Improvements Propel Peak Power Meter

May 13, 2005
A host of analog and digital improvements bring new capabilities to a proven and popular peak and average power measurement instrument.

Consider the challenge of improving a proven performer, the 4500A peak power meter from Boonton Electronics (Parsippany, NJ). That was the task facing the popular instrument's design team, which responded with the new model 4500B after incorporating both analog and digital refinements. The firm's latest instrument brings new test and display capabilities to continuous-wave (CW), modulated-signal, and peak power measurements from 30 MHz to 40 GHz.

Since most modern microwave test instruments represent a blend of analog and digital hardware as well as dedicated software, it is not surprising to find improvements in all three areas of the 4500B. The peak power meter features an improved analog input section designed to provide faster rise times with pulsed signals and flatter overall amplitude response.

The basic architecture of the 4500B includes detectors followed by wide-dynamic-range logarithmic amplifiers capable of a better than 60-dB instantaneous range. For example, the 4500B can measure power levels on pulsed and modulated signals from −40 to +20 dBm and on continuous-wave (CW) signals from −50 to +20 dBm, depending on the sensor connected to the peak power meter. The 4500B employs logamps rather than switching gain stages in order to avoid the variations in bandwidth that are associated with gain-switching architectures, especially with low-level signals.

To provide a strong measure of confidence in its measurements, the 4500B features an integrated precision 1.024-GHz calibration source traceable to the National Institute of Science and Technology (NIST). The source provides well-characterized output levels from −40 to +20 dBm in either CW or pulsed mode of operation with 0.1-dB resolution, allowing operators to quickly verify the performance of the 4500B with both CW and pulsed signals. Using an RF amplitude sweep to permit user calibration of sensor linearity over its full dynamic range avoids the pitfalls of the more traditional single-point RF or DC substitution techniques.

Existing sensors for the 4500B are available with instantaneous measurement bandwidth of 25 MHz over frequency ranges as wide as 0.1 to 18.0 GHz and 0.1 to 40.0 GHz. A new sensor series has also been developed for use with the 4500B, capable of 35-MHz measurement bandwidth at frequencies to 18 and 40 GHz. The 4500B peak power meter is actually capable of making measurements over an instantaneous bandwidth of 100 MHz, although sensors with that capability are not yet available.

The 4500B (Fig. 1) provides 250,000 samples of signal capture memory per channel (compared to 4000 samples per channel in the 4500A version), with simultaneous sampling on two signal channels and two trigger channels. The maximum sampling rate is 50 MSamples/s. The 4500B benefits from a fully integrated dual trigger system that is actually two hardware power meters in a single instrument. Each signal channel and trigger channel is powered by a 32-b floating-point digital signal processor (DSP), allowing fully independent measurements with almost nonexistent crosstalk between channels and between trigger and measurement channel. A powerful field-programmable gate array (FPGA) supports the dual DSPs by manipulating captured samples into the many statistical formats offered by the 4500B.

The 4500B provides much of the triggering functions associated with a digital oscilloscope, while returning test results on power and voltage. The instrument can measure peak and average power levels as well as pulsed power. It can also measure a host of pulse parameters, including rise time, fall time, overshoot, pulse width, pulse period, and duty cycle. Because the peak power meter is also a Pentium-grade computer (Windows XP operating system) with dedicated DSPs and FPGA, it can also perform statistical analysis on complex modulated signals, such as code-division-multiple-access (CDMA) signals. CDMA signals are pseudorandom in nature, appearing much like noise, with periodic power peaks that occur over long time periods. By continuously acquiring as many as 25 million power readings per second on a measurement channel, the 4500B can form histograms which are then presented as cumulative distribution functions (CDFs) or complementary cumulative distribution functions (CCDFs) to show the statistical occurrence of different power levels. The 4500B can also provide a close approximation of a probability density function (PDF). Statistical functions are displayed in a decimating mode that instantly shows the effects of tuning a circuit on the 4500B's screen (Fig. 2).

The 4500B presents test results with a new split-screen function that can simultaneously reveal statistical-domain and time-domain information, especially useful when examining pulsed or modulated signals. Conventional instruments require an operator to switch between domains. Captured signals and test results are clearly visible on a new 8.4-in. color liquid-crystal-display (LCD) screen with 640 × 480-pixel resolution. The powerful display allows operators to color code each menu and trace, to simplify viewing of multiple traces. Built-in marker functions help to identify a power or voltage level at a particular point in a trace or pulse (Fig. 3). In addition to its built-in display screen, the 4500B provides a VGA port for driving an external color monitor.

The 4500B has four operating modes suited for measurements on different types of signals: modulated mode (for modulated or CW signals), (triggered) pulse mode, standard statistical mode, and gated statistical mode (Fig. 4). Once the instrument enters the statistical mode, an operator can choose between standard statistical mode and gated statistical mode (to provide measurements on specific intervals based on defined time gates). The triggering capabilities in pulse mode are extensive, with a timebase range of 5 ns/div to 1 hr/div with timebase accuracy of 0.01 percent and timebase resolution of 100 ps. Pretrigger delays can be set to 4 ms for timebase settings from 5 ns/div to 500 ns/div, 4000 div for timebase settings from 1 µs/div to 10 ms/div and as much as 40 seconds for timebase settings from 20 ms/div to 1 hr/div. Post-trigger delays can be set as long as 100 ms for timebase settings of 5 ns/div to 500 ns/div, as long as 4000 div for timebase settings of 1 µs/div to 10 ms/div, and as long as 100 seconds for timebase settings of 20 ms/div to 1 hr/div.

The 4500B peak power meter is a powerful measurement tools for both commercial and military applications, including telecommunications systems such as cellular communications, WiMAX, and cable-television (CATV) systems, and military systems including radar and identify-friend-or-foe (IFF) systems. The instrument is well equipped with communications ports, including parallel, serial, GPIB, and Ethernet ports, along with a Universal Serial Bus (USB) port on the front panel for data storage (replacing the nearly obsolete floppy disk drive on the 4500A). Boonton Electronics (a Wireless Telecom Group Co.), 25 Eastmans Rd., Parsippany, NJ 07054; (973) 386-9696, FAX: (973) 386-9191, e-mail: [email protected], Internet:

About the Author

Jack Browne | Technical Contributor

Jack Browne, Technical Contributor, has worked in technical publishing for over 30 years. He managed the content and production of three technical journals while at the American Institute of Physics, including Medical Physics and the Journal of Vacuum Science & Technology. He has been a Publisher and Editor for Penton Media, started the firm’s Wireless Symposium & Exhibition trade show in 1993, and currently serves as Technical Contributor for that company's Microwaves & RF magazine. Browne, who holds a BS in Mathematics from City College of New York and BA degrees in English and Philosophy from Fordham University, is a member of the IEEE.

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