High performance circularly polarized microstrip antenna

• US 5,661,494 A
• Filed: 03/24/1995
• Issued: 08/26/1997
• Est. Priority Date: 03/24/1995
• Status: Expired due to Fees

• Current Assignee: National Aeronautics and Space Administration US Government As Represented By The Administrator of The
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Bondyopadhyay, Probir K.
• Primary Examiner(s): Hajec, Donald T.
• Assistant Examiner(s): PHAN, THO GIA
• Application Number:
  US08/410,625
• Time in Patent Office: 886 Days
• Field of Search: 343/700 MS, 343/829, 343/846
• US Class Current: 343/700.0MS
• CPC Class Codes: H01Q 1/364 using a particular conducting material, e.g. superconductor
• CPC Class Codes: H01Q 21/065 Patch antenna array
• CPC Class Codes: H01Q 21/24 Combinations of antenna units polarised in different directions for transmitting or receiving circularly and elliptically polarised waves or waves linearly polarised in any direction circularly polarised patch antennas H01Q9/0428; circularly polarised horns H01Q13/0241; cross-polarised horns H01Q13/0258; polarisation converters H01Q15/242; cross-polarised rear feeds H01Q19/136; crossed polarisation dual antenna H01Q25/001

Abstract

A microstrip antenna for radiating circularly polarized electromagnetic waves comprising a cluster array (20) of at least four microstrip radiator elements (22a-22d), each of which is provided with dual orthogonal coplanar feeds in phase quadrature relation achieved by connection to an asymmetric T-junction power divider (30) impedance notched at resonance. The dual fed circularly polarized reference element is positioned with its axis at a 45° angle with respect to the unit cell axis. The other three dual fed elements in the unit cell are positioned and fed with a coplanar feed structure with sequential rotation and phasing to enhance the axial ratio and impedance matching performance over a wide bandwidth. The centers of the radiator elements are disposed at the corners of a square with each side of a length d in the range of 0.7 to 0.9 times the free space wavelength of the antenna radiation and the radiator elements reside in a square unit cell area of sides equal to 2d and thereby permit the array to be used as a phased array antenna for electronic scanning and is realizable in a high temperature superconducting thin film material for high efficiency.

Claims

1. A microstrip array antenna for radiating circularly polarized electromagnetic waves in the microwave and millimeter wave range, said antenna comprising:

a planar array of microstrip antenna radiator elements formed on one side of a sheet of dielectric material, said array comprising four radiator elements in coplanar relation and arranged with the geometric centers of the radiator elements at the respective corners of a square area having sides with a length dimension d in the range of 0.7 to 0.9 times the wavelength of the operating frequency of the antenna and wherein the four radiator elements reside in a square unit cell area of sides equal to 2d;

an electrically conducting ground plane disposed in parallel spaced relation to said planar array; and

means for providing a feed signal in sequential phasing to said planar array of radiator elements for generating circularly polarized radiation, said means comprising a microstrip feeder network coupled to each said radiator element, said feeder network including four T-junction power dividers, each of which is coupled to a different one of the radiator elements to apply inputs of equal magnitude and frequency at two feed points located on mutually orthogonal input axes of the radiator element coupled thereto, each said power divider providing a 90°

phase shift to one of its said inputs with respect to the other so as to generate circular polarization radiation of the desired sense, said radiator elements being arranged in a symmetrical orientation wherein the radiator elements and their input axes are relatively rotated in a selected direction of rotation with respect to one another by successive incremental angles of 90°

to provide sequential spatial rotation of the feed signal to said radiator elements, said microstrip feeder network further comprising a thin film of high temperature superconducting material disposed in a plane in spaced parallel relation to the plane of said radiator elements and to said electrically conducting ground plane and between said radiator elements and ground plane and positioned relative to said radiator elements such that said radiator elements are electromagnetically coupled to said microstrip feeder network,

said antenna further including a microstrip feed line formed on one side of another sheet of dielectric material in a plane in spaced parallel relation to said electrically conducting ground plane and being adapted for electrical connection to a signal transmission source,

said electrically conducting ground plane being disposed between said microstrip feeder network and said microstrip feed line and provided with an aperture in alignment with said microstrip feed line and said microstrip feeder network such that a signal supplied to said feed line is electromagnetically coupled through said aperture to the microstrip feeder network for transmission to said radiator elements.

2. A microstrip array antenna for radiating circularly polarized electromagnetic waves in the microwave and millimeter wave range, said antenna comprising:

a cluster array of microstrip antenna radiator elements formed on one side of a sheet of dielectric material, said array comprising four radiator elements in coplanar relation and arranged with the geometric centers of the radiator elements at the respective corners of a square area having sides with a length dimension d in the range of 0.7 to 0.9 times the wavelength of the operating frequency of the antenna and wherein the four radiator elements reside in a square unit cell area of sides equal to 2d;

an electrically conducting ground plane disposed in parallel spaced relation to said planar array;

means for providing a feed signal in sequential phasing to said cluster planar array of radiator elements for generating circularly polarized radiation, said means comprising a microstrip feeder network coupled to each said radiator element, said feeder network including four T-junction power dividers, each of which is coupled to a different one of the radiator elements to apply inputs of equal magnitude and frequency at two feed points located on mutually orthogonal input axes of the radiator element coupled thereto, each said power divider providing a 90°

phase shift to one of its said inputs with respect to the other so as to generate circular polarization radiation of the desired sense, said radiator elements being arranged in a symmetrical orientation wherein the radiator elements and their input axes are relatively rotated in a selected direction of rotation with respect to one another by successive angles of 90°

to provide sequential spatial rotation of the feed signal to said radiator elements, said

feeder network further comprising a thin film of high temperature superconducting material disposed in a plane in spaced parallel relation to the plane of said radiator elements and to said electrically conducting ground plane and between said radiator elements and ground plane and positioned relative to said radiator elements such that said radiator elements are electromagnetically coupled to said microstrip feeder network,

a second electrically conducting plane positioned between said array of radiator elements and said high temperature super- conducting feeder network and being provided with four apertures wherein each of said four apertures has a configuration corresponding to the configuration of each of said radiator elements and is positioned in substantial alignment with said high temperature superconducting feeder network and a different one of said radiator elements such that a feed signal applied to said feeder network is coupled from said feeder network through each of said apertures to different ones of said radiator elements; and

a microstrip feed line formed on one side of another sheet of dielectric material in a plane in spaced parallel relation to said electrically conducting ground plane and being adapted for electrical connection to a signal transmission source, said electrically conducting ground plane being disposed between said microstrip feeder network and said microstrip feed line and provided with an aperture in alignment with said microstrip feed line and said microstrip feeder network such that a signal supplied to said feed line is electromagnetically coupled through said aperture to the microstrip feeder network for coupling to said radiator elements.

3. A microstrip array antenna as set forth in claim 2 wherein each said microstrip radiator element is of square shape.