We introduce a new kind of diagnostic sensor that combines multifunctional measurement capabilities for ionospheric research. Multifunctionality is realized through agility in frequency selection over an extended band (1.5 to 50 MHz), system modularity, complete system control by software written in C, and a user-friendly computer interface. This sensor, which we call the frequency-agile radar (FAR), incorporates dual radar channels and an arbitrary waveform synthesizer that allows creative design of sophisticated waveforms as a means of increasing its sensitivity to weak signals while minimizing loss in radar resolution. The sensitivity of the FAR is determined by two sets of power amplifier modules: four 4-kW solid-state broadband amplifiers, and four 30-kW vacuum tube amplifiers. FAR control is by an AT-bus personal computer with on-line processing by a programmable array processor. The FAR does not simply house the separate functions of most radio sensors in use today, it provides convenient and flexible access to those functions as elements to be used in any combination. Some of the first new results obtained with the FAR during recent field campaigns are presented to illustrate its versatility. These include (1) the first detection of anomalous high-frequency (HF) reflections from a barium ion cloud, (2) the first evidence of unexpectedly large drifts and a shear north of the equatorial electrojet, (3) the first HF radar signature of a developing equatorial plasma bubble, and (4) the first measurements by a portable radar of altitude-extended, quasi-periodic back-scatter from midlatitude sporadic E. We also mention the potential of the FAR for atmospheric remote sensing. ¿ American Geophysical Union 1995