Spiral-mode or sinuous microscrip antenna with variable ground plane spacing

Abstract

This is a microstrip antenna which eliminates the cavity used typically in spiral and sinuous type antennas. A small spacer between the antenna element and ground plane replaces the cavity. This significantly reduces the depth of the antenna and permits antenna shapes which conform to a vehicle skin, such as an aircraft. The microstrip has demonstrated higher gain and efficiency than the cavity, but only over a limited bandwidth less than that of existing cavity backed antennas. To increase the bandwidth, the antenna has a variable thickness spacer with the thickness proportional to the distance from the center of the antenna. The employment of this variable spacer results in maintaining the high gain and efficiency of the microstrip antenna over a much larger bandwidth comparable to the existing cavity backed antennas.

What is claimed is: 
     
       1. A microstrip antenna comprising a dielectric member having first and second major surfaces, a spiral radiating member of conductive material connected along the first major surface of said dielectric member, a grounding member of conductive material connected along the second major surface of said dielectric member; wherein said dielectric member is non-uniform in a dimension between the radiating member and the grounding member, being relatively thin at the center and thicker at the periphery, whereby the microstrip antenna has high gain and efficiency over a large bandwidth.   
     
     
       2. A microstrip antenna according to claim 1, wherein said grounding member is cone shaped, and the second major surface of the dielectric member is cone shaped to match the grounding member. 
     
     
       3. A microstrip antenna according to claim 1, wherein said radiating member is cone shaped, and the first major surface of the dielectric member is cone shaped to match the radiating member. 
     
     
       4. A microstrip antenna comprising a dielectric member having first and second major surfaces, a radiating member of conductive material connected along the first major surface of said dielectric member, a grounding member of conductive material connected along the second major surface of said dielectric member; wherein said radiating member is selected from the class consisting of spiral and sinuous elements;   wherein said dielectric member is non-uniform in dielectric properties between the radiating member and the grounding member, with a relatively low dielectric constant at the center and a higher dielectric constant at the periphery, whereby the microstrip antenna has high gain and efficiency over a large bandwidth.   
     
     
       5. A microstrip antenna comprising a dielectric member having first and second major surfaces, a sinuous radiating member of conductive material connected along the first major surface of said dielectric member, a grounding member of conductive material connected along the second major surface of said dielectric member; wherein said dielectric member is non-uniform in a dimension between the radiating member and the grounding member, being relatively thin at the center and thicker at the periphery, whereby the microstrip antenna has high gain and efficiency over a large bandwidth.   
     
     
       6. A microstrip antenna according to claim 5, wherein said radiating member is a sinuous conductor extending away from a common point with the common point the center of a coordinate system (r, φ) with a rotational symmetry such that a rotation of 360/N degrees about an axis containing the common point leaves the structure unchanged, wherein each arm consists of a cascade of cells numbered 1 to P, wherein 1 is the largest cell and the outside and inside radii of the p th  cell, measured from the common point, are given by R p  and R p+1  and are related by the design parameter τ p , which is less than 1, wherein R p+1  =τ p  R p , each cell comprising a conductor portion having a sharp bend with a protusion and wherein the center line of each sinuous conductor of each cell is defined by a line with the angular coordinate φ being an oscillating function of the radius and varying smoothly as a function of radius from φ n  to φ.sub. n +α p  to φ n  degrees for one cell and from φ n  to φ n  -α p  to φ n  degrees for the next cell where the α p  's are positive numbers and φ n  is the angle to the start of the first cell for the n'th arm and the α p  's are such that the cells of adjacent sinuous arms are interleaved and spaced from one another.