and advanced detection methods using the GDD are intended to build the 3D MMW imaging system. This quasi optical setup enables to detect the distance and reflection of each point in object in order to reconstruct a 3D MMW image.
