From Airborne Early Radar Warning System Concepts

6.2 BASICS OF AIRBORNE DOPPLER RADAR

6.2.1 Block Diagrams and Operation

Figure 6.2 shows an example block diagram of the transmitter/receiver for a moving target indicator (MTI) or pulse-Doppler (PD) radar. Coherency of successive transmit pulses is achieved by a stable local oscillator (STALO) and by a so-called coherent oscillator (COHO) that offsets the STALO frequency by an amount corresponding to the receiver intermediate frequency (IF). The offset is accomplished via the transmit mixer, which outputs the radar frequency (RF). The modulator generates the pulses that are transmitted and received via the antenna and duplexer. On reception, the pulses are down-converted to IF frequency by the STALO and receiver mixer. The IF signals are filtered and amplified within the IF amplifier in bandwidth B. Then, the COHO and IF signals, which are both at IF frequency, are moved (down-converted) with two phase detectors (quad phase detector) to two bipolar video signals (zero center frequency with positive and negative values). The two bipolar signals are in-phase (I) and quadrature (Q) components of the IF signal, in that they are the in-phase and 90 out-of-phase projections of the IF signal onto the COHO signal. Therefore, by forming , the root-mean-square (RMS) value, one can in principle obtain the time-dependent IF signal amplitude via a process of linear detection.


Figure 6.2: Transmitter/receiver for coherent radar.

In Figure 6.2, the basic oscillator (output of transmit mixer) runs constantly. If instead a pulsed magnetron is used,...


Products & Services
Weather Radar Systems

Weather radar systems, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, determine precipitation type, and calculate its motion.

Satellite Communications Equipment
Satellite communications equipment is used for the transmission, conditioning, and reception of satellite signals in worldwide telecommunications.
RF Mixers
RF mixers convert RF power at one frequency into power at another frequency to make signal processing easier and more efficient.
IC Phase-locked Loops (PLL)
IC phase-locked loops (PLL) are closed-loop frequency controls that are based on the phase difference between the input signal and the output signal of a controlled oscillator.
Aviation Transponders
Aviation transponders are electronic devices that generate and transmit a signal in response to receiving a radio frequency interrogation for the purposes of identifying aircraft for air traffic control and collision avoidance functions, as well as for IFF (identification friend or foe) military applications.

Topics of Interest

6.3 SELECTED SUBSYSTEMS The major components or subsystems of pulse radar are introduced in Chapter 4. Section 6.3 addresses selected features of the subsystems to which AEW performance is considered...

Overview The detector stage converts the intermediate frequency signals into video signals as in a classical superheterodyne receiver. The intermediate frequency signal has the following types of...

The following abbreviations and acronyms are used in this book. Acronym Meaning AEW Airborne early warning ac Alternating current ADC Analog-to-digital converter A/D Analog-to-digital...

Overview The synchronizer is the source of all timing signals for a radar system. Synchronizers may differ considerably from one radar system to another, but some fundamental design concepts...

Glossary A a noise-to-clutter ratio a auxiliary channel vector ABF adaptive beamforming ACP auxiliary channel processor AEP auxiliary eigenvector processor AEW airborne early warning ASEP...