Development of a low cost, FM/CW transmitter for remote sensing

A generic, low cost, compact Frequency Modulated Continuous Wave (FM/CW) transmitter has been developed for use from 2 to 18 GHz with a transmit bandwidth of up to 1 GHz. This generic design is currently being used in a railway hazard detection system, a synthetic aperture radar, and an altimeter. Capitalizing on the functionality and low cost of wireless communication parts, an inexpensive broad band linear frequency generator was developed which is extremely small in size and lightweight. This design incorporates the functionality of a microcontroller´s counter to measure the frequency at a given voltage and thus calibrate a digital waveform to drive a VCO with linear frequency modulation. The microcontroller communicates with a host using a RS232 serial port, enabling the user to set parameters such as center frequency, bandwidth and repetition count. A trigger is used to synchronize receiver analog to digital conversions with the transmitted signal. Tests show the transmitter waveform has low deviation from linearity and level output power over the entire band