Understanding Smart Sensors - Nomads.usp

Transceivers, Transponders, and Telemetry 185Wall0–20 ftsphericalrangecellNoisePulse-repetitionintervalTransmitter0.1 nspulsewidthStepgeneratorTargetRangeDelayRange gateReceiverRange cellAlarmMotionprocessorImpulsereceiverSensitivityFigure 8.6 Radar sensor schematic.processing circuitry [14]. See Table 8.1 for the microwave frequency range andits various subclassifications.The transceiver in a microwave sensor uses a Gunn diode or a field effecttransistor (FET) to generate a low-power microwave signal. The antennafocuses the energy developed into a beam, the size of which is determined bythe application. The reflection of the beam from an object provides a lowerlevel signal, which can be analyzed by the signal processing circuitry. The signalcan be used for Doppler shift (motion, speed, direction), strength (presence), orphase change (distance), depending on the application.Microwave sensors are experiencing size reductions and performanceimprovements from the integration possible in MMIC chips. An MMIC canhave all of the circuit or large portions of it on a single chip. Flip-chip packaging(see Chapter 10) of an MMIC containing the detector diodes has allowedfrequency operation up to 40 GHz [15].8.3.3 Global Positioning SystemGPS is based on information supplied by 24 satellites located in six orbitalplanes [16]. The satellites pass over the earth at an altitude of 20,183 km