For many customers who need voice and data access, mobile wireless communications are likely now a need rather than a luxury. The fifth generation (5G) of cellular wireless has emerged swiftly from analog Advanced Mobile Phone Service (AMPS) networks, with transmissions stretching from the RF/microwave spectrum deep into the millimeter-wave (mmWave) frequency range from 24 GHz to above 60 GHz. Frequency channels are set aside for 5G use globally with the expectation that those channels will only be used by 5G signals. Dropped calls and sluggish data rates can occur when the channels are not exclusive because of interference caused by the extra signal energy. Fortunately, by performing occupied bandwidth (OBW) measurements, a spectrum analyzer can assist in locating the interference, even at mmWave frequencies.
With 5G networks facing a hurdle compared to past generations of two different spectral regions: below 6 GHz and at mmWave frequencies, cellular telephone antenna towers seek to deliver uniform signal distribution to an increasing number of global customers. It is challenging to distribute the signal energy from the towers uniformly over the cell site due to some downward scatter and signal absorption. Signal energy is also directed toward the horizon. For effective mmWave frequency coverage, many smaller 5G base stations are needed due to the shorter propagation distances of the higher-frequency mmWave signals compared to the longer-wavelength, lower-frequency signals.
Advanced antenna technologies, like the use of active phased-array antennas similar to those found in military radar systems, produce directional signal beams that can be actively guided to users, but 5G networks, with their constantly growing user bases, need dense signal environments spanning wide signal spectrums. And interference can make it difficult to receive a 5G base station’s signal with accuracy. In the bandwidths that affect 5G system designers, service providers, and users, OBW measurements with the right spectrum analyzer show the total integrated signal energy as well as any interfering signals that are strong enough to cause worry.
Advanced antenna technologies, like the use of active phased-array antennas similar to those found in military radar systems, produce directional signal beams that can be actively guided to users, but 5G networks, with their constantly growing user bases, need dense signal environments spanning wide signal spectrums. And interference can make it difficult to receive a 5G base station’s signal with accuracy. In the bandwidths that affect 5G system designers, service providers, and users, OBW measurements with the right spectrum analyzer show the total integrated signal energy as well as any interfering signals that are strong enough to cause worry. Finding the top and lower frequency limits of the range in which the signal power is contained is the goal of the measurements. This requires figuring out the lower and upper frequencies of the range where the measured power is 0.5% of the overall power for the frequency range, where 99% of the signal power is detected.
Taking a Spectrum Survey
It is important to match the equipment’s capabilities to the limitations of the OBW measurements when choosing a spectrum analyzer for OBW testing. Due to the vast measurement bandwidth required for 5G testing—basically from almost DC through 60 GHz and higher—an analyzer’s frequency range and amplitude range are suitable places to start for 5G OBW measurements. An appropriate analyzer should have both the sensitivity to identify low-power signals at the edge of a 5G base station’s coverage area and an amplitude measurement range that can withstand the stronger signals (more than 1 W or +30 dBm) near to the base station. Low spurious and single-sideband (SSB) phase-noise levels allow for the detection and measurement of low 5G signal levels, depending on the sensitivity of the equipment in question (as a function of a measurement antenna and any attached attenuation). The spectrum analyzer’s acquisition bandwidth and sweep rates will also explain how rapidly and efficiently it can scan across a targeted frequency range, such as a 5G transmission channel.
Multiple-signal measurement capability is a useful equipment feature for OBW measurements in crowded signal situations and in 5G coverage areas shared by several base stations. It’s crucial to keep in mind that an equipment’s SSB phase noise is a function of the carrier frequency and the offset from the carrier frequency when comparing spectrum analyzers as potential candidates for 5G OBW measurements. Low phase noise is crucial for discriminating many signals in the same frequency band, especially for the demanding test requirements for 5G mmWave communications in coverage areas with numerous closely spaced tiny base stations. The SSB phase noise normally increases with increasing carrier frequency and reduces with increasing offset from the carrier when comparing analyzers for low noise. The same carrier frequency and offset should be used for all device comparisons.
Larger, rack-mount spectrum analyzers might mechanically offer better performance levels for testing indoors, but they lack the portability of a battery-powered portable spectrum analyzer for drive-by testing in a 5G coverage area. For OBW testing of communications channels, signals with various modulation formats, including frequency-division-duplex (FDD) and time-division-duplex (TDD) formats for 5G, are used to evaluate the total integrated signal strength within a designated frequency band. Therefore, any OBW measurements need demodulation and testing tools, like real-time spectrum analyzers, to capture the power levels of time-varying signals (RSAs).
Observing Cases
Spectrum analyzers offer the means of not only assessing the channel characteristics of installed transceiver hardware but also testing for the existence of interference within the same operational bandwidth when 5G infrastructure is being built. Higher mmWave frequency bands are sensitive to higher-order harmonic noise from lower-frequency sources, even if higher amounts of interference are anticipated at sub-6-GHz frequencies. Wide bandwidth and high-sensitivity spectrum analyzers are effective tools for improving 5G performance at sub-6 GHz and mmWave bands. As an illustration, the Tektronix RSA607A is a small real-time spectrum analyzer (RSA) for laboratories that can record slices of bandwidth 40 MHz wide from 9 kHz to 7.5 GHz.It features a large dynamic range and minimal phase noise and spurious levels required for excellent sensitivity. A high-speed 14-b analog-to-digital converter (ADC) that digitizes received signals at a rate of 112 MSamples/s provides the measuring power for the device.
The Anritsu Co MS2720T portable spectrum analyzer is available with frequency coverage ranging from 9 kHz to 43 GHz and can even contain tracking generators up to 20 GHz in that small housing. It is useful when mobility is required. To assess when signal leakage from closely spaced 5G channels is excessive, it may conduct on-site OBW testing and companion neighboring channel power measurements. The small yet functional device features a three-hour battery life and an integrated power meter with USB power sensors that are available for power measurements up to 26 GHz.
The Rohde & Schwarz FSVR30 can serve as an RSA, a signal and spectrum analyzer, and a spectrum analyzer for spectrum analysis up to 30 GHz. It can capture bandwidths as large as 40 MHz and is well-equipped with sweep and Fast Fourier Transform (FFT) filters for separating signals of interest across scanned frequency ranges (acquisition bandwidth). The Rohde & Schwarz FSW85 signal and spectrum analyzer have an AC-coupled frequency range of 10 MHz to 85 GHz and a DC-coupled range of 2 Hz to 85 GHz for higher-frequency OBW measurements. The measurement range can be increased even further, to 90 GHz, by using an optional YIG filter and turning the filter off.
With available frequency ranges of 2 Hz to 8.4 GHz, 2 Hz to 13.6 GHz, 2 Hz to 26.5 GHz, 2 Hz to 44 GHz, and 2 Hz to 50 GHz, as well as optional frequency extenders up to 110 GHz, the Keysight N9040B is a rack-mountable signal analyzer that is LXI class certified. The standard analysis bandwidth for this powerful analyzer is 25 MHz, and it is also equipped with swept and FFT filters. However, there are options that can bring the analysis bandwidth all the way up to 1 GHz. This analyzer can be fitted with an optional preamplifier with upper-frequency restrictions that match any of the analyzer frequency variants if signal sensitivity is a problem. The Keysight Technologies N9961A is one of its FieldFox analyzers for mobile, portable spectrum analysis, with a measuring range of 9 kHz to 44 GHz.
These are just a few of the Spectrum Analyzers that you have to choose from. By contrasting the equipment’s capabilities with the constraints of the occupied bandwidth measurements you require, you may choose which Spectrum Analyzer is best for your purposes. Visit the US Power And Test Equipment website for more details on these as well as to look at a selection of equipment from various manufacturers that are offered for sale or rental.
