This document discusses microwave communication and digital microwave communication systems. It defines microwave frequencies as ranging from 300 MHz to 300 GHz, but focusing on 3 GHz to 30 GHz for communication. Digital microwave communication modulates a digital baseband signal onto an intermediate frequency or directly onto a microwave carrier frequency using techniques like PSK and QAM. It describes the evolution of microwave systems from analog to digital and small to large capacities. It also outlines different types of digital microwave stations and relay stations.

1. SHREEJEE INSTITUTE OF
TECHNOLOGY AND MANAGEMENT
Microwave communication
• Guided by:- Mr. Prakash
Singh Panwar
• By:-Shubham Yadav
• EC BRANCH 1ST YEAR

2. Definition of Microwave
 Microwave
 Microwave is a kind of electromagnetic wave. In a broad sense, the microwave
frequency range is from 300 MHz to 300 GHz. But In microwave communication,
the frequency range is generally from 3 GHz to 30 GHz.
 According to the characteristics of microwave propagation, microwave can be
considered as plane wave.
 The plane wave has no electric field and magnetic field longitudinal components
along the propagation direction. The electric field and magnetic field components
are vertical to the propagation direction. Therefore, it is called transverse
electromagnetic wave and TEM wave for short.

3. Development of Microwave
Communication
• a
155M
34/140M
2/4/6/8M
480 voice
channels
SDH digital microwave
communication
system
PDH digital microwave
communication
system
Small and medium
capacity digital microwave
communication system
Analog microwave
communication system
Transmission
capacity
bit/s/ch)
1950s
1970s
1980s
Late 1990s to now
Note:
Small capacity: < 10M
Medium capacity: 10M to 100M
Large capacity: > 100M

4. Concept of Digital
Microwave Communication
• Digital microwave communication is a way of transmitting digital information in
atmosphere through microwave or radio frequency (RF).
– Microwave communication refers to the communication that use microwave as
carrier .
– Digital microwave communication refers to the microwave communication that
adopts the digital modulation.
– The baseband signal is modulated to intermediate frequency (IF) first . Then the
intermediate frequency is converted into the microwave frequency.
– The baseband signal can also be modulated directly to microwave frequency, but
only phase shift keying (PSK) modulation method is applicable.
– The electromagnetic field theory is the basis on which the microwave
communication theory is developed.

5. Digital Microwave
Communication Modulation (1)
• Digital baseband signal is the unmodulated digital signal. The
baseband signal cannot be directly transmitted over microwave
radio channels and must be converted into carrier signal for
microwave transmission.
Digital baseband signal IF signal
Basebandsignalrate
Channelbandwidth
Modulation
Service signal
transmitted

6. Digital Microwave
Communication Modulation (2)
• The following formula indicates a digital baseband signal being converted into a
digital frequency band signal.
 ASK: Amplitude Shift Keying. Use the digital baseband signal to change the
carrier amplitude (A). Wc and φ remain unchanged.
 FSK: Frequency Shift Keying. Use the digital baseband signal to change the
carrier frequency (Wc). A and φ remain unchanged.
 PSK: Phase Shift Keying. Use the digital baseband signal to change the carrier
phase (φ). Wc and A remain unchanged.
 QAM: Quadrature Amplitude Modulation. ). Use the digital baseband signal to
change the carrier phase (φ) and amplitude (A). Wc remains unchanged
A*COS(Wc*t+φ)
Amplitude Frequency Phase
PSK and QAM are
most frequently
used in digital
microwave.

7. Types of Digital Microwave Stations
• Digital microwave stations are classified into Pivotal stations, add/drop relay
stations, relay stations and terminal stations.
Terminal
station
Terminal
station
Terminal
station
Pivotal
station
Add/Drop
relay station
Relay
station

8. Types of Relay Stations
• a
Relay station
• Back-to-back antenna
• Plane reflector
Active
Passive
• Regenerative repeater
• IF repeater
• RF repeater

9. Active Relay Station
 Radio Frequency relay station
 An active, bi-directional radio repeater system without frequency shift. The RF relay station
directly amplifies the signal over radio frequency.
 Regenerator relay station
 A high-frequency repeater of high performance. The regenerator relay station is used to extend
the transmission distance of microwave communication systems, or to deflect the transmission
direction of the signal to avoid obstructions and ensure the signal quality is not degraded. After
complete regeneration and amplification, the received signal is forwarded.

10. Passive Relay Station
 Parabolic reflector passive relay station
 The parabolic reflector passive relay station is composed of two parabolic antennas
connected by a soft waveguide back to back.
 The two-parabolic passive relay station often uses large-diameter antennas. Meters are
necessary to adjust antennas, which is time consuming.
• The near end is less than 5 km away.