Scanning antenna with electronically reconfigurable signal feed

1. A scanning antenna system, comprising:

a feed line having first and second ends;

a scanning antenna element disposed with respect to the feed line so that an electromagnetic signal input to one of the first and second ends of the feed line is evanescently coupled to the scanning antenna element, whereby the scanning antenna element is configured to radiate or receive the electromagnetic signal as a shaped beam through an angular scanning field having a stop band, a negative scanning space on a first side of the stop band, and a positive scanning space on a second side of the stop band; and

a switching network operatively coupled to the feed line and configured to switch the electromagnetic signal input to or from the feed line between the first end of the feed line and the second end of the feed line in a controlled sequence, whereby the shaped beam radiated or received by the scanning antenna element is scanned in the negative scanning space, the stop band, and the positive scanning space.

2. The scanning antenna system of claim 1 , wherein the switching network comprises:

a master switch assembly having an input terminal configured for connection to a signal port, and first, second, and third selectable output terminals;

a negative side scan switch assembly having an output terminal connected to the first end of the feed line, a first selectable input terminal connected to the first output terminal of the master switch assembly, a second selectable input terminal connected to the second output terminal of the master switch assembly, and a third selectable terminal connected to an impedance-matched load; and

a positive side scan switch assembly having an output terminal connected to the second end of the feed line, a first selectable input terminal connected to the third output terminal of the master switch assembly, a second selectable input terminal connected to the second output terminal of the master switch assembly, and a third selectable terminal connected to an impedance-matched load.

3. The scanning antenna system of claim 2 , wherein the first and third selectable output terminals of the master switch assembly are configured to direct the signal respectively to the first selectable input of the negative side scan switch assembly and to the first selectable input of the positive side scan switch assembly, and wherein the second selectable output terminal of the master switch assembly is configured to direct half the signal to each of the second input terminal of the negative side scan switch assembly and the second input terminal of the positive side scan switch assembly.

4. The scanning antenna system of claim 1 , wherein the switching network is configured to be actuated in a prescribed sequence to direct the signal to the negative side scan switch assembly when the antenna element is scanning through the negative space of the scanning field, then to direct half the signal to each of the negative and positive side scan switch assemblies while the antenna element is scanning in the stop band, and then to direct the signal to the positive side scan switch assembly while the antenna element scanning from the stop band through the positive space of the scanning field.

5. The scanning antenna system of claim 1 , wherein each of the negative side scan switch assembly and the positive side scan switch assembly comprises a single pole triple throw (SP3T) switch.

6. The scanning antenna system of claim 5 , wherein the master switch assembly comprises a SP3T switch.

7. The scanning antenna system of claim 5 , wherein the master switch assembly comprises first and second serially-connected single pole double throw (SPDT) master switches; wherein the first master switch has an input terminal configured to be connected to the signal port, a first selectable output terminal connected to an input terminal of the second master switch, and a second selectable output terminal configured as the third selectable output terminal of the master switch assembly; and wherein the second master switch has a first selectable output terminal configured as the first selectable output terminal of the master switch assembly, and a second selectable output terminal configured as the second selectable output terminal of the master switch assembly.

8. The scanning antenna system of claim 1 , wherein the negative side scan switch assembly comprises first and second serially-connected SPDT negative side scan switches, and wherein the positive side scan switch assembly comprises first and second serially-connected SPDT positive side scan switches.

9. The scanning antenna system of claim 8 , wherein the master switch assembly comprises first and second serially-connected single pole double throw (SPDT) master switches; wherein the first master switch has an input terminal configured to be connected to the signal port, a first selectable output terminal connected to an input terminal of the second master switch, and a second selectable output terminal configured as the third selectable output terminal of the master switch assembly; and wherein the second master switch has a first selectable output terminal configured as the first selectable output terminal of the master switch assembly, and a second selectable output terminal configured as the second selectable output terminal of the master switch assembly.

10. The scanning antenna system of claim 9 , wherein the first negative side scan switch includes an output terminal connected to a first selectable input terminal of the second negative side scan switch, a first selectable input terminal connected to the first selectable output terminal of the second master switch, and a second selectable impedance matching terminal; wherein the second negative side scan switch includes an output terminal connected to the first end of the feed line, and a second selectable input terminal connected to the second selectable output terminal of the second master switch; wherein the first positive side scan switch includes an output terminal connected to a first selectable input terminal of the second positive side scan switch, a first selectable input terminal connected to the second selectable output terminal of the first master switch, and a second selectable impedance matching terminal; and wherein the second positive side scan switch includes an output terminal connected to the second end of the feed line, and a second selectable input terminal connected to the second selectable output terminal of the second master switch.

11. A method of operating a scanning antenna system including a scanning antenna element evanescently coupled to a feed line having first and second opposed ends, wherein the antenna element is configured to radiate or receive an electromagnetic beam across an angular scanning field having a first angular scanning space, a second angular scanning space, and a stop band between the first and second field angular scanning spaces, wherein the method comprises:

using a switching network operatively connected to the feed line to:

direct a signal solely to the first end of the feed line while the antenna element scans from the first scanning space to the stop band;

direct equal parts of the signal simultaneously to the first and second ends of the feed line while the antenna element scans through the stop band; and

direct the signal solely to the second end of the feed line while the antenna element scans from the stop band through the second scanning space.

12. The method of claim 11 , wherein the switching network comprises a plurality of switches operable in a controlled sequence to provide a radiated or received beam of substantially equal amplitude in each of the first and second scanning spaces.

13. The method of claim 12 , wherein the switches in the switching network are operable in a controlled sequence to provide a radiated or received beam in the stop band that is of at least substantially the same amplitude as the radiated or received beam in the first and second scanning spaces.

14. The method of claim 11 , wherein the switching network comprises a master switch assembly, a first side scan switch assembly, and a second side scan switch assembly;

wherein the master switch assembly has an input coupled to a signal port, a first selectable output connected solely to a first selectable input of the first side scan switch assembly, a second selectable output connected solely to a first selectable input of the second side switch assembly, and a third selectable output connected to a second selectable input of the first side switch assembly and a second selectable input of the second side switch assembly; and

wherein the first side scan switch assembly has an output connected to the first end of the feed line, and the second side scan switch assembly has an output connected to the second end of the feed line.