Communications: directive radio wave systems and devices (e.g. – With particular circuit – With polarization
Reexamination Certificate
1999-09-09
2001-07-17
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
With particular circuit
With polarization
C342S052000, C342S054000, C342S104000, C342S165000, C342S167000, C342S361000, C342S368000
Reexamination Certificate
active
06262681
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of microwave signal generation and, more particularly, to a method and apparatus for generating microwave frequency signals using polarization selective photonic mixing, such method and apparatus being useful for photodiode testing, for local oscillator distribution, or for phased array antenna systems.
BACKGROUND OF THE INVENTION
Microwave frequency signal processing is a common aspect of many modern electronic and/or optical systems. One such system is Doppler radar. If light of a single frequency is incident on a reflecting object that has some component of motion along the light's direction of travel, the frequency of the light will be changed by an amount related to the speed of the object. This is called the Doppler effect. The velocity of the object may be determined if the frequency of the reflected light is compared with that of the incident light. This comparison will be made automatically if the return light and the reference light fall on the receiver. The photocurrent produced will contain components related to the frequency difference that describes the velocity of the reflector, provided that the polarizations are parallel. If two reflectors with different velocities are present, two RF tones will be present in the stimulus. If the receiver is linear each reflector will be represented by a unique RF tone. Otherwise, other tones will be present. This is an important problem if these tones (distortion) are very close to those actually generated by the reflectors. Such tones will be created by 3rd order harmonic distortion. They are difficult to distinguish from those originating from actual reflectors and cannot be filtered out of the RF response since they are mixed in with genuine signal. This is illustrative of one motive to characterize the linearity of an optical receiver. A receiver's 3rd order distortion is often characterized in the laboratory using tones produced synthetically. Therefore, a need exists for an effective method and apparatus for signal generation that can be useful for the testing of photodiodes for intermodulation product distortion.
Two RF tones similar to those originating from moving reflectors may be produced from three optical frequencies if one of the three pairings can be eliminated. This is important since the third tone is not independent of the other two and will create problems in the Two Tone test of a receiver.
Further, many systems applications, such as in microwave signal generation and local oscillator distribution systems for space based radars and antenna systems, require the generation and delivery of very “clean” microwave signals, i.e., signals without unwanted harmonic mixing products and of narrow line width that is achieved via the phase locked loop.
The present invention provides a method and apparatus to meet such needs.
SUMMARY OF THE INVENTION
In accordance with the present invention a method and apparatus for generating microwave frequencies is provided.
In accordance with a first embodiment of the invention, an incident reference signal is provided. A first stimulus signal is also provided, the first stimulus signal having a first polarization and having a first predetermined relationship with the incident reference signal. A second stimulus signal is also provided, the second stimulus signal having a second polarization and having a second predetermined relationship with the incident reference signal. In accordance with the first embodiment of the present invention, the first polarization is horizontal and the second polarization is vertical. The incident reference signal is split into a first polarization reference signal and into a second polarization reference signal. The first stimulus signal is coupled with the first polarization reference signal to provide first polarization mixed signals. The second stimulus signal is coupled with the second polarization reference signal to provide second polarization mixed signals. The first polarization mixed signals are combined with the second polarization mixed signals to provide output signals only having a first component signal at the first predetermined relationship with the incident reference signal and a second component signal at the second predetermined relationship with the incident reference signal.
Further, in the first embodiment the first predetermined relationship with the incident reference signal is provided by a first phase lock loop and the second predetermined relationship with the incident reference signal is provided by a second phase lock loop. The first phase lock loop first couples a portion of the first stimulus signal and a portion of the first polarization reference signal to provide a first phase lock loop difference signal. The first phase lock loop difference signal is compared with a first predetermined difference reference signal to provide a first difference correction signal. The first stimulus signal is then tuned by the first difference correction signal to maintain the first predetermined relationship with the incident reference signal. Similarly, the second phase lock loop first couples a portion of the second stimulus signal and a portion of the second polarization reference signal to provide a second phase lock loop difference signal. The second phase lock loop difference signal is compared with a second predetermined difference reference signal to provide a second difference correction signal. The second stimulus signal is then tuned by the second difference correction signal to maintain the second predetermined relationship with the incident reference signal.
In accordance with a second embodiment of the present invention, an incident reference signal is provided. A first stimulus signal is also provided, the first stimulus signal having a first polarization and having a first predetermined relationship with the incident reference signal. A second stimulus signal is also provided, the second stimulus signal having a second polarization and having a second predetermined relationship with the incident reference signal. The first polarization is horizontal. The second polarization is vertical. The incident reference signal is split into a first reference signal and a second reference signal. However, the incident reference signal, the first reference signal, and the second reference signal are each at 45° polarization. The first stimulus signal is coupled with the first reference signal to provide first polarization mixed signals. The first polarization mixed signals are combined with the second stimulus signal to provide output signals only having a first component signal at the first predetermined relationship with the incident reference signal and a second component signal at the second predetermined relationship with the incident reference signal.
Further, in the second embodiment the first predetermined relationship with the incident reference signal is provided by a first phase lock loop and the second predetermined relationship with the incident reference signal is provided by a second phase lock loop. The first phase lock loop first couples a portion of the first stimulus signal and a portion of the first reference signal to provide a first phase lock loop difference signal. The first phase lock loop difference signal is compared with a first predetermined difference reference signal to provide a first difference correction signal. The first stimulus signal is then tuned by the first difference correction signal to maintain the first predetermined relationship with the incident reference signal. Similarly, the second phase lock loop first couples a portion of the second stimulus signal and a portion of the second reference signal to provide a second phase lock loop difference signal. The second phase lock loop difference signal is compared with a second predetermined difference reference signal to provide a second difference correction signal. The second stimulus signal is then tuned by the second difference correction signal to maintain the second
Gregory Bernarr E.
HRL Laboratories, LLC.
Ladas & Parry
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