Abstract:

With the increasing demands for signal transmission rates or resolution in fields such as wireless communication, radar, satellite communication, and optical communication, the modulation formats used have become increasingly complex, and the signal bandwidth has also widened. Modern real-time oscilloscopes, due to advancements in chip and material technology, can provide real-time measurement bandwidths of up to several tens of GHz. Their intuitive time-domain measurements and multi-channel capabilities have made them widely used in ultra-wideband and RF signal measurements. This article introduces typical applications of high-bandwidth real-time oscilloscopes in RF signal measurement, as well as key indicators such as noise floor, spurious-free dynamic range, harmonic distortion, absolute amplitude measurement accuracy, and phase noise when using oscilloscopes for RF measurements.

Every engineer involved in RF or high-speed digital design faces challenges in both frequency domain and time domain testing. For example, engineers engaged in high-speed digital circuit design typically analyze signal waveforms and eye diagrams in the time domain, while also using frequency domain S-parameters to analyze insertion loss in transmission channels, or phase noise metrics to assess clock jitter. Traditionally, analysis of wireless communication, radar, and navigation signals requires frequency domain tests such as spectrum, spurious, and channel suppression. However, with wider signal bandwidths and the application of techniques such as pulse modulation and frequency hopping, time-domain measurement methods can sometimes be more effective.

The performance of modern real-time oscilloscopes has significantly improved compared to over a decade ago, meeting the testing requirements for high-bandwidth and high-precision RF microwave signals. In addition, the triggering and analysis functions of modern real-time oscilloscopes have become richer, the user interface more user-friendly, data transmission rates higher, and multi-channel support capabilities better, allowing high-bandwidth real-time oscilloscopes to play an important role in broadband signal testing.

Intuitiveness of Time-Domain Measurements

A major reason for conducting time-domain measurements of RF signals is their intuitiveness. For instance, the example below shows four different shapes of radar pulse signals, where the carrier frequency and pulse width are similar. If analyzed only in the frequency domain, it can be difficult to infer the time-domain shape of the signals. The different shapes of these four time-domain pulses are crucial for the final convolution processing algorithms and system performance, necessitating precise measurements of pulse parameters in the time domain to ensure they meet system design requirements.

In traditional RF microwave testing, oscilloscopes with lower bandwidths (<1GHz) are also used for time-domain parameter testing. For example, a detector may extract the envelope of an RF signal for parameter testing, or signals may be down-converted for sampling. At this point, the bandwidth requirements for the oscilloscope used are not high since the RF signal has already been filtered out or converted to an intermediate frequency.

However, with the development of communication technologies, the modulation bandwidth of signals has widened. For instance, modern radars may use frequency or phase modulation within their pulses to balance power and distance resolution, and the typical modulation bandwidth of SAR imaging radars can exceed 2GHz. In satellite communications, to achieve miniaturization and increase transmission rates, the crowded C-band and Ku-band are often avoided, opting for the Ka-band, which offers higher spectral efficiency and available bandwidth, with actual modulation bandwidths reaching over 3GHz or even higher. Additionally, the amplitude-frequency characteristic curve of oscilloscopes is not flat from DC to rated bandwidth; it begins to decline significantly after reaching a certain frequency point. Therefore, when selecting a real-time oscilloscope, its bandwidth should exceed the required analysis bandwidth, and the extent of this excess should be determined by the oscilloscope’s actual frequency response curve and the requirements of the signal being measured.

At such high transmission bandwidths, traditional measurement methods using detectors or down-conversion face significant challenges. It is difficult to find a detector or down-converter on the market that can achieve bandwidths over 2GHz while also maintaining ideal amplitude-frequency/phase-frequency characteristics, leading to severe distortion in test results.

Furthermore, if demodulation of internal modulation information in radar pulses or satellite communication signals is required, very high real-time bandwidth is also necessary. Traditional spectrum analyzers have high measurement accuracy and frequency range, but their real-time analysis bandwidth currently does not reach above GHz. Therefore, the most commonly used method for analyzing and demodulating broadband signals over GHz is to utilize wideband oscilloscopes or high-speed data acquisition systems.

Traditional oscilloscopes, due to their lower bandwidth, cannot directly capture high-frequency RF signals, so their applications in the RF microwave field are limited to intermediate frequency or control signal testing. However, with advancements in chip, material, and packaging technologies, modern real-time oscilloscopes have seen significant improvements in bandwidth, sampling rate, storage depth, noise floor, jitter, and other performance indicators.

For example, indium phosphide (InP) material has become quite popular both internationally and domestically in recent years. Compared to traditional SiGe or GaAs materials, InP offers better electrical performance, providing higher saturation electron velocity, lower surface recombination velocity, and higher electrical insulation strength. During the adoption of new materials, a series of process issues must also be addressed. For instance, while InP has excellent high-frequency characteristics, using traditional aluminum substrates can lead to issues with inconsistent thermal expansion coefficients and heat dissipation efficiency. Aluminum nitride (AlN) is a new ceramic substrate material that has thermal properties closer to InP and better heat dissipation characteristics, but AlN is expensive and hard, requiring laser etching for processing.

With the application of new materials and technologies, modern real-time oscilloscopes can achieve hardware bandwidths exceeding 60GHz. Furthermore, due to the excellent characteristics of indium phosphide (InP) material, the frequency response of oscilloscopes becomes flatter and the noise floor is lower, while its lower power consumption enhances product reliability.

In addition to providing excellent high-bandwidth performance, InP materials also have higher reverse breakdown voltages, allowing oscilloscopes designed with InP materials to achieve input ranges of up to 8V, equivalent to over 20dBm, greatly enhancing practicality and reliability.

To ensure high real-time bandwidth, according to Nyquist’s theorem, the sampling rate of the ADC behind the amplifier must be at least twice the bandwidth (in engineering practice, it is ensured to be over 2.5 times). Currently, there are no single-chip ADCs on the market that can achieve such high sampling rates, so high-bandwidth real-time oscilloscopes typically use ADC stitching technology.

There are two typical methods of ADC stitching: on-chip stitching and off-chip stitching. On-chip stitching integrates multiple ADC cores within a single chip. A typical example is the 40G/s sampling rate 10-bit ADC chip used in Keysight’s S-series oscilloscopes, which first achieved 10-bit resolution within an 8GHz bandwidth range in the industry. The advantage of on-chip stitching is that consistency and delay control between channels can be managed very well, but it poses significant challenges in terms of integration and process.

Off-chip stitching refers to the use of multiple ADC chips on a PCB. A typical example of off-chip stitching is Keysight’s Z-series oscilloscopes, which use eight 20G/s sampling rate ADCs to achieve a sampling rate of 160G/s, ensuring hardware bandwidths of up to 63GHz. Off-chip stitching requires excellent consistency in bias and gain between the chips and precise control of signal and sampling clock delays on the PCB. Therefore, the front-end chips of Z-series oscilloscopes use sample-and-hold technology before signal distribution and analog-to-digital conversion, significantly improving the margin against PCB trace errors and jitter.

Thanks to the rapid advancements in bandwidth and sampling rate brought about by chip, material, and process technologies, wideband real-time oscilloscopes have begun to play a critical role in RF signal testing. Below are some typical applications.

The performance improvements of real-time oscilloscopes allow their bandwidth to directly cover RF, microwave, and even millimeter-wave frequency bands, enabling direct capture and analysis of the time-domain waveforms of signal carriers. This allows for clear observation of the pulse envelope of the signal and the time-domain waveform of the carrier signal within the pulse envelope, making time-domain parameter testing simpler and more intuitive. Since there is no need to down-convert the signal for sampling, the testing system also becomes simpler, thereby avoiding additional signal distortion due to suboptimal down-converter performance.

Furthermore, the time-gate function of the oscilloscope can be used to amplify or perform FFT transformations on specific regions of an RF signal. The image below shows FFT transformation results for two different time windows selected from a segment of RF pulse, clearly displaying the variations in signal spectrum within different time window ranges.

For radar and other pulse-modulated signals, key time-domain parameters such as pulse width, rise time, duty cycle, and repetition frequency are critical. According to the IEEE Std 181 specification, the definitions of some key pulse parameters are illustrated below.

Once a wideband oscilloscope has captured the RF pulse, it can utilize built-in mathematical functions to create a mathematical detector. The black curve in the image below represents the envelope signal extracted from the original signal using the mathematical detector. Once the envelope waveform is obtained, basic pulse parameter testing can be performed using the oscilloscope’s measurement functionality.

Moreover, the oscilloscope’s FFT function can be employed to obtain the frequency spectrum distribution of the signal, and jitter analysis software can be utilized to capture the frequency or phase variations of the internal signal over time, displaying these results together. The image below shows a Chirp radar pulse’s time-domain waveform, frequency/phase variation waveform, and frequency spectrum results. Through the comprehensive display and analysis of these waveforms, the varying characteristics of the radar signal can be visually observed, allowing for simple parameter measurements.

In testing radar and other pulse signals, the ability to capture a sufficient number of continuous pulses for statistical analysis is also crucial. For instance, if a search radar has a pulse repetition period of 5ms and we want to capture 1000 continuous pulses, we need to record data for 5 seconds. If the oscilloscope’s sampling rate is 80G/s, the memory depth required for 5 seconds of data recording would be 80G/s * 5s = 400G samples, which is nearly impossible to achieve.

To address this issue, modern high-bandwidth oscilloscopes support segmented memory modes. The segmented memory mode divides the oscilloscope’s continuous memory space into multiple segments, capturing data for a short time each time a trigger occurs until enough segments are recorded. Many radar pulses have narrow widths, and when testing radar transmitter performance, if we are only interested in the signal during the brief period of pulse transmission, using segmented storage can more effectively utilize the oscilloscope’s memory.

In addition to directly measuring the basic parameters of radar pulses in the oscilloscope, more powerful vector signal analysis software can also be used. The image below shows an example of demodulation analysis of ultra-wideband Chirp radar signals using Keysight’s 89601B vector signal analysis software in conjunction with an oscilloscope. The displayed results include the frequency spectrum, time-domain power envelope, and frequency variation curve over time. The signal under test is generated by the M8195A ultra-wideband arbitrary waveform generator, with a Chirp pulse width of 2us and a frequency range from 1GHz to 19GHz, resulting in an overall signal bandwidth of 18GHz! This fully demonstrates the advantages of real-time oscilloscope bandwidth.

More stringent radar testing does not merely measure basic parameters such as pulse width and modulation bandwidth. For instance, due to insufficient bandwidth of components or suboptimal frequency response characteristics, various frequency components of the Chirp pulse may experience power variations, leading to droop and ripple phenomena on the pulse power envelope. Therefore, rigorous radar performance testing also requires measuring parameters such as peak power, average power, peak-to-average ratio, droop, ripple, frequency variation range, linearity, and changes in frequency and phase between multiple pulses, or analyzing the variation curves and histogram distributions of parameters over time. These more complex tests can be accomplished using the BHQ radar pulse measurement option in the 89601B software. This testing software also supports the oscilloscope’s segmented memory mode, allowing for the capture of multiple continuous pulses for statistical analysis, as illustrated in the example below.

In addition to radar pulse analysis, the oscilloscope’s jitter analysis software or vector signal analysis software can also be used to analyze ultra-wideband frequency-modulated signals. The image below shows the frequency spectrum, time domain, and frequency modulation pattern analysis results of a signal modulated within a bandwidth of 7GHz.

In fields such as satellite communications or navigation, it is necessary to test the absolute delay of RF output (which may be RF or Ku/Ka band signals) relative to internal timing signals (1pps or 100pps signals) and make corrections. This requires at least a 2-channel wideband oscilloscope to simultaneously capture the timing signal and RF output for precise and repeatable measurements.

The image below shows the 1pps timing signal (blue waveform) and QPSK modulated RF output signal (purple waveform) captured by the oscilloscope. The timing signal used for triggering indicates the moment the RF signal power reaches its first zero crossing relative to the timing signal, which is the system delay to be measured. If measured manually using cursors, it is difficult to accurately pinpoint the appropriate power zero crossing position. Utilizing the previously mentioned digital detection function, the power envelope of the RF signal can be detected and amplified (as shown by the gray waveform), and the oscilloscope’s measurement functionality can be employed to measure the time of the minimum point of the power envelope (Tmin), achieving precise testing of the delay of the satellite transponder or modulator. Through multiple automatic tests of the zero crossing moments, long-term statistics can also be performed to analyze the range of delay variations and jitter.

In the WLAN, satellite communication, and optical communication fields, performance testing and demodulation analysis may be required for very high bandwidth signals (>500MHz), which places high demands on the bandwidth and channel count of measuring instruments. For instance, in optical fiber backbone transmission networks, single-wavelength 100Gbps signal transmission has been achieved, utilizing technology that modulates two 25Gbps signals onto a single polarization state of a laser, and then combines them with another two 25Gbps signals modulated in the same manner to achieve 100Gbps signal transmission. In the development of next-generation 200Gbps or 400Gbps technologies, even higher baud rates and higher-order modulation techniques such as 16QAM, 64QAM, or OFDM may be employed, all of which impose very high requirements on the bandwidth and performance of measuring instruments.

The image below shows Keysight’s 100G/400G optical coherent communication analyzer N4391A: the lower half of the instrument is a coherent optical communication demodulator used to decompose the four I/Q signals from the input signal’s two polarization states into electrical signals, with each channel supporting signal baud rates of up to 126Gbaud; the upper half is a high-bandwidth Z-series oscilloscope, which can achieve 4-channel measurements with bandwidths of 33GHz or 2-channel measurements with bandwidths of 63GHz. The oscilloscope runs the 89601B vector signal analysis software, enabling polarization alignment, dispersion compensation, and demodulation and simultaneous display of the four I/Q signals.

The image below displays the results of demodulation analysis of ultra-wideband signals performed using the oscilloscope. The signal under test is a 32Gbaud 16QAM modulated signal generated by the M8195A. Since each symbol in the 16QAM modulation format can transmit 4 bits of effective data, the actual data transmission rate reaches 128Gbps. Through wideband frequency response correction and pre-distortion compensation, a signal-to-noise ratio exceeding 20dB and an EVM (Error Vector Magnitude) of <4% were achieved.

In MIMO (Multiple-input and Multiple-output), phased array, and scientific research scenarios, simultaneous measurements of more than four high-speed signals are often required. To meet this application, modern high-bandwidth oscilloscopes provide support for multi-channel measurements in both hardware and software. Keysight’s N8834A multi-channel oscilloscope software supports multi-channel oscilloscope solutions from the Infiniium 9000, 90000, S, V, and Z series.

The image below shows a multi-channel cascading solution based on the Z-series oscilloscope and the multi-channel measurement software within the oscilloscope, which currently supports cascading up to 10 oscilloscopes, providing 20 synchronized measurement channels with bandwidths up to 63GHz or 40 channels with bandwidths of 33GHz. Through precise delay and jitter calibration, inter-channel jitter can be controlled within 150fs (rms).

Many RF products not only need to comply with EMC specifications, but EMI phenomena also affect product performance, particularly in terms of noise and jitter. If not carefully handled, this may impair the functionality of the entire circuit. Therefore, many circuit design guidelines include protective frequency bands, reference ground planes, loops, power control feedback, and spread-spectrum clocks, all aimed at minimizing EMI effects.

Common causes of EMI issues include switching power supplies, power filtering, ground impedance, LCD screens, static from metal shielding enclosures, poor cable shielding, internal coupling of routing paths, parasitic parameters of components, and incomplete signal loops. A common analysis method for EMI issues is to use a spectrum analyzer receiver. However, many engineers may not be aware that oscilloscopes can also be used for EMI pre-testing. Previously, there were concerns that oscilloscopes generally use 8-bit ADCs, resulting in poor amplitude and phase frequency response. However, with the introduction of 10-bit ADCs in the Infiniium S series oscilloscopes within the 500MHz to 8GHz bandwidth and the V series reducing the noise floor to very low levels within the 8GHz to 33GHz bandwidth, oscilloscopes have gained many functions for EMI pre-testing, including frequency domain templates, near-field probes, simultaneous analysis of up to 8 FFTs, arbitrary position triggering, and simultaneous analysis of analog, digital, and serial signals.

From the typical applications of oscilloscopes in RF testing presented earlier, it is evident that due to technological advancements, the high bandwidth and multi-channel advantages of oscilloscopes are very suitable for various complex ultra-wideband applications, while their comprehensive analysis capabilities in both time and frequency domains have improved measurement intuitiveness.

However, when using oscilloscopes for RF signal testing, we must have certain concerns regarding their accuracy and performance. Although real-time oscilloscopes have very high sampling rates, they generally use 8-bit ADCs, resulting in significant quantization errors and noise floors. Moreover, traditional oscilloscopes only provide bandwidth, sampling rate, and storage depth indicators, with relatively few reference performance indicators in the frequency domain. Therefore, we will analyze some actual tests to understand the RF performance indicators of oscilloscopes.

The noise floor is a very important indicator for measuring instruments, as it affects the signal-to-noise ratio of measurement results and the ability to measure small signals. Traditionally, oscilloscopes have been considered to have high noise floors, making them unsuitable for small signal measurements; however, this is not entirely true, as the main reason lies in the different definitions of noise floor across instruments.

The primary sources of noise floor are thermal noise and noise introduced by the front-end amplifier, both of which are typically approximately proportional to bandwidth. For example, the calculation formula for thermal noise shows that noise power is linearly related to bandwidth.

As a broadband measurement instrument, the noise floor indicator of an oscilloscope reflects the total noise across the entire bandwidth range and is also approximately proportional to bandwidth.

For example, the left side of the image below shows the noise floor indicators provided in the manual for Keysight’s S-series oscilloscopes. At a 50mv/div range, the noise floor of the 4GHz bandwidth S-404 oscilloscope is 768uVrms, which is approximately double that of the 1GHz bandwidth S-104 oscilloscope at the same range, which has a noise floor of 456uVrms. Since power is proportional to the square of voltage, the noise power of the 4GHz oscilloscope is four times that of the 1GHz oscilloscope under the same conditions, corresponding to the bandwidth ratio.

Because the noise floor is approximately proportional to bandwidth, wideband oscilloscopes will have larger noise floors than narrowband ones. To make a fair comparison, we can normalize the noise floor of oscilloscopes at different ranges to per unit Hz, which is also the method used to describe noise floor in RF instruments like spectrum analyzers (DANL – Displayed Average Noise Level).

For instance, at a 50mv range, the full-scale of the oscilloscope is 8 divisions equivalent to 400mV, corresponding to -4dBm full scale. For an 8GHz S-804A oscilloscope, its total noise floor within the 8GHz bandwidth is 1.4mVrms, equivalent to -44dBm, and normalizing it to per unit Hz gives a noise floor of -143dBm/Hz. In smaller ranges, the S-series oscilloscopes can achieve noise floors as low as -158dBm/Hz, which is better than most spectrum analyzers when the preamplifier is not turned on. Even when the preamplifier is turned on, many spectrum analyzers’ DANL indicators are only a few dB better than those of the S-series oscilloscopes.

Thus, after normalizing to per unit Hz, the noise floor of the oscilloscope has already surpassed that of most spectrum analyzers when the preamplifier is not turned on, indicating that this is a fairly good indicator.

Since noise is proportional to bandwidth, if the signal bandwidth is concentrated within a specific frequency range, unnecessary out-of-band noise can be filtered out using appropriate digital filtering techniques to improve the signal-to-noise ratio. For example, many oscilloscopes have a digital bandwidth adjustment function, which is a method to reduce the oscilloscope’s own noise floor.

In RF testing, besides the noise floor, the spurious-free dynamic range (SFDR) is also very important, as it determines the minimum signal energy that can be distinguished in the presence of large signals. For oscilloscopes, the main source of spurious is due to the imperfections caused by ADC stitching. Taking two ADCs as an example, if the phase of the sampling clock is not controlled to be precisely 180 degrees, it may cause signal distortion, resulting in spurious signals appearing in the spectrum at intervals corresponding to the stitching frequency. If distortion is severe, even the highest sampling rates cannot guarantee the authenticity of the captured signals.

For high-bandwidth oscilloscopes, whether using on-chip or off-chip stitching, spurious caused by stitching imperfections objectively exists, and the key factor is the magnitude of the spurious energy. For example, Keysight’s S-series oscilloscopes use a single 40G/s ADC chip, with specialized processes optimizing clock distribution and sample-and-hold circuits to ensure good consistency. The image below shows the frequency spectrum of a 1GHz signal generated by Keysight’s E8267D signal source, filtered to remove harmonics. It can be seen that besides the second and third harmonic distortions, the spurious indicator can reach -75dBc, equivalent to the level of a mid-range spectrum analyzer.

Harmonic distortion is also an important indicator for measuring the fidelity of the measured signal. For oscilloscopes, to ensure high sampling rates, the bit depth of the ADCs (8bit or 10bit) is significantly lower than that of the 14bit ADCs used in spectrum analyzers. Harmonic distortion primarily arises from quantization noise of the ADC, typically represented by second and third harmonic distortions, with the third harmonic usually having greater energy. This differs from the second harmonic distortion caused by mixers in spectrum analyzers.

In the previous test results, the second harmonic distortion was approximately -65dBc, which is somewhat inferior to the average spectrum analyzer. The third harmonic distortion was approximately -49dBc, which is far worse than that of most spectrum analyzers. Therefore, if users are concerned about harmonic distortion metrics, such as in the nonlinear testing of amplifiers, using an oscilloscope may not be the best choice.

Fortunately, harmonic distortions typically occur out-of-band, and can easily be filtered out through simple mathematical filtering processes. Thus, in some applications of wideband signal demodulation, the impact of harmonic distortion on the final demodulation results is not significant due to the measurement algorithms incorporating mathematical filters.

Absolute amplitude accuracy affects the accuracy of power measurements at specific frequency points. For oscilloscopes, the absolute amplitude accuracy indicator = DC amplitude measurement accuracy + amplitude-frequency response. Therefore, both components need to be analyzed separately.

DC amplitude measurement accuracy refers to the nominal dual-cursor measurement accuracy of the oscilloscope, which consists of DC gain error and vertical resolution (as shown in the image below, which presents the DC measurement accuracy indicators for Keysight’s S-series oscilloscopes). For real-time oscilloscopes, the DC gain accuracy is generally 2% of full scale, and the resolution is related to the bit depth of the ADC used. If a 10-bit ADC is used, this corresponds to 1/1024 of full scale. Thus, the DC amplitude accuracy of real-time oscilloscopes is approximately ±0.2dB.

As for amplitude-frequency response, traditionally, the amplitude-frequency response of broadband devices has not been particularly good. However, modern high-performance oscilloscopes undergo frequency response calibration and compensation during manufacturing, resulting in very flat amplitude-frequency response curves. The image below shows the amplitude-frequency response curve of Keysight’s 8GHz bandwidth S-series oscilloscope, demonstrating very good in-band flatness, with fluctuations not exceeding ±0.5dB within 7.5GHz.

Overall, the absolute amplitude measurement accuracy of the S-series oscilloscopes within 7.5GHz can be controlled at approximately ±1dB, which is comparable to the indicators of most mid-range spectrum analyzers. The Keysight V-series oscilloscopes can achieve ±0.5dB absolute amplitude accuracy within a 30GHz range, exceeding the indicators of most high-end spectrum analyzers.

The phase noise of measuring instruments reflects the level of low-frequency noise when testing a pure sine wave. In applications such as radar, it affects the ability to resolve Doppler frequency shifts for slow target recognition. The frequency domain integral of phase noise corresponds to jitter in the time domain. For oscilloscopes, poor phase noise or excessive jitter can introduce additional noise during RF signal sampling, degrading effective bit depth.

Traditionally, oscilloscopes did not focus on sampling clock jitter or phase noise. However, with increasing sampling rates of oscilloscopes and the need to enhance RF testing performance, modern digital oscilloscopes such as Keysight’s S, V, Z series have optimized their clock circuits, even employing classic microwave signal source designs like those in the E8267D, significantly improving phase noise metrics. The image below shows the phase noise curve of the S oscilloscope at a 1GHz carrier frequency, with the RBW set to 750Hz. At a 100kHz offset from the center frequency, the noise energy is approximately -92dBm, normalized to unit Hz energy of about -120dBc/Hz, surpassing most mid-range spectrum analyzers’ phase noise indicators. Even higher-performing V-series oscilloscopes can achieve phase noise metrics of approximately -130dBc/Hz at 100kHz offset, exceeding the corresponding indicators of most mid-range to high-end spectrum analyzers.

From the previous introduction, it can be seen that modern high-performance real-time oscilloscopes, despite being limited by ADC bit depth leading to significantly poorer harmonic distortion metrics, can achieve spurious-free dynamic ranges comparable to mid-range spectrum analyzers, while their noise floor, in-band flatness, absolute amplitude accuracy, and phase noise metrics can be similar to those of mid- to high-end spectrum analyzers.

Moreover, to meet RF testing requirements, modern high-performance oscilloscopes not only provide traditional time-domain indicators but also begin to specify RF metrics to adapt to the usage habits of RF users. The table below presents typical RF indicators provided in Keysight’s V-series oscilloscopes.

Of course, due to different working principles, real-time oscilloscopes still have limitations when performing frequency domain analysis. For instance, at particularly small RBW settings (<1KHz), the waveform update speed will significantly slow down due to the need to collect large amounts of data for FFT calculations, making them unsuitable for narrowband signal measurements.

It is precisely because of the clear high bandwidth, multi-channel advantages, and powerful time-domain measurement capabilities of real-time oscilloscopes, combined with improved RF performance indicators, that they are beginning to play an increasingly important role in the measurement of ultra-wideband RF signals, comprehensive time-frequency domain analyses, and multi-channel measurements.