Phased array antenna having a wave speeding ground plane

Claim 2

In a phased array antenna wherein at certain scan angles there may be produced a spurious TM wave along the ground plane which can cause substantially all the power to be undesirably reflected by the array resulting in a drastic reduction of radiated power, the combination comprising: a plurality of radiating elements for cooperatively producing a beam of electromagnetic energy which is capable of being steered in space by the coupling of signals of differing phase to the radiating elements; a ground plane associated with said plurality of radiating elements for preventing substantial radiation behind the array; and means for providing a reactive impedance in the transmission path formed by said ground plane and free space for increasing the phase velocity of a TM wave which tends to propagate along the ground plane to a phase velocity at least equal to the phase velocity of a free space wave; whereby the range of scan angles over which there is no substantial reflection of power resulting from propagation along the ground plane is increased.

Claim 3

In a phased array antenna wherein at certain scan angles there may be produced a spurious TM wave along the ground plane which can cause substantially all the energy to be undesirably reflected by the array resulting in a drastic reduction of radiated power, the combination comprising: a plurality of radiating elements for cooperatively producing a beam of electromagnetic energy which is capable of being steered in space by the coupling of signals of differing phase to the radiating elements; a ground plane including a planar conductive surface associated with said plurality of radiating elements for preventing substantial radiation behind the array; and means for providing a series capacitance in the transmission path formed by said ground plane and free space for increasing the phase velocity of a TM wave which tends to propagate along the ground plane to a phase velocity at least equal to the phase velocity of a free space wave without reducing the phase velocity of a TE wave which tends to propagate along the ground plane to less than that of a free space wave; whereby the range of scan angles over which there is no substantial reflection of power resulting from propagation along the ground plane is increased.

Claim 4

In a phased array antenna wherein at certain scan angles there may be produced a spurious TM wave along the ground plane which can cause substantially all the energy to be undesirably reflected by the array resulting in a drastic reduction of radiated power, the combination comprising: a plurality of radiating elements for cooperatively producing a beam of electromagnetic energy which is capable of being steered in space by the coupling of signals of differing phase to the radiating elements; a ground plane including a planar conductive surface associated with said plurality of radiating elements for preventing substantial radiation behind the array; and means for providing a series capacitance in the transmission path formed by said ground plane and free space for increasing the phase velocity of a TM wave which tends to propagate along the ground plane to a phase velocity at least equal to the phase velocity of a free space wave without reducing the phase velocity of a TE wave which tends to propagate along the ground plane to less than that of a free space wave; whereby the range of scan angles over which there is no substantial reflection of power resulting from propagation along the ground plane is increased.

Claim 5

In a phased array antenna the combination as claimed in claim 2 in which the means for providing a series capacitance includes a dielectric slab coextensive with said planar conductive surface having a plurality of regularly spaced holes perpendicular to said conductive surface and a plurality of thin conductive pins each positioned in one of said holes and in contact with said conductive surface at one end thereof, the thickness of said slab and the length of said pins being greater than lambda d/4 and less than lambda d/2, where lambda d is the wavelength of said electromagnetic energy in said dielectric.

Claim 6

In a phased array antenna the combination as claimed in claim 3 in which selected ones of said holes positioned at regularly spaced intervals have a larger diameter than the remainder of said holes and which additionally includes a plurality of hollow conductive cylinders each positioned in one of said selected holes and in contact with said conductive surface at one end thereof and in which said radiating elements consists of thin wire loops positioned in front of said dielectric slab and connected to a signal source through said hollow conductive cylinders.

Claim 7

In a phased array antenna the combination as claimed in claim 3 in which selected ones of said holes positioned at regularly spaced intervals have a larger diameter than the remainder of said holes and which additionally includes a plurality of hollow conductive cylinders each positioned in one of said selected holes in contact with said conductive surface at one end thereof, each cylinder having an internal diameter less than the diameter required to propagate said electromagnetic energy as an unloaded waveguide and in which each radiating element consists of a loaded waveguide including said conductive cylinders internally modified to propagate said electromagnetic energy.

Claim 8

In a phased array antenna the combination as claimed in claim 2 which includes a plurality of loaded metal wall waveguides comprising said plurality of radiating elements, each of said waveguides protruding from said planar conductive surface, the length of each waveguide above said conductive surface being between lambda /4 and lambda /2 where lambda is the free space wavelength of the radiated energy.

Claim 9

In a phased array antenna the combination as claimed in claim 2 which includes a plurality of loaded metal wall waveguides protruding from said planar conductive surface comprising said plurality of radiating elements, each of said waveguides having a flange positioned between said conductive surface and free space, flanges of adjacent waveguides being in spatial relationship so as to present a lumped capacitance to an incident TM wave.

Claim 10

In a phased array antenna wherein at certain scan angles there may be produced a spurious TM wave along the ground plane which can cause substantially all the energy to be undesirably reflected by the array resulting in a drastic reduction of radiated power, the combination comprising: a pluRality of radiating elements for cooperatively producing a beam of electromagnetic energy which is capable of being steered in space by the coupling of signals of differing phase to the radiating elements; a ground plane including a planar conductive surface associated with said plurality of radiating elements for preventing substantial radiation behind the array; and means for providing a shunt inductance in the transmission path formed by said ground plane and free space for increasing the phase velocity of a TM wave which tends to propagate along the ground plane to a phase velocity at least equal to the phase velocity of a freespace wave without reducing the phase velocity of a TE wave which tends to propagate along the ground plane to less than that of a freespace wave; whereby the range of scan angles over which there is no substantial reflection of power resulting from propagation along the ground plane is increased.

Claim 11

In a phased array antenna wherein at certain scan angles there may be produced a spurious TM wave along the ground plane which can cause substantially all the energy to be undesirably reflected by the array resulting in a drastic reduction of radiated power, the combination comprising: a pluRality of radiating elements for cooperatively producing a beam of electromagnetic energy which is capable of being steered in space by the coupling of signals of differing phase to the radiating elements; a ground plane including a planar conductive surface associated with said plurality of radiating elements for preventing substantial radiation behind the array; and means for providing a shunt inductance in the transmission path formed by said ground plane and free space for increasing the phase velocity of a TM wave which tends to propagate along the ground plane to a phase velocity at least equal to the phase velocity of a freespace wave without reducing the phase velocity of a TE wave which tends to propagate along the ground plane to less than that of a freespace wave; whereby the range of scan angles over which there is no substantial reflection of power resulting from propagation along the ground plane is increased.

Claim 12

In a phased array antenna the combination as claimed in claim 8 in which the means for providing a shunt inductance includes a plurality of thin conductive wires oriented in the transmission path formed by said ground plane and free space substantially perpendicular to said planar conductive surface, connected at one end thereto and having an effective length between lambda /4 and lambda /2, where lambda is the freespace wavelength of said electromagnetic energy.

Claim 13

In a phased array antenna the combination as claimed in claim 9 which additionally includes dielectric material encapsulating and supporting said thin conductive wires.

Claim 14

In a phased array antenna the combination as claimed in claim 8 in which the means for providing a shunt inductance includes a plurality of thin conductive wires oriented in the transmission path formed by said ground plane and free space substantially perpendicular to said planar conductive surface, said radiating elements include metal wall waveguides terminating in openings in said conductive surface and which additionally includes a plurality of solid cylinders of dielectric material each positioned within one of said waveguides and protruding through said openings into free space, said cylinders encapsulating said thin conductive wires.

Claim 15

In a phased array antenna the combination as claimed in claim 11 which additionally includes a plurality of thin metal discs, each positioned in one of said cylinders on the surface parallel to said conductive surface said thin conductive wires having a low impedance connection at one end to said thin metal discs and at the opposite end to said conductive surface.

Claim 16

In a phased array antenna the combination as claimed in claim 12 in which said thin wires project into said waveguides by a distance equal to lambda /4.