RFRadar Duplexers: Types and Functionality in Radar Systems
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Most wireless communication systems utilize a single antenna for both transmission and reception. In radar systems, this is achieved using a duplexer. The duplexer acts as a switch, connecting the transmitter to the antenna during transmission and the receiver to the antenna during reception.
Crucially, the duplexer isolates the receiver during transmission to prevent damage to its sensitive components. Similarly, during reception, it isolates the transmitter to prevent its high-power electromagnetic pulses from overloading the receiver.
In essence, the duplexer functions as a fast self-actuating SPDT (Single-Pole Double-Throw) switch or a Transmit/Receive (T/R) switch, enabling a single antenna to be shared between the transmitter and receiver by isolating them.
The signal flow in a radar system, both during transmission and reception, is as follows:
- (Transmitting Path): Transmitter → Duplexer → Antenna → Radio Frequency Wave → Target
- (Receiving Path): Display ⟵ Receiver ⟵ Duplexer ⟵ Antenna ⟵ Echo ⟵ Target
How a Duplexer Works
Radar systems operate by emitting short pulses of electromagnetic (EM) energy, typically in the radio frequency range, and then listening for return echoes from targets or objects of interest. A duplexer facilitates rapid switching between transmitting and receiving modes. It’s essential that the duplexer prevents the radar system from damaging its own sensitive receiving components during transmission.
The purpose and operation of a duplexer in a radar system can be summarized as follows:
- Transmit Mode: The radar system generates a high-power pulse of EM energy, which is directed to the antenna for transmission. During this phase, the duplexer connects the transmitter to the antenna while disconnecting the receiver. The antenna radiates the energy into the air as a radar pulse.
- Receive Mode: After transmitting the pulse, the radar system needs to quickly switch to receive mode to listen for echoes. The duplexer then connects the receiver to the antenna while disconnecting the transmitter. This is crucial because the transmitted pulses are quite powerful and could overload the sensitive receiver and its components (e.g., Low Noise Amplifiers - LNAs) if directly exposed to the transmitted energy.
- Duplexer Functionality: It allows a single antenna to be connected to both the transmitter and receiver, but not simultaneously. Essentially, it acts as a switch.
- Isolation: A key feature of the duplexer is providing sufficient isolation between the transmitter and the receiver at all times.
- Switching/Timing: The duplexer operates with precise timing, switching rapidly between transmit and receive modes, often on the order of microseconds. This allows the radar system to alternate efficiently between sending out pulses and listening for echoes.
Radar Duplexer Types
There are three main types of radar duplexers:
- Branched Duplexer
- Balanced Duplexer
- Circulator Duplexer
The following sections describe the functional differences between these types.
Branched Duplexer
This type of duplexer uses a combination of RF switches and filters to separate transmit and receive signals. It’s termed “branched” because it separates the transmit and receive paths into distinct branches.
Figure 2 illustrates a branched duplexer. This is an older design, but it’s still used in low-cost radars in small boats. It employs one or more ATR (Anti-Transmit Receive) tubes and a receiver protector.
The main advantages of a branched duplexer are its simple design, compact size, and low cost. However, its primary disadvantage is its limited operational bandwidth.
Balanced Duplexer
This type of duplexer employs balanced transmission lines, filters, and phase cancellation to separate transmit and receive signals. The goal of this design is to eliminate the need for RF switches, thereby avoiding losses and complexity in the duplexer design.
Figure 3 depicts a balanced duplexer. It utilizes the features of two 3dB short-slot-type hybrid couplers. These couplers control the direction of power flow. The design maximizes isolation without using RF switches.
The advantages of the balanced duplexer type include its power handling capability and operational bandwidth. The main disadvantages are its physical size and the relative port locations.
Circulator Duplexer
This type of duplexer uses a device called a circulator to separate transmit and receive signals. A circulator is a non-reciprocal device that routes signals from one port to another in a specific direction.
Figure 4 shows a circulator duplexer of the ferrite type. This is the most commonly used type in modern radar systems. A circulator duplexer allows signals to flow in only one direction and prevents echoes from entering the transmit path, thereby reducing interference.
Manufacturers
The following is a list of manufacturers of Radar Duplexers in the 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 the sharing of a single antenna for both transmitting and receiving functions by isolating the high-power transmitter and the sensitive receiver as needed. The switching capability of a duplexer allows radar systems to operate efficiently and reliably in various applications without damaging their components. The choice of which type of duplexer to use depends on the specific needs of the radar system and the associated trade-offs.
