Space communications apparatus employing switchable band filters for transparently switching signals on board a communications satellite, payload architectures using such apparatus, and methods of implementing the apparatus and the architectures

• US 5,428,814 A
• Filed: 08/13/1993
• Issued: 06/27/1995
• Est. Priority Date: 08/14/1992
• Status: Expired due to Term

• Current Assignee: Sutton Wireless LLC (Intellectual Ventures LLC)
• Original Assignee: Alcatel Espace
• Inventors: Mort, Robert, Rouffet, Denis
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): FAILE, ANDREW I
• Application Number:
  US08/105,947
• Time in Patent Office: 683 Days
• Field of Search: 455/8, 455/12.1, 455/13.3, 455/13.4, 455/20, 455/101, 455/103, 455/338, 455/339, 333/178, 333/193, 333/132, 333/101, 375/102, 375/103, 379/248, 358/425, 348/659
• US Class Current: 455/12.1
• CPC Class Codes: H04B 7/2046 SS-TDMA, TDMA satellite switching

Abstract

The invention relates to switchable band filter apparatus for switching signals on-board a satellite, enabling signals of different and unforeseeable bandwidths to be switched between multiple input ports and multiple output ports. The invention also provides various payload architectures using such apparatus. Finally, the invention provides methods of implementing such apparatus and architectures for performing transparent switching of signals on-board a satellite.

Claims

1. An apparatus comprising an integrated bank of filters, having outputs that are combinable by switching, for switching input signals Si on n input ports to output signals So on m output ports, each of said input and output signals having a center frequency and occupying a bandwidth about said center frequency, the apparatus comprising at least p bandpass filters of bandwidth Δ

Φ

, with center frequencies f_j where j is an integer in the range p inclusive, the frequency difference between the center frequencies of two filters that are adjacent in frequency being substantially equal to the bandwidth Δ

Φ

of the passband of the bandpass filter, the number p being selected as a function of the bandwidth of the widest signal to be switched, Δ

F_max =pΔ

Φ

, each of said input signals Si being applied to the inputs of p filters, the apparatus further comprising a switching and combining matrix, said matrix having not less than p inputs and not less than m outputs, said inputs to said matrix being connected to said bandpass filters so as to pick up signals passing through said filters, and wherein said filters and paths through said switching matrix are matched in phase and in amplitude.

2. Apparatus according to claim 1, wherein said bandpass filters are implemented in surface acoustic wave component technology.

3. Apparatus according to claim 2, wherein a plurality q of said SAW bandpass filters are integrated on a single substrate, and wherein said bank of filters is made up of r=p/q substrates each including q bandpass filters.

4. Apparatus according to claim 1, wherein said bandpass filters are implemented in digital technology.

5. Apparatus according to claim 1, wherein said switching and combining matrix is integrated with at least one of said p bandpass filters in a common housing thus forming a single switching module.

6. Apparatus according to claim 5, wherein said matrix and said bandpass filters are integrated on a common substrate.

7. Apparatus according to claim 2, wherein said substrate is lithium niobate.

8. Apparatus according to claim 2, wherein said substrate is lithium tantalate.

9. Apparatus according to claim 2, wherein said substrate is quartz.

10. A payload architecture for use in space to enable transparent switching of input signals Si on n input ports to output signals So on m output ports, each of said input and output signals having a center frequency and occupying a bandwidth about said center frequency, said input and output signals being capable of having different center frequencies and being capable of occupying different bandwidths, the architecture further including one or more banks of filters and one or more switching and in-phase summing matrices, wherein

each of said banks of filters comprises at least p bandpass filters of bandwidth Δ

Φ

, with center frequencies f_j where j is an integer in the range 1 to p inclusive, the frequency difference between the center frequencies of two filters that are adjacent in frequency being substantially equal to the bandwidth Δ

Φ

, of the passband of the bandpass filter, the number p being selected as a function of the bandwidth of the widest signal to be switched, Δ

F_max =pΔ

Φ

, each of said input signals Si being applied to the inputs of p filters, and

each of said switching and in-phase summing matrices has not less than p inputs and not less than m outputs, the p inputs being connected to said bandpass filters so as to pick up signals passing through said filters, and wherein said filters and paths through each of said switching matrices are matched in phase and in amplitude.

11. A payload architecture according to claim 10, further including at least one frequency-changing assembly.

12. A payload architecture according to claim 11, said frequency-changing assembly comprising two frequency-changing subassemblies:

a first subassembly that performs a first change from the frequencies of the input signals Si to an intermediate frequency IF, using a first local oscillator which is at the same frequency for all of the input signals and all of the banks of filters and, alter filtering in said filters and after switching and in-phase combining in said matrices, a second subassembly performs a second frequency change, using a second local oscillator, from IF to a final frequency of the output signals So, such that

the bandwidth at intermediate frequency is the same as the bandwidth of the input signals Si and of the output signals So.

13. A payload architecture according to claim 11, said frequency-changing assembly comprising three frequency-changing subassemblies which perform four successive frequency changes:

a first change from the frequencies of the input signals Si to a first intermediate frequency IF₁ is performed using a single local oscillator frequency for all of the input signals Si;

a second frequency change to a second intermediate frequency IF₂ prior to application is performed on the input signals of the input signals to the inputs of said banks of filters, where all of the banks of filters have the same center frequency, said second intermediate frequency IF₂ being the same for all of the banks of filters, thereby requiring a plurality of local oscillators of different frequencies, each of said local oscillators corresponding, respectively, to each of said banks of filters after filtering in said filters and after switching and in-phase combining in said matrices, a third frequency change is performed to the first intermediate frequency IF₁, using the same local oscillators as in the preceding change; and

finally a fourth frequency change is performed by the third subassembly to a final frequency for the output signals So.

14. A payload architecture according to claim 11, said frequency-changing assembly comprising a frequency changing subassembly for each of said input signals Si and for each of said output signals So, and wherein utilization frequencies are distributed in such a manner that the bandwidths of the input and output signals Si and So are integer multiples of the unit bandwidths of a filter of one of said banks of filters.

15. A method of switching on-board a satellite, the method performing switching between input signals Si on n input ports to output signals So on m output ports, each of said input and output signals having a center frequency and occupying a bandwidth about said center frequency, each of said input and output signals being capable of having different center frequencies and being capable of occupying different bandwidths, the method including the following steps for each of said input signals to be switched:

applying an input signal to be switched coming from one of the n input ports and having a bandwidth Δ

F=pΔ

Φ

, via a first switching matrix, to a bank of bandpass filters having a passband Δ

Φ

for all of the filters, thereby splitting the input signal into a plurality, p, of narrow bands of constant width Δ

Φ

regardless of the bandwidth of said input signal Δ

F=pΔ

Φ

, thereby demultiplexing the input signal; and

reassembling the input signal in phase from the p bands of width Δ

Φ

by means of a second switching and summing matrix which sends the p bands of width Δ

Φ

to one of the m output ports, said reassembling step performing a multiplexing operation, and wherein

a configuration of the switching matrix is controlled as a function of the duration of the input signals, of the input ports of the input signals and of the output ports of the output signals, and of the bandwidth Δ

F, i.e. the number p of bandpass filters of bandwidth Δ

Φ

required for transmitting the output signals without degradation.

16. A method according to claim 15, further including the following steps:

prior to the input signal being demultiplexed, and with said input signal being characterized by a first center frequency Fc_i in the microwave range, performing a frequency conversion to a lower intermediate frequency IF; and

after the input signal has been multiplexed at intermediate frequency IF, performing a frequency conversion to a higher second center frequency Fc_o, e.g. in the microwave range, said frequency Fc_o being characteristic of the output signal So.

17. A method according to claim 16, wherein said first center frequency Fc_i is different from said second center frequency Fc_o.

18. A method according to claim 16, wherein said first center frequency Fc_i is similar to said second center frequency Fc_o.

19. A method according to claim 15, wherein each filter of passband Δ

Φ

corresponds to a center frequency f_j where j is an integer in the range 1 to p inclusive, and wherein the frequency difference between adjacent center frequencies f_j and f_j+1 is equal to the filter passbandwidth Δ

Φ

.

20. A method according to claim 15, wherein a bandwidth Δ

Fi of the input signals Si is substantially less than 36 MHz, for at least a major portion of the input signals to be conveyed.

21. A method according to claim 15, wherein the bandwidth Δ

Φ

of the bandpass filters is substantially less than 36 MHz.

22. A method according to claim 15, wherein the bandwidth Δ

Φ

of the bandpass filters is not greater than 6 MHz.