Communications: radio wave antennas – Antennas – Measuring signal energy
Reexamination Certificate
2000-05-12
2001-10-30
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Measuring signal energy
C324S601000, C455S067150
Reexamination Certificate
active
06310579
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to antenna testing, and more particularly, to a method and apparatus for testing the Voltage Standing Wave Ratio (VSWR) to determine performance characteristics of an antenna and cabling connected to the antenna.
2. Description of Related Art
FIG. 1
shows a testing apparatus generally indicated as
10
known in the art for testing the VSWR of one or more receive antennas generally indicated as
12
and cabling associated with a typical cellular base site. The testing apparatus
10
includes test equipment
14
and two directional couplers
16
,
18
for coupling between the antenna
12
to a receive multi-coupler (RMC)
20
.
An antenna connector
22
couples the antenna
12
to the directional coupler
16
. A second directional coupler
18
couples the directional coupler
16
to the receive multi-coupler (RMC)
20
. The antenna connector
22
and the directional couplers
16
,
18
provide a signal path between the antenna
12
and the receive multi-coupler
20
as shown by a signal line
23
.
The receive multi-coupler
20
includes a filter
24
, an amplifier
26
and a splitter
28
. The filter
24
filters the antenna signal received by the antenna
12
and provides a filtered signal. The amplifier
26
amplifies the filtered signal and provides an amplified and filtered antenna signal. The splitter
28
splits the amplified and filtered signal into several component parts and provides split signals to receivers
30
,
32
.
The test equipment
14
includes a test signal source
40
, two receivers
42
,
44
and a signal processor
46
. The test signal source
40
provides a test signal indicated as
41
to the directional coupler
18
. The directional coupler
16
provides one part of the test signal, known as a forward signal indicated as
41
a
, to the receiver
44
. The test signal
41
reflects off the antenna
12
, and the directional coupler
16
provides a reflected part of the test signal, known as a signal indicated as
41
b
, to the receiver
42
. The receivers
42
,
44
respectively measure the amplitude and the signal strength of the forward and reverse signals and provide this measurement information to the signal processing circuit
46
. The signal processing circuit
46
processes the measurement information, and provides signal processing with an indication of the antenna reflection coefficient and the VSWR of the antenna
12
.
The VSWR is an important factor that affects the performance characteristics of an antenna and provides important information about how the antenna will operate. If there is a mismatch of impedance along a circuit including a transmitter or receiver, transmission line and an antenna, there will be an inefficient transfer of energy either from the transmitter via the transmission line to the remote wireless receiver, or from the remote wireless transmitter via the antenna and the transmission line into the receiver. Because of the impedance mismatch, not all of the energy will flow forward from the transmitter to the antenna or similarly from the antenna to a receiver.
When an electromagnetic wave is sent down a transmission line which is not terminated with its characteristic impedance, some of the energy is reflected back from the termination. In some locations along the transmission line, the reflected wave re-enforces the direct wave. In other locations along the transmission line, the reflected wave opposes the direct wave. The result is a stationary pattern of waves along the line called standing waves. The VSWR is the ratio of the maximum to minimum voltage of a standing wave along a transmission line.
More particularly, the standing waves created in a transmission line are standing waves of voltage and current on the line. The voltage maximums and minimums of a standing wave have a constant amplitude. The ratio of the maximum to minimum voltage on a line is called the VSWR and is given by the following equation:
VSWR=V
1
max/
V
1
min
If the source and load impedances match that of the transmission line, there are no standing waves and the VSWR is 1. However, if there is an impedance mismatch between the transmission line and the source and load impedances, the VSWR will be greater than 1.
While the above equipment and method for testing the characteristics of the antenna
12
provides a generally reliable and accurate indication of the antenna and cabling signal transmission characteristics, this test equipment is very expensive to implement because of the requirement of the directional couplers and signal lines. One problem with the known test equipment is that it requires two directional couplers, receivers, and associated cabling, a first for providing the test signal, and a second for returning the unreflected and reflected signals back to the equipment. Directional couplers and associated cabling are expensive (about $150++ depending on quantity) per antenna, and there are a number of antennas per cellular site. Therefore, a method and apparatus for testing the VSWR of an antenna, which is easy and more cost effective to implement, is needed.
SUMMARY OF THE INVENTION
The present invention provides a test apparatus for testing the VSWR of an antenna which is easy and cost effective to implement.
The present invention includes a method and apparatus for calibrating an antenna apparatus and testing an antenna connected thereto. The calibration is conducted without an antenna connected to establish a baseline return loss calibration coefficient. Thereafter, after an antenna is connected, a test may be conducted to measure the performance of the antenna on the antenna site apparatus.
The calibration process includes measuring a leakage signal with the antenna port well terminated and the magnitude of the reflected signal with an open or shorted antenna port. Thereafter, if the antenna is connected and the test signal is swept over frequency, then a new return loss coefficient is computed by subtracting the leakage signal component, and comparing the result to the return signal strength from the open or shorted circuit condition.
An advantage of the present invention is that it provides a reliable and accurate indication of the antenna performance characteristics of an antenna used to receive RF signals at a cellular base site.
The present invention provides a significant improvement over the prior art by providing a method and apparatus for testing the antenna characteristics of an antenna for a cellular base site by eliminating the need for an additional directional coupler, associated cabling and receiver that are otherwise required in the prior art for testing the characteristics of each antenna in the cellular site. Additionally, the method and apparatus of the present invention provides a highly accurate and reliable indication of antenna performance.
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof as illustrated in the accompanying drawings.
REFERENCES:
patent: 4434397 (1984-02-01), Nelson
patent: 4580092 (1986-04-01), Squire
patent: 5408690 (1995-04-01), Ishikawa et al.
patent: 5548820 (1996-08-01), Victorin
patent: 5564086 (1996-10-01), Cygan et al.
patent: 6005891 (1999-12-01), Chadwick et al.
patent: 6094577 (2000-07-01), Han
patent: 6178310 (2001-01-01), Jeong
Chen Shih-Chao
Radio Frequency Systems Inc.
Ware Fressola Van der Sluys & Adolphson LLP
Wong Don
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