I/Q Modulation Generator has 528 MHz Bandwidth for UWB Tests
By Justin Stallings, Rohde & Schwarz

Ultrawideband (UWB) radio transmission technology, which has been in development since the 1960s, has unique capabilities that make it extremely appealing for communications systems, specialized types of radar, tracking systems, and a variety of other applications. One of its defining characteristics is the extremely broad bandwidth over which the signal is transmitted, typically greater than 500 MHz. To satisfy the need for a baseband I/Q signal source that can accommodate this bandwidth, Rohde & Schwarz has introduced the R&S AFQ100B UWB Signal and I/Q Modulation Generator (Figure 1), which has a clock rate of 600 MHz, and features that allow designers to more easily evaluate the performance of UWB-enabled receivers. The R&S AFQ100B complements the company’s R&S AFQ100A I/Q Modulation Generator that has a maximum clock rate of 300 MHz and is widely used to evaluate commercial and military RF and microwave systems.

The R&S AFQ100B has up to 1 Gsample of waveform memory, more than any competitive instrument, which makes it well suited for playing back long signal sequences. It can also equalize the phase and amplitude of external devices such as I/Q modulators to achieve a flat frequency response. Key R&S AFQ100B specifications include a spurious free dynamic range (SFDR) of typically 83 dBc and a typical frequency response flatness of typically 0.1 dB up to 100 MHz I/Q bandwidth. More complete specifications are shown in Table 1.

UWB for USB…and More
UWB systems combine the ability to reliably achieve high data rates over short distances while drawing less current from their power supplies than technologies such as Bluetooth or WiFi. These and other characteristics make UWB appealing as a way to allow the advantages of USB to be delivered via a wireless connection. The obvious benefit is the elimination of cabling between a host (such as a PC) and its peripherals, which is likely to increase its use in transferring large amounts of data (such as video footage and still images) from cameras, camcorders, mobile phones, and media players to a PC or entertainment system. Wireless USB can accommodate the maximum speed of USB 2.0 (480 Mb/s) over a distance between devices up to 3 m and up to 110 Mb/s as far as 10 m. As a result, analysts predict that products equipped with wireless USB will grow from few today to more than 400 million in five years.

Wireless USB is not the only application for which UWB has unique appeal. Since it is inherently resistant to interference and jamming and can provide very accurate information about the location of objects, it is being used by U.S. and other defense forces in radar systems that can peer through walls to identify potential threats and to “see” mines buried in the ground. It is also being used for perimeter detection as well as for asset location tracking, since it can locate an object to within a small area.

The broad bandwidth of the R&S AFQ100B is well suited to serve these aerospace and defense applications, since it can deliver signals with short pulses and short rise and fall times, modulated pulses, or wide, non-linear chirps used by radar systems. The optional R&S AFQ-K6 pulse sequencer software makes it simple to configure pulsed signals and any type of analog or digital modulation as well as importing user-created signals to the R&S AFQ100B. Its accuracy of less than 20 ps when starting several instruments together also makes the R&S AFQ100B the right choice for developing and testing phased-array antennas because large amounts of delay degrade the phase relationship between the various signals.

Another useful feature of the R&S AFQ100B for defense and other high-security applications is its internal removable 160-Gbyte hard drive that allows data and test routines to be removed from the unit.

Designed for Unique UWB Test Needs
To be useful for evaluating the performance of UWB-based components and systems, instruments must have bandwidths greater than the system they are testing. The 600 MHz sampling rate of the R&S AFQ100B makes it well suited for this task. The instrument can operate in two modes. In Mode 1, it functions like the R&S AFQ100A with a user-variable sample rate of 1 kHz to 300 MHz. In the second mode, it provides a fixed 600 MHz sample rate that delivers the bandwidth necessary for evaluating UWB devices. Whether it is operated locally with an external monitor and USB mouse and keyboard, or over a LAN using Windows XP Remote Desktop, the displayed user interface reflects the chosen mode and employs the layout that is becoming standard throughout the company’s portfolio. The approach allows the user to visualize the signal path through the test set-up, modify various parameters, and view their results. “Out-of-limit” and other inappropriate selections are flagged by instrument firmware to keep the user on the right path. Remote control using SCPI commands is also possible. The display for configuring the instrument for tests in compliance with the ECMA-368 UWB PHY and MAC standard is shown in Figure 2.

Broad Versatility
The R&S AFQ100B will often be used as a source for an I/Q modulator, and since the frequency response of I/Q modulators is not linear, the R&S AFQ100B includes the ability to compensate for their phase and amplitude errors using an internal equalizer (available only in Mode 1 operation). The user measures the characteristics of the I/Q modulator and imports them into the R&S AFQ100B. The instrument will correct for them and provide an output that has a virtually flat frequency response. The user can also modify response characteristics to meet his or her preferences in order to evaluate receiver performance. I and Q compensation can also be added for level offset, delay, and gain to minimize effects caused by cables and other external components.

The instrument’s memory depth of 512 Msamples or 1 Gsamples also allows a waveform comprised of multiple segments to be stored in a solid-state (versus slower magnetic) medium, which reduces the time required to switch between different signals. The virtually seamless transition between the different segments of the waveform ensures phase continuity so that the receiver need not be resynchronized. Remote or locally-controlled triggering is available, which is very useful when multisegment waveforms are used.

The R&S AFQ100B can use the company’s free WinIQSIM2 PC simulation software to generate waveforms on a PC in accordance with various wireless standards (for playing back the signal, the appropriate instrument option is needed). Test signals created in MATLAB or other programs can be ported to the instrument as well. In addition to standards such as UMTS and WiMAX, WinIQSIM2 also the ECMA-368 UWB standard on which the most wireless USBs are based. As a result, designers can create standards-based measurement routines in a short time and run them on the R&S AFQ100B.

The R&S AFQ100B can be configured with two types of digital output (in addition to its standard single-ended and differential analog outputs). The first uses the common 68-pin HD-SCSI interface and outputs digital I and Q signals in LVDS format at up to 16-bit resolution. The second output provides digital signals in a multiplexed LVDS data format designed for use with other Rohde & Schwarz instruments. The R&S AFQ100B also provides an IF signal output up to 264 MHz. The digitally-implemented IF allows frequency changes with virtually no delay, which is useful for fast hopping signal environments.

The R&S AFQ100B outputs four independent marker signals in addition to synchronizing the output signal that can be used to start a receiver or to mark a burst in a pulsed signal. For precise adjustments during signal output, the marker outputs can be delayed without interrupting the I/Q output signal. More information can be obtained on our website.

Rohde & Schwarz
www.rohde-schwarz.com
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