Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
2002-08-23
2004-02-24
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S7810CA, C343S840000
Reexamination Certificate
active
06697027
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention consists of improvements to rotationally symmetric dual reflector systems and symmetric cylindrical dual reflector systems. These antennas are used for the transmission and/or reception of electromagnetic waves. The antennas are used in many applications which include point to point links, telemetry and satellite communication.
2. Brief Description of Related Art
Dual reflector systems are commonly used in communication systems. They generally comprise a main reflector usually based on a parabolic shape and a sub-reflector, usually based on a hyperbolic or elliptical shape, and a feed. The systems with sub-reflectors using hyperbolic shapes are referred to as Cassegrain systems while the ones using elliptical shapes are referred to as Gregorian systems. In the transmitting mode, a feed is used to radiate energy towards the sub-reflector. The energy bounces off the sub-reflector towards the main reflector and then bounces again off this main reflector. In a receiving mode, the energy follows the reverse path.
Generally the description above and all of the description below apply to cylindrical geometries (where the cross-section of the geometry remains essentially constant) or rotationally symmetric geometries where each reflector is a surface of revolution. In both of these types there are many variations where the actual reflector shapes are cut from cylindrical or rotationally symmetric shapes. For example, it is common to base the reflector shapes on a portion of rotationally symmetric shapes so that the actual reflector has an elliptical rather than circular projection. In systems which are large in relation to the wavelength of the transmitted or received radiation, the reflector systems and shapes of the reflectors can be designed with the use of optical techniques.
When the dual reflector system is reduced in size, the sub-reflector may become small in relation to the wavelength of the received/transmitted radiation. Also, it is common to support the sub-reflector by attaching it to the feed via a dielectric support structure. Commonly, this is a tube or a rod or a partial cone. In this case the optical techniques used for the design of the bigger systems do not work very well. For the small reflectors more elaborate techniques which account for the near field effects of the sub-reflector, the support and the feed are used.
Common methods of analysis of such antenna systems are the Method of Moments and FDTD (Finite Difference Time Domain). It has been found by many authors that sub-reflector shapes other than those based on hyperbolas and ellipses work well. Furthermore, in early designs, the sub-reflectors were simple metallic plates and the sub-reflector-feed combinations were called “splash plate” feeds. One of the major attractions of the geometries described above is the location of the feed. It protrudes through a hole inthe main reflector and is attached to the main reflector near its vertex. This allows the shortest possible paths from the transmitter and/or receiver which are usually housed behind the main reflector.
The major problem with the geometries described above is the blockage caused by the sub-reflector or sub-reflector-feed combination. This blockage can be easily seen when the antenna is operating as a receiver. The blockage mechanism is crudely described by the following: The radiation that hits the sub-reflector is reflected by it and does not reach the main reflector. However, the radiation that reaches the main reflector is reflected towards the sub-reflector which bounces it into the feed. Generally the blockage causes two undesirable effects to the antenna radiation pattern. The first is a reduction in the antenna's on-axis gain and the second is an increase in the level of the side lobes. In particular, the side lobes close to the main beam (inner side lobes) can be greatly increased by the blockage.
Although the invention can be used for large antenna systems with small frequency bandwidths, it will be particularly useful in smaller antenna systems such as those which previously used “splash plate” feeds. Many workers have studied these reflector systems. In particular, the invention can replace those described in U.S. Pat. Nos. 4,963,878, 6,020,859 and 5,959,590. The first two of these patents describe an evolution of inventions by Kildal. The third patent by Sanford et al. is an improvement on earlier inventions by Kildal. These patents describe various shaped sub-reflectors and main reflectors.
The intention of these above-described inventions is to improve the far-field pattern performance of the antenna system. These inventions improve the gain and far out side lobes of the antenna patterns. They also allow operation of the antenna in a dual polarization mode. U.S. Pat. No. 6,137,449, also by Kildal, describes a number of ways of improving the mechanical design of the antenna plus a method for producing a dual band antenna.
SUMMARY OF THE INVENTION
In modern antenna systems there is increasingly a requirement to produce 1) high gain antennas with 2) low inner side lobes, 3) low far side lobes and 4) low VSWR (Voltage Standing Wave Ratio). With this invention it is possible to produce a better compromise between all four requirements than could be done previously.
The invention described here differs greatly from earlier inventions U.S. Pat. Nos. 4,963,878, 6,020,859 and 6,137,449 by Kildal since these do not address the problem of blockage of the feed and do not place a hole in the sub-reflector. The invention in U.S. Pat. No. 5,959,590 by Sanford et al. partially addresses the blockage problem by producing a small sub-reflector but does not include a hole in the sub-reflector.
Other important differences between the prior art and the present invention is the use of a more elaborate feed aperture and a simpler dielectric support. In the inventions by Kildal and Sanford et al, a simple tube is used as a feed but an elaborate dielectric plug is typically used to support the sub-reflector. In this present invention one or more chokes on the feed aperture help to control the radiation from the feed. Typically the feed aperture will be approximately as large as the sub-reflector. This larger diameter feed aperture produces more control of the radiation from the feed-sub-reflector combination and allows more freedom in the design of the dielectric support. Another benefit is improved control of the VSWR (voltage standing wave ratio) measured in the feed.
Due to the complexity of the interactions between the antenna components, it is not possible to produce closed form formulae for their dimensions. Rather, the goal of the invention is to establish a general geometry from which specific designs can be found which meet the desired requirements for particular applications. The detailed dimensions of the components can only be found by utilizing a computer optimizer which controls an accurate computer analysis program. Nowadays, there are a number of software packages available with these capabilities.
The invention allows the minimization or elimination of the sub-reflector blockage effects. In its simplest form, the invention is the inclusion of a hole or opening in the sub-reflector. This allows some energy to travel directly to or from the feed sub-reflector combination and by-pass the main reflector. In general the radiation that passes through the hole will not be in phase with the radiation which travels via the path that includes the main reflector. Usually, the latter path is much longer. This is where careful design of the reflector system is required.
By appropriate design of all the components in the antenna system, it is possible to force the two paths to be different by approximately an integer number of wavelengths and therefore force the two signals to be in phase. The number of wavelengths difference in the path lengths determines the frequency bandwidth over which the hole produces an improved antenna pattern. Increases to the difference in path length de
Le Hoang-anh
Schaap Robert J.
LandOfFree
High gain, low side lobe dual reflector microwave antenna does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High gain, low side lobe dual reflector microwave antenna, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High gain, low side lobe dual reflector microwave antenna will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3284012