U.S. patent number 3,703,685 [Application Number 04/856,717] was granted by the patent office on 1972-11-21 for multiband antenna with associated r.f. amplifier.
This patent grant is currently assigned to Labtron Corporation of America. Invention is credited to Nicholas T. Simopoulos, James B. Y. Tsui.
United States Patent |
3,703,685 |
Simopoulos , et al. |
November 21, 1972 |
MULTIBAND ANTENNA WITH ASSOCIATED R.F. AMPLIFIER
Abstract
An improved VHF television antenna includes a pair of elongated
antenna elements mounted on a base member and a noise matched
amplifier connected directly to each element to amplify the
received signal which is then transferred by a low impedance cable
to a television set. The input impedance of each amplifier is noise
matched to the impedance of its corresponding element at the center
of the band of wavelengths for which the element is designed to
receive.
Inventors: |
Simopoulos; Nicholas T.
(Dayton, OH), Tsui; James B. Y. (Dayton, OH) |
Assignee: |
Labtron Corporation of America
(Dayton, OH)
|
Family
ID: |
25324336 |
Appl.
No.: |
04/856,717 |
Filed: |
September 10, 1969 |
Current U.S.
Class: |
455/273; 330/126;
330/295; 455/291; 455/334; 330/286; 343/701; 455/292; 455/341 |
Current CPC
Class: |
H01Q
5/48 (20150115); H01Q 21/30 (20130101) |
Current International
Class: |
H01Q
21/30 (20060101); H01Q 5/00 (20060101); H04b
001/16 () |
Field of
Search: |
;178/DIG.13
;325/367,374-376,381,386,479 ;330/30,31,124,126 ;343/701 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Richardson; Robert L.
Claims
What is claimed is:
1. An improved multiband antenna comprising
a pair of elongated antenna elements, one of said elements tuned to
a first frequency and the other of said elements tuned to a second
frequency different from said first frequency, said elements
arranged substantially parallel to each other;
an amplifier integrally connected to said elements, said amplifier
including a first transistor having its base electrode electrically
connected to said first element and a second transistor having its
base electrode electrically connected to said second element, the
input impedance of each of said transistors being adjusted to equal
approximately the optimum noise matching impedance of its
corresponding antenna element at the frequency for which it is
tuned;
a single radio frequency transformer having its primary winding the
ends of which are connected to the collector elements of both said
transistors and a center tap connection through which DC voltage is
applied to said transistors;
means providing a radio frequency ground for said center tap
connection;
said transformer including a single secondary winding which
combines the outputs of both said transistors into a single output.
Description
BACKGROUND OF THE INVENTION
Commercial television broadcasting in the United States in the very
high frequency (VHF) range is divided into a lower band extending
between 54 and 88 mHz (channels 2- 6) and a higher band extending
between 174 and 216 mHz (channels 7- 13). The total band width for
the VHF television channels is therefore in the order 4:1.
When using a single antenna to accommodate this entire frequency
range of the VHF spectrum, it is generally necessary to apply
filtering techniques to reduce the unwanted effects of high
intensity signals occurring in the non-TV portion of the spectrum,
i.e., from 88 to 174 mHz. Another technique is to employ two
antennas, one designed to receive the low band and the other the
high band. These conventional antennas are either flat dipole or a
multimode dipole and are quite large since they are usually
one-half wavelength in length.
SUMMARY OF THE INVENTION
This invention relates to an integrated transistorized television
receiving antenna which is smaller in dimension than conventional
antennas and may employ monopole elements as well as dipoles. The
end of each element is connected directly to an integrally
connected noise matched amplifier which is mounted on the antenna
structure. The impedance of each amplifier is noise matched to the
impedance of its corresponding element at approximately the center
frequency for which the element is designed to receive, and since
the impedance is noise matched, high signal to noise ratios are
obtained. Also, since the antenna may employ monopoles and does not
require the use of dipoles, the length of the antenna may be at
least half that of conventional devices.
The output from the two integrally connected noise matched
amplifiers are coupled together through a high frequency
transformer and this combined signal is carried by a coaxial cable
to the television receiver. The coaxial cable also serves the dual
purpose of supplying DC power to the transistors, and consequently
means to separate the DC power supply from the television signals
are employed.
In a preferred embodiment, the antenna elements are mounted on a
single base member with the element receiving the low band having a
total length in the order of 56 inches, and the element receiving
the high band having a length in the order of 15 inches. The 56
inch element is folded to about 29 inches in order to restrict the
total length of the antenna assembly to about 30 inches. Also, the
spacing between the elements is selected so that the longer antenna
will act as a reflector for the shorter antenna, and the shorter
antenna will act as a director for the longer antenna resulting in
an improved front to back gain ratio.
Accordingly, it is an object of this invention to provide an
improved small antenna system of the type described wherein
integrally connected noise matched amplifier elements are mounted
directly on the antenna supporting structure with their inputs
connected directly to the ends of their respective elements; to
provide an improved antenna system wherein the impedance of each
amplifier is adjusted to noise match the impedance of its
respective element at approximately the center of the band of
frequencies for which that element is designed thus to maximize
signal to noise ratio and minimize noise from the active elements;
and to provide an improved television receiving antenna system
which occupies less space than conventional antennas but yet
provides high gain and improved signal to noise ratios.
Other objects and advantages of the invention will be apparent from
the following description, the accompanying drawings and the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the improved VHF television antenna
constructed according to this invention;
FIG. 2 is a plan view of the VHF television antenna showing
particularly the configuration and relationship of the monopole
elements to each other;
FIG. 3 is an electrical schematic diagram of the amplifier circuit
which is mounted directly on the antenna structure; and
FIG. 4 is an electrical schematic diagram of a power supply which
may be used with the circuit shown in FIG. 3;
FIG. 5 is a plan view of a transformer which combines the outputs
from two transistor amplifier circuits mounted on the antenna
structure.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now particularly to FIGS. 1 and 2, which show a preferred
embodiment of a VHF television receiving antenna constructed
according to this invention, the antenna includes a base member 10
which may be formed from phenolic or other electrically insulating
material. Two monopole elements are formed on the base member 10,
the first monopole element 12 having a length effective to receive
signals in the lower band (channels 2- 6), and a second monopole
element 13 having a length effective to receive signals in the
higher television band (channels 7- 13).
The first monopole element 12 has a total length of approximately
56 inches, however this element is folded so that the total length
of the base member itself is only 30 inches. The length of the
second monopole element 13 is in the order of 14 inches and
represents approximately one quarter wavelength.
The width of each antenna element is preferably one-half inch and
the spacing between the center of elements 12 and 13 is 2 3/8 inch.
This spacing is the minimum found to give an effective front to
back ratio when the elements are mounted in a horizontal plane.
Also mounted on the base member 10 is a transistor amplifier, shown
generally at 15, which amplifies the signals received by the
monopole elements and transmits these signals to a television
receiver by means of a low impedance line, preferably a coaxial
cable 17. As shown in FIG. 2, the area occupied by the amplifier 15
is shown enclosed by dotted lines. Also formed on the base member
10 is a ground buss bar 18, the purpose of which will be described
later.
The amplifier components are mounted directly on the base member 10
in the preferred embodiment, and consequently the base member may
be a printed circuit board on which the interconnecting leads
between elements comprising the amplifier are formed. Also, the
monopole elements 12 and 13 may be formed from the same material
used as the conductor material on the printed circuit board for
ease in construction. Thus, the entire antenna, as shown in FIGS. 1
and 2, is an elongated flat device having a total length of
approximately 30 inches and a total width in the order of 4 inches
and includes two monopole elements and the transistorized
amplifier.
As is well known in the art, the impedance at the end of a monopole
element will vary with frequency, and therefore two elements have
been provided to cover the entire VHF television range, one for
each of the bands identified above. In order to maximize the signal
to noise ratio, the input impedance of the amplifier is noise
matched to the impedance of the source or antenna. For any given
amplifier, there is one source resistance which will provide the
optimum noise match, and in the case of a transistor amplifier, the
source resistance which minimizes the noise figure is given as
follows: ##SPC1##
Where
R.sub.g = Source resistance
r.sub.e ' = emitter resistance
r.sub.b ' = base resistance
H.sub.fe -- forward current gain common emitter
Further discussion of this noise matching technique may be found in
"Vacuum Tube Amplifiers", edited by G. E. Valley, Jr. and H.
Wallman, published by Dover Publications, Inc., 1965, pages 496-
694, and in particular, pages 619 and 681. With respect to
transistors, reference is made to the "Handbook of Semiconductor
Electronics", Second Edition, edited by L. P. Hunter, published by
McGraw-Hill Book Company, Inc., 1956, pages 12- 23 through 12-
29.
The transistor amplifier 15 includes two separate amplifier
circuits, each having an input connected to the end of its
corresponding monopole element. Thus, the base of transistor Q1 is
connected electrically to the end 20 of monopole element 12 while
the base of transistor Q2 is connected electrically to the end 22
of monopole element 13. As shown in FIG. 3, a low pass filter is
connected between the antenna element 12 and transistor Q1 in order
to prevent FM and high band TV signals from causing cross
modulation. The filter includes capacitors C1, C2, C3 and C4 and
inductors L1, L2, and L3. Each of the inductors is an air coil of
No. 22 wire wound on an one-eighth inch inside diameter form.
Similarly, a high pass filter circuit including inductors L4 and L5
and capacitor C5 is placed in the input circuit of transistor Q2 to
prevent FM and other signals of lower frequency from causing cross
modulations. The outputs from the low and high pass filters are
connected to the base elements of transistors Q1 and Q2 through
capacitors C6 and C7, respectively.
A source of DC voltage is applied through the coaxial cable 17 to
both transistor amplifier circuits. The shield of the cable 17 is
connected to the buss bar 18 which forms a common ground for all
components of the system. In the preferred embodiment, this DC
supply is in the order of 20 volts. Resistors R1 and R2 provide a
voltage dropping network which biases the base of transistor Q1 and
resistors R3 and R4 similarly providing a biasing voltage for the
base of transistor Q2.
The DC supply voltage is also applied through the center tap CT of
the primary windings P1 and P2 of transformer T1 to the collector
elements of both transistors. The transistor circuits are completed
by emitter resistors R5 and R6 and radio frequency bypass
capacitors C8 and C9. The center tap CT and one side of the
secondary winding S of transformer T1 are connected to radio
frequency ground through capacitors C10 while allowing them to
remain above direct current ground. Capacitors C11 and C12 also
insure a radio frequency ground near each transistor.
FIG. 4 shows a power supply particularly suited for use with the
preferred embodiment. 115 volts AC is applied through connector 30
and switch 31 to a power transformer T2. The output of this
transformer is applied through rectifier D1 to a filtering circuit
including capacitor C13. A bleeder resistor R7 provides a constant
load to the power supply and also prevents a charge from remaining
on capacitor C13 after the unit has been disconnected from the AC
source. The DC supply is then connected to a coaxial connector 35
to which is attached the coaxial cable 17. Capacitor C14 insures
that no radio frequency (television) signals are fed through the
power supply to the AC service line and prevents interference with
other television receivers.
An impedance matching transformer T3 is connected to the television
set 36 through capacitors C15 and C16, and between the power supply
and the coaxial cable 17. This transformer matches the low
impedance of the coaxial cable 17, which is typically in the order
of 52 to 75 ohms, to the 300 ohm input normally provided on
commercially available television receivers.
The transformer T1 combines the output from both transistors Q1 and
Q2 onto a single low impedance line for transmission to the
television set. In the preferred embodiment, the transformer
includes a toroidal ferrite core 40, shown in FIG. 5, and primary
windings P1 and P2 which consists of 12 turns of No. 30 wire, six
turns on either side of the center tap CT. The secondary winding S
is wound directly over the primary winding and includes four turns
of No. 30 wire, two turns on either side of the center tap. The
total diameter of the ferrite core 40 is approximately 0.375
inch.
The impedance matching transformer T3 is wound on a similar
toroidal ferrite coil, however, other types of impedance matching
transformers or baluns may be employed with equal
effectiveness.
As shown in FIG. 4, an AC convenience receptacle 37 is provided
into which the television set may be plugged. When the power supply
for the antenna is turned on, the television is also turned on.
The following table lists the values for the various components
employed in the preferred embodiment.
R1 3.3 K ohms C6 910 pf R3 33 K ohms C7 12 pf R2 1 K ohms C8
through C12 and 0.01 mfd C14 through C16 R4 12 K ohms R5 120 ohms
C13 250 mfd R6 510 ohms Q1 type 2 N3866 (RCA) R7 2.7K ohms Q2 type
40235 (RCA) C1 75 pf D1 type IN2069 C2,C3 220 pf L1 0.08 UH C4 150
pf L2,L5 0.02 UH C5 15 pf L3,L4 0.04 UH
it is obvious that the transistors used as amplifiers need not be
limited to bi-polar devices. Newer devices such as field effect
transistors may be substituted which may provide higher gain, lower
noise and minimize the possibilities of cross modulation,
intermodulation, etc.
Thus, an improved VHF type television antenna has been described in
which monopole elements, or dipoles if desired, are employed to
capture the signal radiated from a television transmitting station,
with a noise matched amplifier connected directly to each of the
antenna elements to provide maximum signal to noise ratio. The
antenna constructed according to this invention also provides a
front to back gain ratio due to the spacing of the elements thus
providing desirable directional characteristics.
While the preferred embodiment of this invention has been described
as a VHF television antenna, the principles employed in this
invention could also be applied to other multiband antennas where
it is desired to have antenna systems of lengths substantially
shorter than conventional antennas. Thus, in its broad concept this
invention contemplates a multiband antenna employing receiving
elements, such as rabbit ears, with each element connnected
directly to a noise matched amplifier.
This invention also contemplates the use of two or more antennas
tuned to the same frequency, and an integrally noise matched
amplifier connnected to the end of each element. The outputs of the
amplifiers are connected so that they add together. Since the
received signals are coherent and the noise from the transistors
are incoherent, the signal-to-noise ratio will be increased. If
there are N such units tuned for the same frequency, the output
signal is directly proportional to N, the output noise is
proportional to .sqroot.N. Therefore, the signal-to-noise ratio is
improved by the factor of .sqroot.N, ideally. As an example, when
four antennas are connected in this fashion, the signal-to-noise
ratio will increase by a factor of two.
The techniques of this invention have been directly applied to the
design of arrays wherein one section of two elements was used for
the low frequency TV band (55- 88mHz) and another section of two
elements was used for the high frequency band (174- 216 mHz). For
the low frequency band, this application permits one element to be
peaked to Channel 3 (63 mHz) while the other element was peaked to
Channel 5 (79 mHz). By this means, an additional antenna efficiency
was obtained because the effective bandwidth of each element was
reduced by another factor of two. The second section of the array
is then treated in the same manner for the high frequency TV band
using Channels 8 (183 mHz) and 12 (207 mHz). The resulting array
disclosed that the techniques of this invention provide a basic
designer's tool for application to a wide variation of uses to
obtain extremely high efficiency for specific situations.
While the form of apparatus herein described constitutes a
preferred embodiment of the invention, it is to be understood that
the invention is not limited to this precise form of apparatus, and
that changes may be made therein without departing from the scope
of the invention.
* * * * *