Microwaves are a form of electromagnetic radiation with wavelengths ranging from one meter to one millimeter; with frequencies between 300 MHz (100 cm) and 300 GHz (0.1 cm).
Different sources define different frequency ranges as microwaves; the above broad definition includes both UHF and EHF (millimeter wave) bands. A more common definition in radio engineering is the range between 1 and 100 GHz (300 and 3 mm).
Frequencies in the microwave range are often referred to by their IEEE radar band designations
Circulator: A circulator is used to isolate transmitter with the receiver input and to couple transmitter to antenna and antenna to receiver input.
Protection Circuitry: It provides safety to the mixer from overloads.
Mixer (Receiver): It has two outputs. One is the incoming signal and other is the signal from lower band pass filter (BPF).The mixer gives an IF signal of 70Mhz.
Band pass filter (BPF): It provides the necessary selectivity to the receiver and it prevents the interference.
IF amplifier and AGC:- It amplifies the signal up to a intermediate frequency of 70Mhz. and its gain is controlled through AGC (automatic gain control)
Amplitude limiter: As the signal is frequency modulated one so as amplitude limiter is used to avoid unwanted amplitude variations.
Mixer (Transmitter): It is used to convert IF frequency to transmitting microwave frequency band to pass through it and hence prevent interference.
POWER AMPLIFIER:-This amplifier amplifies the transmitted power from a repeater section in the range of 0.2W to 10W.
MICROWAVE SOURCE:- Klystron & Gunn Oscillators were used as microwave source. Now, V H F transistor crystal oscillators are used for microwave source.
POWER SPLITTER:- It divides the output power from a microwave source and feeds a large portion to the transmitter mixer, which converts it into transmitting microwave frequency.
SHIFT OSCILATOR:- It provides one of the inputs to the balanced mixer so that it produces 70MHz IF at the output of receiver mixer.
This microwave link communicates with 600 to 2700 channels per carrier. Thus the number of carriers in each direction can be four to twelve.
➨The microwave spectrum has larger bandwidth and hence large amount of information can be transmitted using it.
➨Day by day radio frequency spectrum is getting crowded. Microwave technology helps to manage crowded spectrum with the use of high selective receivers, modulation (SSB, PSK, QAM etc.) and spread spectrum techniques, data compression etc.
➨Microwave spectrum is divided into different channels as per application. The center frequencies for these channels are allocated with gaps between them so that channels will not overlap and do not cause interference to nearby channels.
➨Microwave communication is used since earlier days as one of the Line of Sight Communication in hilly remote areas where other means of wired communication is not possible to be installed. Microwave and satellite communications are prefect choice in such places.
Disadvantages of Microwave Communication
As we know microwave is used for microwave communication. Following are the disadvantages of Microwaves:
➨For the frequencies which are below 30MHz standard circuit analysis can be applied. For the frequencies in the microwave range, E-H wave analysis need to be applied.
➨As we know lumped components such as resistors, inductors and capacitors do not have same characteristics at microwave frequencies as they have at lower frequencies. Hence it is difficult to implement these components at microwave frequencies.
➨At microwave frequencies, transit time of current carrier i.e. electron is higher which takes large percentage of actual signal. Due to this fact, conventional transistors do not function properly at microwave frequency compare to lower frequency.
➨As microwave communication is limited to line of sight mode only, Other modes of communication are not possible.
Different sources define different frequency ranges as microwaves; the above broad definition includes both UHF and EHF (millimeter wave) bands. A more common definition in radio engineering is the range between 1 and 100 GHz (300 and 3 mm).
Frequencies in the microwave range are often referred to by their IEEE radar band designations
| Band | Frequency range | |
| HF | 0.003 to 0.03 GHz | High Frequency |
| VHF | 0.03 to 0.3 GHz | Very High Frequency |
| UHF | 0.3 to 1 GHz | Ultra High Frequency |
| L | 1 to 2 GHz | Long wave |
| S | 2 to 4 GHz | Short wave |
| C | 4 to 8 GHz | Compromise between S and X |
| X | 8 to 12 GHz | Used in WW II for fire control, X for cross (as in crosshair). Exotic. |
| Ku | 12 to 18 GHz | Kurz-under |
| K | 18 to 27 GHz | Kurz (German for "short") |
| Ka | 27 to 40 GHz | Kurz-above |
| V | 40 to 75 GHz | |
| W | 75 to 110 GHz | W follows V in the alphabet |
| mm or G | 110 to 300 GHz | Millimeter |
Basic Microwave Communication
Link
Microwave signal are used for communication over long distance continental or intercontinental. Microwave is the communication link which make the communication possible. The basic block diagram of microwave communication system is shown in figure.Construction:
Antenna:- Mostly a parabolic refractor types of antenna are used which is used to transmit and receive the signal.Circulator: A circulator is used to isolate transmitter with the receiver input and to couple transmitter to antenna and antenna to receiver input.
Protection Circuitry: It provides safety to the mixer from overloads.
Mixer (Receiver): It has two outputs. One is the incoming signal and other is the signal from lower band pass filter (BPF).The mixer gives an IF signal of 70Mhz.
Band pass filter (BPF): It provides the necessary selectivity to the receiver and it prevents the interference.
IF amplifier and AGC:- It amplifies the signal up to a intermediate frequency of 70Mhz. and its gain is controlled through AGC (automatic gain control)
Amplitude limiter: As the signal is frequency modulated one so as amplitude limiter is used to avoid unwanted amplitude variations.
Mixer (Transmitter): It is used to convert IF frequency to transmitting microwave frequency band to pass through it and hence prevent interference.
POWER AMPLIFIER:-This amplifier amplifies the transmitted power from a repeater section in the range of 0.2W to 10W.
MICROWAVE SOURCE:- Klystron & Gunn Oscillators were used as microwave source. Now, V H F transistor crystal oscillators are used for microwave source.
POWER SPLITTER:- It divides the output power from a microwave source and feeds a large portion to the transmitter mixer, which converts it into transmitting microwave frequency.
SHIFT OSCILATOR:- It provides one of the inputs to the balanced mixer so that it produces 70MHz IF at the output of receiver mixer.
This microwave link communicates with 600 to 2700 channels per carrier. Thus the number of carriers in each direction can be four to twelve.
Advantages of Microwave Communication
Following are the advantages of Microwave Communication:➨The microwave spectrum has larger bandwidth and hence large amount of information can be transmitted using it.
➨Day by day radio frequency spectrum is getting crowded. Microwave technology helps to manage crowded spectrum with the use of high selective receivers, modulation (SSB, PSK, QAM etc.) and spread spectrum techniques, data compression etc.
➨Microwave spectrum is divided into different channels as per application. The center frequencies for these channels are allocated with gaps between them so that channels will not overlap and do not cause interference to nearby channels.
➨Microwave communication is used since earlier days as one of the Line of Sight Communication in hilly remote areas where other means of wired communication is not possible to be installed. Microwave and satellite communications are prefect choice in such places.
Disadvantages of Microwave Communication
As we know microwave is used for microwave communication. Following are the disadvantages of Microwaves:
➨For the frequencies which are below 30MHz standard circuit analysis can be applied. For the frequencies in the microwave range, E-H wave analysis need to be applied.
➨As we know lumped components such as resistors, inductors and capacitors do not have same characteristics at microwave frequencies as they have at lower frequencies. Hence it is difficult to implement these components at microwave frequencies.
➨At microwave frequencies, transit time of current carrier i.e. electron is higher which takes large percentage of actual signal. Due to this fact, conventional transistors do not function properly at microwave frequency compare to lower frequency.
➨As microwave communication is limited to line of sight mode only, Other modes of communication are not possible.
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