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C band RF Transceiver design | RF Transceiver Block Diagram

This page on C band RF transceiver design and development describes various modules as per RF transceiver block diagram.

RF Transceiver consists of RF Up converter, RF down converter, 10MHz OCXO, RF synthesizer, Local oscillator, RF power divider, IF power divider, M & C card, power supply etc.

RF Transceiver is major module in wireless systems which is made of two parts viz. transmitter and receiver. C band RF Transceiver is used in VSAT system or Earth station in order to provide wireless connectivity with satellite from ground. VSAT is used for voice call and data call connections by hilly terrain based users and flat terrain based users.

RF Transceiver Specifications

Following specifications are used in C band RF transceiver design described in this article.
Transmitter part specifications:
Input frequency- 52 to 88 MHz
Output frequency- 5925 to 6425 MHz
RF frequency selection- In the steps of about 1 MHz
Conversion Gain- 20 dB minimum
Gain flatness- +/- 1 dB over entire band
Gain Variation- +/-1 dB over temperature of 0 deg. C to 50 deg. C
Gain adjustment- 10 dB
Input power level- from -5 to -25dBm
Spurious and harmonics level- better than -40 dBc
1 dB compression point- better than +3dBm

Receiver part specifications:
Input frequency- 3.7 to 4.2 GHz
Output frequency- 52 to 88 MHz
RF frequency selection- In the steps of about 1 MHz
Conversion Gain- 40 dB minimum
Input level- -40dBm to -85dBm
Gain flatness- +/- 1 dB over entire band of 36MHz
Gain Variation- +/-1 dB over temperature of 0 deg. C to 50 deg. C
Gain adjustment- 10 dB
Noise Figure- better than 14dB
Image rejection- better than -50dBc
Spurious and harmonics level- better than -40 dBc

RF Transceiver Block Diagram

The function of RF Transceiver is convert modulated IF into RF and vice versa. It interfaces one side with modem (base band part) and other side with PA/LNA. It is also called Outdoor Unit due to location in the VSAT system.

It consists of two main parts Up converter and down converter. As shown in following figure, UP converter converts modulated IF IN (70+/-18 MHz) into modulated RF OUT (5925-6425MHz). DOWN converter converts modulated RF IN (3700-4200) MHz to IF OUT (70+/-18 MHz).

C band RF Transceiver design and development
Figure-1 : C Band RF Transceiver Block Diagram

As shown in the block diagram, RF Transceiver consists of modules which include Up converter, down converter, OCXO, Synthesizer, Local oscillator, RF divider, IF divider, M & C card and power supply.

Guide to C band RF Transceiver design

As mentioned RF Transceiver consists of two major modules RF up converter and down converter. RF up converter converts lower frequency to higher frequency and RF down converter converts higher frequency to lower frequency. Refer design of C band RF up converter and down converter modules. This design of RF frequency converters is carried out using discrete RF components. Microstrip line is etched on PCB for soldering the RF components.

RF Up converter and RF down converter

As shown in the figure 2 and explained above RF Up converter converts modulated IF data in the frequency band of 52-88 MHz to C band. This is done by using mixers and filters. Here Dual conversion approach is followed. In the first conversion 70MHz beats with 1112.5MHz LO and will produce sum and difference frequencies. Out of these sum frequencies are picked up and passed through filter of 1182.5+/- 18 MHz. This 1182.5 band of frequencies beat with 4680-5375 MHz RF synthesizer and will produce C band of about 5925-6425 MHz.

Two RF mixers in up converter and down converter follow heterodyne architecture design.

For the case of RF down converter design, LNA signal frequencies of about 3.7GHz band is converted to IF frequencies of about 70MHz. This is possible again with the use of appropriate mixers/filters. In the first step of conversion 3.7GHz band is converted to 1042.5MHz band after beating with synthesizer. The same 1042.5MHz band is converted to 70MHz IF signal after beating with fixed IF Local oscillator of 1112.5MHz frequency.

rf upconverter downconverter

10MHz OCXO

This RF oscillator is used as reference for both IFLO and synthesizer in the RF Transceiver. Small power divider circuit is designed which splits sinusoidal power output of oscillator to two places. Out of these one is fed as input to IF Local oscillator and the other is fed as input to RF synthesizer. This module is designed by purchasing RF components required along with 10 MHz crystal oscillator of OCXO type and developing micro strip based board.

Radio Frequency synthesizer

Synthesizer is used to change RF frequency of operation in RF Transceiver used for VSAT. RF synthesizer here is of frequency 4680 to 5375 MHz and frequency can be set in the step of 1 MHz. There are many manufactures of RF synthesizer modules which one can buy for the development or can be designed and developed. Refer our page in terminology section to design RF synthesizer using modules/ICs such as VCO, PLL, Loop filters etc.

Local oscillator

RF Local oscillator will generate fixed frequency and cannot be changed unlike RF synthesizer. RF local oscillator value of 1112.5MHz is used here in our design.

RF power divider

RF divider module is designed using micro strip concept. Various methods are available used to develop RF divider; popular among them is Wilkinson power divider. RF divider divides RF output of synthesizer into two paths, one is used as input to mixer for RF up conversion and the other is used as input to mixer for RF down conversion.

IF power divider

IF divider module is designed using micro strip concept. Various methods are available to design and develop this module. IF divider divides IF output of Local oscillator into two paths, one is used as input to mixer for IF up conversion and the other is used as input to mixer for IF down conversion.

M & C card

Monitoring and control card is used here in order to monitor and control various parameters such as power level(Gain), RF carrier frequency, oscillator reference adjustment, synthesizer frequency control and more. M & C card is composed of microcontroller, RAM, EPROM, RS232 interface, DAC/ADC and more. RS232 interface is used to remotely control various parameters using RS232 interface from PC. Sometimes RS485 is used due to its multi-drop and long distance advantages.

Power supply

Very stable power is used in order to achieve better phase noise required for interworking with satellite network. Power supply here converts -48V DC to other DC voltages such as +/-12, +/-15, +/-5 which are fed to other modules in the RF Transceiver. Power supply should have minimum ripple to obtain good performance.

Conclusion : The design steps outlined in this article on RF transceiver design can also be applied to RF transceivers on other frequency bands such as L band, Ku band, K band and Ka bands.



RF Transceiver RELATED LINKS

RF Trasceiver Manufacturers
RF Transceiver Test Procedure, how to test transceiver
5G RF Trasceiver Manufacturers
LoRa RF Trasceivers
Application of RF Trasceiver in VSAT

RF frequency converter applications

Following are the few of the applications in which rf frequency converters are being used.
➤RF Signal Generation and Analysis, Read More
➤C band RF Transceiver design and development, Read More
➤RF up converter design and RF down converter design in mmwave bands, Read More
➤RF Frequency converter used in GSM mobile phone, Read More
➤L Band Satellite modem, Read More

RF and Wireless Terminologies


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