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Switches

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RF and Microwave Switches:- About, Types, Application, Design:

RF and Microwave switches are passive components with control circuits to route RF  signals through different transmission paths with a high degree of efficiency.

Four fundamental parameters which decide the performance of RF and microwave switches are isolation between the channels, insertion loss of the RF switch in a channel, controller switching time, and power handling of the RF switch.

In this article about RF switch, we will cover the following topics.

  • What is an RF Switch?
  • Types of RF Switch?
  • Applications of RF and Microwave Switches?
  • What are the specifications that need to consider in the selection of RF Switches?
  • RF and Microwave SwitchManufactures.

In general RF switches are available in Coaxial, Waveguide, and surface mount packages with USB, Ethernet, and SPI control interfaces for the switching of the RF signal.

To learn more about RF and Microwave, we recommend you to check the following article.

Design and Application

RF SWITCH Design concept?

As there is an increasing need for the RF and microwave switches for switching of RF signals that range up to 40 GHz, mainly RF switches are of connectorised package. For the higher frequency application, both waveguide, as well as the connectorised RF and Microwave switches, are available.

  • Mainly four switching technologies are used for the RF and Microwave switches, hybrid solid-state RF switch, Electromechanical RF switches, MEMS RF switches, and PIN diode RF switches. Each RF switch technology offers various features and RF capabilities uniquely to them.

Efficient RF signal switching within a circuit to route signals from the input port to the output port is a vital part of the RF switch design. In the world of 5G, which is going to be a new wireless standard, RF switching among the multiple-input, multiple-output (MIMO), and beamforming needed to be considered in the design.

RF and Microwave Switch types:

RF and microwave switches can be categorized on the basis of Technology, Number of RF ports, and package types.

Classification Based on Technology:

RF switches are basically classified into 4 types on the basis of technology.

Electromechanical RF switch: 

In Electro-mechanical RF switches, motor-controller and manual mechanical control are used for the switching applications. Due to the incorporation of a series of coils and mechanical contacts for switching purposes Electromechanical RF switches are of larger assemblies.

  • In Electromechanical RF switches, ordinary relays which have electrically energized coils are used to move the relay contacts for the switching of the signals with speeds in the milliseconds.

In Electromechanical RF switches, switching can be controlled remotely through the use of 12 or 24-volt lines.

Advantages:

Low insertion loss (< 0.1 dB), high isolation (>85 dB), operate from DC up into millimeter-wave frequencies, Handle high power levels up to thousand of watts of peak power, and have no video leakage.

Disadvantage:

EM switches are not practical for in-circuit small (size), lightweight, or high-speed RF switching applications.

Hybrid solid-state RF switch:

Solid-state RF switches use semiconductor materials for the switching relay of RF switches. As it is electronic transistors switch, they make the switching of “on” and “off” transition quickly in microseconds and can make in small packages.

  • Solid-State RF switches are again categorized as absorptive or reflective.

In the SS RF switch, switching is controlled by the driver circuit, some have the internal, and some need an external driver with TTL logic functions. Solid-State absorptive and reflective RF switch details are as below.

Absorptive RF switches:

Absorptive RF switches are terminated with a 50-Ω load in each output port. Internal termination offers low VSWR (voltage standing wave ratio) in the channel in both states of the switch. In absorptive RF switch terminating resistance absorbs the incident RF signal energy hence it avoids the reflection of RF signal from the unterminated RF port. Absorptive switches are ideal to use in circuits where it’s important to avoid RF signal refection to the source if the RF ports are not terminated with RF Terminators.

Reflective RF switches:

Reflective RF switches are not terminated internally with resistors. In the open ports of reflective RF switches, the signal will get reflected and it offers lower insertion loss, it can be used for the circuit where VSWR isn’t critical.

Advantages:

High switching speed, low power consumption, and small size make SS RF switch better than an electromechanical RF switch.

Disadvantages:

For Solid State, RF switches isolation and characteristics performance is lower than an Electromechanical RF switches.

PIN diodes RF Switch:

In the PIN diode RF switch, diodes are used for switching the RF signal.PIN diode RF switches offer high switching speed and the performance will match other types of RF switches.

MEMS RF switch:

In MEMS RF switches, the switching mechanism is based on cantilevered MEMS elements. It is similar in operation to MEMS accelerometers. It is an electronically controlled switch that provides metal-on-metal contact for the RF and microwave signal to travel from the input to the output port.

Classification Based on Number of Ports:

RF switches are available in are several design configurations on the base of the number of RF input and output ports. Type is defined on the base of no of input and output RF switching ports. In a single-pole, a single through consists of one input and on-off controllable one output port. In single-pole / Multi through, one input signal can switch between multiple output ports. In Double-pole/double-throw they have four ports, 2 for input and 2 for output this RF switch is the capability to switch two loads between two sources using a controller.

Example:

  • Single-pole / single-throw (SPST)
  • Single-pole/Multiple-throw or higher (SPXT: SP4T, SP6T, SP8T, and SP10T)
  • Double-pole/double-throw (2P2T)

Mechanical and solid-state RF switches in any combination are available for 50-ohm and 75-ohm impedance matches.

Classification Based on the package:

RF switches are available in mainly 3 types, a connectorised package, waveguides, and an SMD package.

Connectorized RF Switch:

Connectorized RF switches are available in a variety of package sizes and connector configurations like SMA, N, BNC in both genders types as per the customer needs.

  • Please check the connectors page for details about different connector capabilities.

In general coaxial packages are used for switching RF signal up to 40 GHz and these switches are capable of handling high-power RF signals on the base of connectors' power handling rate. 

  • Package styles are available in both commercial grades and high-rel grades which are hermetically sealed for the field application which will withstand harsh environmental conditions.

Wave Guide RF switch:

For high-frequency applications, waveguide ports are widely used covering microwave and millimeter-wave frequency bands.

  • Waveguide switches offer the very lowest insertion loss.

SMD RF switches:

RF and microwave switches are available in SMD packages for use in RF boards. Basically, SMD RF switches are for the baseband frequency applications and handle lower power range.

Applications of RF Switch:

In general RF switches are used to root the RF signal in different channels. On the basis of application, we can classify them as multiplexers and general-purpose relay switches.

General-purpose RF relay switches:

RF switches are typically in use to route input RF signal between multiple channels.

Example:

If you have an RF signal from an antenna and need to root among different 2 receiver channels, you can use the SPDT switch at the output of the antenna and connect each receiver at each output port of the switch.

Multiplexers:

RF switch can be used to route multiple inputs to a single unit. Multiplexer help to reduce the cost in the field of testing by avoiding multiple sources and accessories requirements.

Example:

If you need to connect multiple sources to a single antenna and need to operate only one at a time. We can connect multiple sources to multiple input ports of the RF switch and the output port can connect to an antenna. Using a controller, we can switch among the sources.  

Basics & Selection Feature

Main selection specifications for RF Switch.

When selecting an RF Switch following are the prime factors that need to consider for the suitable design of the RF and microwave systems.

Frequency: 

RF switches are optimized for a particular frequency range of operation. It is important to select an RF switch that covers the full range of frequency operations needed.

The number of ports and package types:

The designer needs to select the RF switch which meets the package size matching the overall system requirement. The number of input and output ports need to match as per the application. For the critical application where refection from the open port is a concern, the designer needs to select an absorptive type of RF switch.

Isolation:

Isolation of the RF switch indicates the attenuation between the input and output ports of the switch. It indicates how effectively a switch enters its “off” state. The high isolation RF switch is better for the design.

Power Handling:

Power handling of the RF switch is the maximum RF signal power an RF switch can handle before breaking down.  The power handling input port indicates the amount of received power the RF switch can handle without degradation of electrical performance. Need to select an RF switch with power handling higher than the maximum expected power flow through it.

Insertion loss:

Insertion loss of RF switch is referred to as the amount of RF power lost during the transmission of RF signal through the RF switch during its “on” state. Insertion loss will lead to the addition of the system’s noise level. Need to select an RF switch with lower insertion loss.

Switching time:

Switching time indicates the amount of time an RF switch takes for changing its state from on to off or vice versa. RF switches may take several microseconds for Electro-Mechanical switches and to a few nanoseconds, low-power Solid State switches. Switching time is the measurement of time an RF switch takes to change from 50% of the input control voltage to 90% of the final RF output power.

Maximum VSWR:

VSWR indicates the internal reflection of the RF switch. If the VSWR is lower, better the RF and Microwave switch.

Impedance:

Characteristic Impedance of the RF switch should be matched to the impedance of the RF system. A perfect match of 50 ohms and 75 ohms are generally available for RF switches.

RF connectors and Dimension:

RF connectors of the RF switch need to select as per the application where it is going to use. RF connector options are available in SMA, N, BNC, 2.92, etc need to select as per the frequency of operation requirement. The physical size needs to consider in selection.

Environmental Parameters: 

The designer needs to select an RF switch that meets the environmental parameters like operation and storage temperature, humidity, etc. For external use, it is ideal to select a hermetically sealed RF and Microwave switch.

Conclusion:

RF Switches are RF components used to switch the RF and microwave signals among the different channels. RF and microwave switches are available with different dimensional packages and types like connectorized, waveguide, SMD, etc.

Below is the list of top-rated RF and Microwave switch manufacturers listed with the RF and Microwave Community. If you would like to add a new RF switch manufacturer feel free to recommend us through the contact us or through the manufacture registration button on the top of the RFMWC website.

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RFMWC



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