Patent Application
20120154122
This application claims the priority benefit of Taiwan application serial no. 99144308, filed on Dec. 16, 2010. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
1. Technical Field
The disclosure relates to a method and an apparatus of radio frequency (RF) testing.
2. Background
Radio frequency (RF) testing is always performed in some industries. For example, radio frequency identification (RFID) tags are usually attached to different products by suppliers of the products or staffs in large supermarkets. However, because the performance of RFID tags is easily affected by different products, different types of tags have to be used and they have to be attached to different positions in order to meet the requirement of different products. The starting power testing performed on RFID tags is critical to those in the industry. Herein “starting power” refers to a threshold, and when a RFID tag reader issues a signal to a RFID tag, the RFID tag is started and issues a response signal as long as the power of the signal received by the RFID tag reaches the starting power of RFID tag.
The most ideal environment for performing RF testing is anechoic chamber. This is because absorbers in an anechoic chamber can prevent measurement error caused by reflection and scattering of a RF signal during the transmission of the RF signal. However, the deployment of an anechoic chamber is very costly and special equipments and skilled workers are required for operating the anechoic chamber. Even a rented anechoic chamber incurs a high cost and limitations in the location and timing.
If the RF testing is not done within an anechoic chamber but in less ideal environments, some errors may be produced and different test results may be rendered in different environments or under different conditions.
According to embodiments of the disclosure, a method and an apparatus of radio frequency (RF) testing are provided for resolving aforementioned problem of testing outside anechoic chamber.
The disclosure provides a RF testing method including following steps. A receiver and a transmitting antenna of a transmitter are controlled to move towards a direction, wherein the transmitter transmits a wireless signal to the receiver through the transmitting antenna. A specific power is measured every time when one of a plurality of predetermined sampling points is reached, wherein the specific power is a minimum transmitting power of the transmitter which allows the receiving power of the receiver for receiving the wireless signal to reach a threshold, or the specific power is the receiving power of the receiver for receiving the wireless signal when the transmitter transmits the wireless signal with a fixed power. In foregoing moving and measuring steps, the relative distance and relative azimuth angle between the receiver and the transmitting antenna remain unchanged, and the frequency of the wireless signal also remains unchanged.
The disclosure also provides a RF testing apparatus including a carrier, a transmitting antenna of a transmitter, a driving module, and a control unit. A receiver is fastened on the carrier. The transmitter transmits a wireless signal to the receiver through the transmitting antenna. The driving module drives the carrier and the transmitting antenna to move towards a direction according to instructions of the control unit. The control unit measures aforementioned specific power every time when one of a plurality of predetermined sampling points is reached. During foregoing moving and measuring procedures, the relative distance and relative azimuth angle between the receiver and the transmitting antenna remain unchanged, and the frequency of the wireless signal also remains unchanged.
Several exemplary embodiments accompanied with figures are described in detail below to further describe the disclosure in details.
The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the disclosure.
In step 110, the error produced by a test environment is estimated by using fundamental formulas, and in step 120, the error actually produced by the test environment is measured.
Please refer to
Because the transmitting antenna 210 has its radiation characteristics and many objects in a non-ideal environment reflect the wireless signal, the wireless signal received by the receiver 220 is actually a superposed result of wireless signals coming from different directions. These directions include a direction 240 from the transmitting antenna 210 directly to the receiver 220, a direction 241 to the receiver 220 through the reflection of a floor, a direction 242 to the receiver 220 through the reflection of a ceiling, and a direction 243 to the receiver 220 through the reflection of a wall. When the test is performed in an anechoic chamber, there is no wireless signal from the directions 241-243 but only the wireless signal from the direction 240. In the non-ideal environment illustrated in
In step 110, because different RF signal reflection characteristics, sizes, and surface structures of different objects in the test environment may result in different intensities of the reflected signals and a very complicated combination is produced by foregoing factors, it is very difficult to achieve an accurate estimation. The Friis transmission equation can be used as the fundamental formula of step 110 to calculate the approximation of error caused by signal reflection. The maximum error produced by signal reflection in each direction in the test environment can be calculated by using the Friis transmission equation as long as the gain of the transmitting antenna at different angle, the reflection coefficient, and the distances of reflective objects in each direction are already determined. The Friis transmission equation is an existing technique therefore will not be described herein. If a very intensive reflection signal is detected according to foregoing calculation result, an absorber can be placed in the corresponding direction to adjust the test environment, and the attenuation of the absorber is brought into the calculation.
In step 110 illustrated in
The carrier 302 and the transmitting antenna 310 are both fastened to the rotating arm 304. The rotating arm 304 is pivoted to the moving arm 308 at a pivot point 306. The moving arm 308 can slide vertically along the vertical shaft 312. The vertical shaft 312 is fastened on the base 314. The wheels 320 are disposed at the bottom of the base 314. The control unit 318 is coupled to the driving module 316 through the signal transmission line 322. The driving module 316 drives the wheels 320 to move towards different directions on the floor, drives the moving arm 308 to move vertically along the vertical shaft 312, or drives the rotating arm 304 and the carrier 302 to rotate according to instructions of the control unit 318.
The vertical movement of the moving arm 308 and the horizontal movement of the wheels 320 provide a movement freedom along three axes. The rotating arm 304 rotates around the pivot point 306, and the carrier 302 has a rotational freedom along two axes. As shown in
The control unit 318 controls aforementioned movements and rotations to carry out the actual measurement in step 120. In the present embodiment, the control unit 318 is a notebook computer or any type of processor. However, the type of the control unit 318 is not limited in the disclosure. The signal transmission line 322 between the control unit 318 and the driving module 316 may also be replaced by a wireless connection.
In step 110, the actual measurement of step 120 has to be carried out regarding each reflective object with serious reflection interference. To be specific, regarding each reflective object, the transmitting antenna and the receiver are moved closer to or away from the object. A plurality of sampling points is predetermined according to the wavelength of the wireless signal, and a specific power is measured at each sampling point. The specific power may be a minimum transmitting power of the transmitter which allows the receiving power of the receiver for receiving the wireless signal to reach a predetermined threshold. Such an actual measurement can separate and obtain the testing error caused by each reflective object among many reflective objects in an entire test environment, so as to allow a user to evaluate the test environment.
Besides performing movement measurement regarding each reflective object, movement measurement may also be performed regarding the axes X, Y, and Z of the test environment. To be specific, the specific power may be measured at each predetermined sampling point by moving along only one of the three axes.
In the moving and measuring process illustrated in
If step 120 is performed to actually measure the starting power of a RFID tag, the receiver is a RFID tag under test (referred to as a tag under test thereinafter) or a representative tag for correction purpose (will be explained later on), the transmitter is a RFID tag reader, and the wireless signal is a signal required by the RFID tag reader for reading the tag under test or the representative tag. If the receiver is a tag under test, the threshold of the specific power is the starting power of the tag under test. If the receiver is a representative tag, the threshold of the specific power is the starting power of the representative tag. Thus, the specific power is the minimum transmitting power of the RFID tag reader which allows the receiving power of the tag under test or the representative tag for receiving the wireless signal to reach the starting power thereof.
For example, if the starting power of a RFID tag is measured in an open test environment (for example, a parking space), reflection signals are mostly from the ground. In this case, sampling points are predetermined at different heights from the ground, and the moving arm 308 of the RF testing apparatus 300 is controlled to move vertically to measure the specific power at each sampling point, wherein the measurement data is illustrated in
If a user still finds the reduced error range too large to be accepted, the user can try to move the reflective object or place an absorber at a key location between the transmitting antenna and the reflective object. The location of the absorber should allow the wireless signal reflected by the reflective object to be eliminated. For example, the absorber can be placed on the ground under the transmitting antenna and the tag under test (or the representative tag) to attenuate the reflection signal.
If the reflective object is movable, the results illustrated in
In order to obtain an accurate and meaningful result through aforementioned actual measurement, it should be ensured that the phase difference of only one reflection signal among the many reflection signals in the test environment changes along with the movement of the RF testing apparatus 300 or the reflective object, and the reflection signal to be captured among all the reflection signals should be smaller than the sum of other reflection signals and the main signal transmitted by the transmitting antenna.
As described above, whether a test environment other than an anechoic chamber is usable can be determined through the calculation in step 110 and the actual measurement in step 120. Through the RF testing method illustrated in
If the measurement error cannot be controlled to be within the tolerable range, the reflective object can be moved or an absorber can be placed at a key location to improve the test environment. After that, the actual measurement in step 120 is performed again. Or another test environment may be directly selected. When the maximum error obtained through the actual measurement is within the tolerable range, the test environment is usable. Even though such a test is less accurate than that performed in an anechoic chamber, the measurement error can be controlled to be within a tolerable and fixed range, and the test offers a far lower cost and is more convenient than that performed in an anechoic chamber.
P
ca1
=P
r1
−P
to1 (1)
P
to2
=P
r2
−P
ca1 (2)
The control unit 318 can control the RFID tag reader to gradually increase its transmission power from the minimum transmitting power or measure the minimum transmitting powers Pr1 and Pr2 through binary search. The starting power of the tag under test calculated through the procedure in
The procedure in
The procedure in
The accuracy of testing in a reflective non-ideal environment can be greatly improved by using a representative tag. Even though the starting power of the representative tag needs to be measured in an anechoic chamber, the same representative tag can be used for testing the starting powers of different tags under test in a test environment other than an anechoic chamber as long as foregoing similar conditions are satisfied. In general, the testing cost can still be reduced and a tag can be tested accurately.
To a product manufacturer or supplier, a RFID tag is usually attached to a product. Thus, in step 830 illustrated in
A RFID tag may be tested by using RF signals of different frequencies from different angles or locations. The control unit 318 controls the rotating arm 304 and the carrier 302 to rotate to different angles or control the transmitter to transmit wireless signals of different frequencies according to different user requirements, so as to thoroughly test the RFID tag and the product to which the RFID tag is attached to. Thus, in
The RF testing method and RF testing apparatus provided in the embodiments described above are applicable to testing of the starting power of a RFID tag in an open environment. However, the RF testing method and RF testing apparatus in the disclosure are not limited to the testing of a RFID tag. The RF testing method and the RF testing apparatus provided by the disclosure can be applied as long as a transmitter and a receiver are adopted. For example, aforementioned RFID tag reader can be replaced by a test signal generator, and aforementioned RFID tag can be replaced by a power meter (power meter and a receiving antenna thereof. In this case, the receiver is the receiving antenna of the power meter, and the transmitter is the test signal generator. The specific power is defined as the receiving power of the receiving antenna for receiving the wireless signal detected by the power meter when the test signal generator transmits the wireless signal with a fixed power. The actual measurement in steps 120 and 720 can also be applied to this testing technique.
The testing technique using the test signal generator and the power meter described in foregoing embodiment can also be used for evaluating the materials of the RF testing apparatus in
In summary, in the embodiments described above, a user can flexibly select or design a low-cost and usable test environment other than an anechoic chamber so as to perform various RF testing. Through the RF testing method and RF testing apparatus provided by foregoing embodiments, a user can evaluate the error produced by signal reflection in a test environment and various adjustments done to the test environment, so as to control the error to be within a tolerable range. Because no anechoic chamber is required in foregoing embodiments, no professional specialist or costly equipment is required, so that the testing cost can be reduced. In addition, in foregoing embodiments, a correction procedure can be performed by using a representative tag, so that the starting power of a RFID tag can be accurately measured even in an environment with signal reflections.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 99144308 | Dec 2010 | TW | national |
