Data-intensive Designs Require Signal Generators with Higher Speed
By Leonard Dickstein, Anritsu Company

Frequency switching speed is a critical specification for microwave signal generators in automated test equipment (ATE) applications. Many data-intensive testing requirements in Aerospace/Defense and microwave component manufacturing directly benefit from faster switching speed. Engineers and companies who have to test and verify the performance of microwave antennas or satellite payloads are typically faced with significant repetitive testing, over the rotational azimuth and elevation of the antenna, or of the satellite payload’s many channels, states and configurations. Radar, EW systems and avionics require fast switching for frequency hopping and signals with various degrees of frequency agility, while high volume microwave components including RFICs and MMICs can save test time, lower cost of test and increase productivity with a fast switching synthesizer.

Conventional signal generators utilizing YIG-based architectures are not adequate for data-intensive applications because they simply do not have the high speed necessary for the measurements. They had become the instrument of choice because YIG-based synthesizers have low phase noise, wide frequency range and are relatively inexpensive. On the minus side, they consume a lot of power, and it takes time to tune a YIG from one frequency to another, typically limited to millisecond switching speed by the physics of the electromagnetic tuning.

There is another class of ultra-fast switching signal generators, using direct analog architecture, capable of nanosecond switching speed. But these synthesizers are very expensive, typically costing more than $100K, and often are limited in frequency range, features and options.

VCO-based Architecture
VCO technology has improved in recent years, with new lower phase noise VCOs commercially available. VCOs have a much greater tuning speed than YIGs, and the recent improvements in VCO performance have enabled the development of microwave signal generators with microsecond speed and good phase noise performance, effectively filling the gap between millisecond YIG-based synthesizers and nanosecond direct-analog synthesizers.

Anritsu Company has just introduced a new fast-switching microwave signal generator, the MG37020A (Figure 1), that takes full advantage of VCO technology. Covering 10 MHz to 20 GHz, the MG37020A has an optimized VCO multiplier/divider architecture coupled with high-speed digital control circuitry that gives it best-in-class switching speed of <100 µsec per step when not crossing a filter bandswitch and <500 µsec per step when crossing filter bandswitch points. Switching speeds as fast as 50 µsec (to within 1 kHz of the final frequency) can be achieved for a 100 MHz step size. Fast switching speed is maintained in manual mode and step sweep mode, not just in a list sweep mode.

Figure 2 is an example of the MG37020A’s speed. It shows a 55 µsec frequency settling time (output at 10 GHz) in the top trace and the lock indicator signal in the bottom trace at 10 µsec per division. The lock indicator signal can be used to trigger a measurement, being a true indication of the time from the command to switch frequency to the time the new frequency is within 1 kHz of the final value).

Performance was not sacrificed at the expense of speed with the MG37020A. The signal generator maintains low phase noise of typically -101 dBc/Hz at 10 kHz offset at 10 GHz, and +23 dBm high output power at 20 GHz.

Defense Applications
The MG37020A has been developed with defense electronic applications in mind, as its high performance pulse modulation makes it well suited for radar and EW signal simulation. Pulse modulation capability includes providing 100 nsec leveled pulse widths and 10 nsec unleveled pulse widths, and the internal pulse generator gives the MG37020A swept delay capability for moving target simulation, including single, double, triple, quadruple and burst pulses. Figure 3 is an example of a pulse burst mode signal.

Microwave antenna testing and military satellite payload testing are examples of data intensive applications, where fast switching can significantly reduce the test time. In antenna testing, measurements such as antenna patterns require repetitive testing versus the physical rotation and tilt of the antenna. Satellite payload testing requires repetitive testing for multiple signal paths, under multiple conditions, such as various gain settings, and in multiple locations (integration, thermovac, vibration and on the launch vehicle just prior to launch). Improvements in synthesizer switching speed can reduce the test time, in some cases, by as much as days versus weeks of testing.

Customization is a key part of conducting measurements in today’s design environment. Anritsu provides a number of other options for the MG37020A that allow the instrument to be configured for specific requirements. An ultra-stable phase track option allows users to track the phase of up to four generators with a minimum of phase drift over time. Aerospace/defense applications include testing direction finding (DF) systems where the multiple synthesizers simulate the signals received from multiple DF antennas.

Ease of Use
The ability to conduct measurements quickly is also achieved through the simplicity in which users can operate the MG37020A. It has a Windows XP® Professional environment, including drop-down menus, making it familiar to any PC user. On-screen function keys group tests intuitively, and a color touch screen allows users to view status and measurement setup menus quickly. Users have their choice of entering and editing parameters via a keypad, cursor keys or rotary data knob for convenience.

Recognizing space and connectivity are big considerations in an ATE environment, the MG37020A has an extremely small footprint and enhanced connectivity. It measures only 13.3 H x 45 D (cm), so the MG37020A occupies little rack space. The signal generator comes with USB, Ethernet LAN, GPIB, and RS-232 standard, which not only makes it well suited for ATE configurations but also allows a mouse, keyboard and external VGA monitor to be attached to the instrument. A removable hard drive option is available for use with instruments located in aerospace/defense secure areas.

Summary
For repetitive, high-throughput automated test systems, and antenna and satellite payload testing, there is no substitute for speed. Utilizing an advanced architecture that takes full advantage of modern VCO performance, Anritsu’s MG37020A Fast Switching Microwave Signal Generator delivers the speed and accuracy necessary for defense electronics and manufacturing ATE applications.

ANRITSU COMPANY
www.us.anritsu.com
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