Contiguous channel multiplexer

• US 4,029,902 A
• Filed: 10/22/1975
• Issued: 06/14/1977
• Est. Priority Date: 10/22/1975
• Status: Expired due to Term

• Current Assignee: Hughes Aircraft Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Rosen, Harold A., Bell, H. Clark Jr.
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Popek, Joseph
• Application Number:
  US05/624,801
• Time in Patent Office: 601 Days
• Field of Search: 179/15 FD, 179/15 FS, 179/15 BC, 325/3, 333/6, 333/10, 333/11, 333/73 W
• US Class Current: 370/497
• CPC Class Codes: H03H 7/46 Networks for connecting several sources or loads, working on different frequencies or frequency bands, to a common load or source for use in multiplex transmission systems H04J1/00
• CPC Class Codes: H04J 1/12 Arrangements for reducing cross-talk between channels in line transmission systems H04B3/32; in cables or lines H04B3/26 - H04B3/30

Abstract

An improved multiplexer especially adapted for combining a plurality of microwave signal channels for transmission over a common transmission path is disclosed. A single "directional filter" multiplexer structure is utilized to combine contiguous or adjacent channels without resort to odd-even channel separation or additional equalization and/or compensation networks. By purposely extending the bandpass characteristics of preselected channel filters so that either or both of their cutoff frequencies extend substantially past their associated channel band edges and well into the reflection loss regions of the adjacent channel or channels the adjacent channel mutual interaction effect is exploited. The resultant interaction between the transmission characteristics of one channel and the reflection characteristics of the adjacent channel yields an overall transmission characteristic for each channel which meets the multiplexer loss, loss slope and group delay requirements while minimizing the need for equalizing or compensating devices.

Claims

1. A multiplexer of the type comprising a plurality of directional filters each having at least one input port and an output port, said input ports being adapted to receive signals extending over predetermined bands of frequencies, said filter output ports being connected in a cascaded transmission path to a multiplexer output port, the transmission characteristics of said multiplexer from the respective input ports of a given filter to said multiplexer output port being a function of the transmission coefficient of that filter and the reflection coefficient of the succeeding filters along said transmission path, the improvement comprising the extension of at least one of the cutoff frequencies of preselected ones of said filters into the bandpass region of a channel next adjacent thereto in frequency.

2. An improved signal multiplexer comprising, in combination:

a plurality of input signals, said input signals being divided into separate channels, with each of said channels having a lower band edge and an upper band edge, the upper band edges of each channel being substantially adjacent the lower band edge of a next succeeding channel;

a plurality of directional filters, each of said directional filters having at least one input port and a pair of output ports;

means for coupling one channel of said input signals to the input port of a respective one of said directional filters;

means for coupling the output ports of said directional filters in cascade, an output port of the last filter of said plurality of filters being coupled to the output port of said multiplexer; and

the pass band frequencies of preselected ones of said plurality of directional filters extending substantially beyond at least one of the band edges of the channel of input signals coupled thereto.

3. The multiplexer according to claim 2 wherein said input signal channels are coupled to the input ports of said filters in order of ascending frequency and the pass band frequencies of said preselected ones of said filters extend beyond the upper band edges of the channel of input signals coupled thereto.

4. The multiplexer according to claim 2 wherein each of said directional filters comprises a pair of substantially identical bandpass filters having their input ports and output ports respectively interconnected by means of first and second quadrature hybrid couplers.

5. The multiplexer according to claim 4 wherein said filters are of the quasi-elliptic-function type.

6. The multiplexer according to claim 4 wherein each of said quadrature hybrid couplers comprises coupled sections of TEM transmission line.

7. An improved signal multiplexer comprising, in combination:

a plurality of input signals, said input signals being divided into separate channels defined by upper and lower band edges;

a plurality of directional filters, each of said directional filters having at least one input port and a pair of output ports;

means for coupling each of said channels of input signals to an input port of a respective one of said directional filters;

means for coupling the output ports of said directional filters in cascade, an output port of the last filter of said plurality of filters comprising the output port of said multiplexer;

the transmission characteristics of a given one of said signal channels being substantially a function of the transmission coefficient of the filter associated with said given channel and the reflection coefficient of those channels adjacent thereto in frequency and following said channel in said multiplexer; and

means for altering the transmission loss characteristics of preselected ones of said signal channels by extending the transmission coefficient of the filter associated with said preselected channel past its associated channel band edge and into an adjacent channel.

8. The multiplexer according to claim 7 wherein said channels of input signals are coupled to the input ports of said filters in order of ascending frequency and the transmission loss characteristics of preselected ones of lower frequency channels are altered by extending the transmission coefficient of the filter associated therewith substantially past its upper channel band edge into an upper adjacent channel.

9. The multiplexer according to claim 7 wherein each of said directional filters comprises a pair of substantially identical bandpass filters having their input ports and output ports respectively interconnected by means of first and second quadrature hybrid couplers.

10. The multiplexer according to claim 9 wherein said filters are of the quasi-elliptic-function type.

11. The multiplexer according to claim 9 wherein each of said quadrature hybrid couplers comprises coupled sections of TEM transmission line.