Low cost electronically scanned array antenna
An electronically scanned array (ESA) antenna includes a main line along which an electromagnetic traveling wave may propagate and a plurality of array elements distributed along the main line. Each of the plurality of array elements includes a branch line; an antenna radiator at one end of the branch line; an electronically controllable reflection phase shifter at the opposite end of the branch line; a directional coupler which couples energy between the main line and the branch line.
1. An electronically scanned array (ESA) antenna, comprising:
a main line along which an electromagnetic traveling wave may propagate; and
a plurality of array elements distributed along the main line, each of the plurality of array elements comprising:
a branch line;
a directional coupler having a first port in the main line, a second port in the main line, a third port in the branch line, and a fourth port in the branch line;
a reflective termination at an end of the branch line closest to the third port of the directional coupler;
an electronically controlled phase shifter between the third port of the directional coupler and the reflective termination; and
an antenna radiator at the end of the branch line closest to the fourth port of the directional coupler.
2. The antenna according to claim 1 , wherein the directional coupler in each array element couples transmit electromagnetic energy from the main line to the branch line via an S 31 element of an S-matrix of the direction coupler, wherein the first through fourth ports of the directional coupler are specified by subscript values 1 through 4 of the S-matrix, respectively.
3. The antenna according to claim 2 , wherein the electromagnetic energy coupled to each branch line is reflected by the phase shifter and/or reflective termination.
4. The antenna according to claim 1 , wherein a majority of electromagnetic energy reflected by the phase shifter and/or reflective termination propagates through the branch line, through the directional coupler to the radiator.
5. The antenna according to claim 1 , wherein a majority of electromagnetic energy received by each radiator propagates through a branch past the directional coupler and is reflected by the phase shifter and/or reflective termination.
6. The antenna according to claim 1 , wherein a majority of the received electromagnetic energy reflected by the phase shifter and/or reflective termination in each branch line is coupled via an S 13 element of an S-matrix of the directional coupler to the main line.
7. The antenna according to claim 1 , wherein an S 31 element of an S-matrix of each directional coupler satisfies |S 31 |≦0.3, where first through fourth ports of the directional coupler are specified by subscript values 1 through 4 of the S-matrix, respectively.
8. The antenna according to claim 1 , further comprising a controller, wherein a radiation pattern emitted by the antenna is controllable by the controller via the phase shifters.
9. The antenna according to claim 1 , wherein a magnitude of coupling provided by each of the directional couplers is varied along the main line.
10. The antenna according to claim 1 , wherein the phase shifter in each array element comprises a varactor diode.
11. The antenna according to claim 10 , wherein the reflective termination is a short, and the varactor diode is a shunt element in the branch line.
12. The antenna according to claim 1 , wherein the phase shifters in each array element comprises a plurality of varactor diodes each shunted across a branch line.
13. The antenna according to claim 1 , wherein the mainline and the branch line in each array element are waveguides.
14. The antenna according to claim 13 , wherein the branch line in each array element is a ridged waveguide.
15. The antenna according to claim 1 , wherein the directional coupler in each array element is a cross guide coupler.
16. The antenna according to claim 1 , wherein the antenna radiator in each array element comprises an open-ended waveguide or flared notch structure.
17. The antenna according to claim 1 , wherein a transmission medium for the mainline and branch lines is any one of a waveguide, microstrip, stripline, coplanar waveguide, slotline, or a combination thereof.
18. The antenna according to claim 1 , comprising a plurality of main lines each with a corresponding plurality of the array elements, arranged to form a two-dimensional array.
19. The antenna according to claim 1 , wherein the antenna is constructed in a quasi-monolithic manner in which individual parts comprise structures for a plurality of array elements.
20. The antenna according to claim 1 , wherein the antenna has a quasi-monolithic, multi-layer construction including
a first layer defining the plurality of radiators and upper halves of the plurality of mainlines, directional couplers, and branch lines,
a second layer comprising lower halves of the plurality of mainlines, directional couplers, and branch lines, and
a third layer comprising an array of waveguide offset shorts that terminate the plurality of branch lines.
21. The antenna according to claim 20 , wherein one or more circuit boards are sandwiched between the second and third layers so as to realize phase shifters within each branch line.
22. The antenna according to claim 21 , wherein the one or more circuit boards are flexible circuit boards.
23. The antenna according to claim 22 , wherein the one or more circuit boards are at least partially wrapped around the third layer.
24. The antenna according to claim 20 , further comprising one or more spacer layers between the second and third layers.
25. The antenna according to claim 24 , wherein each spacer layer comprises an array of waveguide shims.
26. The antenna according to claim 1 , wherein the phase shifters comprise analog variable capacitance devices.
27. The antenna according to claim 26 , wherein the analog variable capacitance devices comprise at least one of MEMS varactors, varactor diodes or voltage variable dielectric based capacitors.
28. The antenna according to claim 1 , wherein the phase shifters comprise MEMS-based or semiconductor-based switches.
29. The antenna according to claim 1 , wherein the phase shifters are ferrite-based phase shifters.
30. The antenna according to claim 1 , wherein the phase shifters comprise voltage variable dielectric materials in either film or bulk form.
31. The antenna according to claim 1 , wherein lengths and/or dispersion of the branch lines are variable so as to alter the instantaneous bandwidth of the antenna.
32. The antenna according to claim 1 , comprising two arrays of main lines each with a corresponding plurality of the array elements, said main lines arranged such that array elements of the respective main lines are interleaved to form two co-located two-dimensional arrays.
33. The antenna according to claim 32 , wherein the radiator elements of the two arrays have orthogonal polarizations.
34. The antenna according to claim 32 , wherein neighboring pairs of elements of the two arrays share common dual band radiators.
35. The antenna according to claim 32 , wherein the two arrays are configured to operate at distinct frequency bands.
36. The antenna according to claim 1 , comprising two arrays of main lines each with a corresponding plurality of branch lines and phase shifters, said main lines arranged such that branch lines of the respective main lines are interleaved to form two co-located two-dimensional arrays.
37. The antenna according to claim 36 , wherein neighboring pairs of elements of the two arrays share common dual polarization radiators.
38. The antenna according to claim 1 , wherein the antenna comprises injection molded or cast parts.
39. The antenna according to claim 1 , further comprising at least one of a flared notch, open ended waveguide or patch radiator structure.