Near-isotropic antenna for monitoring electromagnetic signals

1. A method for analyzing a target electromagnetic signal radiating from a monitored system, comprising:

in at least one computer, performing operations for:

monitoring the target electromagnetic signal using a near-isotropic antenna comprising a set of receiving surfaces arranged in a regular polyhedron;

obtaining a set of received target electromagnetic signals from the set of receiving surfaces, wherein obtaining a set of received target electromagnetic signals comprises receiving each electromagnetic signal as the electromagnetic signal arrives from a direction in which a corresponding receiving surface of the antenna faces; and

assessing the integrity of the monitored system by separately analyzing each of the received target electromagnetic signals, wherein separately analyzing each of the received target electromagnetic signals comprises, for each receiving surface in the set of receiving surfaces, using a separate reference model for the receiving surface and at least one of the target electromagnetic signals received at the receiving face to produce an estimated electromagnetic signal fingerprint for the at least one of the target electromagnetic signals.

2. The method of claim 1 , wherein prior to monitoring the target electromagnetic signal, the method further comprises:

monitoring a reference electromagnetic signal radiating from the computer system using a reference near-isotropic antenna comprising a set of reference receiving surfaces arranged in the regular polyhedron;

generating a set of reference electromagnetic-signal fingerprints from a set of received reference electromagnetic signals obtained using the reference receiving surfaces; and

creating a set of reference models from the reference electromagnetic-signal fingerprints to characterize the monitored system.

3. The method of claim 2 , wherein the reference models are created using a nonlinear, nonparametric regression technique.

4. The method of claim 3 , wherein the nonlinear, nonparametric regression technique corresponds to a multivariate state estimation technique (MSET).

5. The method of claim 2 , wherein separately analyzing each of the received target electromagnetic signals involves:

generating a target electromagnetic-signal fingerprint from each of the received target electromagnetic signals;

feeding the target electromagnetic-signal fingerprint into a reference model from the set of reference models; and

comparing the target electromagnetic-signal fingerprint to the estimated electromagnetic-signal fingerprint.

6. The method of claim 5 , wherein comparing the target electromagnetic-signal fingerprint to the estimated electromagnetic-signal fingerprint involves:

computing a residual signal from the target electromagnetic-signal fingerprint and the estimated electromagnetic-signal fingerprint; and

applying a sequential-analysis technique to detect a statistical deviation of the residual signal.

7. The method of claim 6 , wherein the sequential-analysis technique corresponds to a sequential probability ratio test (SPRT).

8. The method of claim 6 , wherein the statistical deviation is used to identify a fault in the monitored system if the assessed integrity falls below a threshold.

9. The method of claim 8 , wherein the fault corresponds to at least one of a modified chip, a counterfeit component, and one or more metal whiskers.

10. The method of claim 1 , wherein the set of receiving surfaces are arranged in an icosahedron.

11. The method of claim 1 , wherein prior to monitoring the target electromagnetic signal, the method further comprises:

monitoring a reference electromagnetic signal radiating from the computer system using a reference near-isotropic antenna comprising a set of reference receiving surfaces arranged in the regular polyhedron; and

for each surface in the set of reference receiving surfaces:

generating a reference electromagnetic-signal fingerprint from a reference electromagnetic signal received using the surface; and

creating a reference model from the reference electromagnetic-signal fingerprint to characterize the monitored system.

12. A system for analyzing a target electromagnetic signal radiating from a monitored system, comprising:

a near-isotropic antenna configured to monitor the target electromagnetic signal, comprising a set of receiving surfaces arranged in a regular polyhedron; and

an analysis apparatus configured to:

obtain a set of received target electromagnetic signals from the set of receiving surfaces, wherein obtaining a set of received target electromagnetic signals comprises receiving each electromagnetic signal as the electromagnetic signal arrives from a direction in which a corresponding receiving surface of the antenna faces; and

assess the integrity of the monitored system by separately analyzing each of the received target electromagnetic signals, wherein separately analyzing each of the received target electromagnetic signals comprises, where, while separately analyzing each of the received target electromagnetic signals the analysis apparatus is configured to, for each receiving surface in the set of receiving surfaces, use a separate reference model for the receiving surface and at least one of the target electromagnetic signals received at the receiving face to produce an estimated electromagnetic signal fingerprint for the at least one of the target electromagnetic signals.

13. The system of claim 12 , further comprising:

a model-generation apparatus configured to:

monitor a reference electromagnetic signal radiating from the computer system using a reference near-isotropic antenna comprising a set of reference receiving surfaces arranged in the regular polyhedron;

generate a set of reference electromagnetic-signal fingerprints from a set of received reference electromagnetic signals obtained using the reference receiving surfaces; and

create a set of reference models from the reference electromagnetic-signal fingerprints to characterize the monitored system.

14. The system of claim 13 , wherein the reference models are created using a nonlinear, nonparametric regression technique.

15. The system of claim 14 , wherein the nonlinear, nonparametric regression technique corresponds to a multivariate state estimation technique (MSET).

16. The system of claim 13 , wherein separately analyzing each of the received target electromagnetic signals involves:

generating a target electromagnetic-signal fingerprint from each of the received target electromagnetic signals;

feeding the target electromagnetic-signal fingerprint into a reference model from the reference

models; and comparing the target electromagnetic-signal fingerprint to the estimated electromagnetic-signal fingerprint.

17. The system of claim 16 , wherein comparing the target electromagnetic-signal fingerprint to the estimated electromagnetic fingerprint involves:

computing a residual signal from the target electromagnetic-signal fingerprint and the estimated electromagnetic-signal fingerprint; and

applying a sequential-analysis technique to detect a statistical deviation of the residual signal.

18. The system of claim 17 , wherein the sequential-analysis technique corresponds to a sequential probability ratio test (SPRT).

19. The system of claim 17 , wherein the statistical deviation is used to identify a fault in the monitored system if the assessed integrity falls below a threshold.

20. The system of claim 19 , wherein the fault corresponds to at least one of a modified chip, a counterfeit component, and one or more metal whiskers.