Waveguides and waveguide switches, specifically those switches used to transfer radio frequency (RF) signals propagating through waveguides, as those terms are commonly understood in the RF communications art, are used in many radio frequency (RF) communications applications. Such devices are described in, for example, U.S. Pat. No. 7,330,087 to Gorovoy, et al., issued on Feb. 12, 2008, the disclosure of which is incorporated herein by reference in its entirety.
One typical use of such a switch is for system configuration purposes, meaning that power is not going through the switches while they are being switched. FIG. 1 illustrates a typical dual channel communications system employing waveguide switches 110A, 110B, 110C, and 110D. Each switch has four waveguide ports 111-114, although only port 111 is annotated for drawing clarity. In use, terminal 120A is shown configured to transmit signal input 123A via high power amplifier (HPA) 125A, low band filter 127A, and the vertical polarization of feed 130A. At the same time, also utilizing switch 110A, the horizontal polarization of feed 130A is connected, via high band filter 135A to low noise amplifier (LNA) 137A and then out on receiver output 140A. The other three terminals 120B, 120C, and 120D are similarly configured as shown.
When the operator desires to reconfigure the equipment, as for example, switching terminal 120A to receive on the vertical polarization instead of the horizontal (as shown in solid lines 150), switch 110A is switched to the position shown by grey lines 155. In this configuration, vertically polarized signals at feed 130A are coupled through low band filter 127A to LNA 137A. As can be seen, terminals 120B, 120C, and 120D would also have to be reconfigured for the overall system to operate correctly.
Such exemplary waveguide switches typically have relatively low propagation (or impedance) losses. Such switches, however, typically only provide a limited amount of signal isolation between switch positions. Prior waveguide switches known in the art typically use a central cylinder that rotates in an enclosure. The enclosure has a waveguide port on each side, and the cylinder has paths milled into it to direct the RF energy from port to port. The interface between the outer housing and inner cylinder is the curvature of the cylinder. By definition, these prior art switches require a gap so the cylinder can rotate in the housing. This gap is the reason isolation is limited to levels such as 60 dB for Ku Band (moving up to 80 dB at C band).
Given this limited isolation, typical waveguide switches (known in the art as “baseball” switches, for the position label on top) commonly leak the high power transmit signal (from the HPA) into the sensitive receive chain, thus saturating the LNA and degrading performance. Thus, when using a switch to separate a high power transmit path from a low power receive path, as depicted in FIG. 1, isolation becomes critical. In fact, analysis has shown that isolation values of 110-120 dB can be required in modern communications systems.
The most direct method of providing high isolation is to eliminate switches 110, replacing them with short sections of waveguide bolted together. Isolation can thus be made extremely robust, although at the expense of the time necessary to reconfigure. In order to reconfigure the system, the operator must remove the waveguide sections and reattach them to effect the cross connection. This mechanical reconfiguration involves handling a good deal of discrete hardware (bolts, nuts, washers) and electromagnetic interference (EMI) gaskets, which is both time consuming and difficult in harsh environments. For example, making such a changeover in a failure situation under Arctic weather conditions, using gloves is nearly impossible. Often gaskets get crushed and the hardware gets lost. The typical field technician is increasingly unfamiliar with RF waveguides and therefore the current method can easily be done incorrectly, adding substantial time to the setup.
Another typical prior art method for providing both configuration switching and high isolation is to string four waveguide “baseball” switches together, as shown in FIG. 2. In this implementation, the functionality of switch 110 at its ports 111-114 is provided by the connection of switches 201, 202, 203, and 204. These switches are interconnected with waveguide sections 211, 212, 213, and 214 as shown, using electromagnetic interference (EMI) gaskets and bolts (not shown) at each RF flange 220. Impedance matching loads 230 are required on the fourth port of each switch 201, 202, 203, and 204 in order to ensure the maximum isolation of each switch is achieved. This arrangement doubles the isolation achieved, but requires four switches, four waveguide sections, and four loads. Such an implementation, while widely used, is costly and consumes much real estate on the (typically) cramped system pedestals and other mounting devices.
FIG. 3 shows a plan view of the physical configuration of the switches and waveguides of FIG. 2. Here, the “baseballs” 310 show the signal path configuration of each switch. As shown by lines 312, input 123 is connected to port 111 (via HPA 125, not shown). Switch 201 is configured to couple the signal, via waveguide section 211 to switch 202 and then out on port 112. The cross-connections using waveguide sections 212 and 213 are terminated into loads 230 on both ends, thus providing the necessary isolation.
Switching all four of switches 201, 202, 203, and 204 activates the cross-connections (port 111 to port 113 and port 112 to port 114) over waveguide sections 212 and 213 while simultaneously terminating the straight connections 111 to 112 (via waveguide 211) and 113 to 114 (via waveguide 211) to loads 230.