The mission of MTT-9 is to provide a central forum for digital activities at microwave frequencies – a broader view than we usually associate with the term “Digital Signal Processing” (DSP). As digital technology has advanced to the extent that most present-day microprocessors have clock frequencies in the microwave band, we must be somewhat selective in our choice of activities, picking those that involve microwaves or microwave techniques.

Our interests tend to fall into two categories – one where the speed of the digital circuit as a major factor, leading to designs using microwave techniques, and the other where the digital circuit’s function as a microwave application; of course, some things include both aspects. The topics we deal with include development of microwave (and above) mixed-signal circuits and modules and associated algorithms for digital signal processing functions. Among the current areas of interest are high-speed A/D and D/A converters; direct digital synthesizers; digital filtering, modulation and coding techniques; high-speed ICs and subsystems for optical fiber communication; electrical/optical interfaces and transmission, signal integrity, backplanes and their equalization; technology for high-speed processing of radiated signals; MIMO, SDR and cognitive systems.

Our membership is drawn from industry, government and academia, and we’re a geographically diverse group, with members from North America, Europe and Japan.

A subset of MTT-9 make up the IMS subcommittee #24 “Signal Processing Circuits and Systems at GHz Speeds”. A lot of the activity is related to the IMS (International Microwave Symposium).

Digital Signal Processing in RF and microwave transmitters and receivers substitutes DSP hardware and software for conventional analog signal processing hardware as well as enabling new radio topologies that are only possible using DSP. The use of DSP in, for example, transmitter linearizers and receiver carrier, clock and data recovery changes the microwave components we use, and the way we use them.

DSP is also a prerequisite for software defined radio, which opens up the realm of protocol-agnostic transmitters and receivers in areas such as mobile communications and wireless LANs. New services, air-interface standards and modulation schemes can be applied by a simple data download. Clearly again, this will have a significant impact on the design of the RF and analog portions of the system.

Signal processing for optical fiber communications is a presently emerging technology, an example of how optical communications is getting more and more like microwave radio. There are a number of factors at work here: silicon CMOS technology can now produce chips with sufficiently fast gates, in sufficient numbers to perform meaningful DSP as well as very powerful forward error correction (FEC) at Multi-Gb/s data rates. Strong FEC means that uncorrected received data can have high bit error rates, rendering some traditional self-optimisation schemes unworkable. At the same time, customer needs for value-for-money are pushing manufacturers to look for alternatives to relatively expensive optical impairment amelioration techniques, and new networking constructs limit the sharing of optical correction across WDM channels, making it worthwhile to replace optics with electronics.

As the examples above show, digital and computer technologies will become more and more important to microwave engineers as time goes by.