WO2012161883A2

WO2012161883A2 - Autonomous multiple-interrogator rf jammer

Info

Publication number: WO2012161883A2
Application number: PCT/US2012/033385
Authority: WO
Inventors: Tyler CHUN
Original assignee: University Of Hawaii
Priority date: 2011-04-12
Filing date: 2012-04-12
Publication date: 2012-11-29
Also published as: WO2012161883A3

Abstract

An RF receiving/transmitting array is provided. The array includes an array of antenna elements, a number of phase detecting blocks that are each coupled to a respective pair of adjacent antenna elements, a phase shifter associated with each of the antenna elements, and a control circuit coupled with the phase detecting blocks and phase shifters. The controller receives information indicative of a phase difference between adjacent antenna elements of a received RF signal and outputs a signal to each phase shifter responsive to the phase difference. An RF transmitter may transmit RF signals from the array of antenna elements having one or more beams directed in the direction of RF signals received by the plurality of antenna elements.

Description

AUTONOMOUS MULTIPLE-INTERROGATOR RF JAMMER

Background

[0001 ] In various environments, radar is used to locate and/or track the activities of equipment operating in an area. Radar may be used, for example, in a military setting to determine the locations of one or more enemy aircraft and/or ground equipment. This information may be used to coordinate a response to the activities of the enemy. In cases where an entity has assets performing operations in a hostile location, it would be desirable to block radar communications of the enemy, thereby denying the enemy information that may be obtained from their radar installations. In many cases, the radar installations may have multiple different radar interrogators operating at both fixed and mobile locations. Radar

communications of all of the different interrogators would be desired to be blocked, thus presenting a challenge for an entity attempting to perform such blocking of the enemy radar.

Summary

[0002] According to various embodiments, an radio frequency (RF)

receiving/transmitting array, comprises: (a) an array of antenna elements; (b) a plurality of phase detecting blocks, each phase detecting block communicatively coupled to a respective pair of adjacent antenna elements; (c) a phase shifter associated with each of the antenna elements; and (d) a control circuit communicatively coupled to the phase detecting blocks and phase shifters, and configured to receive information indicative of a phase difference between adjacent antenna elements of a received RF signal and output a signal to each phase shifter responsive to the phase difference. In some embodiments, the array may include an RF transmitter operable to transmit RF signals from the array of antenna elements having a beam directed in the direction of RF signals received by the plurality of antenna elements. The received RF signal may comprise multiple RF signals from a plurality of RF sources, and the transmitted RF signals may comprise multiple RF signals transmitted toward the plurality of RF sources. The RF

receiving/transmitting array in some embodiments is operable to transmit RF jamming signals toward a source of the recei ved RF signals autonomously.

Brief Description of the Drawings [0003] FIG. 1 is an illustration of a broadcast tower and a number of users.

[0004] FIG. 2 is an illustration of multi-path transmissions between an interrogator and retrodirective array.

[0005] FIG. 3 is an illustration of an aircraft and an RF array according to various embodiments of the disclosure.

[0006] FIG. 4 is an illustration of multiple sources and an RF sensor of various embodiments.

[0007] FIG. 5 is an illustration of a portion of an array according to various

embodiments.

[0008] FIG. 6 is an illustration of a portion of another array according to various embodiments.

[0009] FIG. 7 is an illustration of a portion of another array according to various embodiments.

[00010] FIG. 8 is an illustration of a portion of another array according to various embodiments.

[0001 1 ] FIG. 9 is an illustration of a portion of another array according to various embodiments.

[00012] FIG. 10 is a graph illustrating output voltage versus detected phase difference of arrays of various embodiments.

[00013] FIG. 1 1 is a schematic of an exemplary phase-detecting block according to various embodiments.

[00014] FIG. 12 is a graph illustrating output voltage vs. phase difference response (VA and VB vs. Δφ2 ΐ) for phase detectors of an embodiment.

[0001 5] FIG. 1 3 is a graph illustrating measured control voltage versus phase shift relationship of the two cascaded phase shifters.

[00016] FIG. 14 is an exemplary radar cross section according to various embodiments.

[00017] FIG. 15 shows a setup for a set of measurements according to various embodiments.

[00018] FIG. 16 shows exemplary measurements from RF arrays of various embodiments. [00019] FIG. 17 shows exemplary measurements from RF arrays of various embodiments.

Detailed Description

[00020] The present disclosure provides a retrodirective array (RDA), that when interrogated by a source signal, has the ability to retransmit a signal directly back to the interrogator without any prior knowledge of its location. There are numerous applications where an RDA could be interrogated by multiple sources and where a response to each interrogator is desired. An example is a mobile wireless network of FIG. 1 , where each node in the network would contain an RDA front end. For multiple nodes to communicate simultaneously, the RDA front end must to be able to respond to multiple interrogating sources. Another example of an RDA operating under multiple-interrogator conditions occurs in a multipath environment of FIG. 2, where each reflected signal can be interpreted as a separate interrogator. Figure 3 illustrates an airborne vehicle towing a retrodirective array. The RDA can receive signals from multiple enemy radars and autonomously direct a jamming beam back at each received enemy radar. Figure 4 illustrates passive sensing that may collect information on received signals and relay the collected data for use in analysis of operations in a particular area. In each of the examples of Figs. 1 -4, an RDA provides an autonomously steerable, directive beam without the processing requirements typically required of an antenna that uses complex steering algorithms to perform beam forming. The retrodirective array autonomously steers its beams in the direction of interrogating signals, thereby obtaining maximum directivity in those directions. By increasing the directivity of the retrodirective array toward desired targets, most of the signal power is radiated in those directions. The autonomous steering characteristics of the

retrodirective array is done in the analog realm and does not have processing requirements typical in other antennas which employ complex steering algorithms.

[00021 ] Several RDA architectures utilizing phase-detecting and phase-shifting elements, and power-detecting and phase-shifting elements have exhibited the ability to resolve and respond to multiple interrogators with varying levels of success. Such an architecture may include a planar 4-element phase-conjugating array (PCA) configured to respond to multiple interrogators. Figure 5 illustrates an array that uses heterodyne mixing, where the signal at each element is phase conjugated. Such an architecture provides the benefits of a simple design and ability to handle planar and nonuniform wavefronts, but a total path loss of retrodirected signal is proportional to R⁴. Figure 6 illustrates power detecting and phase shifting in an array. This architecture has the benefit of having an R² path loss maintained, can handle nonuniform wavefronts, and DOA is determined with a simple microcontroller. However, constant rescanning is necessary to determine DOA, the design is not full duplex, and is not 100% analog. Figure 7 illustrates a phase detecting and phase shifting array. The architecture of Fig. 7 provides an array in which R² path loss is maintained, which is suitable for line-of-sight mobile environments, is completely analog and full-duplex. This array, only works in line-of-sight environments, and therefore is not able to handle nonuniform wavefronts. Figure 8 illustrates an array having inter-element phase detecting and phase shifting. Such an array provides an antenna having R² path loss maintained, which can handle nonuniform wavefronts, is completely analog, and is full-duplex. The design of Fig. 9 has a relatively higher DC power consumption than other arrays, however. Any of the architectures of Figs. 5, 6, and 7 may be used in an autonomous retrodirective array to provide autonomous RF jamming of multiple interrogators. The architecture of Fig. 7 may be used to provide RF jamming of a single interrogator.

[00022] With further reference to Fig. 8, an array of one specific embodiment utilizing this architecture is discussed. Fig. 8 is a block diagram of a four-element retrodirective array using phase detection and phase shifting, showing the three major modules: phase-shifting array, phase-detecting blocks, and control circuit. An electromagnetic wave impinging on the array sets up a phase difference between successive antenna elements. The induced phase gradient across the array can be uniform in the case of a single plane wave or nonuniform due to wavefronts such as those caused by multipath. Each phase-detecting block produces an output voltage proportional to the phase difference between respective element pairs. These voltages serve as inputs to the control circuit that autonomously outputs the necessary phase-shifter control voltages to retrodirect a phase-conjugated version of the arriving wave while at the same time eliminating the phase gradient of the arriving wave to allow in-phase combination at the array output. The phase-shifting array and phase-detecting blocks are integrated to eliminate the need for separate transmit and receive circuitry. The use of S-Band quasi-Yagi antenna elements with a 49% bandwidth ( 1.85-3.05 GHz) accommodates the desired 2.4-GHz receive and 2.45- GHz transmit frequencies. The four-element array is spaced λο/2 at 2.45 GHz and is fabricated on Rogers T 1 Oi (thickness = 2.54 mm, er = 9.8).

[00023] Fig. 9 illustrates the phase detecting blocks according to an embodiment. The received signal at each element passes through the network shown in Fig. 9. The signal is first split by a 1 :2 Wilkinson power divider, and part of each split signal is then fed to a 3-dB quadrature coupler. The coupled ports feed the received signal, now decreased by 6 dB, from each element into phase-detecting blocks on both sides of the coupling network. The through ports of the two quadrature couplers at each element are then combined using a 2: 1 Wilkinson power combiner and passed to the phase-shifting array. The phase-detecting blocks sense the phase difference between elements according to the equation:

where c j is the phase on element i, with i = 1 corresponding to the leftmost element. After determining the phase difference between signals arriving at its input, each phase detecting block outputs a voltage, V₍j₊i₎(i₎ that is proportional to Δφ^₊ιχ_ΐ) as shown in Fig. 10.

[00024] Fig. 1 1 shows a schematic of the phase-detecting block. Signals from Ports A l and A2 of Fig. 2 are split by a 1 :2 Wilkinson power divider, and then feed phase detectors, such as Analog Devices AD8302 phase detectors. Two chips are needed in the illustrated embodiment because a single AD8302 has a maximum detection range of 1 80° which is not sufficient for steering. Chip A samples A l and A2, while Chip B samples A2 and a 90°- delayed version of A 1 .

[00025] Figure 12 shows the ideal output voltage vs. phase difference response (VA and VB vs. Δφ₂ι) for the AD8302 phase detectors. It can be seen that V_B > 0.9 V corresponds to the range - 180° < Δφ₂ι < 0° on Chip A's response curve and V_B < 0.9 V corresponds to the range 0° < Δφ_{2 ]} < + 180° on Chip A's response curve. Hence the full - 180° < Δφ₂ι < 180° range may be obtained by:

where V_cti is a voltage proportional to Δφ₂ι and has the range - 1 .8 V to 1 .8 V.

[00026] Vc_ti is physically realized by the op-amp and comparator circuit shown in

Fig. 12. If VB≥ 0.9 V, the comparator outputs whatever its V- terminal is connected to (V_A- 1 .8 V, for the case of this circuit). If V_B < 0.9 V, the comparator's output is an open circuit; a pull-up resistor forces the output to be 1 .8 - V_A to satisfy the V_C,| equation. To match the measured phase-shifter sensitivity, V_cti is scaled by a factor of k = 1.16, finally resulting in a phase-detector output voltage, -2.09 V <V₂i< 2.09 V, corresponding to the phase difference -180° < Δφ₂ι < 180° between antenna elements 1 and 2. Identical processes occur between the other antenna-element pairs.

[00027] Referring again to Fig. 8, the phase-shifting array, with the help of the two other modules, achieves retrodirectivity through the use of phase shifters to create a phase- conjugated version of the arriving signal. Additionally, once the phase-shifting array has set up the appropriate phase-shifter configuration, coherent reception and retrodirective transmission can occur simultaneously because the phase shifters eliminate the phase gradient across the array allowing the signals to be combined in phase at the array output. Sufficient isolation (32 dB) between the transmit and phase-detecting block ports from the quadrature couplers ensure that the phase detector does not detect the retrodirected signal.

[00028] Given that the maximum phase difference between elements that can be measured is 180°, the maximum phase, q that the phase shifters would need to provide would correspond to

where N is the number of elements on the array. For a four element array (N=4), (p_max = 540°. A single phase shifter, such as a Pulsar ST-21044, provides a maximum phase shift of 360°; this range is extended to the desired 540° range by cascading two of these phase shifters in series and controlling both by a single voltage. The measured control voltage versus phase shift relationship of the two cascaded phase shifters at 2.45 GHz is shown in Fig. 13. Assuming a linear control voltage to phase-shift relationship, the phase shift, cp_s, is approximated by:

(p_s ¾ SVs + ψ

where S [deg/V] is the sensitivity of the phase shifter and ψ [deg] is the phase when V_s = 0. Based on the calculated value of S = 1 16.64 [deg/V], the maximum phase shift the phase shifters can provide for the 0-4.64 V control-voltage range is the difference, ( _s,4.64v - <p_s,ov ~ 540°. The reference phase, (p_ref, is chosen to be at the center of the array (q>_ref ⁼ 270°).

[00029] For an array with an even number of elements, N, the phase at each element may be written as:

[00030] Referring again to Fig. 8, the control circuit is now described. To physically obtain the necessary phases (p_p,j at element i, the correct control voltages, Vj, must be provided to the phase shifter corresponding to the i^th element. This is achieved with an op-amp control summing circuit. V₍j₊i₎₍j₎ feeds into the op-amp circuit to produce Vj. The relationship between V₍j₊i₎₍j₎ and Vj is given by:

N

V.

2 ) _k x where V_ref = 2.32 V is the control voltage corresponding to cp_ref. Note that the algebraic signs in •the φ, equation are reversed from those in the Vj equation, which is a result of the necessary conjugation of Δφ^₊ιχ,₎ between elements.

[0003 1 ] Using an array of the embodiment of Fig. 8, Three different sets of measurements were taken: a monostatic radar cross section (RCS), a bistatic RCS using a single interrogator, and a multistatic RCS using two interrogators. For the monostatic measurement a 2.4-GHz transmitting horn was fixed on a computer-controlled rotating arm. A second horn was fixed on the same rotating arm to receive the 2.45-GHz signal transmitted by the RDA. The arm was swept from -60° < Θ < +60° to obtain the pattern shown in Fig. 14. The result of this measurement corresponds to theory and shows the operable range of the RDA.

[00032] Fig. 1 5 shows the general experimental setup for a set of measurements. For the bistatic RCS, a 2.4-GHz horn antenna is fixed and the 2.45-GHz receive horn is swept. Measurements were taken for 2.4-GHz fixed-horn positions of 0°, -20°, +20°, and +40° and are shown in Fig. 16. These results correspond to theoretical expectations and demonstrate the retrodirective capabilities of the design. To measure the muhistatic RCS, a second fixed 2.4-GHz horn was employed, yielding the results in Fig. 1 7 for interrogator configurations located at +20°/-20°, and +30 - 15°. The multistatic RCS patterns presented show that the RDA can handle these nonuniform wavefronts. There is some beam pointing error, but this is to be expected. Of course, it is understood that the exact mathematical characterization of these wavefronts is not only dependent on the angular separation of the horn antennas from the array, but distance as well.

[00033] The priority document for this application includes several articles authored by one or more inventors of the present patent application. These articles are incorporated herein in their entirety.

[00034] The previous description of the disclosure is provided to enable a person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure.

Throughout this disclosure the term "example" or "exemplary" indicates an example or instance and does not imply or require any preference for the noted example. Thus, the disclosure is not to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

What is claimed is:

1. An radio frequency (RF) receiving/transmitting array, comprising:

an array of antenna elements;

a plurality of phase detecting blocks, each phase detecting block communicatively coupled to a respective pair of adjacent antenna elements;

a phase shifter associated with each of the antenna elements; and

a control circuit communicatively coupled to the phase detecting blocks and phase shifters, and configured to receive information indicative of a phase difference between adjacent antenna elements of a received RF signal and output a signal to each phase shifter responsive to the phase difference.

2. The radio frequency receiving/transmitting array of claim 1, further comprising an RF transmitter operable to transmit RF signals from the array of antenna elements having a beam directed in the direction of RF signals received by the plurality of antenna elements.

3. The radio frequency receiving/transmitting array of claim 2, wherein the received RF signal comprises multiple RF signals from a plurality of RF sources.

4. The radio frequency receiving/transmitting array of claim 3, wherein the transmitted RF signals comprise multiple RF signals transmitted toward the plurality of RF sources.

5. The radio frequency receiving/transmitting array of claim 1, wherein the RF receiving/transmitting array is operable to transmit RF jamming signals toward a source of the received RF signals autonomously.