On this utility be aware, we are going to take a look at frequency-modulated steady waveform (FMCW) radar expertise intimately, significantly the wideband 76 – 81 GHz vary. We’ll describe how you should use Keysight’s options to check your designs to make sure most effectivity, reliability, repeatability, and most significantly, make sure that your units work to the very best security requirements attainable.
Introduction
It’s reported that 1.35 million folks die from street accidents yearly, with 1000’s extra injured. That is the primary purpose why radar specialists have been recruited by key gamers within the automotive business, to develop automotive radar methods that not solely enhance automobile security but in addition meet key standards similar to measurement and value. Due to this market demand, numerous radar methods, similar to adaptive cruise management (ACC), stop-and-go, blind spot detection (BSD), lane change help (LCA), and rear crash warning (RCW), are actually broadly utilized in autos.
Radars primarily based on a frequency modulated steady waveform (FMCW) is the important thing expertise utilized in most automotive radar purposes at present. Not like extra conventional pulsed radar, FMCW radar utilizing steady wave modulation can keep away from a excessive peak-to-average energy ratio (PAPR) in transmission, which simplifies the design course of for antennas and RF elements like energy amplifiers. Consequently, an automotive radar system primarily based on this expertise provides extra benefits, similar to higher efficiency with simplified RF elements, small measurement, light-weight, and low value.
On this utility be aware, we are going to research FMCW radar expertise in slightly extra element, significantly the wideband 77 – 81 GHz vary, and describe how Keysight’s options might help you check your designs to make sure most effectivity, reliability, repeatability and most significantly, make sure that your units work to the very best security requirements attainable. Key check parameters mentioned embody frequency linearity, chirp charge, section error, energy deviation and lots of extra.
What Is FMCW and Why Use It?
FMCW is a kind of radar sensor that may repeatedly transmit alerts like a easy continuous-wave (CW) radar. Nevertheless, in contrast to CW radar, the working frequency of FMCW may be modified through the measurement, subsequently we will say that the transmitted sign is frequency modulated. Any such radar has been round for a few years, however today essentially the most broadly used utility is throughout the automotive radar area.
So why is FMCW used so broadly in automotive radar? Listed below are the benefits:
- The potential slim decision permits measurement of very small The minimal measurable vary is corresponding to the transmitted wavelength.
- Very excessive accuracy of vary
- Not like pulsed radar, with FMCW you may concurrently transmit and measure the acquired
- As a result of the transmit and obtain alerts are “at all times on”, there’s zero blind vary. Which means there isn’t any “blind spot” between transmit and obtain, the place one thing might be
- Pulsed radar methods have excessive ranges of peak energy; this isn’t the case for
- The acquired sign is blended right down to decrease frequencies, so the processing circuitry and algorithms needn’t be so sophisticated.
- Due to the easier circuit design, and the capabilities of contemporary digital sign processors (DSPs), the general value and the dimensions and weight of FMCW radar modules are decrease than different radar requirements.
FMCW – How does it work?
Figures 1a and 1b give a visible overview of FMCW radar detection. A shift in each time and frequency between the transmit and obtain alerts decide vary and velocity of targets.
The acquired sign is a time-delayed model of the transmitted sign the place the delay, Δt (delay in time), provides the vary info and fd (delay in frequency) is the Doppler info. As a result of the sign is at all times sweeping by a set frequency band (for instance 77 – 81 GHz), at any second through the sweep, the frequency distinction between the transmit and obtain alerts, f1 and f2, is fixed.
Each f1 and f2 are often known as the beat frequency, and there are two measurements made, each on the rising and falling fringe of the sign (additionally known as the chirp). Within the case of a single goal, each the rising and falling beat frequencies are required to make sure the equations may be solved unambiguously. As a result of the sweep is linear, we will derive the time delay from the beat frequency, and from this additionally calculate the vary.
Determine 2 provides us a extra in-depth overview of the totally different parameters required to make actual measurements to calculate the vary and velocity.
Δf1 = ktr – fd Δf2 = ktr + fd
okay = frequency slope
tr = time delay and ktr is the frequency shift as a consequence of time delay.
To calculate the Doppler shift, fd = (2 / lc )*Vr, the place Vr is the novel velocity of the item.
To calculate ktr, ktr = ((2 / C)*(Bw / Ts))*R, the place C = fixed, Bw is the sign bandwidth, Ts is the chirp period and R is the vary to the goal
Use the beat frequency for each the rising and falling chirp to find out the speed and vary.
Δf1 = ((2 / lc )*Vr) – (((2 / C)*(Bw / Ts))*R)
Δf2 = ((2 / lc )*Vr) + (((2 / C)*(Bw / Ts))*R)
Key measurements
Listed below are the important thing questions you could ask, to precisely characterize an FMCW radar sign.
- Is the sweep bandwidth of the sign right? Typical automotive radar expertise works within the 24 GHz, 77 GHz and 79 GHz frequency bands, and every of those can have a unique sweep For instance, at 24 GHz, we sometimes see bandwidths within the order of 100’s of MHz, the place on the increased frequencies, bandwidths may be 1 GHz and higher. A conventional swept-tuned spectrum analyzer can sweep throughout the whole band to view the envelope of the sign.
- Why a bigger bandwidth at increased frequency bands? Higher bandwidths permit finer decision, thus permitting significantly better goal separation functionality. Utilizing increased heart frequencies additionally will increase the Doppler decision. Due to this fact, automotive radar requirements are transferring from 24 GHz to 77/79
- Validate the linearity of the FM sweep. Since FMCW is comprised of a frequency sweep, the linearity of that sweep is essential. Any ripples or anomalies with the sweep may cause a degradation within the accuracy and determination of the vary and radial
- Measure the chirp size and chirp charge. The chirp size and charge have an effect on the power to find out the radial velocity. Resulting from attainable “ghost targets”, a number of chirps are analyzed to provide higher measurement
- What about sign energy?
System Validation – How Does It Work?
Efficient radar system design requires complete system validation – a time-consuming and costly course of. Radar engineers will not be solely required to validate the radar transmitter efficiency (sign evaluation) but in addition want to check the radar receiver efficiency. Radar receivers should be examined with practical threats, sensitivity and jamming eventualities. Producing ultra-wideband (UWB) alerts with Doppler frequency offsets, goal echoes and muddle to carry out receiver verification may be difficult. Designing and testing UWB radar methods requires a wide range of sign sources, goal atmosphere setups and measurements. Fastidiously designed and optimized waveforms are important to make sure glorious real-world efficiency.
Sign Technology
Earlier than we present a measurement, we wish to present how you should use Keysight sign mills to create an FMCW sign. That is helpful if you happen to do not need a number of units accessible to check, or if you wish to create a sign interference resolution to permit testing of your units within the presence of different (not essentially FMCW) alerts.
On this part, we are going to introduce sign era utilizing a Keysight M8195A arbitrary waveform generator (AWG), after which present how you should use choice BHP of Keysight’s VSA (vector sign evaluation) software program to investigate FMCW radar alerts. Choice BHP is a devoted choice for FMCW sign sorts and permits straightforward setup and detection of those alerts. Whereas there are a number of configurations accessible for automotive radar evaluation with Keysight, we will probably be utilizing choice 060 which incorporates the Keysight N9041B, 2 Hz to 110 GHz spectrum analyzer to seize the sign. This permits us to seize the sign with out utilizing any exterior mixing, thus sustaining the very best sign integrity.
The sign era configuration consists of the three devices under:
- M8195A 65 GSa/s Arbitrary Waveform Generator
- N5183B MXG Microwave Analog Sign Generator, 9 kHz – 40 GHz
- N9029ACST-U12 WR12 VDI compact Upconverter
Channel 1 Knowledge Out on the M8195A is related to the intermediate frequency (IF) enter of the N9029ACST-U12 by way of a 6-dB attenuator pad, whereas the Channel 1 Complement Knowledge Out is terminated with a 50 Ohm load. The IF enter energy is really helpful to be saved at < -15 dBm for linear area operation.
The native oscillator (LO) sign is offered by N5183B analog sign generator. The N9029ACST-U12 upconverter requires a LO frequency that’s half of the provider frequency Fc, thus customers can choose the LO frequency within the vary of 30 – 45 GHz.
A simplified block diagram of the system is proven within the determine under. M8195A AWG offers an IF sign to be blended with a set LO sign from the MXG to provide a millimeter wave sign. The up-conversion course of generates a millimeter wave sign with each higher and decrease sideband spectrum. The blending product is both FC – FIF (decrease sideband) or FC + FIF (higher sideband), subsequently a bandpass filter is required to take away the undesirable mixing sign. On this instance, the IF sign is a linear frequency sweep from 2 GHz – 6 GHz and is blended with the LO sign at frequency 75 GHz (37.5 GHz x 2) to provide a 77 – 81 GHz FMCW radar sign. As radar alerts on the decrease 24 GHz frequency vary are nonetheless broadly in use, the identical instrumentation can be utilized at this decrease frequency.
Automotive Radar Automation
One portion of our resolution that now we have not spoken about but is the KS83200A Automation Software program for Automotive Radar. It is a Keysight Pathwave Take a look at Automation Platform (TAP) primarily based software program that may sit on a separate Home windows PC or on any Home windows-based instrument in your measurement setup. It is a check administration suite which can be utilized to regulate all {hardware} and software program in your setup, from {hardware} connections and management to hook up with acceptable software program similar to VSA to make one-click measurements.
Along with easier setups, many requirements our bodies together with the European Telecommunications Requirements Institute (ETSI) are working in direction of conformance and compliance testing for radar units which require particular instrument setups for every check. As a result of the KS83200A can management and setup a number of devices, organising your Keysight sign analyzer or sign generator to make measurements is made a lot easier because the instrument setups for all ETSI requirements 3 are built-in, so it’s a one-click setup to allow compliance testing. Under you may see an inventory of a few of the ETSI exams accessible. It easy takes one click on so as to add them to your check plan, after which working the TAP software program automates the instrument setup.
The figures under present how the KS83200A software program provides a transparent diagram of the {hardware} setup, relying on the Keysight automotive radar resolution configuration. You too can see that the software program is able to controlling the era {hardware} together with an AWG, sign generator and radar goal simulator.
Measurement Instance
For extra in-depth info on easy methods to arrange this measurement, please seek advice from the E8740A start-up information. As talked about within the radar era part, there are a number of configurations accessible, all of that are highlighted in nice element within the above configuration information, however for this measurement, we are going to use E8740A-060 which is predicated on the Keysight N9041B UXA collection sign analyzer plus DSOS604A oscilloscope.
The N9041B, has an inside evaluation bandwidth of 1 GHz. Nevertheless, as future radar modules are anticipated to have as much as 4 GHz of bandwidth, this instrument has the aptitude to route this wideband IF sign exterior to an oscilloscope of acceptable bandwidth. The VSA software program can be utilized to regulate the oscilloscope to carry out the measurements.
The measurement instrumentation used on this part consists of, and is grouped as half quantity E8740A-060:
- Keysight N9041B UXA sign analyzer
- Choice-H1G, 1 GHz Evaluation Bandwidth
- Choice-CRW, Wideband (> 5 GHz) IF out connector
- Keysight D/MSOS804A Oscilloscope
- Keysight 89600 collection Vector Sign Analyzer (VSA) software program
- Keysight 89601200C, Primary vector sign evaluation and {hardware} connectivity
- Keysight 89601BHPC, FMCW radar evaluation choice
- Keysight KS83200A Automation Software program for Automotive Radar
The pattern sign to be measured is a repeating FMCW modulation sign sample consisting of a number of repeating linear FM (LFM) up-chirps. The sign contains of a repeating sample of LFM up-chirps deviating from -500 MHz to +500 MHz relative to the middle frequency (1 GHz whole deviation) over a 90 usec time interval. The facility stage stays on continuously, and there’s no time hole between every successive LFM up-chirp incidence.
The principle software program part of this resolution is the highly effective Keysight VSA software program, used together with choice BHP (FMCW radar evaluation choice) which incorporates the measurement algorithms that will probably be used to make measurements on the FMCW alerts.
Abstract and Conclusion
On this utility be aware, now we have mentioned the modulation schemes and applied sciences presently getting used throughout the automotive radar area. We gave an outline of the automotive radar sign era and evaluation options accessible from Keysight and a fast snapshot into the capabilities of the VSA software program. Utilizing VSA together with the Keysight N9041B UXA sign analyzer and S-series oscilloscope ensures that your machine is working accurately, and likewise adheres to the strictest tolerances, giving a number of insights to many sign parameters that may have an effect on the top high quality of the radar machine. Keysight’s patented measurement science allows the efficiency of all of the above-mentioned devices, whether or not used individually or in tandem, guaranteeing your time is spent measuring the parameters of your machine and never the specs of your check gear.
We additionally mentioned the Keysight sign era capabilities and the flexibleness an AWG provides us: broad bandwidth and multi-channel sign era which, when used together with the evaluation resolution and a radar goal simulator, can be utilized for lab-based interference testing utilizing the AWG to create real-world alerts.
Lastly, we spoke concerning the KS83200A software program which can be utilized to regulate all {hardware} and software program in your setup, from {hardware} connections and management to hook up with acceptable software program similar to VSA to make one-click measurements. As well as, many requirements our bodies together with the European Telecommunications Requirements Institute (ETSI) are working in direction of conformance and compliance testing for radar units which require particular instrument setups for every check – these check setups are one-click setups permitting for much less setup time and extra time to check.
Courtesy: Keysight Applied sciences
