Patent Description:
In prior instruments, such as a tracking generator or vector network analyzer (VNA), a plurality of phase-stable measurements of a device under test (DUT) reflection and/or transmission must be made. Single or multiple generators and receivers share a common local oscillator (LO) to assure phase stability. Calibration of the system is performed using external reflection standards, which rely on coherent phase between the calibration moment and the measurement moment. For reasons of cost reduction and simplification of the hardware, it would be desirable to use phase-incoherent but frequency-stable LO sources for the receiver and generator rather than sharing a common synthesizer architecture. The common VNA has a reflection bridge or coupler arrangement of various types on the generator port. A signal reference coupled from the generator is routed to the receiver but has a phase error that is proportionate to the reflection coefficient of the (arcsin( Vref/Vnorm)), making the reference generator phase relative to the receiver difficult to obtain from this port alone without relying on the phase coherence of a common LO system between the generator and receiver.

<FIG> is a block diagram illustrating an example of a prior vector network analyzer (VNA) or tracking generator <NUM> having multiple receivers <NUM> and <NUM> and a shared signal <NUM> (e.g., from a control processor <NUM> by way of an LO <NUM>). In the example, a common source <NUM> provides an injection signal to a radio frequency (RF) bridge <NUM> (e.g., via a transmission line <NUM>), as well as reference signals 107a and 107b to multiple receivers <NUM> and <NUM>, respectively.

It should be noted that, while two receivers <NUM> and <NUM> are shown to measure two signals (e.g., Reference and Reflection ports of a bridge), any number of multiple receivers can be used to measure a high number of signals from more complex multi-channel bridges, couplers, or similar networks. Multiple receivers can be eliminated with a single receiver if a phase-stable switch can be connected in such a way that the bridge loading is not disturbed when the paths are switched.

<FIG> is a block diagram illustrating an example of a prior VNA or tracking generator <NUM> having a single receiver <NUM> and a shared signal <NUM> (e.g., from a control processor <NUM> by way of an LO <NUM>). Similar to the VNA or tracking generator <NUM> illustrated by <FIG>, a common source <NUM> provides an injection signal to a radio frequency (RF) bridge <NUM> (e.g., via a transmission line <NUM>), as well as reference signals 207a and 207b to switching circuitry <NUM> that is coupled with the receiver <NUM>. In general, the shared signal may be the bridge stimulus itself or an LO created in a phase stable way within the signal source.

Document <CIT> discloses an electronic arrangement and method for providing a signal characterized by reduced phase noise having a signal source for providing a stimulus signal, a modulator coupled to the signal source for generating a modulated signal as function of the stimulus signal and a local oscillator signal, and a mixer combining the stimulus and modulated signals to generate a mixed signal that includes a component characterized by a mathematical difference of the stimulus signal and the modulated signal.

Embodiments of the invention are provided according to the appended claims.

Implementations of the disclosed technology generally include systems or devices that use an additional signal path in order to allow for a relative phase measurement between a generator and a receiver, insensitive to external load conditions. Such embodiments may advantageously allow a receiver and generator having relatively unstable independent local oscillators (LOs) to be used in a phase-stable measurement of network response. This may advantageously allow a single receiver and generator to establish their relative phase or, in embodiments involving multiple receivers and multiple generators, to establish their relative phase.

Implementations of the disclosed technology generally include electronic test and measurement devices, such as vector network analyzers (VNAs) having a calibration path. Such embodiments may advantageously include separate signal sources in the receiver(s) and signal source to allow for higher stability and accuracy in the bridge measurement. Also, variable static phase offsets in either the receive synthesizer or source synthesizer may be sensed and removed as an error term in the measurement. Further, costs may be reduced due to the availability of single integrated circuit (IC) integrated synthesizers that cover wide bandwidths at low cost.

<FIG> is a block diagram illustrating a first example of a VNA or tracking generator <NUM> having a load <NUM>, a transmission line <NUM>, a radio frequency (RF) bridge <NUM> to provide reference signals 307a and 307b to switching circuitry <NUM>, and a calibration path in accordance with certain implementations of the disclosed technology. In the example, a separate signal source <NUM> (e.g., by way of a generator <NUM>, an LO <NUM>, and a switch <NUM>) and receive reference <NUM> are shown with a phase shift <NUM> shown in series with the signal source to represent the random phase offset to the receive channel. Each of the signal sources is phase locked to a common reference and controlled by a common control processor <NUM>, and the signal source may have an unknown phase. While a single receiver <NUM> is shown, it should be noted that multiple receivers may be synchronized using similar implementations.

In the example, the signal channel generator <NUM> has a single channel receiver for sensing the magnitude and phase of a single reflection bridge/coupler <NUM>, e.g., used in a one-port VNA. The generator <NUM> and receiver <NUM> may use either continuous wave or modulated data. The receiver(s) may be constructed each having an independent local oscillator, e.g., with independent phase. The phase offset <NUM> from the source may be determined by sampling the "Source Reference path. " Here, S1 may either refer to a switch or a coupling or power dividing network. In embodiments where a single receiver is used to sample a single port or multiple bridge ports, the switch may be designed to provide a consistent load to the bridge in all switch positions. This may be accomplished using signal path attenuation, impedance matching, buffering by amplification, and terminated switch networks, for example.

<FIG> is a block diagram illustrating an example of a VNA or tracking generator <NUM> having a common generator source (e.g., from a control processor <NUM> by way of an LO <NUM>) in accordance with certain implementations of the disclosed technology. In the example, multiple receivers <NUM>, <NUM>, and <NUM> having independent LOs 410a, 411a, and 412a, respectively, and multiple phase offsets may be synchronized to a common reference. In this view, the multiple source reference signals are distributed by way of a coupler/power divider network <NUM>. In alternate embodiments, a switch may be implemented instead of the coupler/power divider network <NUM>.

In the example, the receivers <NUM>-<NUM> and generators can be phase synchronized by tuning each to the same frequency, switching to the "Source Reference" signal, and measuring the relative phase. Frequency offsets between the source and receivers may be accommodated if these signals are within the processing bandwidth of the receivers <NUM>-<NUM>. It should be noted that the receivers <NUM>-<NUM> are generally analog or digital receivers with superheterodyne, homodyne, direct conversion, or similar receiver techniques. Single or multiple LO signals may be generated by each receiver. For example LO <NUM> (410a) may be actually three LO signals (e.g., LO1a, LO1b, and LO1c for a three-stage superheterodyne converter). The generator may either be a direct signal source (e.g., a VCO and PLL, direct digital source, or direct analog source) or an indirect signal source (e.g., with a local oscillator and baseband signal, or multiple location oscillators and a baseband signal), with either a modulated or continuous wave baseband signal.

<FIG> is a block diagram illustrating a first example of a VNA or tracking generator <NUM> having multiple receivers that are synchronized by a common reference signal in accordance with certain implementations of the disclosed technology. In the example, a single control processor <NUM> may control multiple receivers <NUM>, <NUM>, and <NUM> having independent LOs 510a, 511a, and 512a, respectively with random phase offsets. N Source reference signals are routed from a single generator. While simplified signal source is shown in the figure, this signal source may be an indirect signal source (e.g., with a local oscillator and baseband signal, or with multiple LOs and a baseband signal) with either a modulated or continuous wave baseband signal or a direct signal source such as a VCO and PLL, direct digital source, or direct analog source. The phase offset represents random phase offset that may be present between each receiver and the generator.

<FIG> is a block diagram illustrating a second example of a VNA or tracking generator <NUM> having multiple receivers that are synchronized by a common reference signal in accordance with certain implementations of the disclosed technology. In the example, synchronizer circuitry <NUM> consists of a signal source (Gen1), a common reference clock (e.g., which produces <NUM> <NUM>. <NUM> N outputs to synchronize n external spectrum analyzers <NUM>, <NUM>, and <NUM>), a <NUM> or other suitable signal to synchronize the reference generator "Gen <NUM>", signal routing and switching circuitry 610a, 611a, and 612a, respectively, to each spectrum analyzer RF input, and N-RF inputs. Signal <NUM> to Signal n inputs to the control processor <NUM> may include several USB data signals or any other common data bus, such as USB/PXI/VXI etc..

<FIG> is a block diagram illustrating an example of a VNA or tracking generator <NUM> having multiple signal sources that are synchronized by a single receiver in accordance with certain implementations of the disclosed technology. In the example, generator channel SPDT switches may be of internal-terminated form when the path is open. The stability of bridge response during switching may be improved using buffers, amplification, attenuation, or other suitable mechanisms. Signal <NUM> may be modulated or a continuous wave signal. The signal source may be a direct source of heterodyne source. The phase offset of each generator may be sensed relative to the others by way of a common receiver, for example.

Examples provide a vector network analyzer, comprising a control processor, a plurality of receivers coupled with the control processor, the plurality of receivers having a common signal generator source from the control processor, and a coupler/power divider network configured to distribute each of a plurality of source reference signals to a corresponding one of the plurality of receivers.

In some examples, each of the plurality of receivers has an independent local oscillator (LO).

In some examples, at least one independent LO is configured to generate multiple LO signals.

In some examples, each of the plurality of receivers is one of a group consisting of: a superheterodyne receiver, a homodyne receiver, and a direct conversion receiver.

In some examples, the common signal generator source is a direct signal source.

In some examples, the direct signal source is one of a group consisting of: a voltage controlled oscillator (VCO) and a phase-locked loop (PLL).

In some examples, the direct signal source is one of a group consisting of: a direct digital source and a direct analog source.

In some examples, the common signal generator source is an indirect signal source.

In some examples, the indirect signal source is one of a group consisting of: a single LO with a baseband signal and multiple LOs with a baseband signal.

Examples provide a vector network analyzer, comprising a control processor, a receiver coupled with the control processor, switching circuitry coupled with the receiver, a radio frequency (RF) bridge coupled with the switching circuitry, a transmission line coupled with the RF bridge, wherein the transmission line is configured to be coupled with a load, and a signal generator coupled with the RF bridge.

In some examples, the RF bridge is configured to provide a plurality of reference signals to the switching circuitry.

In some examples, the signal generator is configured to provide a source signal to the RF bridge.

Some examples further comprise a local oscillator (LO) coupled with the receiver.

Some examples further comprise a local oscillator (LO) coupled with the signal generator.

Some examples further comprise a switch coupled with the signal generator and configured to switch between the RF bridge and the receiver.

Claim 1:
A vector network analyzer, comprising:
a control processor (<NUM>);
a receiver (<NUM>) coupled with the control processor;
switching circuitry (<NUM>) coupled with the receiver;
a radio frequency, RF, bridge (<NUM>) coupled with the switching circuitry;
a transmission line (<NUM>) coupled with the RF bridge, wherein the transmission line is configured to be coupled with a load (<NUM>); and
a signal generator (<NUM>) coupled with the RF bridge;
wherein the RF bridge is configured to provide a plurality of reference signals (307a and 307b) to the switching circuitry.