Measurement of Voltage Standing Wave Ratio of Antenna System

• US 20130245976A1
• Filed: 03/19/2012
• Published: 09/19/2013
• Est. Priority Date: 03/19/2012
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Hind, Krista Joleen
• Granted Patent: US 9,482,705 B2
• Time in Patent Office: Days
• US Class Current: 702/65
• CPC Class Codes: G01R 27/06 Measuring reflection coefficients; Measuring standing-wave ratio
• CPC Class Codes: G01R 29/10 Radiation diagrams of antennas
• CPC Class Codes: H04B 17/103 Reflected power, e.g. return loss
• CPC Class Codes: H04B 17/17 Detection of non-compliance or faulty performance, e.g. response deviations H04B17/18 takes precedence

Abstract

The present invention provides methods and apparatus to detect the presence of interferers in a wideband digital VSWR measurement signal. Interferers cause power differences over different intervals of time and frequency, and may be detected by comparing the measured signals in both time and frequency domains with the original signal. Frequency components in the measured signals may be discarded if the interference is deemed too large. The remaining frequency components can then be used to compute the VSWR.

Claims

1. A method implemented in a wireless transmitter of calculating a voltage standing signal ratio (VSWR), said method comprising:

converting time-domain measurement signals for a forward signal and a reflected signal to a frequency domain;

computing reflection coefficients for a plurality of frequency bins based on said measurement signals;

computing interference detection metrics for one or more of said frequency bins as a function of the reflection coefficients;

discarding reflection coefficients for one or more frequency bins based on the interference detection metrics; and

computing the VSWR based on the reflection coefficients for the remaining frequency bins.

2. The method of claim 1 wherein converting time-domain measurement signals for a forward signal and reflected signal to a frequency domain comprises computing discrete Fourier transforms of the measurement signals for the forward signal and the reflected signal.

3. The method of claim 1 wherein computing reflection coefficients for a plurality of frequency bins based on said reflection coefficients comprises dividing a magnitude of the measurement signal for the reflected signal by a corresponding magnitude of the measurement signal for the forward signal.

4. The method of claim 1 wherein discarding reflection coefficients for one or more frequency bins comprises:

comparing the interference detection metrics for one or more frequency bins to a detection threshold; and

discarding frequency bins where the interference detection metrics satisfy the detection threshold.

5. The method of claim 1 wherein computing interference detection metrics for one or more of said frequency bins comprises computing measurement errors for each of the frequency bins as a function of its corresponding reflection coefficient.

6. The method of claim 5 wherein discarding frequency bins comprises discarding frequency bins where the measurement error satisfies an error threshold.

7. The method of claim 5 wherein computing measurement errors for each of the frequency bins as a function of its corresponding reflection coefficient comprises:

computing a forward coupling factor for each frequency bin as a function of the measurement signal for the forward signal and a reference signal; and

computing the measurement error as a function of the difference between the forward coupling factor and a reference value.

8. The method of claim 5 wherein computing measurement errors for each of the frequency bins as a function of its corresponding reflection coefficient comprises computing the measurement error based on a difference between the computed reflection coefficient and an expected reflection coefficient.

9. A measurement circuit for measuring a voltage standing signal ratio (VSWR), said measurement circuit comprising:

a directional coupler connected between a transmitter and an antenna;

a receiver circuit to generate time domain measurement signals for forward and reflected signals; and

a processing circuit configured to;

convert time-domain measurement signals for a forward signal and a reflected signal to a frequency domain;

compute reflection coefficients for a plurality of frequency bins based on said measurement signals;

compute interference detection metrics for one or more of said frequency bins as a function of the reflection coefficients;

discard reflection coefficients for one or more frequency bins based on the interference detection metrics; and

compute the VSWR based on the reflection coefficients for the remaining frequency bins.

10. The measurement circuit of claim 9 wherein the processing circuit is configured to compute discrete Fourier transforms of the measurement signals for the forward signal and the reflected signal to convert the measurement signals to the frequency domain.

11. The measurement circuit of claim 9 wherein the processing circuit is configured to divide a magnitude of the measurement signal for the reflected signal by a corresponding magnitude of the measurement signal for the forward signal to compute the reflection coefficients.

12. The measurement circuit of claim 9 wherein the processing circuit is configured to discard the frequency bins where the interference detection metric satisfies a detection threshold.

13. The measurement circuit of claim 9 wherein the processing circuit is configured to compute measurement errors for each of the frequency bins as a function of its corresponding reflection coefficient, and wherein said measurement errors comprise the interference detection metrics.

14. The measurement circuit of claim 13 wherein the processing circuit is configured to discard reflection coefficients for the frequency bins where the corresponding measurement error satisfies an error threshold.

15. The measurement circuit of claim 13 wherein the processing circuit is further configured to:

compute a forward coupling factor for each frequency bin as a function of the measurement signal for the forward signal and a reference signal; and

compute the measurement error for a frequency bin as a function of the difference between the forward coupling factor and a reference value.

16. The measurement circuit of claim 13 wherein the processing circuit is configured to compute the measurement error for a frequency bin as a function of a difference between the computed reflection coefficient for the frequency bin and expected reflection coefficient.