Horn antennas with integrated feeds

1 . A apparatus, comprising:

a horn aperture having a footprint projected along a longitudinal axis, and integrated with a multimode feed network disposed within an envelope of the footprint;

the multimode feed network comprising:

a first feed section having a folded serpentine arrangement and coupled between a first feed port and a first polarizer port of a polarizer, the first feed section comprising a first waveguide filter perpendicular to the polarizer and first waveguide stubs parallel to the polarizer establishing first transmission zeros;

a second feed section having a folded serpentine arrangement and coupled between a second feed port and a second polarizer port of the polarizer, the second feed section comprising a second waveguide filter perpendicular to the polarizer and second waveguide stubs parallel to the polarizer establishing second transmission zeros; and

the polarizer comprising a stepped septum positioned between the first polarizer port and the second polarizer port and having a shared port coupled to the horn aperture.

2 . The apparatus of claim 1 , wherein the first waveguide filter and the second waveguide filter correspond to different bandpass frequencies and comprise a series of iris-coupled resonant cavities.

3 . The apparatus of claim 2 , wherein the iris-coupled resonant cavities comprise H plane iris discontinuities.

4 . The apparatus of claim 1 , wherein the first waveguide filter and the second waveguide filter are folded in corresponding E-planes in the folded serpentine arrangement and disposed within the envelope of the footprint of the horn aperture.

5 . The apparatus of claim 4 , wherein the first feed section and the second feed section comprise first H-plane bends coupled to corresponding feed ports arranged perpendicularly to an associated waveguide filter; and

wherein the first feed section and the second feed section comprise second H-plane bends coupled to corresponding polarizer ports arranged perpendicularly to the associated waveguide filter.

6 . The apparatus of claim 1 , wherein the first transmission zeroes and the second transmission zeros comprise at least four rejection nulls with frequency configurations selected among high side rejection nulls and low side rejection nulls with respect to a corresponding waveguide filter bandpass frequency range; and

wherein the configuration of the four rejection nulls is established based at least on sizing of cavities and irises of the corresponding waveguide filter.

7 . The apparatus of claim 1 , wherein the horn aperture integrated with the multimode feed network comprises a monolithic workpiece of material formed by an additive manufacturing process.

8 . The apparatus of claim 7 , wherein cross-sectional areas of the first feed section and the second feed section comprise pentagonal waveguide shapes.

9 . The apparatus of claim 1 , wherein the first waveguide stubs and the second waveguide stubs comprise short-circuited resonant cavities aligned perpendicularly to a corresponding waveguide filter.

10 . The apparatus of claim 1 , wherein the polarizer comprises a step down in cross-sectional waveguide diameter between the shared port and an input port of the horn aperture.

11 . The apparatus of claim 10 , wherein the step down comprises a reduced cross-sectional diameter selected to attenuate selected propagation modes.

12 . The apparatus of claim 1 , wherein the stepped septum comprises three steps and establishes a power split among the first polarizer port and the second polarizer port and a phase shift among radio frequency signals propagated by the first polarizer port and the second polarizer port.

13 . A method, comprising:

forming a horn aperture having a footprint projected along a longitudinal axis, and integrated with a multimode feed network disposed within an envelope of the footprint;

wherein the multimode feed network comprises:

a first feed section having a folded serpentine arrangement and coupled between a first feed port and a first polarizer port of a polarizer, the first feed section comprising a first waveguide filter perpendicular to the polarizer and first waveguide stubs parallel to the polarizer establishing first transmission zeros;

a second feed section having a folded serpentine arrangement and coupled between a second feed port and a second polarizer port of the polarizer, the second feed section comprising a second waveguide filter perpendicular to the polarizer and second waveguide stubs parallel to the polarizer establishing second transmission zeros; and

the polarizer comprising a stepped septum positioned between the first polarizer port and the second polarizer port and having a shared port coupled to the horn aperture.

14 . The method of claim 13 , wherein the first waveguide filter and the second waveguide filter correspond to different bandpass frequencies and comprise a series of iris-coupled resonant cavities; and

wherein the iris-coupled resonant cavities comprise H plane iris discontinuities.

15 . The method of claim 13 , wherein the first waveguide filter and the second waveguide filter are folded in corresponding E-planes in the folded serpentine arrangement and disposed within the envelope of the footprint of the horn aperture;

wherein the first feed section and the second feed section comprise first H-plane bends coupled to corresponding feed ports arranged perpendicularly to an associated waveguide filter; and

wherein the first feed section and the second feed section comprise second H-plane bends coupled to corresponding polarizer ports arranged perpendicularly to the associated waveguide filter.

16 . The method of claim 13 , wherein the horn aperture integrated with the multimode feed network comprises a monolithic workpiece of material formed by an additive manufacturing process; and

wherein cross-sectional areas of the first feed section and the second feed section comprise pentagonal waveguide shapes.

17 . The method of claim 13 , wherein the polarizer comprises a step down in cross-sectional waveguide diameter between the shared port and an input port of the horn aperture; and

wherein the step down comprises a reduced cross-sectional diameter selected to attenuate selected propagation modes.

18 . The method of claim 13 , wherein the stepped septum comprises three steps and establishes a power split among the first polarizer port and the second polarizer port and a phase shift among radio frequency signals propagated by the first polarizer port and the second polarizer port.

19 . A radio frequency aperture assembly, comprising:

a horn aperture having a footprint projected along a longitudinal axis; and

a feed network disposed within an envelope of the footprint, the feed network comprising:

a transmit feed section having a folded serpentine arrangement and coupled between a transmit feed port and a transmit polarizer port of a polarizer, the transmit feed section comprising a transmit waveguide filter perpendicular to the polarizer and transmit waveguide stubs parallel to the polarizer establishing first transmission zeros;

a receive feed section having a folded serpentine arrangement and coupled between a receive feed port and a receive polarizer port of the polarizer, the receive feed section comprising a receive waveguide filter perpendicular to the polarizer and receive waveguide stubs parallel to the polarizer establishing second transmission zeros; and

the polarizer comprising a stepped septum positioned between the transmit polarizer port and the receive polarizer port and having a shared port coupled to the horn aperture.

20 . The radio frequency aperture assembly of claim 19 , comprising:

the transmit waveguide filter and the receive waveguide filter comprising the folded serpentine arrangement in corresponding E-planes to establish routing disposed within the envelope of the footprint of the horn aperture;

the transmit feed section and the receive feed section comprising first H-plane bends coupled to corresponding feed ports arranged perpendicularly to an associated waveguide filter;

the transmit feed section and the receive feed section comprising second H-plane bends coupled to corresponding polarizer ports arranged perpendicularly to the associated waveguide filter; and

the transmit waveguide stubs and the receive waveguide stubs comprising short-circuited resonant cavities aligned perpendicularly to a corresponding waveguide filter.