Wideband polarization-transforming electromagnetic mirror

• US 4,228,437 A
• Filed: 06/26/1979
• Issued: 10/14/1980
• Est. Priority Date: 06/26/1979
• Status: Expired due to Term

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Shelton, J. Paul
• Primary Examiner(s): Lieberman, Eli
• Application Number:
  US06/052,298
• Time in Patent Office: 476 Days
• Field of Search: 343/756, 343/909, 343/753, 343/754, 343/755
• US Class Current: 343/909
• CPC Class Codes: H01Q 15/242 Polarisation converters

Abstract

A reflecting mirror for transforming the polarization of electromagnetic ) waves independently of the frequency of the waves and, thus, over an arbitrarily wide RF bandwidth includes two interleaved sets of planar arrays of resonant elements, both being orthogonally polarized, and each set comprising layers of the arrays which are arranged so that the layered elements of each set form a log-periodic configuration. The difference in phase between the reflection coefficient functions of the first and second sets of arrays is independent of the frequency of EM waves. Each of the arrays resonates at a different frequency and the arrays resonate over the frequency band of operation. A plane EM wave, the polarization of which has two vector components, strikes the mirror on the array having the shortest strips. The two polarization components of the wave travel into the mirror. Each component is reflected as it encounters strips of an array having a resonance which matches the resonant frequency of the component. The components being non-parallel to each other are reflected from different arrays which causes the components to change in phase relative to each other, thereby transforming the polarization of the wave.

Claims

1. A reflecting mirror for transforming the polarization of incident electromagnetic waves independently of the frequency of the waves and over an arbitrarily wide frequency bandwidth, comprising:

two interleaved sets of planar arrays of resonant elements, the two sets being orthogonally polarized,

the arrays of the first set being alternately layered with the arrays of the second set,

the layered elements of each set being spaced apart according to a logarithmic function,

each set having a reflection coefficient function which varies approximately linearly with the logarithm of frequency,

the difference in phase Δ

φ

between the reflection coefficient functions of each set being essentially constant with change in frequency, said difference in phase being a function of the scale factor between adjacent arrays of dissimilar polarization and being defined by

space="preserve" listing-type="equation">Δ

φ

=2π

log (f.sub.x /f.sub.y)/log τ

where f_x is a resonant frequency of an array of the first set,

f_y is a resonant frequency of an array of the second set, the arrays applicable to f_x and f_y being adjacent,

τ

represents the scale factor between adjacent arrays of similar polarization,

and f_x /f_y represents the scale factor between adjacent arrays of dissimilar polarization.

2. The reflecting mirror as recited in claim 1 wherein each of said arrays comprises a regular lattice of parallel resonant elements.

3. The reflecting mirror as recited in claim 2 wherein each array resonates at a different frequency.