Title of Invention

A SLEEVE MONOPOLE ANTENNA FOR BROAD BAND COMMUNICATION

Abstract The present invention provides a sleeve monopole antenna for broad band communication comprising a conductor antenna base (1) with an insulator base cap (2) on one side of the antenna base (1) and a signal connector (12). An extended center pin (13) is provided extending through the base cap (2) attached to the other side of the antenna base (1). A tubular outer conductor (5), a tubular inner conductor (6) with an insulator cap (7) is provided at the bottom end and located inside the tubular outer conductor (5) providing a gap (G2) between lower end of the tubular inner conductor (6) and the signal connector (12). An insulator cap (8) is attached to the top end of the tubular inner conductor (8) providing a gap (G 1) between the top end of the tubular inner conductor (8) and a center conductor (9) attached to the extended center pin (13) and passing through the insulator cap (10) attached to the top end of the tubular outer conductor (5) . An insulator radome (3) is provided with an insulator cap (4) at the top end, housing the antenna, the top end of the center conductor (9) being fixed to the insulator cap (4) at the top end of the radome (3).
Full Text The invention relates to a sleeve monopole antenna for broad band communication ham omni-directional radiation coverage. It has an octave bandwidth and improved radiation characteristics which is insensitive to equency variation. It is excellent for broad band communication applications.
Improvement of the impedance characteristics of the sleeve antenna by means of adjusting the sleeve and radiator dimensions has been given primary emphasis in the sleeve monopole design known in the prior art. As a result extensive work has been carried out on the impedance characteristics of the sleeve antenna which radiation patterns have not been given significant consideration. In particular the possibility of achieving good impedance characteristics and a radiation pattern insensitive to frequency variation, within a wideband, has not been achieved before this invention. PRIOR ART
Modem wireless communication systems operate in two or more frequency bands, requiring dual or triple band operation of fundamentally narrow band antennas. These dual band and triple band elements tend to get complicated and may be prone to proximity detuning in some circumstances. New communication technologies especially spread spectrum, fi-equency hopping and frequency agile systems demand the widest possible antenna bandwidth. In this context, single broadband antennas are simpler and becoming very attractive.
One of the most popular antennas employed in vehicular and mobile communication systems is the monopole antenna and its derivatives, mounted on a metallic ground

plane of size comparable to the wavelength of operation. These antennas generally have a simple structure with prominent features such as pure vertical polarization and uniform azimuthal distribution of radiation. These antennas also have to be robust in construction, easy to use and of lightweight with a high power handling capability .
One such anterma is reported in "IEEE Transactions on vehicular communications, Vol.VC-15, No.2, October 1966" by RBrueckman. The antenna operating in the frequency band 30-76 MHz with a V.S.W.R of 3:1 is a derivative of monopole. The performance of the "antenna greatly depends on the large groomed plane (approximately 10m) associated with it, which make it bulky. The antenna uses lumped tuning elements and variable reactor for broadband matching. The internal broad band tuning circuit may limit the power handling capacity of the antenna.
Another anteima, disclosed in "A survivable low profile VHF monopole" IEEE APS-19-5 1985, pp. 617-620" by E.M. Newman and V.R Milligan, claims a V .S. W.R of 3: f over 30-88 MHz frequency band. A 40 cm diameter circular disc, attached to the top end of the antenna makes it much bulkier and no improvement in V .S. W.R is reported compared to the work disclosed by Brueckman. Also physical size of the antenna is far from compact due to the large ground plane size required for its satisfactory perfromance. A lossy network attached to improve the impedance matching of the antenna, deteriorates its efficiency considerably.
It was discovered in "Sleeve Antennas, Ch.5 in very high frequency techniques, pp. 119-137" by Bock. E.L, J .A. Nelson and A. Dome, that if a short tube (sleeve) is

attached around a conventional monopole anteima, the resuUing device would have satisfactory impedance match to its transmission line over a broader frequency range than if the sleeve were not present, hnprovement of the impedance characteristics of the sleeve antenna by means of adjusting the sleeve and radiator dimensions has been given prunary emphasis in the sleeve monopole antenna design ,known in the prior art. As a result, extensive work has been carried out on the impedance characteristics of the sleeve antenna, while radiation pattern has not been given significant consideration. In particular, the possibility of achieving good impedance characteristics and a radiation pattern insensitive to frequency variation within a wide band, has not been attempted before this invention.
It would be highly desirable to disclose a compact antenna with a substantially small ground plane and a very low V.S.W.R of 2:1, considerably improved from 3:1 or 3.5:l,reported in prior art. A low V.S.W.R is a significant performance parameter for the efficient operation of a antenna in many communication systems.
The present invention provides a sleeve monopole anteima as amulti-band device in view of the fact that the pattern optnnized sleeve monopole antenna has good pattern and impedance characteristics. The approach here is to adjust the external dimensions of the antenna to achieve pattern stability. With a maximum variation of 3 dB, and then to use the region within the sleeve for impedance matching.

The portion of the radiating structure of the antenna according to the invention is composed of a sleeve and a radiator. It is merely an extension of the c-axial transmission line beyond the ground plane with a discontinuity in the radii of conductors and with the center conductor projecting farther then the outer conductor.
The antenna according to the invention essentially comprises the following four
parts :
1. A conductor rod acts as the radiator having a length.
2. A co-axial line transformer of length 1| using an extension of the radiator with length "I" as inner conductor and a sleeve of length "L" as the outer conductor with characteristic impedance Zoi,
3. A coaxil transformer of length "l2- using the transmission line as the irmer conductor and the sleeve as the outer conductor with characteristic independence Z02
4. A series reactance network of length "I3" composed of a shorted transmission line of charcteristic impedance Z03 whose under conductor is an extension of the feed co-axial line and those outer conductor is the sleeve.
Details regarding various lengths of the antenna are as follows :

"1" = 0.16A. - 0.18X
"L" = 0.09^- o.ia
"ir = 0.O05X-O.0U
"I2" = 0.084X - 0.098X
"I3" = 0.0008X-0.0016X









It is preferable to nake the antenna base (1>, the tubular outer conductor (5) and the tubular inner conductor at the bottom end of the tubular inner conductor (6), the insulator cap (10) attached to the top end of the tubular outer conductor and the spacer (11) are all preferably made of teflon to provide good insulation characteristics. The center conductor (9) is preferably made of chromated alunlniun. The signal connector (12) attached to the antenna base (1) is preferably a flange mount co-axial connector.
The antenna radiates energy in, all directions, resulting in a radiation envelope or pattern. In other words, the radiation pattern presents the angular variation of the radiation at a fixed distance from the antenna, when the antenna is transmitting energy. Input impedance of the antenna is matched to the characteristic impedance of the feeder line. It has acceptable performance as measured with one or more parameters such as gain, pattern and impedance over a 2:1 bandwidth ratio of upper to lower operating frequency.

The antenna according to the invention offers good impedance match, showing a typical voltage standing vvave radio (VSWR) less than 2 to 1 over a band representing a frequency ratio of more than 2 to 1. The electrical performance of a typical antenna provides 0 dB gain, vertical polarization, omni-directional azimuth plane pattern and 200 watts continuous wave transmit power capacity. The antenna according to the invention exhibits a relatively insensitive radiation pattern to frequency variation. In a typical antenna according to the invention, the length of the radiating element is 30cm to 34.8 cm and diameter is 28 to 32 mm. The antenna according to the mvention is of a simple and low cost construction, encapsulated in a dielectric radome, tightly sealed for protection against moisture, ice, temperature and other environmental hazards. The anterma according to the invention is excellent for using in vehicular communications and jamming of unwanted signals.



WK OLAIH :
1 . A sleeve monopole antenna for broad band communication comprising a conductor antenna base on one side of the antenna base (1) and a signal connector (12) with an extended center pin with an insulator cap (7) at the bottom end and located inside the tubular outer conductor (5) providing a gap (G2) between lower end of the tubular inner conductor (6) and the signal connector attached to the top end of the tubular inner conductor (6) providing a gap (Ql> between the top end of the tubular inner conductor (6) and a center conductor with an insultor cap (4) at the top end, housing the antenna, the top end of the center conductor (9> being fixed to the insulator cap (4) at the top end of the radone (3>.
2. The antenna as claimed in clan 1, wherein at least one
spacer (11) is provided inside the radone along the length of
the center conductor (9) as a guide.
3. The antenna as claimed in blains 1 or 2, wherein the antenna
isle (1), the tubular outer conductor (5) and the tubular inner
inductor (6> are Bade of nickel coronet plated brass.

4. The antenna as clained in any one of the previous clains, wherein base opal and the insulator cap (4) at the top end of the radii (3) are and© of polypropylene.
b. The antenna as clained in any one of the previous clains,
wherein the radone (3) is node of polycarbonate.
6. The antenna as clained in any one of the previous claina,
wherein the insulator cap at the botton end of the tubular
inner conductor (6), the insulator cap (10) attached to the top
end of the tubular outer conductor (5) and the spacer node of Teflon.
7. The antenna as clained in any one of the previous clains,
wherein the center conductor (9) is a chromate aluminium rod.
8. The antenna as clained in any one of the previous clains,
wherein the signal connector (12> is a flange noun coaxial
connector.
9. A sleeve monopole antenna for broad band communication.
substantially as hereinabove described and illustrated with
reference to the accompanying drawings.

Documents:

982-mas-1999 abstract-duplicate.pdf

982-mas-1999 abstract.pdf

982-mas-1999 claims-duplicate.pdf

982-mas-1999 claims.pdf

982-mas-1999 correspondence-others.pdf

982-mas-1999 correspondence-po.pdf

982-mas-1999 description (complete)-duplicate.pdf

982-mas-1999 description (complete).pdf

982-mas-1999 drawings-duplicate.pdf

982-mas-1999 drawings.pdf

982-mas-1999 form-1.pdf

982-mas-1999 form-19.pdf

982-mas-1999 form-26.pdf


Patent Number 216231
Indian Patent Application Number 982/MAS/1999
PG Journal Number 13/2008
Publication Date 31-Mar-2008
Grant Date 10-Mar-2008
Date of Filing 08-Oct-1999
Name of Patentee SAMEER-CENTRE FOR ELECTROMAGNETICS
Applicant Address CIT CAMPUS, 2ND CROSS ROAD, TARAMANI, CHENNAI - 600 113,
Inventors:
# Inventor's Name Inventor's Address
1 KARIMPUMANNIL GEORGE THOMAS CIT CAMPUS, 2ND CROSS ROAD, TARAMANI, CHENNAI - 600 113,
PCT International Classification Number H01Q 001/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA