Abstract:
A circuit card can include a circulator for routing a signal from a first amplifier to an antenna and for routing a signal from the antenna to a second amplifier, replacing a traditional transfer switch. The circulator can be a surface mount element to enable the circulator, first amplifier, and second amplifier to be mounted on the same circuit card thereby minimizing the size of a transceiver that employs the circuit card. Multiple circulators can be included on the same circuit card to allow for multi-band operation.

Description:
BACKGROUND 
     A transceiver is a device that includes both transmit (Tx) and receive (Rx) capabilities. Oftentimes, a transceiver will employ a single antenna to both transmit and receive signals. To enable the use of a single antenna, a switch is often used. For example,  FIG. 1  illustrates a circuit diagram  100  of a typical transceiver that employs a switch  102  for controlling the function of the transceiver. In particular, switch  102  controls whether a signal received from a Tx amplifier  101   a  is output to antenna  103 , or whether a signal received from antenna  103  will be routed to an Rx amplifier  101   b.    
     Various problems exist with the circuit configuration depicted in  FIG. 1 . For example, switches are relatively lossy thereby limiting the performance of such circuits or requiring additional circuitry to account for the losses. Also, switches are currently incapable of relaying sufficient RF signal power at higher frequencies. In particular, the insertion loss of a switch is proportional to its operating frequency. Power that is dissipated due to the switch&#39;s insertion loss causes a temperature rise at the switch. If the temperature exceeds the switch&#39;s thermal limits, the switch can be irreversibly damaged. Additionally, the power that is dissipated in the switch is also proportional to the RF power transferring through the switch. This dissipated power also increases the temperature of the switch. For these reasons, transceivers that operate at higher frequencies (e.g. in the Ku Band) cannot be operated at sufficient power levels (e.g. 20 watts) for many applications due to the risk that the switch will be damaged from excessive temperatures. 
     Further, switches suitable for use at RF to millimeter wave frequencies are relatively large and are connectorized. Connectorized refers to the use of a coaxial connector attached directly to the RF component signal path used to route the intended signal between components via an RF cable assembly. For example, a connectorized component typically includes one or more coaxial connectors. In  FIG. 1 , these connectors are identified as elements  102   a - 102   c .  FIG. 2  also provides an example of a connectorized switch  202  that includes three coaxial connectors  202   a - 202   c . Connectorized switch  202  is an example of a suitable switch that can be used as switch  102  in some transceiver implementations. 
     As can be seen, the connectors of a connectorized component increase the size of the component substantially. Also, because the connectors of a connectorized component are not directly connected to the circuit board, separate wires (such as coaxial cables) are required to connect other components to the connectorized components. Usage of connectorized components therefore requires a much larger overall system footprint and increases the weight of the transceiver. Further, the size of a connectorized component must increase with increased power loading to adequately dissipate temperature rise. Therefore, even if a connectorized switch is available at a high frequency (which is not the case at certain higher frequencies), the size of a suitable connectorized switch is oftentimes prohibitively large. 
     SUMMARY 
     In some embodiments, the present invention is implemented as a circuit card assembly that comprises a circulator having a first port, a second port, and a third port. The second port is configured to be connected to an antenna to allow radio frequency signals to be provided to the antenna and received from the antenna. The circuit card assembly also comprises a first amplifier having an output that is connected to the first port of the circulator such that radio frequency signals output by the first amplifier are output from the second port of the circulator. The circuit card assembly further comprises a second amplifier having an input that is connected to the third port of the circulator such that radio frequency signals input to the second port of the circulator are received at the input of the second amplifier. 
     The circulator may be a surface mount element. The circulator may be configured to operate at power levels up to 20 watts and/or at frequencies of at least 12 GHz. The first amplifier may be a power amplifier while the second amplifier may be a low noise amplifier. The circuit card assembly may also include a filter connected to the second port of the circulator for filtering radio frequency signals transmitted to and received from the antenna. 
     In some embodiments, the circuit card assembly may include a second circulator, a third amplifier, and a fourth amplifier. The second circulator may have a first port, a second port, and a third port. The second port may be configured to be connected to the antenna to allow radio frequency signals to be provided to the antenna and received from the antenna. The third amplifier may have an output that is connected to the first port of the second circulator such that radio frequency signals output by the third amplifier are output from the second port of the second circulator. The fourth amplifier may have an input that is connected to a third port of the second circulator such that radio frequency signals input to the second port of the second circulator are received at the input of the fourth amplifier. The first and second amplifiers may be configured to operate at different frequencies than the third and fourth amplifiers. 
     In some embodiments, the circuit card assembly may include a first filter connected to the second port of the circulator for filtering radio frequency signals transmitted to and received from the antenna, and a second filter connected to the second port of the second circulator for filtering radio frequency signals transmitted to and received from the antenna. 
     In some embodiments, the circuit card assembly may include a connector separate from the circulator for connecting the second port of the circulator to a separate assembly that includes the antenna. In some embodiments, the circuit card assembly may include a limiter connected between the third port of the circulator and the input to the second amplifier. 
     In other embodiments, the present invention is implemented as a system that comprises a circulator having a first port, a second port, and a third port. The second port is configured to be connected to an antenna to allow radio frequency signals to be provided to the antenna and received from the antenna, a first amplifier having an output that is connected to the first port of the circulator such that radio frequency signals output by the first amplifier are output from the second port of the circulator, and a second amplifier having an input that is connected to the third port of the circulator such that radio frequency signals input to the second port of the circulator are received at the input of the second amplifier. The circulator, the first amplifier, and the second amplifier are surface mounted on the same circuit card. The system may be configured to operate at frequencies about 12 GHz and at power levels of up to 20 watts. 
     In some embodiments, the system may include an antenna assembly that is separate from the circuit card. In such embodiments, the circuit card of the system may include a connector separate from the circulator for connecting the second port of the circulator to the antenna assembly. 
     In some embodiments, the system may include a second circulator, a third amplifier, and a fourth amplifier that are surface mounted on the circuit card. The second circulator may have a first port, a second port, and a third port. The second port may be configured to be connected to the antenna to allow radio frequency signals to be provided to the antenna and received from the antenna. The third amplifier may have an output that is connected to the first port of the second circulator such that radio frequency signals output by the third amplifier are output from the second port of the second circulator. The fourth amplifier may have an input that is connected to the third port of the second circulator such that radio frequency signals input to the second port of the second circulator are received at the input of the fourth amplifier. 
     In other embodiments, the present invention is implemented as a circuit card assembly that includes a first circulator having a first port, a second port, and a third port. The second port is configured to be connected to a first antenna to allow radio frequency signals to be provided to the first antenna and received from the first antenna. The circuit card assembly also includes a first amplifier having an output that is connected to the first port of the first circulator such that radio frequency signals output by the first amplifier are output from the second port of the first circulator, and a second amplifier having an input that is connected to the third port of the first circulator such that radio frequency signals input to the second port of the first circulator are received at the input of the second amplifier. The circuit card assembly further includes a second circulator having a first port, a second port, and a third port. The second port is configured to be connected to a second antenna to allow radio frequency signals to be provided to the second antenna and received from the second antenna. The circuit card assembly additionally includes a third amplifier having an output that is connected to the first port of the second circulator such that radio frequency signals output by the third amplifier are output from the second port of the second circulator, and a fourth amplifier having an input that is connected to a third port of the second circulator such that radio frequency signals input to the second port of the second circulator are received at the input of the fourth amplifier. The first amplifier outputs radio frequency signals that have a different frequency than radio frequency signals output by the third amplifier. 
     In some embodiments, the first circulator, the first amplifier, the second amplifier, the second circulator, the third amplifier, and the fourth amplifier are all surface mounted on the circuit card assembly. The second ports of the first and second circulators may both be connected to a separate connector that is also mounted on the circuit card assembly. The separate connector may be used to connect the second ports to a separate antenna assembly that includes the antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a circuit diagram of a typical transceiver configuration in which a switch is employed to connect the Tx and Rx amplifiers to the antenna. 
         FIG. 2  illustrates an example prior art connectorized component. 
         FIG. 3  illustrates an example circuit diagram in which a circulator is used as a Tx/Rx switch in accordance with one or more embodiments of the invention. 
         FIG. 3A  illustrates a variation to the circuit of  FIG. 3  that includes a limiter between the circulator and the Rx amplifier in accordance with one or more embodiments of the invention. 
         FIG. 4  illustrates another example circuit diagram in which two circulators are used as Tx/Rx switches to enable dual band operation. 
         FIG. 5  illustrates a portion of an example circuit card assembly on which surface mount amplifiers and a circulator are employed in accordance with the techniques of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     This specification describes exemplary embodiments and applications of the invention. The invention, however, is not limited to these exemplary embodiments and applications or to the manner in which the exemplary embodiments and applications operate or are described herein. Moreover, the figures may show simplified or partial views, and the dimensions of elements in the figures may be exaggerated or otherwise not in proportion. In addition, as the terms “on,” “attached to,” or “coupled to” are used herein, one element (e.g., a material, a layer, a substrate, etc.) can be “on,” “attached to,” or “coupled to” another element regardless of whether the one element is directly on, attached to, or coupled to the other element or there are one or more intervening elements between the one element and the other element. Also, directions (e.g., above, below, top, bottom, side, up, down, under, over, upper, lower, horizontal, vertical, “x,” “y,” “z,” etc.), if provided, are relative and provided solely by way of example and for ease of illustration and discussion and not by way of limitation. In addition, where reference is made to a list of elements (e.g., elements a, b, c), such reference is intended to include any one of the listed elements by itself, any combination of less than all of the listed elements, and/or a combination of all of the listed elements. 
     As used herein, “substantially” means sufficient to work for the intended purpose. The term “substantially” thus allows for minor, insignificant variations from an absolute or perfect state, dimension, measurement, result, or the like such as would be expected by a person of ordinary skill in the field but that do not appreciably affect overall performance. When used with respect to numerical values or parameters or characteristics that can be expressed as numerical values, “substantially” means within ten percent. The term “ones” means more than one. 
     The term “surface mount” means that a component has leads that are designed to be soldered or otherwise attached on the same side of a circuit board or card on which the component is placed. The term “circulator” is used herein to represent a magnetic ferrite element with at least three ports that allows radio frequency signals to be transferred between adjacent ports only in one direction. 
       FIG. 3  illustrates an example circuit diagram  300  representing how a circulator  302  can be employed as a Tx/Rx switch. Circulator  302  is an example of a three port surface mount circulator that can be used to interconnect a Tx amplifier  301   a  and a Rx amplifier  301   b  to an antenna  303 . Tx amplifier  301   a  can typically be a power amplifier while Rx amplifier  301   b  can typically be a low noise amplifier; however, other types of amplifiers could also be employed. 
     As shown, the output of Tx amplifier  301   a  is connected to a first port  302   a  of circulator  302 . Circulator  302  is configured to operate in a clockwise direction as represented by the arrow in  FIG. 3 . Therefore, radio frequency signals output by Tx amplifier  301   a  will be allowed to pass from port  302   a  to port  302   b  and ultimately to antenna  303 . In contrast, the input of Rx amplifier  301   b  is connected to a third port  302   c  of circulator  302 . Therefore, radio frequency signals received by antenna  303  will be routed from port  302   b  to port  302   c  and ultimately to Rx amplifier  301   b . Filter  304  can be configured with a passband to match the operational frequencies of Tx amplifier  301   a  and Rx amplifier  301   b.    
     In some embodiments, the components depicted in circuit diagram  300  can be configured to operate at frequencies in excess of 12 GHz. For example, Tx amplifier  301   a  can be configured to output radio frequency signals in the Ku band (12-18 GHz). Additionally, the components depicted in circuit diagram  300  can be configured to operate at high power. For example, Tx amplifier  301   a  can be configured to operate at power levels up to or exceeding 20 watts. 
     To enable operation at these high frequencies and power levels, circulator  302  can be designed as a surface mount element. As a surface mount element, circulator  302  can provide high thermal conductivity connections to thermal vias formed within a circuit card. These high thermal conductivity connections dissipate heat generated by the high power operation thereby allowing circulator  302  to be relatively small since the circulator itself is not the primary heat sink. Additionally, as a surface mount element, circulator  302  can provide low loss transitions to minimize loss as the radio frequency signals pass between the ports of circulator  302 . Low loss transitions are significantly beneficial for both Tx and Rx paths. On the Tx path, the low loss transitions provide a higher available output power at the antenna. On the Rx path, the low loss transitions provide increased sensitivity for low signal levels received from the antenna. 
     Because each of Tx amplifier  301   a , circulator  302 , Rx amplifier  301   b , and filter  304  can be surface mount elements, each can be mounted on the same circuit card and only require a small footprint. In this way, the circuit card can be reduced in size in comparison to circuit cards that employ connectorized switches. For example, because no coaxial connectors or cables are required to interconnect each component, the complete circuit can have a much smaller footprint on the circuit card. 
     Although not shown in  FIG. 3 , second port  302   b  can be connected to a separate connector (e.g. a coaxial connector mounted to the circuit card) to which a separate antenna assembly may be connected. For example, each of the components depicted in  FIG. 3  other than antenna  303  may be surface mounted on the same circuit card. The separate connector can be used to interconnect the circuit card with a separate antenna assembly such as by connecting a coaxial cable between the separate connector on the circuit card and the antenna assembly. 
       FIG. 3A  illustrates a variation to circuit diagram  300 . In  FIG. 3A , the circuit also includes a limiter  305  positioned between port  302   c  of circulator  302  and the input to Rx amplifier  301   b . Limiter  305  can be employed to minimize the power level of radio frequency signals that are reflected by antenna  303  or other components connected to port  302   b  (e.g. due to impedance mismatch). For example, if any or a portion of the radio frequency signals output by Tx amplifier  301   a  (which may be at a power level up to or exceeding 20 watts) are reflected by antenna  303 , they will be routed towards Rx amplifier  301   b . Limiter  305  can function to minimize the power level that will be able to pass through to the input of Rx amplifier  301   b  thereby protecting Rx amplifier  301   b.    
       FIG. 4  illustrates an example circuit diagram  400  representing how two circulators  402 ,  412  can be employed as Tx/Rx switches to enable dual band operation of a transceiver. Circuit diagram  400  includes a Tx amplifier  401   a , a circulator  402 , an Rx amplifier  401   b , and a filter  404  that are arranged in the same manner as Tx amplifier  301   a , circulator  302 , Rx amplifier  301   b , and filter  304  in circuit diagram  300 . 
     Additionally, circuit diagram  400  includes a second set of components arranged in a similar manner, namely Tx amplifier  410   a , circulator  412 , Rx amplifier  410   b , and filter  414 . This second set of components can function in the manner described above except that they may be configured to operate at different frequencies. For example, Tx amplifier  401   a  and Tx amplifier  410   a  can be configured to output radio frequency signals at different frequencies. Similarly, Rx amplifier  401   b  and Rx amplifier  410   b  can be configured to receive radio frequency signals at different frequencies. In this way, the transceiver can transmit and/or receive over two different bands. Although not shown, a limiter can be used with Rx amplifiers  401   b  and  410   b  as described with respect to  FIG. 3A . 
     The second port of each of circulator  402  and circulator  412  (which are not labeled in circuit diagram  400  for sake of clarity) are both connected to antenna  403 . For example, the second port of each circulator may be connected to traces that join and connect to a separate connector to which an antenna assembly containing antenna  403  could be connected. 
       FIG. 5  illustrates a portion of an example circuit card assembly on which surface mount amplifiers and a circulator are employed. A circulator  502  is surface mounted on circuit card  500  and has three ports. A first port  502   a  is connected to the output of a Tx amplifier  501   a . A second port  502   b  is connected to a connector  515  via a filter  504 . A third port  502   c  is connected to the input of an Rx amplifier  501   b . As shown, each of Tx amplifier  501   a , circulator  502 , Rx amplifier  501   b , and filter  504  are surface mounted. 
     Although Tx amplifier  501   a , circulator  502 , and Rx amplifier  501   b  are shown with leads, any of these component could also be configured without leads as is known in the art. Similarly, filter  504 , which is shown without leads, could also be configured with leads. 
     Connector  515  is used to connect second port  502   b  to a separate antenna assembly. As shown, connector  515  represents a coaxial connector to which a coaxial cable could be connected for interconnecting the transceiver configuration of circuit card  500  with an antenna on the separate antenna assembly. Any other type of suitable connector could also be used. 
     In some embodiments, filter  504  can be located off the circuit card allowing second port  502   b  to be directly connected to connector  515 . This will allow flexibility in the type of filter that is used as filter  504  in a particular implementation. 
     By employing surface mount elements for Tx amplifier  501   a , circulator  502 , and Rx amplifier  501   b , a much smaller footprint is required for these components. For example, if connectorized switch  202  were used in place of circulator  502 , a much larger footprint would be required. Specifically, switch  202  itself, due primarily to coaxial connectors  202   a - 202   c , would require a much larger footprint than surface mount circulator  502 . Additionally, in order to interconnect Tx amplifier  401   a , Rx amplifier  401   b , and filter  404  with switch  202 , Tx amplifier  401   a , Rx amplifier  401   b , and filter  404  would also require coaxial connectors thereby increasing the footprint required by these components. Further, additional coaxial cables would be required to interconnect the components. Accordingly, the use of surface mount components can greatly reduce the size and weight of a circuit card assembly. 
     Although specific embodiments and applications of the invention have been described in this specification, these embodiments and applications are exemplary only, and many variations are possible.