The present invention generally relates to the field of
avionic communication systems and, more particularly, to a method and apparatus
for a multifunction radio.
Modern aircraft rely on multiple radio systems to provide
information to the pilot. For example, an aircraft may include radio systems such
as distance measuring equipment (DME), transponder system equipment including the
air traffic control radar beacon system (ATCRBS) and Mode-S systems, and automatic
dependence surveillance-broadeast (ADS-B) system equipment such as universal access
transceivers (UAT), 1090 MHz extended squitters and UHF digital link (VDL) Mode
Distance measuring equipment (DME) is used to determine
the distance between an aircraft and a ground station. The transmitter for DME operates
in the 978-1212 MHz range. The transmitter sends out narrow pulses that are received
by the ground station, which returns a reply pulse transmission. The reply pulses
are received by the DME receiver which calculates distance to the ground station
by the elapsed time between the sending of the initial pulse to reception of the
In transponder systems, an interrogation signal is received
at a transceiver on the aircraft and a reply to the interrogation signal is sent
to the entity that sent the interrogation signal, such as a ground station. One
transponder system is the ATCRBS. The ATCRBS is designed to send, in reply to an
interrogation signal, information from an aircraft regarding identification of the
aircraft and the altitude of the aircraft. In operation, an aircraft transponder,
which includes a transceiver, receives an interrogation signal sent at a frequency
of 1030 MHz. The interrogation signal is typically received at regular intervals
from a ground station. After receiving the interrogation signal, the transponder
determines a response and transmits a reply. In one embodiment, the reply comprises
an identification of the aircraft transmitted as a series of timed pulses. The ground
station decodes the reply to obtain the identification of the aircraft. Also, the
ground station can calculate the range to the aircraft based on the round trip time
between the sending of the interrogation pulse and the reception of the reply. The
altitude of the aircraft can be determined based on the direction the antenna of
the ground station was facing when the reply was received.
Another type of transponders are Mode-S transponders. Mode-S
transponders operate on the same frequency as ATCRBS transponders but represent
a significant improvement over older transponder systems in that interrogations
can be sent to specific aircraft.
ADS-B system equipment on an aircraft sends out messages
without first receiving an interrogation. These messages can be received by other
aircraft and by ground station devices. ADS-B systems can periodically broadcast
the aircraft's altitude, velocity and other information. In the United States two
different ways of implementing ADS-B have been approved by the Federal Aviation
Authority: 1090 MHz Mode-S extended squitters (ES) and universal access transceivers
(UAT). 1090 MHZ ES have been chosen for use in commercial aircraft and UAT have
been chosen for use in general aviation applications.
In a 1090 MHz ES system a 1090 transmitter can be used
to periodically transmit ES messages. ES messages from other 1090 MHz systems can
be received by the 1090 MHz system. The ES message can comprise such information
as position, velocity and heading. UAT systems broadcast messages at 978 MHz (in
the U.S.) and receive messages from other UAT systems at the same frequency. UAT
messages can comprise information such as that sent in 1090 MHz ES messages, as
well as other information, such as traffic information from other aircraft and flight
information from ground stations.
Each of the various radio systems, DME systems, transponder
systems and ADS-B systems provide valuable information to the operator of the aircraft.
Unfortunately, each system is deployed separately as each radio system requires
its own receiver, its own transmitter, and its own antenna and each radio system
operates at a specific frequency. This adds weight to the aircraft and requires
additional space to house the multiple radios.
Accordingly, it is desirable to provide a method and apparatus
for a multifunction radio. Furthermore, other desirable features and characteristics
of the present invention will become apparent from the subsequent detailed description
of the invention and the appended claims, taken in conjunction with the accompanying
drawings and this background of the invention.
In one embodiment of the present invention a method for
sending and receiving transmissions from multiple radio systems on a single radio
comprises a first step of receiving a radio signal from one of the multiple radio
systems. Next, the radio signal is converted to a digital signal. Then the digital
signal is digitally downconverting. The digitally downconverted signal is processed
to extract data from the radio signal.
A multifunction radio for receiving radio signals from
and sending transmissions to multiple radio systems comprises an antenna and a transmit/receive
switch coupled to the antenna. The radio further comprises a receiver section coupled
to the transmit/receive switch and configured to receive radio signals from one
or more multiple radio systems. The receiver section includes a digital downconverter
configured to digitally downconvert radio signals sent from one or more of the multiple
radio systems and a digital signal processor coupled to the digital downconverter
for processing the downconverted signals. A transmitter section is coupled to the
transmit/receive switch and configured to generate a transmission signal for reception
by one or more of the multiple radio systems.
In yet another embodiment, a radio for receiving transmissions
from and sending transmissions to multiple radio systems is disclosed. The radio
comprises a receiver section configured to receive radio signals transmitted by
one or more radio systems and to process the received radio signals using a digital
downconverter having multiple channels corresponding to each of the multiple radio
systems. The radio further includes a transmitter section configured to generate
a transmission for each of the multiple radio systems. An antenna is selectively
coupled to the receiver section and the transmitter section.
IN THE DRAWINGS
The present invention will hereinafter be described in
conjunction with the following drawing figures, wherein like numerals denote like
FIG. 1 is a block diagram of an exemplary embodiment of
a multifunction radio in accordance with the teachings of the present invention;
FIG. 2 is a block diagram of an alternative embodiment
of a transmitter section in accordance with the teachings of the present invention;
FIG. 3 is a flowchart of an exemplary method of operating
a receiver section of a multifunction radio in accordance with the teachings of
the present invention;
FIG. 4 is a flowchart of an exemplary method of operating
a transmitter section of a multifunction radio in accordance with the teachings
of the present invention;
FIG. 5 is a block diagram of an exemplary embodiment of
a receiver section in accordance with the teachings of the present invention;
FIG. 6 is a flowchart of an exemplary method of operating
a receiver section in accordance with the teachings of the present invention;
FIG. 7 is a block diagram of an exemplary embodiment of
a transmitter section in accordance with the teachings of the present invention;
FIG. 8 is a flowchart of an exemplary method of operating
a transmitter section in accordance with the teachings of the present invention.
The following detailed description of the invention is
merely exemplary in nature and is not intended to limit the invention or the application
and uses of the invention. Furthermore, there is no intention to be bound by any
theory presented in the preceding background of the invention or the following detailed
description of the invention.
In the discussion below, the present invention is discussed
as used in an avionics environment. However, the present invention is not limited
to just one area of use and can be utilized to replace multiple radio systems with
one radio in many different embodiments. These can include naval and terrestrial
FIG. 1 illustrates an exemplary embodiment of a multifunction
radio 100 for receiving radio signals from and sending radio signals to one or more
different radio systems in accordance with the teachings of the present invention.
In the present invention, radio 100 transmits to and receives data from multiple
radio systems by acting as, or emulating, multiple radios. The present invention,
therefore, can replace multiple radios in an aircraft. In one embodiment, the different
radio systems can comprise DME systems, transponder systems and ADS-B systems, such
as UAT systems. Other radio systems can also communicate with multifunction radio
100. In one exemplary embodiment, multifunction radio 100 comprises a receiver section
102 and a transmitter section 104 coupled to a transmit/receive switch 108. An antenna
106 is coupled to the transmit/receive switch 108. A controller 110 couples to the
receiver section 102, the transmitter section 104 and the transmit/receive switch
Antenna 106 receives RF signals from at least one of several
different sources such as DME signals 101, transponder signals 103 and UAT signals
105. As discussed previously, in one exemplary embodiment, DME signals 101 are sent
and received in a frequency range of 978-1212 MHz, transponder signals 103 are sent
at 1030 MHz and received at 1090 MHz and UAT signals 105 are sent and received at
978 MHz. Antenna 106 can be, in one exemplary embodiment, a single antenna for sending
and receiving signals. Alternatively, multiple antennas in one or more groupings
can be utilized.
Transmit/receive switch 108 switches the antenna 106 between
the receiver section 102 and the transmitter section 104. In one exemplary embodiment,
transmit/receive switch 108 receives a signal to switch the antenna 106 between
the receiver section 102 and the transmitter section 104 via a switch control signal
121 supplied from the controller 110.
Controller 110 controls one or more switches or other devices
in radio 100 based on control signals generated at a processor, such as a digital
signal processor, discussed further below. Controller 110, in one exemplary embodiment,
controls the operation of transmit/receive switch 108 via switch control signal
Receiver section 102 receives RF signals 107 from at least
one or more radio systems that can be emulated by radio 100 and extracts information
from the received signals to obtain data and/or to generate a response. In one exemplary
embodiment of the present invention, the receiver section 102 comprises a preselector
filter 112 coupled to an analog downconverter 114, which, in turn, is coupled to
an analog-to-digital (A/D) converter 116. The A/D converter 116 couples to a digital
downconverter (DDC) 118, which, in turn, couples to a digital signal processor (DSP)
Preselector filter 112 filters the received RF signal 107
to pass frequencies used by the radio systems that communicate with radio 100. In
one exemplary embodiment, preselector filter 112 is a broadband band-pass filter
that passes frequencies in the range of 978 MHz to 1212 MHz, while attenuating frequencies
outside of that range. The frequency range can be adjusted based on the frequencies
expected to be received by the radio 100 from the various radio systems emulated
by the multifunction radio 100. The design of preselectors, such as preselector
filter 112, is known in the art.
Analog downconverter 114 downconverts RF signal 107 received
at antenna 106 and filtered by preselector filter 112 to an intermediate frequency
(IF) signal 109 for further processing. Typically, analog downconverters, such as
analog downconverter 114, include amplification stages, mixing stages and filtering
stages and are well known in the art. In an exemplary embodiment, the analog downconverter
114 downconverts the received RF signal 107 by 966 MHz.
A/D converter 116 converts the IF signals 109 into digital
signals 111. In one exemplary embodiment, A/D converter 116 is a high speed A/D
converter that operates at 520 MHz. The digital signals 111 are supplied to the
DDC 118 downconverts the digital signal 111 to multiple
baseband data streams via digital signal 113 for further processing. In one exemplary
embodiment, DDC 118 includes multiple channels corresponding to each radio system
emulated by multifunction radio 100 to downconvert digital signals 111 at different
frequencies. For example, DDC 118 can include a channel for downconverting DME signals
101, a channel for downconverting transponder signals 103 and a channel for downconverting
UAT signals 105. In one exemplary embodiment, DDC 118 can continuously downconvert
each channel at the same time. The DDC 118 can receive a signal, downconvert the
signal to a baseband digital signal 113 and isolate the desired frequency using
a filter such as a programmable finite impulse response (FIR) filter using pulse
DSP 120 processes the baseband digital signal 113. In one
exemplary embodiment, DSP 120 can decode received DME signals, transponder interrogations
and UAT signals. DSP 120 can also generate responses to received signals or generate
other transmissions. DSP 120 also provides data and control signals 115 to controller
110, the purpose of which is discussed further below. In one exemplary embodiment,
DSP 120 is a hardware based DSP implemented using an application specific integrated
circuit (ASIC), a field programmable gate array (FPGA) or similar circuit. Alternatively,
the DSP 120 functions can be implemented as software running on a processor.
Transmitter section 104 generates messages to be sent to
ground stations and/or other aircraft. Depending on the radio system, the message
can be a reply to a received message or can be a message that is generated at the
aircraft. For example, the message can be a reply signal generated in response to
a transponder signal received by the radio 100. The message can also be a UAT signal
or a DME signal. Transmitter section 104, in one exemplary embodiment, comprises
frequency synthesizers 122 coupled to function controller 124. The output of the
function controller 124 is coupled to an I/Q modulator 126, which in turn couples
to an amplifier 128.
Frequency synthesizer 122 generates a waveform at a certain
frequency. In an exemplary embodiment, there is at least one frequency synthesizer
122 for each radio system emulated by radio 100. For example, in one exemplary embodiment,
there can be a DME frequency synthesizer 125 operating at a 1040-1150 MHz frequency
range, a transponder frequency synthesizer 127 operating at a 1090 MHz frequency
and an UAT frequency synthesizer 129 operating at a 978 MHz frequency. The frequency
synthesizer 122 generates the frequency and outputs the synthesized frequency signals
to function controller 124.
Function controller 124 selects which of the frequency
synthesizers 122 will be used for transmission. Since the transmitter section 104
is preferably configured to transmit only one message at a time, the function controller
124 selects which frequency synthesizer 122 is to be used for transmission. The
function controller 124 is coupled to the controller 110 which provides a function
controller signal 117 to select the proper frequency synthesizer 122 to use for
transmissions. As previously mentioned, the controller 110 also receives data and
control information from the DSP 120 via a data and control signal 115. The control
information indicates which frequency synthesizer 122 should be selected and when
the frequency synthesizer 122 should be selected. The data, which represents the
contents of the messages, provides an indication as to how to operate the function
controller 124 to send messages that includes the required data.
I/Q modulator 126 modulates any of the synthesized signals
that require modulation in order to encode data. For example, for a 978 MHz UAT
signal, modulation of the inphase and quadrature signals is needed for the pulses
to include the data sent in an UAT message. The modulation is controlled by the
controller 110 using a modulation control signal 119, which receives the modulation
information from the DSP 120. If the output of function controller 124 does not
need modulation, it will pass through I/Q modulator 126.
Amplifier 128 amplifies the signals from I/Q modulator
126 for presentation to the antenna 106 for transmission. Amplifier 128 can be any
amplifier capable of linearly amplifying the frequency range required by the radio
100. In one exemplary embodiment, amplifier 128 amplifies signals in a 978-1150
FIG. 2 illustrates an alternative transmitter section 104.
In FIG. 2, the transmitter section 104 comprises a DSP 120 coupled to a direct digital
synthesizer 202, which is coupled to an analog upconverter 204 and an amplifier
DSP 120 generates the messages to be transmitted by transmitter
section 104. For example, DSP 120 can generate a response to a received interrogation.
In one embodiment, the responses are a series of timed pulses at a fixed frequency.
The DSP 120 determines the necessary frequency and the pulse timing needed to generate
Direct digital synthesizer 202 creates waveforms at a set
frequency based on received inputs. In one exemplary embodiment, direct digital
synthesizer 202 receives the frequency to be used for responding to a received transmission
as well as receiving the data of the message to be sent. As discussed previously,
in some exemplary embodiments the data is sent as a series of timed pulses at a
fixed frequency. In other exemplary embodiments the data is sent in a modulated
waveform. For these embodiments, the direct digital synthesizer 202 can also perform
modulations on any synthesized waveform.
Upconverter 204 is used to upconvert the frequency of the
output signal of the direct digital synthesizer 202. The upconverted signal is then
amplified by amplifier 128 for transmission by antenna 106. The upconversion process
can be rendered unnecessary if the direct digital synthesizer 220 can run at a fast
rate, such as 976-1150 MHz.
FIG. 3 is a flowchart illustrating a method of operating
the multifunction radio 100 for receiving RF signals generated by one or more radio
systems in accordance with the teachings of the present invention. In a first step,
step 302, an RF signal is received at antenna 106. As discussed previously, radio
100 can receive RF signals from multiple radio systems. In one embodiment, the RF
signals can be DME signals, transponder signals and/or ADS-B signals such as UAT
Next, in step 304, the received RF signal 107 is filtered
by preselector filter 112 and downconverted to an IF signal 109 via analog downconverter
114. In step 306, the IF signal 109 is converted to a digital signal 111 via A/D
The digital signal 111 is then processed at the DDC 118
in step 308. In one exemplary embodiment, the digital signal 111 is downconverted
by one of a plurality of channels in the DDC 118. Each channel corresponds to a
frequency range of a radio system emulated by the radio 100. As discussed previously,
in one exemplary embodiment, there can be a DME signal channel, a transponder signal
channel and a UAT signal channel and the DDC 118 can process each channel continuously
and simultaneously. As discussed previously, DDC 118 downconverts the digital signal
111 to a baseband for further processing in the DSP 120.
In step 310, the DSP 120 receives the downconverted digital
signal and processes the signal to extract and process data and perform any additional
calculations. For example, if the received signal is a DME transmission, DSP 120
could determine the time of arrival of the DME transmission and, based on when the
original DME transmission was sent, calculate the distance to the ground station.
If the received signal is a transponder signal, also known as an interrogation,
the DSP 120 can recognize the signal as an interrogation and generate a reply. If
the received signal is a UAT signal, the data in the signal is received and the
data can be utilized by various other aircraft systems.
FIG. 4 is a flowchart illustrating the operation of multifunction
radio 100 for transmitting a signal in accordance with the teachings of the present
invention. In a first step, step 402, one or more frequency synthesizers 122 generate
a frequency used for transmissions for one or more radio systems emulated by multifunction
radio 100. In one exemplary embodiment, the frequency synthesizer 122 includes a
DME frequency synthesizer 125 that can synthesize a channel having a range of 1041-1150
MHz from the total range of 978-1212 MHz, a transponder frequency synthesizer 127
that can synthesize a 1090 MHz signal and a UAT frequency synthesizer 129 that can
synthesize a 978 MHz signal.
In step 404, one of the frequency synthesizers 122 is coupled
to the antenna 106 by function controller 124. Controller 110 sends the function
controller signal 117 to function controller 124 to couple one of the synthesizers
to antenna 106 for transmission. The sending of the function controller signal 117
is determined by data and control signals 115 sent by DSP 120. For example, in the
case of transmitting a transponder reply that comprises a series of pulses separated
in time, the function controller 124 couples the frequency synthesizer 122 to the
antenna 106 for the length of each pulse and uncouples the frequency synthesizer
122 from the antenna 106 during periods of no signal in the series of pulses. Alternatively,
the frequency synthesizer 122 can remain coupled to the antenna 106. The I/Q modulator
126 can supply the necessary modulation.
In step 406, the signal generated by the frequency synthesizer
122 and the function controller 124 are modulated by the I/Q modulator 126 if needed.
For example, in one embodiment, UAT signals are constant phase frequency shift keying
(CPFSK) modulated signals. Thus, the UAT frequency signal generated by the frequency
synthesizer 122 is modulated by the I/Q modulator 126. The modulation is controlled
by controller 110 based on data and control signals 115 sent by the DSP 120.
In step 408, any processing needed before transmission
is done, such as signal amplification. In step 410, the signal is transmitted via
antenna 106. The transmit/receive switch 108 is placed in the transmission position
via the switch control signal 121 from controller 110.
FIG. 5 illustrates an alternative receiver section 501
for radio 100 in accordance with the teachings of the present invention. Receiver
section 501 comprises an antenna 106 coupled to a transmit/receive switch 108. Transmit/receive
switch 108 in turn is coupled to a filter bank 502, which is coupled to an amplifier
504 which in turn couples to an A/D converter 506. The output of the A/D converter
506 is sent to a digital downconverter 508. The digitally downconverted output of
the digital downconverter 508 is received for further processing at a digital signal
processor (DSP) 510. A controller 512 is coupled to the filter bank 502 and the
Antenna 106, as discussed previously, receives the output
of broadcasted RF signals from several sources such as DME signals 101, transponder
signals 103 and UAT signals 105. As discussed previously, DME signals 101 are sent
at a frequency of 978-1212 MHz, transponder signals 103 (the interrogation signal)
are sent at 1030 MHz and UAT signals 105 are received at 978 MHz. Antenna 106, in
one embodiment, is a single antenna, although multiple antennas in one or more groupings
can be used.
Transmit/receive switch 108 switches the antenna 106 between
the transmitter and the receiver. In one exemplary embodiment, transmit/receive
switch 108 receives a switch control signal to switch from receive to transmit and
vice-versa. Transmit/receive switch 108 can be any such switch that can switch antennas
using both the transmitter and receiver.
Filter bank 502 filters received RF signals 107 in the
frequency range used by the filter. In an exemplary embodiment where receiver section
501 receives DME signals 101, transponder signals 103 and UAT signals 105, filter
bank 502 can filter one or more channels in the DME frequency range of 978-1212
MHz, the 1030 MHz signal of the transponder system and the 978 MHz signal of the
UAT system. In one embodiment, the filter bank 502 filters the entire received RF
signal 107 for each of the frequency ranges. Alternatively, filtering elements in
the filter banks 502 can be activated via a controller 512 to select a central frequency
and a frequency range that is filtered by filter bank 502. While filter banks 502
is shown with three banks for filtering DME signals, transponder signals and UAT
signals, additional and/or different banks can be present in the filter banks 502.
In one embodiment, filter banks 502 can be a microelectronic mechanical system (MEMS)
filter bank, although, filter banks 502 fabricated using non-MEMs techniques can
Amplifier 504 amplifies the filtered output of the filter
bank 502. A/D converter 506 converts the filtered analog RF signals to digital signals
for further processing. In one embodiment, A/D converter 506 is a high speed A/D
converter operated around 488 MHz. A/D converter 506 can be of any conventional
design. In this example, the A/D converter 506 undersamples the RF signal such that
analog downconversion is not needed. If the A/D converter 506 is not a high speed
converter, undersampling can not be performed.
Digital downconverter 508 downconverts a digital signal
received from the A/D converter 506 for further processing in receiver section 501.
The digital downconverter 508 can include channels for each radio system emulated
by radio 100. For example, the digital downconverter 508 can include a channel for
downconverting the DME signal 101, the transponder signal 103 and the UAT signal
105. Digital downconverter 508, for each channel, downconverts the signal to a baseband
and isolates the desired frequency through filtering, such as pulse shape filtering
using a programmable FIR filter.
DSP 510 performs any necessary demodulation and signal
processing on received digitized signals. For example, DSP 510 can decode an interrogation
from a DME transmitter or an UAT transmitter. DSP 510 can be a hardware or software
DSP. DSP 510 can be selected from any suitable DSP known in the art.
Controller 512 couples to the DSP 510 and receives instructions
511 from the DSP 510 to control the filter bank 502. As discussed previously, controller
512 can set the central frequency and bandwidth of the filter bank.
In one exemplary embodiment of FIG. 5, analog downconversion
is not needed because of either the use of high frequency A/D converter 506 (256
Hz) or through the use of very high quality (high Q value) filters, such as the
MEMS filter in the filter bank 502. This allows for undersampling in the A/D converter
506, eliminating the need for analog downconversion.
FIG. 6 is a flowchart illustrating an exemplary operation
of receiver section 501. In a first step, step 602, one or more RF signals 107 are
received at antenna 106. As discussed previously, the RF signals may include DME
signals 101, transponder signals 103 and/or ADS-B signals, such as UAT signals 105.
Next, in step 604, the received signal passes through filter
bank 502. Since this discussion is on receiving a signal, the transmit/receive switch
108 is selected to receive. The filter bank 502 filters the received signal using
banks and filters selected by controller 512. For example, if the received signal
is an interrogation, the filter bank 502 would be set to filter the received signal
through the transponder filter, which, in an exemplary embodiment, will filter at
In the next step, step 606, the output of the filter bank
502 is digitized by A/D converter 506. A/D converter 506 uses a high sample-rate
(high speed) sampler. In one embodiment, the A/D converter 506 operates at 488 MHz.
In this embodiment, the signals are undersampled such that the DME signal appears
to be at 128 MHz, the transponder signal at 54 MHz and the UAT signal at 2 MHz.
In step 608, the digital downconverter 508 digitally downconverts
the 128/54/2 MHz digital signals to baseband for processing. As discussed previously,
digital downconverter 508 downconverts and filters received digital signals such
that the signal can be further processed.
In step 610, the downconverted signal is processed at DSP
510. DSP 510 interprets the received signal and, if needed, generates a reply. For
example, if the original received signal was an interrogation pulse in the transponder
system, the DSP 510 would recognize the transmission as a transponder pulse, determine
the appropriate response and generate the reply.
FIG. 7 is a block diagram of an alternative transmitter
section 701 in accordance with the teachings of the present invention. Transmitter
section 701 comprises DSP 510 coupled to a digital upconverter 702. The digital
upconverter 702 is coupled to a digital to analog (D/A) converter 704, which is
coupled to an analog front end 706. Analog front end 706 couples to the transmit/receive
switch 108 and the antenna 106.
DSP 510 is, in one embodiment, shared with receiver section
501, although the transmitter section 104 can include a dedicated DSP. DSP 510 generates
the digital data that comprises responses (replies) to transponders, as well as
broadcasts for ADS-B systems and DME systems. For example, in response to an interrogation
from a ground station in an ATCRBS system, the DSP 510 may generate a reply including
aircraft identification encoded as a series of pulses.
Digital upconverter 702 receives the digital data generated
by the DSP 510 as a baseband signal. In one exemplary embodiment, digital upconverter
702 then digitally upconverts the baseband signal for the DME signal to 71 MHz for
a RF signal of 1150 MHz and 8 MHz for the 978 MHz UAT signal. Digital upconverter
702 also performs any received signal filtering and other signal processing needed
to produce the digitized baseband signal.
D/A converter 704 receives digitized signals to produce
analog signals. In one exemplary embodiment, D/A converter 704 has a high sampling
rate of 400 MHz. D/A converter 704 can be selected from any number of suitable D/A
converters that are known in the art.
Analog front end 706 receives analog signals and prepares
the signal for transmission. In one exemplary embodiment, the analog front end 706
upconverts the baseband signal received from the D/A converter 704 to an appropriate
RF signal. In one exemplary embodiment, a mixer (not pictured) and a local oscillator
(not pictured) operating at 978 MHz are used to upconvert the baseband signal. Analog
front end 706 can also include a filtering system to filter out any signals beyond
those used by the radio 100 and any amplification necessary to transmit the signal
When transmitting a signal, the transmit/receive switch
108 is set to transmit. The signal is transmitted over the antenna 106. As discussed
previously, antenna 106 can be a single antenna, a single grouping of antennas or
multiple groupings of antennas.
FIG. 8 is a flowchart illustrating an exemplary embodiment
of the operation of transmitter section 104 in accordance with the teachings of
the present invention. In a first step, step 802, a transmission of digital data
is generated by the DSP 510. In one exemplary embodiment, the transmission can be
a reply to an interrogation, a DME transmission and/or an ADS-B transmission, such
as an UAT transmission.
In step 804, the digital data is upconverted by digital
upconverter 702. Digital upconverter 702 converts the digital data generated by
the DSP 510 to digital intermediate frequency (IF) signals. Digital upconverter
702 also provides any necessary filtering.
The digitized baseband signal is converted to an analog
signal at D/A converter 704, in step 806. As discussed previously, D/A converter
704 is a high speed D/A converter. In step 806, the analog signal is upconverted,
filtered and amplified for transmission. In step 808, the signal is transmitted
via antenna 106.
While at least one exemplary embodiment has been presented
in the foregoing detailed description of the invention, it should be appreciated
that a vast number of variations exist. It should also be appreciated that the exemplary
embodiment or exemplary embodiments are only examples, and are not intended to limit
the scope, applicability, or configuration of the invention in any way. Rather,
the foregoing detailed description will provide those skilled in the art with a
convenient road map for implementing an exemplary embodiment of the invention, it
being understood that various changes may be made in the function and arrangement
of elements described in an exemplary embodiment without departing from the scope
of the invention as set forth in the appended claims.