Claims
- 1. A fin-line horn antenna assembly comprising:
- a waveguide horn having a longitudinal axis and having an open end for radiating and receiving electromagnetic energy;
- a planar, dielectric card positioned within said waveguide, the plane of said card being parallel to said longitudinal axis;
- a layer of conductive material disposed on a surface of said card;
- a fin-line slot for propagating electromagnetic energy, formed in said layer of conductive material;
- a dipole radiator formed on said dielectric card and coupled to said fin-line slot for propagating electromagnetic energy therebetween; and
- energy transition means formed on said dielectric card and operably coupled to said fin-line slot for providing coupling of electromagnetic energy from said waveguide to said fin-line slot.
- 2. The antenna assembly of claim 1 wherein:
- said waveguide is a rectangular waveguide having first and second broadwalls and first and second narrow walls; and
- wherein said dielectric card is positioned orthogonal to said first and second broadwalls.
- 3. The antenna assembly of claim 2 wherein:
- said layer of conductive material is in electrical contact with said first and second broadwalls.
- 4. The antenna assembly of claim 3 wherein:
- said dipole radiator extends outside said waveguide approximately .lambda./4 from said open end, where .lambda. is the wavelength at the midband operating frequency of said antenna assembly.
- 5. The antenna assembly of claim 4 wherein:
- said dipole radiator is comprised of first and second conducting surfaces having a separation therebetween.
- 6. The antenna assembly of claim 5 wherein:
- said separation between said first and second conducting surfaces gradually increases as the longitudinal distance of said first and second conducting surfaces from said open end increases.
- 7. The antenna assembly of claim 5 wherein:
- said first and second conducting surfaces are formed and disposed with respect to each other so as to form a generally horn shaped opening therebetween.
- 8. The antenna assembly of claim 1 wherein:
- said dipole radiator extends outside said waveguide approximately .lambda./4 from said open end, where .lambda. is the wavelength at the midband operating frequency of said antenna assembly.
- 9. The antenna assembly of claim 8 wherein:
- said dipole radiator is comprised of first and second conducting surfaces having a separation therebetween.
- 10. The antenna assembly of claim 9 wherein:
- said separation between said first and second conducting surfaces gradually increases as the longitudinal distance of said first and second conducting surfaces from said open end increases.
- 11. The antenna assembly of claim 9 wherein:
- said first and second conducting surfaces are formed and disposed with respect to each other so as to form a generally horn shaped opening therebetween.
- 12. The antenna assembly of claim 1 wherein:
- said energy transition means is a single ridge tapered transition.
- 13. The antenna assembly of claim 1 wherein:
- said energy transition means is a dual ridged tapered transition.
- 14. In a combined dipole antenna and waveguide assembly which includes a dipole antenna extending from an open end of a waveguide, the improvement comprising:
- a slotline electromagnetic energy feed positioned within said waveguide and operably connected to said dipole antenna for directly coupling electromagnetic energy from within said waveguide to said dipole antenna.
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
The present invention relates generally to the fields of waveguides, antennas and millimeter wave devices. More specifically, the present invention relates to millimeter wave antennas and especially to those antennas suitable for use in electronic warfare direction finding and surveillance applications.
Waveguide horns are excellent radiators at the millimeter wave frequencies. They can be designed to achieve good circular symmetry and low voltage standing wave ratios (VSWR). In order to achieve broad beamwidth the waveguide horns must have small openings or apertures. This is due to the fact that the focal point of the radiating beam is behind the rim of the horns or within the waveguide itself. The smallest horn with the broadest beam is achieved by use of an open ended waveguide. Open ended waveguides have a beamwidth of 70 to 55 degrees as a function of the frequency over the normal waveguide bandwidth.
Surveillance systems that obtain the angle of arrival by means of amplitude comparison from four antennas disposed in quadrature, i.e. pointing 90 degrees apart, require antenna beams that ideally have 90 degree widths and little or no variations in beamwidth over the desired bandwidth. Smaller beamwidths and variations can be tolerated but will degrade the accuracy and sensitivity of the receiving system. Efforts to broaden the beam by means of dielectric lenses have been attempted but have not been satisfactory due to the variations in beamwidth with frequency and to losses associated with the dielectric.
The present invention comprises a waveguide/antenna assembly that achieves a nearly constant 90 degree beamwidth in the frequency range of the normal waveguide band. It has a good VSWR and circularity. Further, the antenna assembly of the present invention is comprised of a miniaturized antenna that may be manufactured for little cost and that is particularly suitable for use in electronic warfare direction finding and surveillance applications.
The antenna assembly of the present invention is comprised of a fin-line dipole radiator that extends outside an open ended waveguide by a quarter wavelength. The dipole radiator is a planar configuration and is formed on the fin-line circuit card. Electromagnetic energy propagation between the dipole radiator and the waveguide is achieved via a fin-line slot formed on the fin-line circuit card. By using this dipole antenna structure and feed arrangement integration with millimeter wave receiving circuits is facilitated because the fin-line impedance is low and well matched to diode beam-lead circuits or the like.
The present invention achieves the broad beamwidth pattern by focusing the antenna beam from a point outside the waveguide opening and therefore provides a broader beam than possible by using the waveguide horn or waveguide opening alone. In accordance with the present invention the tendency to broaden the beam with frequency counters the tendency of the horn characteristics such that the present invention can be used over a broad frequency range while maintaining a nearly constant beam shape.
Accordingly, it is the primary object of the present invention to disclose a millimeter wave antenna that provides a relatively constant antenna beam pattern with a near 90 degree beamwidth over a large frequency band.
It is a further object of the present invention to disclose a waveguide/antenna assembly that has a low VSWR and a circular symmetric radiation pattern and that is small and inexpensive.
These and other objects of the invention will become more readily apparent from the ensuing specification and claims when taken in conjunction with the attached drawings.
US Referenced Citations (11)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 2490025 |
Mar 1982 |
FRX |
Patent Grant
4905013
