U.S. patent number 3,594,805 [Application Number 04/807,277] was granted by the patent office on 1971-07-20 for ferrite rod antenna with longitudinally split sleeve.
This patent grant is currently assigned to Pye Limited. Invention is credited to Eric G. Chardin.
United States Patent |
3,594,805 |
Chardin |
July 20, 1971 |
FERRITE ROD ANTENNA WITH LONGITUDINALLY SPLIT SLEEVE
Abstract
This invention relates to aerials comprising a ferrite rod
disposed within a longitudinally split sleeve of electrically
conducting material and where a substantially uniform capacitance
exists or is provided across the split. According to this invention
the resonant frequency of the aerial can be adjusted by varying the
inductance of the split sleeve disposed around the ferrite rod.
Inventors: |
Chardin; Eric G. (Cambridge,
EN) |
Assignee: |
Pye Limited (Cambridge,
EN)
|
Family
ID: |
10039562 |
Appl.
No.: |
04/807,277 |
Filed: |
March 14, 1969 |
Foreign Application Priority Data
Current U.S.
Class: |
343/746; 343/787;
343/788 |
Current CPC
Class: |
H01Q
7/08 (20130101) |
Current International
Class: |
H01Q
7/08 (20060101); H01Q 7/00 (20060101); H01q
007/08 () |
Field of
Search: |
;343/787,788,746,748,908 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lieberman; Eli
Claims
I claim:
1. A magnetic dipole aerial comprising a ferrite rod, a split
sleeve of electrically conducting material disposed around said
ferrite rod, an aperture in said sleeve and a member of
electrically conducting material movable to cover or uncover said
aperture, thereby to vary the inductance of said split sleeve to
adjust the resonant frequency of the aerial.
2. A magnetic dipole aerial comprising a ferrite rod, a
longitudinally split sleeve of electrically conducting material
disposed around said rod over part of its length, an aperture in
said sleeve, and a member of electrically conducting material in
contact with the external surface of said sleeve and movable so as
to cover or uncover said aperture.
3. An aerial as claimed in claim 2, wherein the aperture is a slot
extending longitudinally of the sleeve over part of its length.
4. An aerial as claim in claim 2, wherein the member is a further
sleeve which is axially slidable on the external surface of the
split sleeve between a position in which it covers the aperture and
a position in which it uncovers the aperture.
5. An aerial as claimed in claim 2, wherein substantially uniformly
distributed capacitance is provided across the split in the sleeve
by connecting capacitor means of effectively equal capacity across
the split at spaced points along the sleeve.
6. An aerial as claimed in claim 5, wherein the coupling to the
aerial is effected in a capacitive manner by forming one of the
capacitor means connected across the split in the sleeve from at
least two serially connected capacitors whose effective capacity is
equal to that of the other capacitor means connected across the
split and means connecting the leads to the aerial across one of
the serially connected capacitors.
7. An aerial as claimed in claim 2, wherein the split sleeve and
the member of electrically conducting material are made of
beryllium copper.
Description
The present invention relates to aerials comprising a ferrite rod
and particularly intended for operation in the upper HF, VHF or UHF
frequency bands.
The invention is particularly concerned with such aerials in which
a ferrite rod is disposed within a longitudinally split sleeve of
electrically conducting material and where a substantially uniform
capacitance exists or is provided across the split, which in
conjunction with the inductance of the sleeve causes the aerial to
be resonant at a required operating frequency.
From one aspect the invention provides a magnetic dipole aerial
employing a ferrite rod wherein the resonant frequency of the
aerial can be adjusted by varying the inductance of a split sleeve
of electrically conducting material disposed around said ferrite
rod.
From another aspect the invention provides a magnetic dipole aerial
comprising a ferrite rod, a longitudinally split sleeve of
electrically conducting material disposed around said rod over port
of its length, an aperture in said sleeve, and a member of
electrically conducting material in contact with the external
surface of said sleeve and movable so as to cover or uncover said
aperture.
Preferably the aperture is a slot extending longitudinally of the
sleeve over part of its length. The member may advantageously be a
further sleeve which is axially slidable on the external surface of
the split sleeve between positions in which it covers or uncovers
the slot.
Advantageously the slot extends for about one-third of the axial
length of the split sleeve, and the further sleeve is slightly
longer.
The member, such as the further sleeve, may be provided with a
projection to facilitate its adjustment relative to the slot or
other aperture in the split sleeve.
According to a feature of the invention, substantially uniformly
distributed capacitance is provided across the split in the sleeve
by connecting capacitor means of effectively equal capacity across
the split at spaced points.
According to a further feature of the invention, the coupling to
the aerial is effected in a capacitive manner by forming one of the
capacitor means connected across the split in the sleeve from at
least two serially connected capacitors whose effective capacity is
equal to that of the other capacitor means connected across the
split and connecting the leads to the aerial across one of the
serially connected capacitors. The serially connected capacitors
are also of such relative values as to provide a required power
match of the aerial to a load.
The invention will now be further described, by way of example,
with reference to the accompanying drawings, in which:
FIG. 1 is a plan view of one embodiment of aerial according to one
embodiment according to the invention, looking in the direction of
the split in the sleeve.
FIG. 2 is a plan view of the aerial of FIG. 1, looking in a
diametrically opposite direction, and
FIG. 3 illustrates a method of providing coupling to the aerial of
FIG. 1.
FIGS. 1 and 2 show, not to scale, an embodiment of a magnetic
dipole aerial intended, for example, for use over a frequency range
of approximately 142 to 152 Megacycles. The aerial assembly
comprises a ferrite rod 1, embraced for a major part of its length
by an electrically conductive cylindrical sleeve 2 having a
longitudinal split defining a gap 3 throughout its length. The
opposite edges of the gap 3 are capacitively connected to each
other by a plurality of capacitors, such as C1, C4 and serially
connected capacitors C2 and C3, uniformly distributed over a length
of the sleeve 2. The capacitors may be connected directly to the
sleeve 2, or, as shown, be attached to lugs 4 formed from turned up
projections at the edge of the gap 3. Partially surrounding the
cylinder 2, and a sliding fit thereon, is a split electrically
conductive sleeve 5 of a length less than one-half the length of
the sleeve 2 and slightly greater than a longitudinal slot 6 in the
sleeve 2, the length of slot 6 being about one-third of the length
of the cylinder 2. As shown the slot 6 is diametrically opposite
the gap 3, though its position is not critical. The effect of the
slot is to increase the inductance of the sleeve 2. A tab 7, either
attached to or formed from the sleeve 5, is utilized to move the
sleeve 5 axially, so as to adjust the inductance of the sleeve 2.
Minimum inductance is obtained when the slot 6 is completely masked
by the sleeve 5 and maximum inductance is obtained with slot 6
completely exposed, i.e. uncovered by the sleeve 5.
To maintain equal distribution of capacitance along the gap 3 in
the sleeve 2, all the bridging capacitors should be approximately
equal, i.e. the effective capacity of serially connected capacitors
C2 and C3 at the center of the gap 3 should be substantially equal
to that of the other capacitors bridging the gap. With the size of
aerial involved, at the relevant midfrequency of 147 Megacycles it
has been found that capacitance provided at three points, i.e. at
the center and near each end, is adequate.
The outer surface of the sleeve 2 tends to be electrically `dead`
and a tapping on the inductance of the cylinder is therefore not
effective as a coupling means to the aerial. The coupling to the
aerial is therefore made capacitive, as illustrated in FIG. 3,
which shows the cylindrical sleeve 2, gap 3 and capacitors C1 to
C4, with leads 8 and 9 being taken from each terminal of capacitor
C3 to form the connections for the aerial. Capacitors C2 and C3 are
of such value as not only to provide an effective capacitance equal
to that of each of capacitors C1 and C4 but also to provide a
substantially optimum power match of the aerial to a load.
Preferably the sleeve 2 and the sleeve 5 are made from a material
such as beryllium copper and preformed so that sleeve 2 firmly
grips the ferrite rod 1 and the sleeve 5 is a spring fit on the
sleeve 2 to give good electrical contact therewith. In order to
obtain a high Q factor when using such material, both the sleeve 2
and the sleeve 5 are preferably silver plated.
The sleeve 2 may be locked in position on the ferrite rod 1 by
known means, such as a sealing glue, as may the sleeve 5 on the
sleeve 2, after adjustment of the sleeve 5 as a trimming operation,
e.g. in setting up a receiver operating on a fixed frequency.
In the embodiment described the slot 6 is 0.7 inches long, the
cylindrical sleeve 2 is 1.8 inches long and the rod 1 has a length
of 2.2 inches. Movement of the sleeve 5 provides about 14 percent
change in inductance and a turning range of .+-.5 Megacycles on a
center frequency of 147 Megacycles. The range of adjustment of
inductance with slot length is nearly linear, but the mean position
lies slightly short of half the slot length from the inner closed
end of the slot. For maximum control it is desirable to fit the
capacitors C1 and C4 as near to the ends of the sleeve 2 as is
possible.
The aerial as described provides the following advantages:
1. Reduced material cost as only one accurately ground ferrite rod
is required, whereas previous constructions require two such
rods.
2. Easier assembly due to discarding the internal coupling loop,
used in prior constructions.
3. Provision of a simple and cheap means of adjustment that
requires little space.
4. A mechanically strong assembly as only a single ferrite rod is
used with no break at the center and the rod is supported
throughout the majority of its length by the conductive split
sleeve.
The ability to vary the inductance of the aerial and hence its
resonant frequency with little increase in overall size is of
particular advantage in small portable radio sets designed to be
carried unobtrusively on the person.
Tests on about 170 Megacycles have shown that an aerial as
described using a ferrite rod 2.2 inches long and of 0.3 inches
diameter is of the order of 16 db. down in performance on a half
wave dipole aerial about 36 inches in length. This degradation is
offset to some extent in practice by the fact that the high Q of
the magnetic aerial enables a tuned circuit employed with a dipole
or quarter wave aerial to be dispensed with, so removing the
insertion loss of the circuit. Also, due in part to the outer
surface of the split sleeve being electrically `dead` the resonant
frequency of the aerial is not materially affected by proximity to
an object, such as the human body, as is the case for a half or
quarter wave rod aerial. This characteristic is particularly
important for radio sets carried on the person.
* * * * *