Communications: radio wave antennas – Antennas – With lumped reactance for loading antenna
Reexamination Certificate
2002-01-07
2003-08-19
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
With lumped reactance for loading antenna
C343S745000, C343S773000, C343S774000
Reexamination Certificate
active
06608598
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to broadband antennas. More specifically, the present invention is directed to antennas that are small compared to the operating wavelength over much of the frequency band of operation. The invention further relates to a means of reducing the size of a conical radiating resonator in a manner so that a collection of such resonators provides a repetitive variation in input impedance. The amount of the variation in impedance can be controlled by the selection of lumped tuning elements. The invention provides a means of switching the tuning elements in a manner that yields several wide operating bands having similar performance characteristics, thereby providing an electrically small antenna that can operate across a very wide range of frequencies.
2. Description of the Related Art
For a number of years now radio communication systems have been increasing in complexity and numerous different communications services may be employed by a typical user, even a typical member of the general public. Furthermore, an increasing variety of communications tools is available and in use by the average consumer. Therefore, individuals are using a greater number and wider range of frequencies for these communication purposes. For example, a typical person in day-to-day tasks may use AM and FM radios, cellular telephones and, more recently, GPS systems. This ever-increasing trend in the use of communication devices is not likely to change.
The explosion in the use of communications technology is having an impact on the antennas that are an integral part of the every radio system. However, there are currently no known single, small antenna systems available that can operate as a practical matter across the varied range of frequencies that are currently in use by individuals on a regular basis.
Multiple services may operate on widely disparate frequency assignments. Some systems use spread-spectrum or frequency agile techniques that need much wider instantaneous bandwidths than those used with older modulation methods. The examples set forth above cover the kilohertz range through low gigahertz frequencies. Moreover, this push for wider bandwidth is accompanied by a desire to reduce the physical size of the antenna commensurate with the reductions that have been achieved in the size of the electronic components of the systems that use them. Currently, each of the systems mentioned above typically employs a separate dedicated antenna. As radio communication systems become more integrated, particularly those in vehicular services, it is desirable to employ a single antenna for all functions of the system. However, none are currently available to provide the necessary range of operating capability.
A review of known small-antenna designs confirms this fact. A comprehensive account of the state-of-the-art in small antenna design at that time was given in
Proceedings of the ECOM
-
ARO Workshop on Electrically Small Antennas,
G. Goubau and F. Schwering (eds.), Fort Monmouth, 1976. The small antenna art in more recent years is summarized in
Small Antennas,
K. Fujimoto, A. Henderson, K. Hirasawa and J. R. James, Wiley, New York, 1987. Two principal methods of reducing antenna size, reactive loading and material coating, are discussed. Since loading with reactive elements reduces the bandwidth of the antenna, resistive loading is often used to regain the lost bandwidth. However, resistive loading results in loss of efficiency and gain.
A Study of Whip Antennas for Use in Broadband HF Communication Systems,
B. Halpern and R. Mittra, Tech. Rep. 86-1, Electromagnetic Communication Laboratory, University of Illinois, Urbana, 1986 gives an example of one of many attempts that have been made to use lumped loading elements to substantially reduce the length of a whip antenna while retaining the ability to cover a wide range of frequencies. Not only is it difficult to maintain coverage of wide bandwidths with whip antennas, but the problem is compounded by using loading elements to shorten them. Hence, this approach has not been very successful when an objective of the design has been to produce a structure with low profile, a feature that is particularly desirable for vehicular antennas.
A new approach to low-profile antennas that are electrically small was introduced in
Series
-
Fed, Nested, Edge
-
Loaded, Wide
-
Angle Conical Monopoles,
P. E. Mayes and M. O'Malley, Digest of IEEE Antennas and Propagation Society International Symposium, Ann Arbor, Mich., 1993. It was shown there that a conducting cone with apex angle near ninety degrees, even though quite small in terms of the wavelength, could, at a certain frequency, display zero reactance (resonance) at the input terminals. The cone was fed against a ground surface from a coaxial cable (center conductor to tip of cone, shield to ground). The reduction in size was achieved by placing lumped inductive loads between the rim of the cone and the ground surface. It was also shown there that two such cones could be nested, connected in series, fed against ground to a transformer in such a way that low values of reactance could be maintained over a band of frequency. Additional data on edge-loaded conical monopoles are given in
Experimental Studies of Two Low-Profile, Broadband Antennas,
M. F. O'Malley and P. E. Mayes, Electromagnetics Laboratory Report 94-6, University of Illinois, Urbana, 1994.
A resonant radiator formed by the space between two nested open-ended conducting cones is one basic prior-art element that is used in the present invention. A single radiator of this form is shown generally in cross section at
10
in
FIG. 1A
wherein the polar angle defining cone
11
is ninety degrees. This is an example of the special case where the member
11
is actually a planar circular disc. Accordingly, as used in this specification, the term cone can mean either a metal plate or an open-ended angled cone. The second or upper cone
12
of smaller polar angle is positioned above the lower member
11
with cone
12
having a tip
18
at the center of cone
11
and with the axis of cone
12
substantially coincident with the normal through the center of cone
11
. A small circular aperture
14
is provided in cone
11
with its center substantially coincident with the center of cone
11
. A coaxial cable
15
is attached to the antenna so that the shield
16
of the cable
15
is electrically connected to the rim of the aperture
14
. The center conductor
17
of the coaxial cable
15
is electrically connected to the tip
18
of cone
12
. Alternatively, this connection may be accomplished with a panel jack having a center PIN connected to tip
18
of cone
12
. The outer conducting shield of the panel jack may be attached to the rim of the aperture
14
.
Networks of one or more lumped elements
20
are positioned at respective locations
21
a
,
21
b
,
21
c
,
21
d
spaced around the periphery of the conical antenna between the upper cone
12
and the lower cone
11
as shown in FIG.
1
B. The networks are electrically connected to the upper and lower cone members
11
and
12
as shown in FIG.
1
A. Usually, several similar networks will be distributed around the periphery of cone
12
in order to render sufficient symmetry to the system to maintain in azimuth the desired degree of uniformity in radiation.
Continuous electronic tuning of an edge-loaded conical resonator was demonstrated in
Tunable, Wide
-
Angle Conical Monopole Antennas with Selectable Bandwidth,
P. E. Mayes and W. Gee, Proceedings of the Antenna Applications Symposium, Allerton Park, Ill., 1995. The frequency of the high-impedance resonance was varied by placing voltage-variable capacitors (varactors) in series with the inductors on the rim of the cone.
FIGS. 2A-2C
show possible design choices for the network elements of the prior art.
FIG. 2A
shows a network comprised of a single inductor
32
as taught by O'Malley and Mayes.
FIG. 2B
shows an inductor
33
in series with a varact
Gee Walter
Mayes Paul E.
Depke Robert J.
Holland & Knight LLC
Le Hoang-anh
LandOfFree
Tuning circuit for edge-loaded nested resonant radiators... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tuning circuit for edge-loaded nested resonant radiators..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tuning circuit for edge-loaded nested resonant radiators... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3115405