Introduction to RF and Microwave Systems

RF and Microwave Frequency Bands

RF (“radio frequency”) is used to indicate the frequency band from hundreds of MHz to about 3 GHz

Microwave frequencies start from 300 MHz and goes up to 30 GHz, ( wavelength of 1m to 0.01m)

The frequency bands above 30 GHz is called Millimeter waves, and extend up to 300 GHz. Its technology is very similar to microwaves.

Electromagnetic Spectrum

Electromagnetic Spectrum (comparable)

What is different about the RF/Microwave band?

Circuit theory / transmission lines / electromagnetics all needed, because:

– The size of the circuit (let’s call it d) for RF and microwave circuits

– Question: what relationship between d and exists for (a) low frequency circuits (kHz range), and (b) optical circuits (where the wavelength is on the order of µm), keeping in mind that the circuits themselves are all on the order of cm?

Advantages of the use of higher frequencies

Larger instantaneous BW for much information, Higher resolution for radar, imaging and sensing,

bigger doppler shift, Reduced dimensions for components, Less interference from nearby applications Higher speed for digital systems, signal

processing, data transmission Less crowded spectrum Difficulty in jamming (military)

Disadvantages of the use of higher frequencies

More expensive components,Higher atmospheric losses,Reliance on GaAs instead of Si technologyHigher components losses, lower output

powers from active devices,Less accurate design tools, less mature

technologies.

RF and Microwave Applications

Wireless Communications (space, cellular phones, cordless phones, WLANs, Bluetooth, satellites etc.)

Radar and Navigation (Airborne,vehicle, weather radars, GPS, MLS, imaging radar etc.)

Remote sensing (Meteorology, mining, land surface, aviation and marine traffic etc.)

RF Identification (Security, product tracking, animal tracking, toll collection etc.)

Broadcasting (AM,FM radio, TV etc.)

RF and Microwave Applications

Automobiles and Highways (Collision avoidance, GPS, adaptive cruise control, traffic control etc.)

Sensors (Temperature, moisture sensors, robotics, buried object detection etc.)

Surveillance and EW (Spy satellites, jamming, police radars, signal/radiation monitoring etc.)

Medical (MRI, Microwave Imaging, patient monitoring etc.)

Radio Astronomy and Space Exploration (radio telescopes, deep space probes, space monitoring etc.)

Wireless Power Transmission (Space to space, space to ground etc. power transmission)

Radiated Power and Safety

Organic tissue absorbs RF and microwave energy and converts it to heat (e.g. Microwave oven)

This is not a good thing when the tissue is you! Heating is dangerous to areas such as brain, eyes, and

stomach organs Radiation may cause cataracts, cancer, and sterility ANSI/IEEE standard sets safety standard for exposure

limits (e.g. limited to 10 mW/cm2 above 15 GHz where radiation is absorbed by the skin)

Handheld cell phones limited to maximum radiated power of 0.76 W, while base stations are limited to 500 W.

The main purpose of the course is to provide the following questions:

At what upper frequency does conventional circuit analysis become inappropriate?

What characteristics make the high-frequency behavior of electric components so different from low-frequency behavior?

What “new” circuit theory has to be employed? How is this theory applied to practical design of

high-frequency analog circuits?

Sample Tranceiver

Power Amplifier: Circuit

Power Amplifier: PCB layout

RF Behavior of Passive Components

Lumped(discrete) or distributed elements: Inductor