Smaller aperture antenna for multiple spot beam satellites

• US 7,013,137 B2
• Filed: 07/16/2001
• Issued: 03/14/2006
• Est. Priority Date: 07/14/2000
• Status: Expired due to Fees

• Current Assignee: COMSAT Corporation (Reorganized ISA SA)
• Original Assignee: COMSAT Corporation (Reorganized ISA SA)
• Inventors: Zaghloul, Amir I., Williams, Albert E., Killic, Ozlem
• Primary Examiner(s): D AGOSTA, STEPHEN M
• Application Number:
  US09/904,624
• Publication Number:
  US 20020039883A1
• Time in Patent Office: 1,702 Days
• Field of Search: 455/427, 455/428, 455/429, 455/430, 455/12.1, 370316-326, 342/352, 342/354, 342/357.1, 342/368, 343/824, 343/853, 244/158.R, 244/FOR.104
• US Class Current: 455/429
• CPC Class Codes: H04B 7/18528 Satellite systems for providing two-way communications service to a network of fixed stations, i.e. fixed satellite service or very small aperture terminal [VSAT] system
• CPC Class Codes: H04B 7/2041 Spot beam multiple access

Abstract

This disclosure describes a method to generate large numbers of spot beams for multiple-beam satellite systems using smaller apertures. This is done by dividing the basic spot beam that has 3 to 4 dB of gain drop within the beam into a number of smaller 1-dB sub-beams. This has the effect of reducing the required peak gain for the antenna by 2–3 dB, thus reducing its size by as much as 50%. The frequency band allocated to the basic beam will be divided among the sub-beams. However, the frequency re-use among the basic beams can be maintained. Frequency allocations have to be coordinated among all beams. This concept is especially applicable to phased arrays using digital beam formers. The DBF complexity is a function of the number of array elements, and is less dependent on the number of beams. Reducing the array size, and consequently reducing the number of elements helps in reducing the complexity, power and mass of the DBF.

Claims

1. A method of communicating via satellite in a system comprising a satellite having a first type antenna capable of transmission of communication signals to a region on the earth'"'"'s surface and a plurality of earth stations disposed in said region, each earth station having a second type antenna capable of reception of said signals, said method comprising;

transmitting from said first type antenna multiple sub-beams within bandwidth allocated to a basic spot beam to said plurality of antennas in said region,

wherein the number of said sub-beams N are defined by the mathematical equation N=i²+j²+ij, where i and j are non-negative integers.

2. A method of communicating via satellite in a system comprising a satellite having a first type antenna capable of transmission of communication signals to a region on the earth'"'"'s surface and a plurality of earth stations disposed in said region, each earth station having a second type antenna capable of reception of said signals, said method comprising;

transmitting from said first type antenna multiple sub-beams within bandwidth allocated to a basic spot beam to said plurality of antennas in said region,

wherein said sub-beams require less peak gain than said basic spot beam, and

where each sub-beam is defined by a contour level, said contour level determined by a required edge gain.

3. A method as claimed in 2, wherein the gain relationship between said basic spot beams and said sub-beams can be defined by the equation G_b−

x_b=G_s−

x_s where G_b and G_s refer to said peak gain values of said basic spot beams and said sub-beams respectively, and x_b and x_s denote the contour levels for which each beam is defined.

4. A method as claimed in 3, wherein the peak gain of said antenna can be related to its half power beam width (hpbw), θ

₃ by an the equation $G=10<br><br><br><br>\log <br><br>\left(\frac{A}{{\mathrm{\theta <br><br>}}_3^2}\right),$

where A is a constant partly defined by antenna efficiency.

5. A method as claimed in 4, wherein the beamwidth of a phased array at an arbitrary contour level to its hpbw is determined by the equation θ

_x=θ

₃*0.59*x^0.4806, where the units of the beamwidth are in degrees.

6. A method as claimed in 3, wherein the contour levels of said basic and said sub-beams can be related to their beamwidths by the equation $9.612$

⁢

log⁡

(xsxb)+xb-xs=20⁢

⁢

log⁡

(θ

sθ

b),

where θ

_b is basic beamwidth and θ

_s is sub-beam beamwidth.