Abstract:
A system for measuring a frequency response of an electrical network, comprises a signal source, a signal source path, a reflectometer receiver interactively associated with the signal source path by a directional coupler, and one or more additional reflectometer receivers arranged in series along the signal source path and associated with the signal source path by one or more respective additional directional couplers. The directional coupler and one or more respective additional directional couplers operate at different frequency ranges.

Description:
PRIORITY CLAIM 
       [0001]    This application claims priority to the following U.S. Provisional Patent Application: 
         [0002]    U.S. Provisional Patent Application No. 60/862,180, entitled “Apparatus for Extending the Bandwidth of Vector Network Analyzer Receivers,” Attorney Docket No. ANRI-08079US0, filed Oct. 19, 2006. 
     
     TECHNICAL FIELD 
       [0003]    The present invention relates generally to network analyzers. 
       BACKGROUND OF THE INVENTION 
       [0004]    A vector network analyzer (VNA) is a reflectometer-based electronic instrument that can be used to measure the frequency response (magnitude and phase) of a device under test (DUT) such as an electrical network, component, circuit, or sub-assembly. A VNA makes use of a frequency sweeping source or stimulus, directional couplers, and one or more receivers that provide ratioed amplitude and phase information such as reflection and transmission coefficients. Directional couplers are widely used in VNAs to separate the waves that are incident on, reflected from, and transmitted through a DUT. A directional coupler diverts signal power from a main line to which it is coupled. The wave-separation property of directional couplers makes them fundamental in VNA design. It can be desirable for a directional coupler to have good wave-separation across wide frequency ranges. This desire is driven at least in part by the fact that wide-band directional couplers make possible the design of wide-band VNAs. However, couplers in accordance with the prior art have limited bandwidth. 
         [0005]    Referring to  FIG. 1 , a VNA  100  is shown connected to a DUT  110 . The VNA makes use of a reflectometer receiver  102  for signal separation and detection. A reflectometer receiver  102  uses a local oscillator (LO)  108  to mix a radio frequency (RF) signal or stimulus from an RF source (also referred to herein as an input)  106  down to a lower intermediate frequency (IF) signal. The LO  108  is either phase-locked to the RF or the IF signal so that the reflectometer receiver  102  is tuned to the RF signal present at the RF source  106 . The incident wave and related signal source paths are indicated by an “a” and the reflected wave and related signal source paths are indicated by a “b”. The IF signals are bandpass-filtered to improve sensitivity and dynamic range and are provided to a processor/display  112 . 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Further details of embodiments of the present invention are explained with the help of the attached drawings in which: 
           [0007]      FIG. 1  is a circuit diagram of a system including a reflectometer receiver coupled to a signal source path connecting an RF source to a device under test in accordance with the prior art. 
           [0008]      FIG. 2  is a circuit diagram of an embodiment of a system in accordance with the present invention having a broadened useable bandwidth, the system including a reflectometer receiver and one or more additional reflectometer receivers operating across different frequency ranges. 
           [0009]      FIG. 3  is a flowchart of an embodiment of a method in accordance with the present invention for extending an operating bandwidth of a VNA receiver. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Embodiments of systems in accordance with the present invention can extend an operating bandwidth of a VNA by employing one or more integrated and/or remote reflectometer receivers disposed along an RF source path in addition to a VNA reflectometer receiver. An embodiment of one such system  200  is shown in  FIG. 2 . As above, the incident wave and related signal source paths are indicated by an “a” and the reflected wave and related signal source paths are indicated by a “b.” A VNA reflectometer receiver  202   1  is illustrated in simplified form interactively associated with an RF source path  201 . An RF source  206  is connected to a device under test (DUT)  210  between which is disposed the RF source path  201 . One or more integrated and/or remote additional reflectometer receivers  202   i , i=2 . . . n are arranged serially along the RF source path  201  so that the additional reflectometer receivers  202   i , i=2 . . . n can be interactively associated with the RF source path  201 . An additional reflectometer receiver  202   i  is activated when a frequency range of its couplers falls within the frequency range of the sweeping RF source. Reflectometer activation is achieved by connecting the main strobe source (LO  208 ) and the IF a  and IF b  channels to the appropriate ports of the reflectometer receiver  202   i  by switches  216   i ,  218   i ,  220   i , i=2 . . . n that connect the reflectometer receiver and provide a down-converted version of the signals that the couplers sense. The switches  216   i ,  218   i ,  220   i , i=2 . . . n of a reflectometer are activated when the frequency range of the couplers and the sweeping RF source coincide. For example, in an embodiment, activation of switches  216   i ,  218   i ,  220   i , i=2 . . . n can occur by way of software and/or hardware signals that detect or determine a frequency range of the sweeping RF source and control switch activation accordingly. Alternatively, switches for the appropriate reflectometer receiver  202   i , i=2 . . . n can be activated by a user of the VNA to correspond with an observed frequency range of the sweeping RF source. 
         [0011]    Additional reflectometer receivers  202   i , i=2 . . . n can be selected to complement the VNA reflectometer receiver  202   1  to operate within frequency ranges that collectively include substantially the entire frequency range targeted for an RF source  206 . In some embodiments, the additional reflectometer receiver  202   i , i=2 . . . n can be mixer or sampler based and the frequency ranges of the couplers of the VNA reflectometer receiver  202   1  and the additional reflectometer receiver  202   i , i=2 . . . n may or may not overlap. In other embodiments, the system can comprise still other components. Further, the VNA reflectometer receiver  202   1  and/or the additional reflectometer receiver  202   i , i=2 . . . n need not be limited to the arrangement shown in  FIG. 2 . In other embodiments, the VNA reflectometer receiver  202  and/or the additional reflectometer receiver  202   i , i=2 . . . n can include more components than shown. Further, VNA reflectometer receiver  202  and/or the additional reflectometer receiver  202   i , i=2 . . . n can include different components from one another. In still other embodiments, one or more of the additional reflectometer receivers  202   i , i=2 . . . n can be remote (i.e. external) to the VNA. The embodiment of  FIG. 2  is meant to demonstrate in a straight forward manner, a technique in which the present invention can be employed. One of ordinary skill in the art will appreciate in light of these teachings the myriad different variations with which systems employing reflectometers can be employed to expand an operating bandwidth of a VNA. 
         [0012]    Referring to  FIG. 3 , embodiments of methods in accordance with the present can extend an operating bandwidth of a VNA by employing a reflectometer receiver and one or more integrated and/or remote additional reflectometer receivers disposed along an RF source path. In an embodiment of a method, a system—for example as described above employing one or more additional reflectometer receivers arranged serially along an RF source path associated with a RF source—can be connected with a test subject (the test subject becomes a DUT) (Step  100 ). An appropriate reflectometer receiver is coupled to the RF source path between the RF source and the test subject (Step  102 ). An appropriate reflectometer can be, in an embodiment, any reflectometer having an operating frequency within which the frequency of the RF signal falls. The reflectometer receiver provides an intermediate frequency signal to a processor and/or display for analysis (Step  104 ). The frequency bandwidth for which an intermediate frequency signal can be obtained is extended by the inclusion of the one or more additional reflectometer receivers in the system. 
         [0013]    The foregoing description of preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to one of ordinary skill in the relevant arts. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalence.