H-PLANE METAL PLATE LENS ANTENNA

WHAT IS LENS ANTENNA ?

Lens Antenna may be divided into two distinct types:

1. Delay lenses : lenses in which the electrical path length is increased by the lens medium. Dielectric lenses and H-plane metal-plate lenses are of the delay type.

These lenses are constructed of nonmetallic dielectrics such as lucite or polystyrene.And also constructed of metallic or artificial dielectrics.

Dielectric lens

2. Fast lenses : lenses in which the electrical path length is decreased by the lens medium. E-plane metal plate lenses are of fast type.

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E-plane metal-plate lens

INTRODUCTION

What is H- plane metal plate lens antenna ?

It is a kind of delay lens antenna , in which the electrical path length is increased because of retardation of wave by the lens medium.

H PLANE STACK OF FLAT METAL PLATES

Wave entering stack of metal plates oriented parallel to the H plane as in the figure (a) is little affected in its velocity.

H PLANE STACK WITH INCREASED PATH LENGTH

Here in the figure (b),the path length of wave is increased by deforming the plates in the stack.

SLANTED H-PLANE PLATES

An increase in path length can also be produced by slanting the plates as seen in fig (c).

The increased path length is S-T.

H PLANE METAL PLATE LENS ANTENNA USING SLANTED PLATE CONSTRUCTION

WHY IS IT CALLED H PLANE METAL PLATE LENS ANTENNA?? Because plates in the stack are parallel to the magnetic field…(i.e. perpendicular to the E plane).

DESIGN!! Can be designed by applying the principle of equality of electrical path length.

the condition for equality of electrical path length requires that

R = L + Rcosθ – L _________ cos ξ Or

R = (n-1)L ______ ncosθ-1

Where n=1/cos ξ =effective index of refraction of the slant-plate lens medium.

The index n depends only on the plate slant angle ξ and is not a function of the frequency as in the E-plane type of metal-plate lens.

The most critical dimension is the path length S in the lens this may be affected by a change in T or in ξ . Assuming a maximum allowable variation δ =λ /8 in electrical path length the tolerance in S is given by

ΔS=±0.06 λ

ADVANTAGES OF H PLANE METAL PLATE LENS ANTENNA :

1. In lens antenna, the rays are transmitted away from the feed system,hence the aperture is not obstructed due to the feed and feed support.

2. In lens antenna, as the waves enter from one side and leaves out from other end,greater extent of wrapping and twisting is possible without disturbing electrical path length.

3. Lens antenna can be used to feed at a point off the axis, so it is most extensive used in applications where beam is needed to be moved angularly with respect to axis.

DISADVANTAGES OF H PLANE METAL PLATE LENS ANTENNA :

1. Design of lens antennas is complicated.

2. lens antennas are expensive for the same gain and bandwidth requirements that can be got by using reflectors.

3. Lens antennas are bulkier.

4. H plane metal plate type of construction tends to produce unsymmetrical aperture illumination in the E plane.

THANK YOU

by Kshitij Rao (U11EC094) Tanvi Sethia (U11EC095)