London Digital PR

Digital PR

Latest News

More About RF Switches


 

RF Switches are used in cellular/PCS test facilities, OEM test equipment, VSAT, commercial, military and space applications, avionics, ground based and satellite communications, broadcasting, and various other applications. An RF Switch Matrix is used in design verification and manufacturing tests, to route high frequency signals between the device and the test & measurement equipment. Besides signal routing, the RF Switch Matrix can have signal conditioning devices, like attenuators, filters, and directional couplers, and amplification and frequency converters. Since the requirements of different test systems are different, a Matrix has to be custom designed by the test system engineer or a hired contractor each time. The RF Switch Matrix has switches and signal conditioners mounted together. Cables connect the switches and signal conditioners. It uses a driver circuit and power supply to power and drive the switches and signal conditioners.

The RF Switch Matrix can use connectors to reroute some signal paths fixtures can also be used for the measurement apparatus of the device being tested. It is located close to the device in the test system to reduce the signal paths to the device in order to lower insertion loss and signal degradation. RF switching products can be described by the usage of  two central specs: topology and  certain bandwidths. While these specifications are important, the following specifications must also be considered when designing a RF switch network:

Characteristic impedance: This transmission line parameter is determined by the physical structure of the line. It also helps to determine how propagating signals in the line are transmitted or reflected. Impedance of RF components is not a DC resistance; it can be calculated for a transmission line.


Bandwidth: Though an important specification, bandwidth only gives an approximation of the performance of a given product, as different vendors use different processes for establishing a bandwidth specification for an RF switch.

Insertion Loss: Power loss in the signal chiefly occurs if the length of the transmission line it is made to broadcast through is greater than 0.01 of its own wavelength. The “insertion loss” specification of a switch module is a measure of this power loss and signal reduction. To calculate the power loss or voltage attenuation caused by the switch on a signal at a certain frequency, insertion loss of a switch module at that frequency can be used.

Return loss and voltage standing-wave ratio (VSWR): This is the ratio of reflected-to-transmitted waves. High-frequency signals take the form and shape of waves when passing through a transmission line or cable. Reflections occur when the signal traverses over different media, like it does for sound and light waves. VSWR can be used to compute the amount of power loss in the transmission line because it is a measure of the power of the reflected wave.

Topology: Consider this feature carefully before settling for an RF switch as the wrong topology can impact insertion loss and VSWR. The main topologies available for RF are multiplexers and single-pole double-throw (SPDT) relays. Different applications call for different combinations of RF switch topologies.


Isolation and crosstalk: Isolation is the magnitude of a signal that gets coupled across an open circuit. Crosstalk is the magnitude of a signal that is coupled between circuits (such as separate multiplexer banks on an RF module).

Frequency - Specify the actual frequency to be used a minimum bandwidth. This often results in reduced testing time and associated costs. Electromechanical switches are capable of higher frequencies and greater bandwidths than what is actually used.

Phase & amplitude matching - Switches are offered with phase and/or amplitude matching between two ports of a switch, or between similar ports on different switches, or a combination of the two.

In conclusion, to select the best and most cost-effective RF switch for an application, a thorough review of the datasheet of the product is needed to determine whether its specifications meet the requirements of the system.

 

Bookmark and Share

© 2009 London Digital PR Ltd - Designed by The Creative Clinic