Phase modulator operated in saturation and with small angle modulation

• US 5,126,698 A
• Filed: 12/20/1990
• Issued: 06/30/1992
• Est. Priority Date: 06/02/1989
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Strasser, William E., Fischer, Michael C.
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US07/633,653
• Time in Patent Office: 558 Days
• Field of Search: 332/103, 332/105, 332/144, 332/146, 328/155, 307/241, 307/242, 307/243, 307/262, 333/100, 333/103, 333/109, 333/117-123, 333/139, 333/164, 375/52, 375/53, 375/54, 375/67, 455/42, 455/110
• US Class Current: 332/105
• CPC Class Codes: H03C 3/00 Angle modulation H03C5/00, H03C7/00 take precedence
• CPC Class Codes: H03C 3/40 using two signal paths the outputs of which have a predetermined phase difference and at least one output being amplitude-modulated
• CPC Class Codes: H04L 27/2064 using microwave technology

Abstract

An input carrier signal is applied to two paths. The two paths are such that the phase difference between the output of the two paths is substantially 90°. At least one of the two paths responds to a modulating signal to select the polarity of the phase difference between the outputs of the two paths. The two paths are such that the phase angle between the output and input of the modulator is substantially independent of the amplitude of the modulating signal. In specific embodiments, one of the two paths includes a mixer or a quadrature hybrid with reflective diodes where the mixer or the diodes are operated in saturation. The outputs of the two paths are combined to provide a modulated carrier signal.

Claims

1. A phase modulator for providing a modulated carrier signal which is phase shifted by an angle relative to an input signal, comprising:

(a) a first and a second signal path for the input signal;

(i) the two paths being such that the phase difference between the outputs of the first and second paths is substantially 90°

;

(ii) wherein at least one of the two paths includes a mixer which responds to a modulating signal for selecting the polarity of the phase difference; and

(iii) said mixer operating in saturation so that the amplitude of the angle is substantially independent of the amplitude of the modulating signal;

(b) means for splitting the input signal and applying the split input signal to the two paths such that the amplitude of the input signal in said path having the mixer is at least 20 dB lower than the amplitude of the input signal in the other path; and

(c) means for re-combining the outputs of the two paths forming a vector sum to provide a modulated carrier signal.

2. The modulator of claim 1, wherein

a. the two paths have different path lengths;

and

b. wherein the difference in path lengths is such that the phase difference between the outputs of the two paths is substantially 90°

at the frequency of the input signal.

3. The modulator of claim 2, wherein the mixer is a double-balanced mixer.

4. The phase modulator of claim 2, wherein the mixer comprises a circulator and a reflective diode.

5. The phase modulator of claim 4, wherein the diode is connected to the circulator and the modulation signal is applied to the diode by means of a diode holder.

6. The modulator of claim 1, wherein:

a. the two paths have different time delays;

b. the difference in the two time delays in such that the phase difference between the outputs of the two paths is substantially 90°

; and

c. the polarity of the phase difference is selected according to the value of the modulating signal.

7. The phase modulator of claim 1, wherein:

(a) the mixer includes a quadrature hybrid and two reflective diodes operating either in cut-off or in saturation; and

(b) alternately the diodes being responsive to the modulating signal for introducing a phase shift of substantially 90°

or -90°

in accordance with the value of the modulating signal, between the outputs of the two paths.

8. The modulator of claim 7, wherein the two paths are of substantially equal lengths.

9. The modulator of claim 7, wherein the diodes are connected to the quadrature hybrid and the modulating signal is applied to the diodes by means of diode holders.

10. The modulator of claim 1, wherein the splitting means is a directional coupler.

11. The modulator of claim 1, wherein the splitting means is a power splitter.

12. The modulator of claim 1, the modulator further comprising:

a. at least a third and a fourth signal path for the input signal;

i. the third and fourth paths being such that the phase difference between the outputs of the third and fourth paths is substantially 90°

; and

ii. wherein at least one of the third and fourth paths responds to a second modulating signal for selecting the polarity of the phase difference;

b. means for splitting the input signal and applying the split input signal to the third and fourth paths; and

c. means for re-combining the outputs of the third and fourth paths with the re-combined outputs of the first and second paths in predetermined phase relation to provide a modulated carrier signal with more than two states, wherein the amplitude of the angle is substantially independent of the amplitude of the modulating signal.

13. A phase modulator for providing a modulated carrier signal which is phase shifted by an angle relative to an input signal, comprising:

(a) a first and a second signal path for the input signal;

(i) the two paths being such that the phase difference between the outputs of the first and second paths is substantially 90°

;

(ii) wherein at least one of the two paths includes a mixer which responds to a modulating signal for selecting the polarity of the phase difference; and

(iii) said mixer operation in saturation so that the amplitude of the angle is substantially independent of the amplitude of the modulating signal;

(b) means for splitting the input signal and applying the split input signal to the two paths wherein the splitting means is such that the amplitude of the input signal in said path having the mixer is about 10 dB to 100 dB lower than the amplitude of the input signal in the other path; and

(c) means for re-combining the outputs of the two paths forming a vector sum to provide a modulated carrier signal.

14. A phase modulator for providing a modulated carrier signal which is phase shifted by an angle relative to an input signal, comprising:

(a) a first and a second signal path for the input signal;

(i) the two paths having different time delays such that the phase difference between the outputs of the first and second paths is substantially 90°

;

(ii) wherein the first path includes a first and second branch, and wherein the first and second branch paths each includes two diodes and a node between the diodes, wherein a modulating signal is applied to the node of each path and wherein the diodes are of such polarities that when the modulating signal is at a first predetermined value, the first path is selected and the first but not the second branch path passes the input signal, and when the modulating signal is at a second predetermined value, the second path is selected and the second but not the first branch path passes the input signal;

(iii) said diodes operating in saturation or cutoff so that the amplitude of the angle is substantially independent of the amplitude of the modulating signal;

(iv) wherein the first and second branch paths include time delays; and

(v) wherein the time delays in the second path and in the first and second branch paths are such that;

(1) when the first branch path is selected, the output of the first path is substantially 90°

in advance of the output of the second path; and

(2) when the second branch path is selected, the output of the first path is substantially 90°

behind the output of the second path;

(b) means for splitting the input signal and applying the split input signal to the two signal paths such that the amplitude of the input signal in the first path having the two branch paths is at least 20 dB lower than the amplitude of the input signal in the second path; and

(c) means for re-combining the outputs of the two paths forming a vector sum to provide a modulated carrier signal.

15. The modulator of claim 14, wherein the time delays in the first path, comprised of the first branch path and second branch path, and in the second path, are caused by the differenct lengths of the three signal routes at a predetermined value of the frequency of the input signal.

16. The modulator of claim 14, wherein:

(a) the second path includes a fifth diode and a sixth diode, each having a saturating DC bias; and

(b) the diodes being coupled in series with respect to each other and with respect to the second path.