Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-02-16
2001-09-04
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S830000
Reexamination Certificate
active
06285325
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of microstrip antennas, and more particularly to a compact wideband leaky-wave excitation microstrip antenna.
BACKGROUND OF THE INVENTION
Microstrip antennas are lightweight, low profile and low cost devices with a cylindrical and conformal structure suitable for replacing bulky antennas. Microstrip antennas have an inherently narrow (less than 5%) frequency bandwidth that limits more widespread usage. Numerous attempts to increase this bandwidth have met only limited success. Conventional microstrip antennas use a resonant cavity model to achieve a narrow bandwidth. Previous wide-band antennas like the horn, helix and log periodical antennas all suffer from being bulky, heavy and nonconformal. Combining the best characteristics of the microstrip and wideband antenna into one antenna would be most advantageous.
Up until now, it has not been possible to employ microstrip antennas without the disadvantages, limitations and shortcomings associated with a narrow bandwidth. By applying leaky-wave excitation to microstrip antennas, the present invention provides wideband microstrip antennas with compact size. This invention's wideband leaky-wave microstrip antenna provides a small antenna size making it ideal for antenna array elements. A leaky-wave can be excited in a waveguide of periodically placed microstrip patches on a dielectric substrate backed by a ground plane. While most transmission lines are designed to carry electromagnetic energy without much loss, a leaky-wave loses its energy along the propagation path. A simple way to produce a leaky wave is to excite the high-order modes in the transmission line. However it can be difficult to match the input impedance because the characteristic impedance and propagation constant of the leaky-wave depend on the strip width, which is the only variable in the design process at a given layer thickness with a standard substrate material. In this invention's antenna, gaps are introduced periodically in the microstrip transmission line. The resultant leaky-wave structure provides greater antenna design freedom and flexibility making it possible to design an antenna for a desired propagation constant while the input impedance is properly matched.
The compact wideband leaky-wave excitation microstrip antenna of the present invention provides the same high efficiency as in conventional microstrip antennas, with the key advantage over prior art antennas of having wide bandwidth and a similar surface area. The present invention advantageously answers the long-felt need for the low cost, compact, planar and conformal properties of microstrip material in an antenna with expanded frequency bandwidth using leaky-wave radiation.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a compact wideband leaky-wave excitation microstrip antenna.
Another object of the present invention is to provide a group of microstrip patches placed on a dielectric substrate and conductive ground plate for a compact wideband leaky-wave excitation microstrip antenna with a reduced antenna surface area.
These and other objects are advantageously accomplished with the present invention by providing a compact wideband leaky-wave excitation microstrip antenna comprising a group of microstrip patches disposed on a dielectric substrate stacked on a conductive ground plane. The dielectric substrate has a top region on a top surface of the dielectric substrate, and the top region and the dielectric substrate can be composed of either the same or different dielectric materials. In this invention, a means for feeding an RF signal, which can be a center feed pin, is electrically isolated from the radiating microstrip patches.
The antenna of the present invention is a compact wideband leaky-wave excitation microstrip antenna comprising a group of microstrip patches disposed on a dielectric substrate stacked on a conductive ground plane, with an electrically isolated center feed mechanism. The inventors herein have discovered that when several patches form a microstrip antenna cavity, the radiation comes from not only the traditional radiation edges, as would be expected, but also from the top surface, which is usually covered by a single patch in a conventional rectangular microstrip antenna. Thus, the radiation from the top surface of the leaky-wave microstrip antenna is much stronger than that from the edge surfaces. When the radiated power increases relative to the stored energy in the cavity, the Q factor becomes small, resulting in a large bandwidth. However the impedance matching will be increasingly difficult for a larger bandwidth because the resistive part of the input impedance exceeds the maximum value when a conventional feeding technique is used.
To overcome the problems associated with difficulties in impedance matching, the present inventors developed a new current feeding scheme to provide impedance matching when the Q value becomes very small. In the compact wideband leaky-wave excitation microstrip antenna of the present invention, a means for feeding an RF signal, such as a center feed pin, which normally touches the top conducting patch is electrically isolated from the radiating patches. In this way, the feed current is confined within the probe pin to give an increased input resistance. In accordance with the present invention, significant reductions in antenna surface area have been achieved, resulting in shorter microstrip antennas.
REFERENCES:
patent: 4924236 (1990-05-01), Schuss et al.
patent: 5319378 (1994-06-01), Nalbandian et al.
patent: 5448252 (1995-09-01), Ali et al.
patent: 5561435 (1996-10-01), Nalbandian et al.
patent: 5767810 (1998-06-01), Hagiwara et al.
patent: 6005519 (1999-12-01), Burns
Lee Choon Sae
Nalbandian Vahakn
Tereschuk George B.
The United States of America as represented by the Secretary of
Tran Chuc
Wong Don
Zelenka Michael
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