Prepared by Dr. Mrs. J P Shinde Sinhgad Academy of Engineering, Kondhwa

1. 404183 Radiation and Microwave Techniques Unit-6 Microwave Systems and Microwave Measurement Techniques Prepared by Dr. Mrs. J P Shinde Sinhgad Academy of Engineering, Kondhwa Dr. Mrs J P Shinde, SAE, Kondhwa

2. Unit VI : Microwave Systems and Microwave Measurement Techniques (6Hrs) • Microwave terrestrial and satellite communication system and industrial applications of microwaves such as microwave heating, thickness and moisture measurement, medical application such as microwave diathermy. Microwave measurement devices such as slotted line, tunable detector, VSWR meter, power meter, and their working principles. Microwave measurement techniques to measure S-parameters, frequency, power, attenuation, phase shift, VSWR, impedance. Radiation hazards and protection. Dr. Mrs J P Shinde, SAE, Kondhwa

3. Low frequency measurement vs. Microwave measurement • At low frequency, it is convenient to measure voltage and current and use them to calculate power. However at microwave frequencies, they are difficult to measure and since they vary with position in a transmission line, are of little value in determining power. • Therefore at microwave frequencies, it is more desirable and simpler to measure power directly. 2. At low frequency, circuits use lumped elements which can be identified and measured. • At microwave frequencies circuit elements are distributed and as such it is usually not important to know what element make up a line. • It is possible and also satisfactory to measure the impedance of a circuit without regard to the individual distributed elements making up that circuit. Dr. Mrs J P Shinde, SAE, Kondhwa

4. 3. Unlike low frequency measurements, many quantities measured at microwave frequencies are relative and it is not necessary to know their absolute values. • Further for power measurement, it is usually sufficient to know the ratio of two powers (or their difference in dBs) rather than exact input or output powers. Dr. Mrs J P Shinde, SAE, Kondhwa

5. Microwave Bench General Measurement Setup Dr. Mrs J P Shinde, SAE, Kondhwa

6. Microwave Test Bench  Dr. Mrs J P Shinde, SAE, Kondhwa

7. Measurement Devices and Instrumentation Dr. Mrs J P Shinde, SAE, Kondhwa

8. 1. Slotted line Dr. Mrs J P Shinde, SAE, Kondhwa

9. Slotted line contd.. • This system consists of a transmission line (waveguide), a traveling probe carriage and facility for attaching/detecting instruments. • The slot made in the center of the broad face do not radiate for any power of dominant mode. • Slotted section is basically used to measure Standing wave ratio (VSWR). • The precision built probe carriage having centimeters scale with a vernier reading of 0.1 mm least count is used to note the position to the probe. • Additionally slotted section can be used to measure impedance, reflection coefficient and the return loss. Dr. Mrs J P Shinde, SAE, Kondhwa

10. 2. Tunable Detector • The Tunable Probe comprises a crystal, plus a small wire antenna in a coaxial housing. • Its depth of penetration in to the slotted section is variable and may be locked at any position of penetration. • This is designed very carefully keeping in the specifications • Tunable detector helps detect the low frequency square wave modulated microwave signal. • Point contact type or metal- semiconductor Schottky Barrier Diode (SBD) is used. Dr. Mrs J P Shinde, SAE, Kondhwa

11. 3. VSWR meter • A VSWR meter basically consists of a high gain, high Q, low noise voltage amplifier normally tuned at a fixed frequency (1KHz) at which the microwave signal is modulated. • The VSWR meter uses the detected signal out of the detector as its input, amplifies the same and provides the output on a calibrated voltmeter. • The meter itself can be calibrated in terms of VSWR. Dr. Mrs J P Shinde, SAE, Kondhwa

12. Dr. Mrs J P Shinde, SAE, Kondhwa

13. Dr. Mrs J P Shinde, SAE, Kondhwa

14. 4. Power meter • It basically consists of a power sensor that converts the microwave power into heat energy. • The temp change so produced provides an output current in the low frequency circuit that indicates power. • Sensors used for power measurements are SBD, bolometer and the thermocouple Dr. Mrs J P Shinde, SAE, Kondhwa

15. Microwave measurement techniques The following parameters can be conveniently measured at microwave frequencies Frequency Power Attenuation and phase shift VSWR and impedance Dr. Mrs J P Shinde, SAE, Kondhwa

16. Refer 3. TB “Microwave Engineering”by Annapuurna Das and S K Das for • Microwave terrestrial and satellite communication system: section: 11.3, pp. 424-438. • Industrial applications of microwaves such as microwave heating, thickness and moisture measurement, section: 11.4, pp. 438-443. • Radiation hazards and protection. Chapter 12, pp. 445-449. Dr. Mrs J P Shinde, SAE, Kondhwa

17. Medical application such as microwave diathermy. : wikipedia.org Diathermy is electrically induced heat or the use of high-frequency electromagnetic currents as a form of physical or occupational therapy and in surgical procedures. Diathermy is commonly used for muscle relaxation, and to induce deep heating in tissue for therapeutic purposes in medicine. It is used in physical therapy and occupational therapy to deliver moderate heat directly to pathologic lesions in the deeper tissues of the body. Diathermy is produced by three techniques: 1. ultrasound (ultrasonic diathermy), 2. short-wave radio frequencies in the range 1–100 MHz (shortwave diathermy) or 3.  microwaves typically in the 915 MHz or 2.45 GHz bands (microwave diathermy), the methods differing mainly in their penetration capability. It exerts physical effects and elicits a spectrum of physiological responses. Dr. Mrs J P Shinde, SAE, Kondhwa

18. Thank you Dr. Mrs J P Shinde, SAE, Kondhwa