Telecommunications – Transmitter – With coupled antenna
Reexamination Certificate
1999-05-04
2001-10-02
To, Doris H. (Department: 2682)
Telecommunications
Transmitter
With coupled antenna
C455S117000, C455S127500, C330S298000
Reexamination Certificate
active
06298223
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a detector circuit and method of detecting antenna mismatch.
BACKGROUND ART
Conventional portable two-way radios usually have an antenna port to which an antenna is removably coupled. If an incorrect or damaged antenna is coupled to the port then undesirable relatively large standing waves will result. These standing waves are due to mismatch between the antenna and power amplifier circuitry inside the two-way radio. Unfortunately, these standing waves affect the performance of the radio and can cause damage to the amplifier circuitry. Accordingly, upon detection of mismatch, conventional radios will reduce the amplifier circuitry's output power to decrease current drain. However, this can still cause damage to the amplifier circuitry especially if unduly large standing waves are created by mismatch.
SUMMARY OF THE INVENTION
It is an aim of this invention to overcome or alleviate at least one of the problems associated with detecting antenna mismatch.
According to one aspect of the invention there is provided a detector circuit for detecting antenna mismatch, the circuit comprising:
a coupler having at least one primary port and at least one reflector port, said primary port having an input node for receiving radio frequency signals from an amplifier and said primary port also having an output node coupled to an antenna port;
a rectification circuit having an input coupled to said reflector port;
a low pass filter coupled to an output of said rectification circuit; and
a comparator having a reference input, a signal input and comparator output, said reference input being set to a voltage threshold level and said signal input being coupled to an output of said low pass filter,
wherein in use signals at said comparator output are indicative of a missing or mismatched antenna coupled to said antenna port.
Preferably, said rectification circuit may include a direct current amplifier.
Suitably, said rectification circuit may comprise at least two diodes and at least two capacitors, one of said capacitors being in series with said diodes and the other of said capacitors being coupled to ground.
Preferably said rectification circuit may be a voltage doubler.
Suitably, said comparator output may be coupled to a controller.
Preferably said controller may have an amplifier control output for controlling said amplifier, wherein said amplifier control output disables said amplifier when a signal indicative of antenna mismatch is provided at the output of said comparator.
Suitably, said controller may be a microprocessor.
Preferably, said coupler may be a transformer. In an alternative form said coupler may be a strip line coupler.
Suitably said primary port may comprise at least part of a transmission line.
According to another aspect of the invention there is provided a method for detecting antenna mismatch, the method comprising the steps of:
supplying alternating current signals from a reflector port of a coupler, said coupler having a primary port with an input node coupled to an amplifier and said primary port also having an output node coupled to an antenna port;
rectifying said alternating current signals to provide a rectified signal;
low pass filtering said rectified signal to provide a direct current voltage; and
comparing a voltage level of said direct current voltage with voltage threshold level to provide a signal indicative of a missing or mismatched antenna coupled to said antenna port.
Preferably, said step of rectifying further includes the step of amplifying said rectified signal.
Preferably said method may be further characterised by the step of:
disabling said amplifier when a signal indicative of antenna mismatch is provided.
REFERENCES:
patent: 4439741 (1984-03-01), Turner, Jr.
patent: 4580092 (1986-04-01), Squire
Garrett Scott M.
Motorola Inc.
To Doris H.
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