In the field of radio technology and telecommunications, one is sure to come across two fundamental passive device RF components, couplers and power dividers, which are used to split/combine or divide electromagnetic signals. Although they are the same class of device, there are some notable differences between them in how the signals are split/divided as well as in terms of their actual roles.
Power dividers and couplers are passive devices as they have no source of energy to add to the signal that goes through them. Power dividers are terms often used interchangeably with power splitters – in reality, the two devices are separate components and have different characteristics.
The similarity lays in the fact that they both split/divide power in two separate lines. The devices differentiate themselves as far as physical characteristics and applications.
A power splitter is a unidirectional passive device that cannot be used as a power combining device. It has an input port with higher resistance than its two output ones. This allows it to be used as a calibrating and leveling device.
A power divider is bi-directional (reciprocal) and all ports (one input and two output ports) have the same resistance. This allows the device to be able to not only divide one signal in two lines but also two signals into one transmission line.
A directional coupler is a passive device with four different ports: It has an input port, transmitted port, couples port and an isolated port. The device allows one signal coming in through an input port to be divided in two signals of different amplitude (on two lines that are coupled).
The main line has the larger output while the coupled line is smaller and the difference can be calculated through a “coupling factor”. This device has several applications and can be used in amplifiers, receivers and transmitters as well as in measuring devices.
A special case of directional coupler is the hybrid coupler (3 dB directional coupler). This coupler divides the power equally. The phase difference of the output determines what type of hybrid coupler is at hand: a 90 degree hybrid or a 180 degree hybrid. These special couplers are important for devices such as mixers, power combiners, dividers, modulators, and some radar antennas.
• Power dividers have 3 ports and are used to divide a signal in 2 parts with equal power – they provide equal amplitude and phase balance splitting of the signal between the two output ports. A directional coupler has 4 ports and provides unequal splitting except as in hybrid couplers. It splits the power so that what comes through the first port is split in a part that goes through port 2 (the coupled port) while the remaining power is conveyed through the third port. The 4th port is isolated and no power is sent through it (ideally at least).
• A 4-port coupler uses no internal resistor and has one “terminated” isolated port. 3-door dividers, instead, have no internal resistor and have no isolated port.
• Couplers have no loss (no power radiates out of the network or is converted to heat). Power dividers offer no isolation as in the case of the simplest of the power dividers, the T-junction.
• Power dividers are used mainly for signal sampling so that two characteristics of a signal (frequency and power for example) can be measured. They are also used to distribute power to more than one antenna. Being bidirectional they can be used as power combiners. Couplers are used to sample signals by grabbing a fraction of the energy from a transmission line. This fragment is proportional to the transmitted energy which can then be measured without stopping the flow. They can also be used as a means to insert another signal within a system.
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