Antenna design using a high index, low loss material

Abstract

Antenna elements and systems and other radio and microwave frequency devices are constructed with a high index of refraction medium having high matched values of relative permeability and relative permittivity, and a low loss tangent. By making the permeability of the transmission medium substantially equal to its relative permittivity, the impedance of the material is matched to that of the surrounding free space or air. By immersing a radiating element in such a material, and / or by using such a material between adjacent radiating elements or between a radiating element and a reflective ground plane, the physical size and / or the spacing of the elements may be substantially reduced without appreciable performance loss, thereby resulting in a more compact device that is particularly desirable for mobile applications. At least one exemplary such material is formed in layers and has electrical properties which are anisotropic and homogeneous and which vary as a function of frequency; the layers of such a material are preferably oriented such that the particular frequencies of radiation propagating through each layer are presented with high matched values of relative permittivity and relative permeability, and low values of dielectric and magnetic loss tangents.

Description

FIELD OF THE INVENTIONThe present invention relates generally to the use of a high-index of refraction, low loss transmission medium in an electromagnetic device, and more particularly to relatively compact antenna elements and systems containing a high index of refraction medium having matched values of relative permittivity and relative permeability and low values of dielectric and magnetic loss tangents.BACKGROUND ARTAntenna elements and systems, and other radio and microwave devices, are conventionally constructed from conductive radiating elements, transmission lines and ground planes, and non-conductive spacers, mechanical supports, and other components. Their design typically requires the selection of appropriate materials. Size, weight, electrical properties and environmental resistance are primary parameters of interest.For example, the current trend in mobile antenna designs, such as those required by aircraft, ships and other vehicles, result in a need for low profile, di...

AI Technical Summary

Benefits of technology

In accordance with a second specific aspect, the present invention increases the effective size of the radiating element by orienting at least one layer of an anisotropic transmission medium such that a substantial portion of the radiation propagating through the transmission medium in the vicinity of the radiating element has its electrical and magnetic components aligned with an axis of the transmission medium having high relative permittivity and with an axis having high relative permeability, respectively (i.e., the ratio is essentially equal to one).

In accordance with a third specific aspect, the present invention provides an improved impedance match between the transmission medium and the surrounding free space by ensuring that a substantial portion of the radiation at an interface between the transmission medium and the surrounding air or free space has its electrical and magnetic components aligned with respective axes of the transmission medium having substantially equal respective values of relative permittivity and relative permeability.

Problems solved by technology

Projections from mobile antennas mounted on such vehicles are not only hazardous, but also cause drag and instability to the vehicle and vibration while the vehicle is in motion.

When the plane of the elements are brought closer to the ground plane, the reflected waves from the surface interferes with the directed waves, producing a loss in signal strength and in radiation efficiency.

When a high dielectric material is placed between the ground plane and the radiating element, the incident radiation is slowed down by the index of refraction (H) of the material; however, increasing the dielectric constant (relative permittivity--.epsilon..sub.r) to 10 or more without a similar increase in relative permeability (.mu..sub.r) results in a severe impedance mismatch and thus is not technically desirable for many broadband applications.

When such devices are applied to apertures which are less than approximately one wavelength in size or when they are forced into the flares of small horns, a serious deterioration in performance results.

Conventional radio and microwave frequency polarizers are also subject to losses caused by high loss tangents and severe impedance mismatching at the entrance and exit ports.

Prior art radio frequency and microwave lenses and other electromagnetic devices operating in the radio and microwave frequency ranges suffer from similar drawbacks.

It has also been proposed to use a commercially available surface wave absorber material having a relatively high refractive index to microwave radiation as a low propagation velocity material between various planar radiating elements of a broadband antenna and their respective ground planes; however, the heretofore known such materials had a relatively high loss tangent (on the order of 0.3) and the resultant efficiency is an order of magnitude less than acceptable for most commercial applications.

Although the patent hints at the possibility of other uses requiring a "reduced" magnetic loss tangent, the disclosed examples are intended only to absorb incident radiation and do not appear to have either matched values of relative permittivity and relative permeability, or low magnetic loss tangents, at the microwave frequencies of interest.