Insights > RF + Microwave

Improve Your Signal Generation to Surpass Bandwidth Requirements

2022-09-12  |  6 min read 

 

In today’s rapidly growing wireless environment, wider bandwidth requirements are increasing for diverse applications. Cellular communication is moving from 4G to 5G to enable extreme data throughputs, and satellite communication providers are building networks in space to enable high-speed communications from anywhere. These developments demand higher frequency bands and wider channel bandwidths to obtain the needed data throughput. Engineers need a consistent test system that delivers optimal performance to meet the requirements of these technology developments.


Wide Bandwidth Applications

Exceeding growth for faster data rate applications has triggered the need for new technology systems capable of wide signal bandwidth. Multiple spectrum allocations at higher frequencies can support wider bandwidths that provide a faster data rate, and regulators are setting new standards to address this need.


Satellite and Non-Terrestrial Networks


Satellite communications provide connectivity for television, phone, broadband internet services, and non-terrestrial networks. Satellites operate in a large variety of frequency bands, and the use of each band was determined by international regulations, as shown in Table 1. As the use of Ku and C bands continues to grow, the congested, global focus on the Ka-band for commercial satellite communications is increasing linearly. The International Telecommunication Union (ITU) specifically allocates the 71 to 76 GHz / 81 to 86 GHz segment of the W band to satellite services. These segments are of increasing interest to commercial satellite operators for wider bandwidths. Because increasing channel bandwidth enables higher data rates per client, it also extends the number of channels for higher system capacity; see Table 1.


       Table 1. Satellite frequency applications


       
       
5G New Radio


Moving into 5G New Radio (NR), we have enhanced Mobile Broadband (eMBB) as one of the use cases for this space. It uses new and existing technologies to achieve the anticipated extreme data throughputs, including wider channel bandwidths, carrier aggregation, high modulation density, and multiple antennas. The 5G NR maximum channel bandwidth is 400 MHz for the frequency range (FR2), and the maximum aggregated channel bandwidth (intra-band contiguous) goes up to 1.2 GHz.


Wide Bandwidth Signal Generation


Although increasing signal bandwidth offers an excellent way to achieve faster data rates, it also introduces a new challenge to meet the signal quality requirements at higher frequency ranges. Some examples include channel flatness typically decreasing as channel bandwidth increases or wideband I/Q modulator imperfection resulting in poor modulation quality.
Three common solutions to generate a wide bandwidth signal at high frequencies include:
• Use an arbitrary waveform generator (AWG) to generate baseband I and Q signals. A  vector signal generator (VSG) for upconverting the signals could also improve the frequency.
• Generate an intermediate frequency signal (IF) with a wideband VSG and upconvert the IF signal to the desired frequency with a frequency extender.
• Produce required signals with a fully integrated VSG. 

Table 2. Keysight’s wide bandwidth vector signal generation solutions


Direct IF / RF with DDS Technology


Traditional signal generators use I/Q modulators. However, next-generation VSGs with a direct digital synthesizer (DDS) architecture can generate an IF / RF signal directly from a high-resolution, high sampling rate digital-to-analog converter (DAC). 
In addition, through VSG channel bonding, engineers can combine two channels into a single RF output for up to 5 GHz modulation bandwidth to generate the widest required bandwidth. Figure 1 shows a traditional baseband block diagram with an analog I/Q modulator and a direct IF / RF with DDS technology for multitone signal generation. As shown on the right side of Figure 1, the traditional method creates intermodulation between tones.
The lower panel of Figure 1 shows a direct RF / IR VSG block diagram. It implements the I/Q modulator digitally and uses a high-speed DAC to output an RF / IF signal directly. This architecture eliminates signal impairments caused by the I/Q modulator and improves the signal’s dynamic range, especially for wideband signal generation.


Figure 1. Analog and digital up-conversion method comparison


Summary


As network traffic increases because of rapidly evolving wireless communications systems, a strong demand for increased bandwidth also increases to support next-generation wireless standards and technologies. The need carries on to an accurate and relatable test system that delivers optimal performance to meet the requirements for wide bandwidth test applications.
Keysight’s new VXG signal generation solutions enable the highest signal fidelity for wide bandwidth test applications with advanced DDS technology. The fully integrated, calibrated, and synchronized signal generation helps minimize measurement uncertainty.

Learn more about Keysight’s M9484C VXG Vector Signal Generator.