Fast and Accurate Spectrum Analysis to 40 GHz

Tektronix Inc.
Beaverton, OR

Many communications systems operate in the mm-wave range in today's market. Satellite equipment, video local multipoint distribution systems, and many military and avionics systems employ frequencies exceeding 26.5 GHz. Radar and line-of-sight communications links operate in the microwave range but have harmonics extending beyond 26.5 GHz. As a result, there is a need for test equipment to address mm-wave frequencies.

Equally important, this test equipment must offer good accuracy due to the fact that high frequency designs require tight tolerances. At millimeter wavelengths, minute variations in design values and physical layout have profound effects on system performance.

The FSEK series microwave spectrum analyzers comprise two flexible, high performance models designed for precision measurements in the mm-wave range. These new models extend the FSE spectrum analyzer line to 40 GHz. The model FSEK20 is a cost-effective production test instrument, while the model FSEK30 is aimed at advanced research and development applications. The new analyzers are designed to meet the needs of commercial, military and aerospace applications.

Features
The FSEK analyzers are synthesizer based and feature a minimum spectrum mode sweep time of 5 ms with a fully synchronized sweep. This fast sweep speed is not at the expense of tuning accuracy. The shortest zero-span sweep time is 100 ns/div, which is ideal for high resolution measurements on pulse edges. Up to 25 sweeps per second allow for rapid and easy alignments and for production applications. This high measurement speed and ease of operation make the analyzers capable of highly complex measurements in the shortest possible time. Figure 1 shows a typical screen display of a 1.9 GHz signal.

The FSEK analyzers feature extremely low noise floors without sacrificing dynamic range. For example, a 1 dB compression point of +10 dBm yields a dynamic range of 100 dB at a resolution bandwidth of 1 MHz. In addition, a wide intermodulation-free dynamic range ensures reliable measurements on highly linear amplifiers and enables detailed analysis of complex broadband signals.

The model FSEK20 analyzer operates from 9 kHz to 40 GHz while the model FSEK30 operates from 20 Hz to 40 GHz. Frequency tuning is synchronous to the reference frequency for each span including full span. As a result, each point on the frequency axis is determined with the accuracy of the internal reference frequency. Thus, when reducing the measurement span for detailed analysis, no center frequency adjustment is required.

The FSEK analyzers offer many convenient test functions, such as four markers and four delta markers; and marker functions for direct measurement of phase noise and noise power density, bandwidths and shape factor, and next minimum or peak. Functions for measurements of channel power, adjacent-channel power and occupied bandwidth are available, as is a frequency counter with selectable resolution. Low noise, and normal and low distortion measurement modes are selectable for low intermodulation and low noise operation. Simultaneous measurements of four active traces are possible as well as split screen capability with independent measurement windows. Level, frequency and user-defined limit lines help to determine pass/fail information, and one button provides a printer or plotter hard copy output.

Despite these comprehensive capabilities, the analyzers feature ease of operation. Basic functions and frequently used help tools can be called up with a single keystroke. A wide variety of evaluation routines and marker functions can be accessed via the internal menus. All test data, scale factors and parameter settings are arranged logically and are easy to find. Setups, traces and graticules are displayed in color. The model FSEK30 is equipped with a large 24 cm color display with 640 x 480 pixel resolution. The analyzers offer uncomplicated logging of results and support a wide variety of printers and plotters. Print files also can be stored on diskette or the internal hard disk.

Applications
The FSEK30 analyzer is tailored for sophisticated engineering applications such as critical phase modulation measurements involving AM-PM conversion. The analyzer's 40 GHz frequency range combined with its optional analog modulation/vector signal analyzer feature (option B7) makes the instrument ideal for detecting and measuring phase distortion, as well as for measuring LO settling time.

The FSEK20 analyzer is aimed at manufacturing test applications, offering fast sweep repetition rates and test result processing. The instrument is fully equipped for general-purpose interface bus-equipped automated operation via external computers. Both analyzers are designed to accept modular options to adapt to a wide range of specific measurement needs.

The instruments can be used to perform intermodulation measurements involving two-tone inputs. These measurements are enhanced by the instruments' wide intermodulation-free dynamic range. Harmonic measurements are facilitated using the instruments' split screen capability. The low noise floor makes measuring low level spurious and harmonics possible, and enables a lower level of phase noise to be detected.

Using the RMS detector, the power of a code-division multiple access signal can be measured without correction factors and adjacent-channel effects can be displayed. The fast sweep time along with gap sweep and pretrigger functions make simultaneous measurements of pulse rise and fall times easy, as shown in Figure 2 . The gated sweep function is indispensable for analyzing time-division multiple access (TDMA) signals. Using this function, the spectrum of burst signals can be investigated without interference caused by switching the signals off and on.

In conjunction with the optional vector signal analyzer, the instruments are capable of demodulating and measuring digitally modulated signals. Figure 3 shows the display of p/4-digital quadrature phase-shift keying (DQPSK) modulation error in the form of a constellation diagram.

In addition, the spectrum analyzers are capable of power ramp measurements on TDMA systems in line with the appropriate system standards, where reference must be made to synchronization sequences in order to establish a time reference. These measurements are not possible using conventional analyzers. The FSEK analyzers are capable of testing analog and dual-mode radio equipment and determining their transient response in frequency and amplitude.

Conclusion
The FSEK series spectrum analyzers are ideal for use in automatic test systems, affording fast processing of results, high accuracy and ease of operation. The instruments are low cost and are equipped with a modular construction that makes them versatile and easy to retrofit. The FSEK spectrum analyzers and optional vector signal analyzer provide universal test capabilities in one unit.

The FSEK series spectrum analyzers are part of the larger FSE family of analyzers, which include models that operate at 3.5, 7 and 26.5 GHz. The entire instrument family provides a combination of RF and microwave spectrum analysis, and universal digital signal demodulation and analysis using the vector signal analyzer option.

The FSEK20 and FSEK30 spectrum analyzers are available eight weeks after receipt of order. US pricing starts at $55,950 and $74,250 for the FSEK20 and FSEK30, respectively. Option B7 (analog demodulation) is priced starting at $17,600. For more information, contact the company's Web site at http://www.tek.com/Measurement.

Acknowledgment
The FSE series spectrum analyzers were developed by Rohde and Schwarz, Munich, Germany, and are marketed and supported in the US and Canada by Tektronix under a strategic alliance formed in 1993.

Tektronix Inc.,
Tektronix Measurement Business Division,
Pittsfield, MA
(800) 426-2200.