Polarization And Lnb - Deviser S7200 User Manual

Part III: Background and Concepts
9-2

Polarization and LNB

Satellite signals have two types of polarization: circular and linear. Circular polarization can be divided into
right-handed (or clockwise) and left-handed (or counterclockwise); while linear polarization can be divided
into horizontal and vertical. Most satellites use the horizontal and vertical polarization transmission signals.
Today, many new products combine the LNB and Feedhorn into one: LNBF (LNB with Feedhorn).
The LNBF usually provides two mutually perpendicular probes in different feedhorn positions. One probe
receives horizontal-polarization signal and the other vertical; then they couple the signal to microwave LNA.
The IRD uses the 13V/18V signal to control two polarization paths and turn the power amplifier on or off.
The C band downlink frequency range (3.7GHz to 4.2GHz) and LNB are universal. But in the Ku band, each
satellite uses a different range (e.g., some satellites use 11.7~12.2GHz while others use 12.25~12.75 GHz).
Users receiving Ku band signals should choose the correct frequency band LNB for their satellite's range.
About the LNB Local Oscillator
The LNB single local oscillator uses the frequencies 5150MHz and 5750MHz on the C-band. The IRD receives
frequencies between 950~2150MHz, and the C-band's full bandwidth is only about half of this, at around
500 MHz. Some recent products provide two sets of circuits to handle horizontal and vertical polarization
signals respectively. Two local oscillators respectively occupy the frequencies of 5150MHz and 5750MHz.
After signal mixing, the horizontal and vertical polarization respectively output 950~1450MHz (5150 – 4200 =
950, 5150 – 3700 = 1450) and 1550~2050MHz (5750 – 4200 = 1550, 5750 – 3700 = 2050). These signals fall within
the IRD's received frequency range.
Ku band downlink frequencies can range from 10.7 ~ 12.75GHz, with bandwidth of about 2.05GHz (about 4
times the C band bandwidth). Using a local oscillator frequency to receive full bandwith signal is difficult on
Ku band. So the 2.05GHz bandwidth can be divided into several frequency bands, each using a different
local oscillator frequency such as 9.75GHz, 10.6GHz, 10.75GHz, 11.25GHz, 11.3GHz, etc.
The table below lists all local oscillator frequencies and corresponding received frequencies/IF ranges.
110
Received Signal
LO (GHz)
Freq. (GHz)
9.75 10.7 ~ 11.9
10 10.95 ~ 12.15
10.6 111.55 ~ 12.75
10.75 11.7 ~ 12.75
11.25 12.2 ~ 12.75
11.3 12.25 ~ 12.75
LNB Output IF
Range (GHz)
950 ~ 2150
950 ~ 2150
950 ~ 2150
950 ~ 2000
950 ~ 1500
950 ~ 1450