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Demonstration Kit Provides Hands-On Radar Experience

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by Pasternack Enterprises

Learning the fundamentals of radar is a daunting task, and while textbooks and lectures are invaluable tools, nothing beats hands-on experience. With this in mind, Pasternack has introduced a radar demonstration kit that includes the hardware and software required to demonstrate how radar works. Although the radar itself is very basic, it still provides a wealth of opportunities for discovering how radar systems work, their elements, waveforms, effects of filtering, and many other functions that are easier to understand when seeing them in action.

The PEM11000-KIT consists of a radar system board that operates in the 2450 MHz Industrial Scientific and Medical (ISM) band used by Wi-Fi, Bluetooth®, and many other unlicensed systems (Figure 1), two simple antennas, RF and power cable assemblies, software, plus a detailed instruction guide. The system can also be purchased as the PEM11002-KIT which includes a USB-enabled battery pack and a tripod on which the radar antennas are mounted. The battery pack requires a Bluetooth connection to interface with the radar board and operates for up to 2 hours on a charge.

Figure 1: The radar kit is deceptively simple and provides a window into radar operation
Figure 1: The radar kit is deceptively simple and provides a window into radar operation

The radar demonstration kit provides for single tone, frequency ramp, and sawtooth waveforms; provides an audio output and onboard speaker for understanding changes in the received signal; and an array of LEDs used for error alerts and other purposes. The system also allows the user to apply different types of filters and view the results, and is controlled by either USB or Bluetooth. USB is used to control a desktop or laptop computer and Bluetooth provides control when paired with an Android smartphone or tablet or any Bluetooth-enabled computer.

A variety of typical radar applications can be illustrated using the system. Radio Detection and Ranging (RaDaR, i.e. range vs. time), for example, one of the core functions of every radar, can be used to detect either fixed or moving objects in any of the system’s sweep modes. To detect objects in motion, it can be configured for continuous wave mode and the resulting Doppler frequency shift of the received signal determines the object’s speed. Combining these two principles, a frequency-modulated continuous-wave (FMCW) signal [1] such as a linear ramp can be used to determine both object speed and range detection simultaneously (such as detecting someone entering a room). The sawtooth waveform is another form of FMCW that allows the “sign of the Doppler” to be determined, to tell if a person or object is moving away or towards the radar.

What’s in the Kit 

Figure 2: The radar board includes all digital and RF hardware, a speaker, interfaces for power and USB, and includes an area dedicated to filter prototyping
Figure 2: The radar board includes all digital and RF hardware, a speaker, interfaces for power and USB, and includes an area dedicated to filter prototyping

The radar board (Figure 2) that is the core of the system contains all required digital and RF hardware as well as interfaces for power, control, and RF output to the antennas. The radar board is subdivided into digital, Bluetooth, audio feedback, RF, and filter prototyping sections. The digital section contains a PIC microcontroller and ADC as well as USB and power interface. The controller orchestrates all functions on the radar board in response to control commands delivered via USB or Bluetooth.

The ADC digitizes the received signal after filtering and is stored in system memory or streamed via Bluetooth. The antennas themselves are classic “cantennas;” cylinders about the size of a soup can with one end open and the other sealed. The sealed end is drilled to accept an SMA flange connector that acts as a reflector. A metal rod is soldered to the center connector and functions as a launch for the RF signal. The PEM11002 model includes a mounting plate that accommodates the radar board and antennas and is drilled for tripod mounting (Figure 2).

The RF section on the board generates the transmit signal and downconverts the received signal to a frequency that can be digitized by the ADC. The transmit signal is generated by a VCO whose output is locked using PLL and an onboard clock reference. The VCO output is amplified before being sent to the antenna.

An important area on the board is dedicated to filter prototyping so that the received and downconverted IF signals can be acted upon using active or passive filters supplied by the user. This essentially functions as a test bed for evaluating various types of filters, their characteristics, and their effect on the signal. A test signal can be sent directly to the filter via an onboard MCX connector, bypassing the rest of the RF and IF chains. A known good test signal can also be sent directly to the ADC via the MCX connector.

Operation

The software accompanying the radar demonstration kit provides a graphical interface into the operation and configuration of the system (Figure 3). The kit is designed to function as a USB Test and Measurement Class (USBTMC) device and no additional drivers are required. USBTMC is an open standard for control of USB-based test instruments and defines commands used to send messages to and from an instrument. It is programmed using SCPI commands similar to those employed by IEEE-488.

Figure 3: The user interface lets the user orchestrate all of the system’s functions, and can display a variety of conditions depending on the operating mode
Figure 3: The user interface lets the user orchestrate all of the system’s functions, and can display a variety of conditions depending on the operating mode

USB communication is accomplished using Virtual Instrument Software Architecture (VISA) libraries for National Instruments, Keysight Technologies, and Tektronix instruments. These libraries can be purchased from either Pasternack or the instrument vendors.

Audio and visual feedback to the user concerning signal strength, presence of errors, and other conditions is provided by a bar of LEDs on the radar board. As the system’s IF frequency is in the audible portion of the spectrum, the onboard speaker lets users listen to changes in the received frequency. Volume is controlled by a potentiometer.

The output frequency profile is controlled by the start and stop frequencies and sweep type, the latter determining the ramp profile of the output waveform. Ramp, triangle, automatic triangle, and CW modes can be selected. When configured for ramp sweep (the time required to sweep from start to stop frequencies), the system sweeps between a specified start and stop frequency and once the stop frequency is reached, it goes back to the start frequency. The ramp process then begins again based on a hardware or software trigger signal. The ramp time can be set by the user to any value between 1 and 65,536 ms and the maximum usable ramp time is determined by the start and stop frequencies, reference frequency, and reference divider.

When configured for triangle sweep, the output frequency starts from the start frequency and increases linearly until the stop frequency is reached after which the output frequency is linearly decreased until the start frequency is reached. The process is repeated if a trigger is received.

Table 1: Radar demonstration kit features
Table 1: Radar demonstration kit features

In automatic sweep mode, the sweep begins at the start frequency and increases linearly until the stop frequency is reached, after which the output is linearly decreased until the start frequency is reached. This process is performed automatically without requiring a trigger until a stop command is received. In CW mode a single frequency tone is output at a specified frequency.

Both radar demonstration kits include a user manual that describes all aspects of how the system works, how it can be controlled and includes a section on radar basics as well. The PEM11000-KIT is priced at $2,399.97 and the PEM11002-KIT is $2613.30; they are available for same-day delivery. More information is available at www.pasternack.com.

[1] M. I. Skolnik, Introduction to Radar Systems, Second Edition, McGraw-Hill, NY, 1980. (Note: The discussion on FMCW radar is not covered in the Third Edition). 

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