How to Choose Microwave Signal Generator?

Abstract: The signal generator has clearly defined tasks in the test system : Analog device under test (DUT) signals that may be encountered during normal operation . This sine wave signal in the past only , or through an analog pulse modulation signal. However, with the continuous development of communication format is no longer limited to simple amplitude modulation (AM) and frequency modulation (FM), for the letter.
 

    Signal Generator with clearly defined tasks in the test system : Analog device under test (DUT) signals that may be encountered during normal operation . This sine wave signal in the past only , or through an analog pulse modulation signal. However, with the continuous development of communication format is no longer limited to simple amplitude modulation (AM) and frequency modulation (FM), the signal generator requirements are becoming increasingly high. As more and more devices using digital modulation format ( non- conventional signal format , such as frequency hopping , and ultra-wideband (UWB) communications ) , a new signal generator must be capable of simulating complex digital modulation schemes using a multi -frequency signal . Moreover, the shape of the signal generator is also changing , from the traditional rackmount or desktop instrument to a more compact module, once inside a space occupied by the signal generator can now put more than one discrete source.

   The traditional rackmount signal generator is still in testing tasks within their parts , sometimes as a separate instrument , sometimes as part of the automated system, and most of the major test equipment manufacturers can provide a wide range of microwave signal generator, and usually classified according to the frequency range . Select a signal generator instrument performance levels required to match the actual application requirements, and frequency range , output power, frequency and level switching speed and spectral purity are key parameters such people usually make a reasonable choice.


   Of course, no one can meet the needs of all signal generator test applications , trying to provide enough bandwidth , output power, tuning speed and spectral purity will lead to high , probably more than most ( if not all ) budget price. Thus , most commercial signal generator in the sale will be divided into broadband , General Instrument ( eg 10MHz to 18GHz) or " specific band " instruments ( interest cover specific frequency users , such as for satellite communications and telecommunications applications 3.7 GHz to 4.2GHz and 5.9GHz to 6.4GHz). This article will focus on the more traditional broadband test signal source. Subsequent articles will describe some of the other signal generator types, including arbitrary waveform generator (AWG) and vector signal generator (VSG).

   In the first class of the signal generator has a wide tuning range , Giga-tronics 2550B company's products ( Figure 1 ) and a mere one instrument (2.4mm) connector on the cover of the 2GHz to 50GHz frequency range , and It can also be an option to extend the frequency range of 10kHz. 2500B series and some other signal generator, respectively covering 10kHz to 2.5GHz, 2GHz to 8GHz, 2GHz to 20GHz, 2GHz to 26.5GHz and 2GHz to 40GHz frequency range , all of which signal generator has a frequency tuning 0.001Hz resolution. The signal generator can provide many applications for satellite testing valuable features, including high output power , fast switching speed and low phase noise. Standard output power at 20GHz under less than +20 dBm, stability to the time required for new frequencies below 500MHz less than 550μs, the magnitude of the settling time of less than 500μs. 10GHz carrier , 1kHz offset phase noise is -102dBc/Hz; 10GHz carrier phase noise at 10kHz offset is -108dBc/Hz, in the 50GHz range harmonics typically less than -30dBc, spurs typically less than -50dBc.

Figure 1:2550 B -type signal generator has a wide tuning range, the standard frequency range 2GHz to 50GHz, and expandable to 10kHz.

   In the understanding of these indicators spectral purity , the need to pay attention to the performance level is a function of frequency , especially in comparing different manufacturers when the signal generator . In 2550B type, for example , from 100MHz up to 39.6GHz range of harmonics is usually within -50dBc, at higher and lower band harmonic performance is lower. Similarly, in the frequency range up to 10.1GHz , spurious performance up to -66dBc, 10.1GHz to 39.6GHz range in spurious performance up to -54dBc. These performance levels are not only the fundamental frequency oscillator , a reference oscillator , the frequency of the function generator used in the microwave frequency synthesizer generating method , and a function to generate the highest frequency band is used for the multiplication program.

   Other wideband signal generator includes a desktop Agilent Technologies (Agilent Technologies) for MXG and PSG equipment , Anritsu Company MG37000A series signal generator and Rohde & Schwarz (R & S) of the R & S SMF100A microwave signal generator. All of these are included to achieve millimeter-wave signal generator frequency version , and has good output power and excellent spectral purity . For example , the frequency range MXG signal generator series of 100kHz to 20GHz, 31.8GHz or 40GHz, and has a frequency resolution 0.01Hz . 20GHz following standard output power +11 dBm, output power 20GHz to 40GHz standard is +7 dBm, another option may be to 20GHz output power increased to +18 dBm, the 20GHz to 40GHz range of output power increased to +12 dBm.

   When operating in the frequency range of the programming ( list mode ) , the switch to the new indicator as a measure of the frequency within a specific time resolution - the switching frequency or speed stabilization time 5ms 5ms or less ( when comparing these figures , recognizing different manufacturers may use different definitions of settling time is very important ) . As an optional feature , the switching speed can be accelerated to a typical 600μs. Unlike many typical signal generator , the output level of the standard time can be reduced to about -20dBm, with the optional internal step attenuator can also be reduced to -90dBm. Typical phase noise is -98dBc/Hz (6GHz or 12GHz carrier , 20kHz offset ) . 20GHz following harmonics typically -60dBc, 20GHz to 40GHz harmonics typically -56dBc. The following stray 24GHz typical -50dBc, stray typical 24GHz to 40GHz when is -45dBc. MXG signal generator has a lot of modulation options, including amplitude modulation (AM), frequency modulation (FM), phase modulation and pulse modulation.

   E8257D Agilent PSG signal generator products in one, this series of products covering a frequency range from 250kHz to 20GHz, 31.8GHz, 40GHz and 67GHz, and all products have 0.001Hz frequency in continuous wave (CW) mode resolution, with 0.01Hz resolution scan or list mode. Standard frequency settling time of less than 9ms, 20GHz following signal output level of +20 dBm. In the standard models of these output power can be reduced to -20dBm, output with optional step attenuator products in power can be reduced to -110 or -135dBm. Phase noise is typically -107dBc/Hz (20GHz carrier , 1kHz offset ) , and the harmonics below 20GHz is -55dBc, 40GHz following spurious typically -58dBc.

   Rohde & Schwarz R & S SMF100A microwave signal generator has a very easy to use front panel display with menu selection and testing of the system settings ( Fig. 2 ) above . Standard models of the frequency range from 1GHz to 22GHz, can be an option to be extended to 100kHz, can also be extended to 43.5GHz through another option. Frequency resolution is 0.001Hz, typical settling time is 2ms. The output power of about 20GHz or less +12 dBm, the product can be reduced to a standard -20dBm, the product with the internal parts of the step attenuator can be reduced to -130dBm. 10GHz carrier , the phase noise at 20kHz offset typical -115dBc/Hz; 20GHz carrier , typically 20kHz offset value -109dBc/Hz. 22GHz following harmonics typically -55dBc, 21GHz following spurious typically -56dBc.

   Anritsu Company MG37020A is another desktop broadband signal generator is designed for automatic test equipment (ATE) systems require faster switching speed applications designed products. The products cover the frequency range from 10MHz to 20GHz , the switching speed of 100μs, can deliver up to +19 dBm output power in the range below 10GHz , providing up to +17 dBm output power in the range of 10GHz to 20GHz . Through the optional step attenuator output power can be reduced to -110dBm. 10GHz carrier , 1kHz and 10kHz typical phase noise offset is -92dBc/Hz; 20GHz carrier , 1kHz and 10kHz offset phase noise is -86dBc/Hz. 20GHz following harmonics typical value is -50dBc, 20GHz typical value is less stray -40dBc.

   To save desktop space , many manufacturers developed a more compact signal generator, such as from AnaPico company APSIN20G. The size of the signal generator is 4.21x6.77x8.66 inches (106x172x220mm), only six pounds (2.5kg) weight , but the functionality is complete ( Figure 3 ) , in the range of 10MHz to 20GHz frequency of 0.1MHz with a resolution rate (which can be extended by the low-frequency option to 100kHz). -20dBm output power in the range of +7 dBm to 0.01dB resolution can be adjusted using the attenuator when the optional output power can be as low as -90dBm. This mini signal generator provides a universal serial bus (USB) port , through this port can be connected to a personal computer. While providing an AC-DC converter, the operating voltage is +6 VDC, operating current of 2.5A. The signal generator can also use the battery , which makes it very suitable for portable test applications.

Figure 3: This miniature signal generator can be tuned to 20GHz, it can work with the battery pack.

   APSIN20G at 10GHz carrier , 1kHz offset phase noise is -100dBc/Hz, at 10GHz carrier phase noise at 20kHz offset is -108dBc/Hz. Harmonic performance 20GHz less than -50dBc, 20GHz typical value is less stray -40dBc. Typical frequency switching speed or scan mode in the list is 100μs. APSIN20G also has a wide range of modulation formats including AM, broadband FM, phase modulation, frequency shift keying (FSK), phase shift keying (PSK), frequency chirp , and pulse modulation.

   April Instrument Company until the small size provides high performance signal generation 26.5GHz also enjoy a high reputation. For example, the company's 8004 products can provide 1MHz resolution in the range of 2GHz to 26.5GHz , 25GHz output power up the following +8 dBm. 20kHz carrier offset phase noise all the time for -80dBc/Hz, spurious typically -60dBc.

   Vaunix Technology company eliminates the signal generator 's display, they designed a comprehensive test source Lab Brick USB port and provides a computer-based graphical user interface (GUI). The GUI software with each Lab Brick with a memory stick for sale. Lab Brick signal generators are compact , measuring 4.90x3.14x1.59 inches and weighs less than one pound , there are a variety of models to choose from, covering a frequency range is divided into 4GHz to 8GHz ( Model LMS-802), 5GHz to 10GHz ( model LMS-103) and 8GHz to 12GHz ( model LMS-123). All models have a 100Hz frequency resolution , frequency switching speed of 100μs and +10 dBm output power. Lab Brick provides pulse modulation, phase-continuous frequency scanning executable .

   Finally , in order to achieve a smaller signal generator, and provides a variety of purposes , National Instruments (NI) of NI PXI-565x series signal generator using a PXI modular format , so you can build out in a rack cabinet a compact test system , about the size of a conventional signal generator. NI PXI-545x generator covering the frequency range of 500kHz to 6.6GHz , the switching speed of less than 2ms, and supports a variety of modulation formats.

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