Note: Descriptions are shown in the official language in which they were submitted.
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ANTENNA COUP~ER
Background o~ the Invention
The pre ent ~nvention relates to an ant~nna coupler for use
ln ~ RF (Radio ~r~quency) transmitting system.
The two ~a~or componen~ of a transmitting station are ~he
transmitter and the antenna. The transmitter generates a
high power RF ~ignal and the antenna receive~ this signal
and radiates it. To lnsure that most of the RF power is
properly coupled ko th2 antenna, the antenna must match the
output impedance o~ the transmitter. Unfortunately, ir.
broadband ~F 6ystems, unless a large elab~rate antenna
system i ~mployed, the an~enna will not provide a good
impedanc~ ~atch over the en~lr~ frequency range. There-
~ore, for s~mple ~ntenna installatlons, a device called an
antenna coupler must be use~ to maximize the radiated power
of the ~tation.
An ant~nna coupler is ~ varlabl~ impedance matching network
desi~ned to match the $mpedance o~ the antenna ~o that of
the transmitter. It i~ usually compo ed o~ an L~network or
a ~-network using &ervo driven, variable c~paci~ors and
roller inductor6, although more mod~rn implementa~ions use
digitally ~witched ~n~uc~or and capaci~or banks. They also
i~lud~ ~imple impedance de~ectors and con~rol logic t~
~acllitat~ automati~ tuninga
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Each time the frequency is chanyed, the antenna coupler must
go through a tune sequence. This involves setting the network to
a known home position, and then while transmitting, changing one
of the elements in one direction until a desired conclition takes
pla~e, as for instance, the sign of the phase changing. Then
another element of the network is changed in a desired direc~ion
until its desired condition occurs, bringing the coupler to a
closer ma~ch. This process is repeated until the desired
impedance match is obtained and the process stops. Normally, the
tune sequence takes a few seconds to complete. Unfortunately, the
tune sequence of such tuners is too slow to track FM CW signals
(or swept signals) or to avoid detection by clirection finding
equipment in a military environment.
Summary of ~he Invention
It is an object of the invention to provide for an
automatic antenna coupler for use in swept high frequency (HF)
transmission systems.
It is a more particular object of the present invention
to provide for an automatic antenna coupler which :Ls suitable fos
use in a range from 1.6-30 MHz.
The present invention provides an automatic antenna
coupling capability and includes adjustable impedance matching
means for matching the output impedance of a transmitter to the
input impedance o~ a non-broadband antenna. In one preferred
embodiment, the coupler further includes means for tracking the
frequency of a s~ept transmitted signal and mean~ responsive to
the tracked signal for automatically adjusting the adjustable
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impedance matching means to provide proper lmpedance ma~ching.
Aceording to a broad aspect of the invention ~here is
provided an antenna coupler comprisiny
adjustable lmpedance matching network means for matching ~he
ou-tput impedance o f a transmitter at a radio frequency (RF) input
to the input impedance of a non-broadband antenna,
means for tracking a swept, transmitted signa:L at sald RF
input, and
processor means responsive to the tracked signal for
automatically adjusting said impedance matching network means to
provide an impedance match between said output impedance and said
input impedance wherein said processor means includes means for
dividing the swept frequency range into discrete bands,
means for determining the frequency of said input signal to
be matched for each of said bands, and for determining any changes
in the frequency of said input signal,
means for measuring and quantifying the value o~ the
impedance itself at said antenna for each of the determined
frequencies, and
means for calculating the amount of adjuskment needed to
match said output impedances and said input impedances based upon
measured value of impadance for each of said determined
frequencies, so as to provide an impedance match for each of said
discrete bands.
According to another broad aspect of the invention there
is provided an antenna coupler comprising
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adjustable lnput impedance matching network means for
matching the output impedance of a transmitter at a raclio
frequency (RF) input to the input impedance of a non-broadband
antenna,
means for detecting changes in said output impedance when an
RF signal is transmitted to said RF input,
means for measuriny and quantifying khe value of the
impedance itself at said antenna,
means for calculating the amount of adjustment needed to
match said output impedances and said input impedances based upo~
the measured value of impedance,
means for rematching said output impedance to said input
impedance if the detected changes vary from a certain
predetermined value.
According to another broad aspect of the invention the~e
is provided an antenna coupler comprising
adjustable impedance matching network means for matching the
output impedan~e of a transmitker at a radio frequency (RF) input
to the input impedance of a non-broadband antenna,
means for measuring and quantifying the impedance value
itself of said antenna~
means for calculatiny the amount of adjustmen~ needed to
match said output impedances and said input impedances based upon
the measured impedance value, and
means for adjusting said adjustable impedance matching
network means to match said output and input impedances.
Other objects, features and advantages of the present
invention will become apparent from the followiny ~etailed
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description when taken in conjunction with the accompanying draw-
ings.
Brief Description of -the Drawings
Fig. 1 depicts block diagram of an antenna coupler
according to the present invention.
Fig. 2-10 depict schematic diagrams of -the an-tenna
coupler depicted in Fig. 1. Figs~ 3-9 comprise parts "A" and "B"
and Fig. 10 comprises parts "A", "B" and "C".
Detailed Description of the Drawings
The aspects of the automatic antenna coupler according
to the present invention will now be described in conjunction with
Figs. 1-10.
The automatic antenna coupler according to the presen-t
invention is an automatically tuned network that, in one preferred
embodiment, matches the output impedance of typically a 5~-ohm
transmitter to the input impedance of a non-broadband antenna,
such as a whip, dipole or long wire. The resulting increase in
transmit coupling efficiency provides greater radia-ted power than
that available from an unmatched antenna. The present invention
is designed for use with any 1-150 watt ~F (high frequency) trans-
mitter operating from 1.6 to 30 MHz.
Fig. 1 depicts a block diagram of an antenna coupler
according to the present invention. In Fig. 1, an RF (radio
frequency) input signal is input to a 4:1 impedance transformer
12. A suitable VSWR (voltage standing wave ratio) detector 1~
provides suitable detection of forward voltage 22, reflected vol
tage 20, phase 1~ and frequency 16 of the RF input.
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An A/D ccnverter 26 r~ceives the forward voltage signal 22,
re~lected voltage ~ignal 20 and p~ase signal 18, and
provides appropriate corresponding digi~al signals on lead
28 to micropro~essor 40.
Frequency counter 24 receives the rrequency detected signal
on lead 16, and provides a suitable frequency signal to
~icr~processor 40 on lead 32.
Th~ present invention includes a suitab~e adjustable or
adaptable matching network 30 which includes adjustable
inductsrs 34 and adjustable capacitors 36. Matching
network 30 ls co~trolled by co~trol signals on lead 42 from
microprocessor 40. The control ~ignals on lead 42 include,
in one e~bodiment, eigh~ capacitor leads and twelve induc-
tor leads - ~ total of twen~y lines.
The reason most antenna couplers take so long to tune is
the ~act that it is unknown how much an element needs to be
changed. Therefore, it is changed incrementally in one
direction until a predefined condition is met. If the
coupler were implemented with digitally switched el~ments,
and the desired value of the elements could be calculate~
~ccurately, then the antenna coupler tune sequence could be
reduced to th~ time it takes to select those elements,
l.e., the relay settling time. This i5 what ~he present
lnvention accomplishes.
In on~ preferred embodiment, the coupler According to the
present lnvention includes ~n ~-ne~work using relay
Ewitched chunt cap~citor~ and series ~nductors. The RF
~ro~ the tr~n~mitter passes through a 4:1 RF transformer 12
tQ give ~ nominal ~mpedanee ~ ~2.5 ohms. Then it passes
30 through . . ~irec~ ional coupler ~r detector to the network
20. On~ of the import~nt aspects of the coupler is the
dir~ction~l coupler 1~. The ~orward (22) and re~lected
(20) ou~puts are ~ed ~o an accurat~ phase deteckor and the
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measured pha~e ~nd amplltudes o~ the forward and reflected
voltag~s ~re read into ~icroprocessor 40 with an A/D
converter 26. Consequently, micrDprocessor 40 has an
accurate measurement of the impedance, and therefore can
calculate the needed inductance to match the antenna 50.
In one ~mbodiment, t~e ~eries inductor section was composed
of eleven binary weighted inductor~ connected in a parallel
~ashion. ~he large6t inductor was 82.0 uH. The inductance
value ~ aelec~d by a b~nary number N. Therefore, the
r~lationshlp between inductance and N is 82/N uH, and
$nd~uctive re~ct~nce and N would be 82.0~w/N, where w is the
~requency in radians/secO
I~ the inductor was set at Nl and ~he inductive reactance
ne~ds to be changed by dX, then the new value of ~, N2
would ~e determined ~y solving the following equatio~:
82.0E-6~w/N2 ~ 82.OE-6~w/Nl = dX
or:
N2 3 82.0E-6~w~Nl / (82.0E-6*w + dX*Nl)
The pr~sent invention is a "smart" c~pler which can learn
~i.e., measure, correct ~nd store) the tuning character
i6tics of an antenna for all ~requencies from 2 ~o 30 MHz
in 0n8 6we~p of ~ tr~nsmitter. While tuned to a fixed
fr~quency or ~ollowing a Chirp sweep, the coupler divides
th~ 2-30 MHz ran~e ~nto disGret~ b~nd~ as narrow as 20 kHz,
th~n lQarns and store~ the v~lu~s o~ the regu~red matching
n~twork ~or e~ch b~nd. Typical tuning time during the
learning process lc 100 mill$second~ per frequency band.
. A~ter learnin~, all tuning corr~c~lons are recalled from
non-volatile ~emory ~nd wlll be completed in less than 20
~illi6econd~ per fregu~ncy ~or ~oth sw~eps ~nd fixed
Xrequencie~ (SS~/CW~, even when following widely spaced
~r~quency ~u~p~ or ~ops. ~ the antenna characteristics
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change tdue to 1ce loading, 6alt, sag, damage, etc.) the
coupler automatically rev~rts to the learn mode.
During the learning process, the present invention uses
impedance ~et~c~or~ and a microprocessor algorit~m to
measure the antenna impedance and compute the LC matching
network required to match the an~enna to 50 ohms. Whenever
~ requency change ~5 detected, a built-in frequ2ncy
~ountQr ~easures the ~nput RF freguency and the micropro-
ce~or check6 the tunin~ m~tch. If the antenna match chec~
10 ~how~ a VSW~ sreater than 2.~-1, the microprocessor 40 will
ad~u~t the ~atchlng network to reduce ~he VSWR ~o less than
1.5:1. The inductor6 and capacitors are switched into the
matching network ~y relays controlled by ~he microproces-
60r. Because the microprocessor computes the inductance
and capacitance based on impedance measurements, fewer
steps are required to tune. Iterative search methods 5uch
as the common "return to home and search for 50 oh~s"
technique are not used, greatly reducing tuning time and
relay chatter. To extend relay life, the relays are cold-
switched by momentarily PIN-diode-switching the input RF to
an internal 50 ohm dummy load during tuning operations.
Antennas of v~ry high VSWR will be ma~ched as closely as
possible to 50 ohms, limited only ~y the coupler's ~uning
21ement6. When antenna VSWRs exceed 10:1, the match
prQsented ~o the ~ransmi~ker may exceed 2.5:1.
The pressnt invention can al~o be used to tune an antenna
ln the receivo mode. On a previously learned antenna, the
transmi tt~r can s~nd a recsive ~re~uency command to the
. antenn~ coupler. The coupler will rec~ll the ma~ched
netwsrk ~ettlngs ~rom memory and tuns the antenna to that
~r~guancy without ~ tr~nsm~t tune ~equence.
Figs. 2, 3 and 4 depict schematic diagrams of the antenna
coupler which show the aspects of ~he adjustable matching
network 30 of Fig. 1.
Figs. 5-10 depict 6chematlc diagrams of the antenna tuner
control of Fig~ 1.
The components of Fi~s. 2-10 are well known in the prior
~rt, and consequently the operation of those schematic
dlagrams need not be described in any great detail.
