Antenna Reflected Power Measurement Using VSWR Correlation
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Solution Overview
Problem
Existing radio transmitter test systems fail to accurately measure reflected wave power of an antenna due to reflection occurring at the power feeding point, which is conducted via the external conductor of the coaxial cable, making it difficult to determine the accurate power transmission efficiency.
Innovation Solution
A radio transmitter test system that includes a simulative antenna with variable voltage standing wave ratio, a directional coupler, a power meter, and a control device to calculate reflected wave power by correcting measured values with a correlation coefficient, allowing for accurate measurement of reflected wave power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If reflected wave power is measured using a directional coupler connected to the antenna via coaxial cable, then the measurement system is simple and easy to implement, but the measurement precision deteriorates because reflection at the power feeding point is conducted via the external conductor making accurate measurement difficult
Solution Approach 1:
A correlation coefficient is introduced as an intermediary parameter to bridge the relationship between measured power values and actual reflected wave power. The correlation coefficient, calculated from the relationship between traveling wave power and reflected wave power at different voltage standing wave ratios, serves as a correction factor that compensates for measurement errors caused by reflection at the power feeding point
Solution Approach 2:
The measurement approach combines multiple parameters (traveling wave power, reflected wave power, voltage standing wave ratio, and correlation coefficient) to create a composite measurement system. By integrating these parameters through the formula P_r = k × (P_m - P_t), the system achieves accurate reflected wave power measurement despite the limitations of the simple directional coupler configuration
2Power
If transmitted high-frequency power is increased to improve signal strength, then the power transmission efficiency improves, but the reflected wave power increases causing potential power amplifier breakdown
Solution Approach 1:
The system implements feedback by continuously monitoring both traveling wave power and reflected wave power, calculating their relationship through the correlation coefficient, and using this information to control the transmitted power. This feedback mechanism prevents reflected wave power from exceeding safe levels while maintaining optimal transmission efficiency
Solution Approach 2:
The correlation coefficient is calculated in advance through preliminary measurements at different voltage standing wave ratios. This pre-calculated coefficient is then used to predict and control reflected wave power before actual transmission occurs, allowing the system to adjust transmitted power levels to prevent amplifier breakdown
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise measurement of reflected wave power and effective power transmission to the antenna, preventing power amplifier breakdown and facilitating stable transmitter operations.
Implementation Method 1
a directional coupler that is connected between the power amplifier and the antenna, is configured to couple high-frequency signal whose power has been amplified to the antenna
Implementation Method 2
a power amplifier that is configured to amplify power of the high-frequency signal
Implementation Method 3
a signal generator configured to generate a high-frequency signal
Data Source
AI summary
Provided is a radio transmitter test system that enables accurate measurement of reflected wave power of an antenna. A radio transmitter test system includes: a power amplifier that amplifies power of a high-frequency signal from a signal generator; a simulative antenna for which a voltage standing wave ratio is variable and that is connected to a coaxial cable in place of an antenna; a directional coupler that is connected between the power amplifier and the simulative antenna, couples the high-frequency signal to the simulative antenna, and outputs traveling wave power and reflected wave power between the power amplifier and the simulative antenna; a power meter connected downstream of the directional coupler; and a control device, wherein the control device calculates, for each voltage standing wave ratio of the simulative antenna, a correlation coefficient indicating a correlation between traveling wave power and reflected wave power of the simulative antenna and traveling wave power and reflected wave power measured by the power meter, and calculates reflected wave power of the antenna by correcting, with the correlation coefficient, the traveling wave power and the reflected wave power measured by the power meter in a state where the simulative antenna is replaced by the antenna.