Crosspoint matrices are created from arrays of SPST relays arranged as a simple grid. Tree Matrices are created from Tree
Multiplexers to provide solutions for matrices requiring very high RF or microwave bandwidths. In creating these matrices
they also restrict the connectivity that can be provided. Implementation of Tree Matrixes can be complicated by the difficult
routing that they impose on PCB designs as there are large numbers of crossing tracks. or by the number of coaxial connections
required. In products such as the 60-700 series this is managed by constructing matrices from PCB assemblies which are
at right angles to each other using an internal interconnect system that avoids coaxial cable connections.
(Find more information on Crosspoint and Tree Matrices)
There is another type of matrix used by Pickering Interfaces whose purpose is to increase bandwidth but without some of the routing issues associated Tree Matrices. This is the basis of the matrix design contained within our LXI Wideband Modular Chassis (model 65-110).
Crosspoint matrices always have tracks on the design which are "stubs" acting as un-terminated transmission lines. These load the transmission lines and limit the bandwidth of the matrix. A basic objective of the stubless architecture is that it avoids these long transmission line stubs by using the relays in a different way.
Instead of implementing the crosspoints with an SPST relay each crosspoint is constructed from two changeover relays as shown. Those two changeover relays can be in the same package or can be independent relays depending on the level of performance required.
With the relays in the position shown signals on the Y axis (blue) pass straight through the matrix. To enable an Y to X connection then blue and red relays at the intersection are operated and a path is established which also disconnects the onward track, so creating a path with no large stubs that limit the bandwidth.
As with matrices based on Tree multiplexers the routing imposes a restriction that only one connection from a given X or Y is permitted, but permitting more than one would create RF issues that cannot be easily avoided. Each path has a different number of series relays so unlike matrices based on tree networks insertion loss cannot easily be made the same for all paths.
The 65-100 matrix was chosen by CERN for monitoring purposes and uses a stubless matrix construction. To minimize the number of relays in each path an interleaving system is also used.