The RF-Head is mounted in the antenna transmission line for measurements with the RF Performance Monitor Series 9000.
The RF-Head model 323 consists of two directional couplers by which both the Output and the Reflected Power in the radar system can be measured and hence the VSWR can be calculated.
Model 324 has a single directional coupler and is suitable for systems where measurement of only the Output Power is required. Each directional coupler is a precision cross-guide coupler which consists of two waveguide sections joined at right angles.
These directional couplers features extreme flatness of coupling across the frequency band and high power handling capacity. In the auxiliary arm of the coupler a precision attenuator is mounted for compensation of any variation in the coupling caused by the manufacturing process. This level setting attenuator is adjusted with high accuracy at the factory.
The Thermistor Mount is the device which senses the RF-power through the head. Each Thermistor Mount contains a pair of thermistors matched for thermal characteristics. The pair is enclosed in a common thermal environmental arrangement which results in cancellation of the effect from changes in ambient temperature. The RF-Heads are intended for use in pressurized waveguide systems, and are normally manufactured in aluminum.
The RF-Head model 326 is a combination of model 323 and Noise Injection Unit model 150. By this head both the Output and the Reflected Power and Noise Figure in a radar system can be measured. Two of the couplers are used for power measurements. To the third coupler a Solid State Noise Source is connected. High power protection may be incorporated if necessary.
Noise Injection Unit model 150 provides an accurate noise reference source for use with the RF Performance Monitor Series 9000. Noise Injection Unit model 150 is designed for injecting a reference noise signal into a radar receiver without disruption to normal operation. It consists of a Solid State Noise Source and a high precision crossguide Directional Coupler with a low power termination. The low power termination is built into the cross-guide directional coupler to save space. The unique characteristics of these couplers are the flatness and the absolute accuracy of the coupling across the frequency band.
For use with Monitor Series 9000, the noise source is manufactured to deliver symmetrical Gaussian noise at an Excess Noise Ratio of 35 dB with a drive power of +28V. Units with ENR up to 40 dB are available.
When Solid State Noise Sources are operated in systems with high peak and average power, an isolator is required to protect the noise source. The Noise Injection Unit is a very important link in the chain giving the total system accuracy of the Noise Figure measurement.