MICROWAVE ENGINEERING

Course Outline (a.a. 2012/2013):

1) Introduction to Microwave Systems

2) Waveguides and Resonators

3) Microwave Network Analysis (S-Parameter Analysis)

4) Periodic Structures and Filters

5) Passive Microwave Devices

Textbooks:

D. M. Pozar, Microwave Engineering, Wiley, 2012.

C. G. Someda, Electromagnetic waves, CRC Press, 2006.

Slides available: http://nora.ing.unibs.it

Teacher: Costantino De Angelis (deangeli@ing.unibs.it)

Operating frequency here is in between f=300 MHz and f=300 GHz (i.e. wavelength in between

=1 m and =1 mm).

The wavelength is of the same order of magnitude as the circuit elements; it follows that we can not

make use of the lumped element approach (summarized into Kirchhoff laws).

We need here to resort to the solution of the full electromagnetic problem described by Maxwell

equations.

310 210 10 1 110 210 310 410 510 610

5103 7103 8103 11103 13103 14103V

HF

TV

FM

rad

io

AM

radio

Far

infr

are

d

Infr

are

d

Vis

ible

lig

ht

MICROWAVES

WAVELENGTH (m)

FREQUENCY f (Hz)

MICROWAVES AND MILLIMETER WAVES

Microwave applications

Since most constraints are on the fractional bandwidth, the higher the carrier, the bigger the available frequency bandwidth.

The antenna gain increases with increasing frequency.

Microwaves can be focused in beams with limited angular aperture, thus increasing the directivity in a point to point radio link and the achievable

resolution in a radar.

4

2

GAeff

4

2

EFFECTIVE AREA=GAIN

2

2

0

0 1

w

zwzw

22

01z

wzzR

0w

Angular aperture of

a gaussian beam

20wz

EH E

H

Magnetic field distribution

on the output aperture

Electric field distribution

on the output aperture

Example of a microwave antenna: the horn

The horn is feeded by means of a single mode

rectangular waveguide (only the TE10 mode is above

cut off).

x

y

z

Wavelengths below 1 meter are not reflected by the ionosphere: we can use them for satellite communicaton

Due to solar radiation, we find ions in the ionosphere: the ionosphere thus behaves like

a plasma with a plasma frequency determined by a density N of ions.

Plasma permittivity

(neglecting damping)

2

2

0 1

pe

0

2

m

Nqp

Electron charge

m

q

Electron mass

Lossless propagation in the plasma is possible only for: p

Frequencies below 8 MHz are reflected by the ionosphere.

Attenuation level in the atmosphere: frequency dependence

Below 10 GHz the attenuation can be considered negligible

Radiometer f=20 GHz

Radiometer f=55 GHz

Radar

f=35 GHz

Radar=135 GHz

Frequency Bands Designation Typical service

3-30 kHz VLF

Very Low Frequency

Navigation

30-300 kHz LF

Low Frequency

Radio beacons

300-3000 kHz MF

Medium Frequency

AM transmission

3-30 MHz HF

High Frequency

Citizens band

30-300 MHz VHF

Very High Frequency

FM transmission

Television

300-3000 MHz UHF

Ultra High Frequency

Television

Satellite communications

Wi-Fi

Radar

3-30 GHz SHF

Super High Frequency

Satellite communications

Radar

30-300 GHz EHF

Extreme High Frequency

Radar

Some examples

Television (VHF) 50-88 MHz Television (UHF) 470-890 MHz Mobile Communications: GSM 900 MHz, 1800 MHz, 1900 MHz Mobile Communications: AMPS 824-894 MHz Mobile Communications: UMTS 1885-2025 MHz, 2110-2200 MHZ

GPS (Global Positioning System) 1575.42 MHz and 1227.60 MHz Bluetooth 2.4 GHz WLAN (Wireless Local Area Network) 902-928 MHz, 2.4-2.484 GHz, 5.725-5.850 GHz

DBS (Direct Broadcast Satellite) 11.7-12.5 GHz Radar (Air Traffic Control) 1-2 GHz Short range Radar: 2-4 GHz, 27-40 GHz Radar for weather forecast 4-8 GHz US Ultra Wide Band (UWB) 3.1-10.6 GHz US Industrial, Scientific and Medical bands (ISM):

902-928 MHz, 2.400-2.484 GHz, 5.725-5.850 GHz

Frequency Band

(GHz)

Wavelength (cm) Designation

1-2 30-15 L

2-4 15-7.5 S

4-8 7.5-3.75 C

8-12.4 3.75-2.4 X

12.4-18 2.4-1.67 Ku

18-26.5 1.67-1.13 K

26.5-40 1.13-0.75 Ka

40-300 0.75-0.1 Millimeter waves

IEEE, ITU designation in the 1-40 GHz frequency band

Superheterodyne Radio Receiver

X BPF

OL

RF amp IF amp mixer

Local oscillator Tuning is achieved by

varying

Pass band

filter

demodulator

fRF fIF fOL

Cables, waveguides, connectors. Filters, isolators. Active devices: amplifiers, oscillators, mixers.

antenna

signal

fOL

In monostatic radars the same antenna is used to transmit and to receive.

In bistatic radars two different antennas are used to transmit and to receive.

OL C

riceiver

1 2

3

Circulator: the power goes

from port 1 to port 2

from port 2 to port 3

ports 1 and 3 are perfectly isolated

G

R

The source (the transmitter) sends a signal which is partially reflected by the target

located in the far field region; the reflected signal is sensed by a receiver.

We can thus measure the distance of the target by computing the time of flight (the

time needed for the electromagnetic signal to travel from the transmitter to the target

and back to the receiver).

For big enough antenna directivities (small enough angular aperture of the main

lobe) also the angular position of the target can be measured accurately.

TARGET Local

oscillator

antenna

gain

RADAR: Radio Detection and Ranging

Friis formula

(radio-link with two antennas) TTRR PR

GGP

2

4

Intensity at the target

location 24 R

PGS TIN

Radar cross section

IN

S

S

P

The target is equivalent to a transmitting antenna radiating backward. The power received by

the monostatic radar is thus:

RTT

ReffR PPR

G

RR

PGGSAP

43

22

22

2

44

1

44

Radar equation

Power level at the receiver in a monostatic RADAR

Transmitted power Back scattered power TP RP

Received power SP

PULSED RADAR

Generated

pulses

Transmitted

signal

Riceived

signal

RT

eco del target

t2

ctR

Frequency repetition rate

kHz

Tf RR1001.0

1

Pulse duration

Position

of the

target

mixer

mixer LNA

Power

amplifier 0f

IFf

output stage

switch

transmitter

riceiver

antenna

CW DOPPLER RADAR

The phase of the reflected signal is:

0

0

222

Rtf

If the target is moving away with velocity

0

0

42

vtRtf

v

The frequency of the received

signal shifts (Doppler shift ) 0002

2

1f

c

vf

tff d

0f

0fdff 0

0f

mixer

circulator

pass-band filter

df

Moving target

(velocity ) v

output stage

IN

S

S

P

As a simple example let us consider the cross section of a metal sphere of radius a

Rayleigh region Optical region

2a 4

a

a2

2a

The oscillatory behaviour is due to

the phase difference among

different reflected components

RADAR CROSS-SECTION (RCS): depends on the nature and

shape of the object