What is duplexer in radar ?
Most of the wireless communication systems use single antenna to transmit and receive. During transmission, duplexer connects transmit section to the antenna where as during reception, it connects receive section to the antenna. During transmission, receiver part is isolated to prevent damage to its sensitive components. During reception, transmitter part is isolated so that its high power electromagnetic pulses do not overload receiver. The function of duplexer is to act as fast self actuating SPDT switch or Transmit/Receive Switch so that single antenna is shared between transmitter and receiver by isolating them.
Signal in radar flows in both transmitting and receiving path as follows:
(Transmitting Path) : Transmitter ￫ Duplexer ￫ Antenna ￫ radio frequency wave ￫ Target
(Receiving Path) : Display ￩ receiver ￩ Duplexer ￩ Antenna ￩ Echo ￩ Target
How does a duplexer work
Radar systems operate by sending out a short pulse of electromagnetic (EM) energy usually in radio frequency range and then listen for return echo from any targets or objects as desired. A duplexer enables radar to switch between transmitting and receiving modes rapidly. It should ensure that the radar system does not damage its own sensitive receiving components while transmitting.
The purpose of duplexer in radar system and its working are explained as follows.
• Transmit mode : In this mode, radar system generates high power pulse of EM energy that is sent to antenna for transmission.
Duplexer connects the transmitter to the antenna (& disconnect the receiver) during this period. The antenna radiates the energy into the air as radar pulse.
• Receive mode : After transmitting the pulse, radar system needs to quickly switch from transmit to receive mode to listen for echo.
Duplexer connects the receiver to the antenna (& disconnect the transmitter) during this period. This is needed as transmitted pulses are quite powerful
and could overload the sensitive receiver & its components (e.g. LNAs), if it is directly exposed to transmitted energy.
• Duplexer functionality : It allows single antenna to be connected to both transmitter and receiver but not simultaneously. It acts as a switch.
• Isolation : The key feature of duplexer is to provide sufficient isolation between transmitter and receiver at all the times.
• Switching/Timing : The duplexer operates on precise switching process which happens in very short time frame, often on the order of
microseconds. It rapidly switches between transmit and receive modes allowing the radar system to alternate between sending out pulses and
listening for echoes.
Radar duplexer types
There are three main types of radar duplexers viz. Branched duplexer, Balanced Duplexer and Circulator duplexer. Following section mentions functional difference between them.
Branched Duplexer
This type of duplexer utilizes combination of RF switches and filters to achieve separation between transmit and receive signals. It is called "branched" as it separates transmit and receive paths into distinct branches.
Figure-2 depicts branched duplexer. It is very old design but still in use in low cost radars used in small boats. It employs one or more ATR and a receiver protector. ATR is the short form of Anti Transmit Receive Tubes.
The main advantages of branched duplexer is simple in design, compact in size and its low cost. The main disadvantage of this duplexer is limited operational bandwidth.
Balanced Duplexer
This type of duplexer employs balanced transmission lines, filters and phase cancellation to separate transmit and receive signals. The purpose of this type is to eliminate need of RF switches to avoid losses and complexity in the duplexer design.
Figure-3 depicts balanced duplexer. It uses features of two 3dB short slot type hybrid couplers. It is used to control direction of power flow. It is designed to maximize isolation without using RF switches.
The advantages of balanced duplexer type is its power handling capability and operational bandwidth. The main disadvantages are physical size and relative port locations.
Circulator Duplexer
This type of duplexer uses device called circulator to separate transmit and receive signals. A circulator is a non-reciprocal device that routes signals from one port to another in specific direction.
Figure-4 depicts circulator duplexer of ferrite type. It is most commonly used in modern radar systems. Circulator duplexer allows signals to flow in only one direction and prevents echoes from entering the transmit path and reducing the interference. Refer 3 port circulator➤➤.
Manufacturers
Following are the manufacturers of Radar Duplexer in USA.
| Companies |
|---|
| Amplitronix, CA, USA |
| Anatech Electronics, NJ, USA |
| CERNEX, CA, USA |
| ClearComm Technologies, MD |
| CMT Filters |
| CTS Corporation |
| KMW, CA, USA |
| KR Electronics, NJ, USA |
| LUXCONN Technology, Korea |
| Maxim Integrated, CA, USA |
| Microwave Filters, Italy |
| Murata Electronics, GA |
| Panasonic, NJ |
| RTx Technology Co. Ltd, South Korea |
| Triquint Semiconductor, FL, United States |
| TELSA, Italy |
Conclusion : In summary, a duplexer enables sharing of single antenna for both transmitting and receiving functions by isolating the high-power transmitter and the sensitive receiver as required. The switching capability of duplexer allows radar systems to operate efficiently and reliably in various applications without damaging its own components. The choice of which type of duplexer to use depends on the specific needs of the radar system and various trade-offs.