Expandable analog manifold

An n input, radio frequency (RF) signal matrix is formed of a plurality of two-to-one RF signal routing units each including first, second, and third switching units selectively connecting either a first input to an output via a bypass conductive path while electrically isolating first and second signal combining conductive paths from the output or first and second inputs to the output via first and second signal combining conductive paths while electrically isolating the bypass conductive path from the output. The RF signal routing units are connected in at least two levels with outputs from a first level connected to inputs for a second level to form the n inputs for the RF signal matrix. Any number of the n inputs may be employed without unused inputs loading the output.

TECHNICAL FIELD

The present disclosure is directed in general to analog combination and/or routing of radio frequency signals, and, more particularly, to an expandable analog manifold for radio frequency signals.

BACKGROUND OF THE DISCLOSURE

Analog manifolds are employed to combine and/or route radio frequency (RF) signals from an arbitrary number of inputs to an arbitrary number of outputs. For example, an analog manifold may be employed to reconfigure the subarray size for a phase array. However, designs that accommodate up to n inputs may introduce unacceptable signal losses when employed to route less than n inputs.

There is, therefore, a need in the art for an improved analog manifold design that minimizes loss regardless of the number of input elements and output ports.

SUMMARY OF THE DISCLOSURE

An n input, radio frequency (RF) signal matrix is formed of a plurality of two-to-one RF signal routing units each including first, second, and third switching units selectively connecting either a first input to an output via a bypass conductive path while electrically isolating first and second signal combining conductive paths from the output or first and second inputs to the output via first and second signal combining conductive paths while electrically isolating the bypass conductive path from the output. The RF signal routing units are connected in at least two levels with outputs from a first level connected to inputs for a second level to form the n inputs for the RF signal matrix. Any number of the n inputs may be employed without unused inputs loading the output.

Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Additionally, other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description.

DETAILED DESCRIPTION

An analog manifold with low power loss for unused ports would be useful for changing the subarray size of an antenna array employed for radar or communications. Digital beamforming is one way to arbitrarily change the subarray size, but analog manifolds could potentially consume much less power than digital beamforming. RF designers use RF splitters for many applications, but the split is always fixed. Similarly, RF manifolds for combining and/or routing RF signals are typically fixed in size, with a defined number of inputs and outputs. However, changing subarray size requires two combinations of input:output port numbers, one having a larger number of inputs or outputs than the other. When used for fewer inputs or outputs, terminating the unused ports into loads results in unnecessary power losses that could exceed the power loss of digital beamforming.

FIG. 1diagrammatically illustrates an expandable RF signal matrix for routing and/or combining RF signals from any number of inputs to any number of outputs in accordance with embodiments of the present disclosure. The signal matrix100is formed by a tiered arrangement of 2:1 RF signal routing units each having two inputs and a single output. In the example shown, a 16:1 signal matrix is formed by fifteen 2:1 RF signal routing units, eight in a first level, four in a second level, two in a third level and one in the last level. Each 2:1 RF signal routing unit in the first level has two of inputs101(that is,101a/101b,101c/101d,101e/101f,101g/101h,1010i/101j,101k/1010l,101m/101n, and1010/101p), which also serve as the inputs to the signal matrix100. The RF signal routing units in the first level include outputs102(that is,102a,102b,102c,102d,102e,102f,102gand102h) connected to the two respective inputs and a bypass103(that is,103a,103b,103c,103d,103e,103f,103gand103h) that may be selectively activated to bypass the structure connecting the two inputs to the output. For example, bypass103abypasses the structure connecting inputs101aand101bto output102a. Each 2:1 RF signal routing unit in the remaining levels has the same structure just described, with the RF signal routing units in the second level having pairs of inputs104(that is,104a/104b,104c/104d,104e/104f, and104g/104h) connected to respective ones of the outputs (105a,105b,105cand105d) and with a selectively activated bypass106(106a,106b,106cand106d). As depicted, each input104of a second level RF signal routing unit is connected to an output102of a first level RF signal routing unit. Likewise, each output105of a second level RF signal routing unit is connected to an input107of a third level RF signal routing unit. Input pairs107a/107band107c/107dare connected to outputs109aand109b, respectively, with a structure that may be selectively bypassed by bypasses108aand108b, respectively. The sole fourth level RF signal routing unit has inputs110aand110bconnected to the outputs109aand109bof the third level RF signal routing unit, a single output111that serves as the output for the signal matrix100, and a bypass112. It should be noted that each of the outputs102,105and109of the first, second and third level RF signal routing units may be selectively employed as outputs for the signal matrix100, as discussed further below.

FIG. 1Aillustrates an RF signal routing unit within an expandable RF signal matrix in accordance with embodiments of the present disclosure. The layout120depicted is similar to a layout for a Wilkinson power divider with a bypass path, and is used for each of the RF signal routing units described above in connection withFIG. 1. Each RF signal routing unit has two inputs121aand121bfor receiving either a single signal (at one of the two inputs) or two signals (each at one of the two inputs). The inputs121aand121bare connected by switching units and conductive paths to an output122. A first switching unit122connects one of two conductive paths124and125to the input121a, where each conductive path124and125extends (in parallel) between switching device123and switching device126. A second switching unit126connects the same one of the two conductive paths124and125to the output122. A third switching unit127connects a third conductive path128, which is fixedly connected to the second input121band extends between input121band switching device127, to the output122.

In operation, the three switching units123,126and127are controlled in tandem to provide either 2:1 signal routing or 1:1 signal routing. To provide 2:1 signal routing, switching unit123is controlled to connect conductive path125to the first input121a(disconnecting conductive path124from the input121a), and switching units126and127are controlled to connect signal paths125and128, respectively, to the output122. (By connecting conductive path125to the output122, the switching unit126disconnects conductive path124from the output). To provide 1:1 signal routing, switching units123and126connect conductive path124to the input121aand output122, respectively (thus disconnecting conductive path125from the input121aand output122), and switching unit127is controlled to disconnect conductive path128from the output122.

The layout120is designed with an impedance for conductive path124that differs from the individual impedance of each of conductive paths125and128. Conductive path124is designed to be employed as the bypass in each of the RF signal routing units, while conductive paths125and128are designed to perform signal combining of signals received at respective inputs121aand121b. When the switching units123,126and127are set in a first configuration, a single signal received at input121ais routed, substantially unchanged, through the conductive path124to the output122by switching units123and126. Switching units123and126electrically isolate conductive path125from the input121aand output122, and switching unit127electrically isolates conductive path128from output122, preventing input121bfrom appearing as a load at output122. When the switching units123,126and127are set in a second configuration, two signals each received at one of inputs121aand121bare routed through conductive paths125and128, respectively, by switching units123,126and127and combined at output122. With the second configuration, conductive path124is electrically isolated from input121aand output122. As used herein, an unused input and associated conductive paths are said to “not” appear as load(s) at the output (or, equivalently, do “not” load the output) and/or “not” contribute to insertion loss or phase change because (and when) the respective load or contribution is negligible.

When the layout120is employed for each of the RF signal routing units depicted inFIG. 1, the input pairs (that is, input pairs101a/101b,101c/101d,101e/101f,101g/101h,1010i/101j,101k/1010l,101m/101n, and101o/101pfor the first level, input pairs104a/104b,104c/104d,104e/104f, and104g/104hfor the second level, input pairs107a/107band107c/107dfor the third level, and input pair110a/110bfor the fourth level) for each RF signal routing unit are implemented by the inputs121aand121bof the respective instance RF signal routing unit layout120. The outputs (that is, outputs102a,102b,102c,102d,102e,102f,102gand102hfor the first level, outputs105a,105b,105cand105dfor the second level, outputs109aand109bfor the third level, and output111for the fourth level) are each implemented by the output122of the respective instance RF signal routing unit layout120. The bypasses (that is, bypasses103a,103b,103c,103d,103e,103f,103gand103hfor the first level, bypasses106a,106b,106cand106dfor the second level, bypasses108aand108bfor the third level, and bypass112for the fourth level) are each implemented by the conductive path124of the respective instance RF signal routing unit layout120.

FIG. 2diagrammatically illustrates the expandable RF signal matrix ofFIG. 1configured to operate as a three input, one output manifold in which three inputs out of four are used and one input is not used. (In actuality, three inputs out of sixteen are used, with twelve of the sixteen inputs being electrically isolated from one of the outputs at the second level and one of the inputs electrically isolated from an output at the first level, so that those thirteen inputs do not appear as loads at the matrix output). By selectively controlling the switching units within the respective RF signal routing layout instances for each RF signal routing unit, all of the inputs except inputs101a,101band101care electrically isolated from the output111(and are therefore shown in phantom, along with the respective signal paths and connections to the output111). The RF signal routing unit connected to inputs101aand101bis configured by the switching units therein to combine the RF signals received at those inputs at output102a, while the RF signal routing unit connected to input101cemploys the switching units therein to exploit the bypass103b, connecting only the input101cto output102b. Outputs102aand102bare connected to inputs104aand104b. The RF signal routing unit connected to inputs104aand104bis configured by the switching units therein to combine the RF signals received at those inputs at output105a. Output105ais connected to input107a. The RF signal routing units connected to inputs107aand110aeach employ the switching units therein to exploit the respective bypasses108aand112(where input110ais connected to output109a) to route the signal at output105ato the output111of the matrix circuit. Signals received at the three inputs101a,101band101care thus combined at the output111, without losses due to apparent loads at the remaining inputs.

FIG. 3diagrammatically illustrates the expandable RF signal matrix ofFIG. 1configured to operate as a twelve input, one output manifold in which twelve inputs out of sixteen are used and four inputs are not used. Eight inputs101a,101b,101c,101d,101e,101f,101gand101hare received and combined by RF signal routing units in the first, second and third levels, while four inputs101i,101j,101kand101lare received and combined by RF signal routing units in the first and second levels only, with the bypass108bat the third level being employed. The fourth level RF signal routing unit combines the outputs of the third level RF signal routing units at the matrix output111.

For each of the different numbers of possible inputs, different numbers of possible outputs may also be selected. For example, by using the outputs105a,105band105cas the matrix outputs, a 12:3 matrix circuit may be formed. Fewer than all inputs of each RF signal routing unit may also be employed. For example, a 12:4 matrix circuit could be formed using only three of four inputs for adjacent pairs of RF signal routing units in the first level, and using all four outputs105a,105b,105dand105dof the second level.

FIGS. 4A, 4B, 4C and 4Dare illustrations relating to simulation of the operating of an expandable RF signal matrix in accordance with embodiments of the present disclosure.FIG. 4Aillustrates a floor plan for a four input, one output RF signal matrix, andFIG. 4Bdepicts an equivalent circuit diagram. The structures depicted inFIGS. 4A and 4Bthus model one quarter of the matrix illustrated inFIG. 1—for example, the structure between inputs101a/101band101c/101dand output107a. The inputs sub1, sub2, sub3and sub4inFIG. 4Bcorrespond to inputs101a/101band101c/101dinFIG. 1, and the output BMF-sub inFIG. 4Bcorresponds to output107a. The switching devices123,126and127within the layout120ofFIG. 1Aare electrically modeled as switches, and the conductive paths124,125and128are electrically modeled as impedances. Phase compensation when a select subset of the inputs (e.g., inputs sub1, sub2and sub3) are employed is included. The circuit ofFIG. 4Bmodels three interconnected instances of the general layout ofFIG. 1A, using the floor plan ofFIG. 4A.

FIGS. 4C and 4Dillustrate, respectively, plots as a function of frequency (in giga-Hertz or “GHz”) of insertion loss in decibels (dB) of the signal path and change in phase (in degrees) for the signal path between the input(s) and the output for use of 1, 2, 3 or 4 of the inputs of the structure depicted inFIG. 4Aand electrically modeled by the circuit inFIG. 4B. As apparent, the difference in signal loss and phase when using different numbers of the inputs is very small. Because unused inputs and conductive paths are electrically isolated from the outputs of each RF signal routing unit, those inputs and conductive paths do not contribute to the impedance losses at the output.

FIG. 5depicts an accordion subarray circuit functional block diagram for a four input, one output RF signal matrix in accordance with embodiments of the present disclosure. The circuit depicted implements a four input (sub1, sub2, sub3and sub4), one output (BMF) signal matrix, where any of 1, 2, 3 or all 4 inputs may be employed without substantial change in insertion loss and phase. The circuit also includes a switch controlling whether the signal matrix is employed for transmission (TX) or reception (RX) of RF signals by a beamforming antenna. The remainder of the circuit is employed to couple the signal matrix to a beamforming antenna having multiple elements. The common leg circuit functionality501is duplicated four times within the circuit, and includes phase shifting (in the upper right circuit leg, alternative phase shifting is provided for phase compensation, if necessary), together with a variable resistance and a low noise amplifier (LNA) and high power amplifier (HPA) within the common leg circuit functionality. The outputs BMF of each common leg circuit501are selectively combined or routed to form the beamformed (BMF) output signal at the output.

The application specific integrated circuit (ASIC) floor planning for an implementation of the RF signal matrix and associated circuitry illustrated byFIG. 5predicts only a single reticle will be required for SiGe 8HP fabrication, so no exotic fabrication processes are required. A digital core may be formed below the combiners (RF signal routing units), with the entire circuit fitting within a 10.0 millimeter (mm) by 9.88 mm area.