Patent Application
20130176164
The present invention relates to the field of phased antenna arrays, and, more particularly, to phased antenna arrays with optical components and related methods.
Wireless communications devices are an integral part of society and permeate daily life. The typical wireless communications device includes an antenna, and a transceiver coupled to the antenna. The transceiver and the antenna cooperate to transmit and receive communications signals.
One particularly advantageous antenna type is the phased array antenna. The phased array antenna comprises a plurality of antenna elements, and processing circuitry to vary the related phase of the signals received from the individual antenna elements. The varying of the related phase of the antenna elements may provide for changing the effective radiation pattern of the antenna. In particular, the radiation pattern can be changed to be highly directional, i.e. reinforcing signals received from one direction and rejecting those received from other directions. Each directional pattern is commonly described as a beam, and the changing of the directional pattern is known as beam forming.
Beam forming operations may be performed either in the analog domain or in the digital domain. For example, in the analog approaches, the phased array antenna includes some form of time delay mechanism downstream from the antenna elements. In digital beam forming applications, the signal from the antenna element is converted into a digital signal, and digital signal processors perform the time delay operations.
As the operational frequency of the phased array antenna increases, the physical size of the individual antenna element becomes smaller. Moreover, the computational requirements for digital beam forming may become onerous. Indeed, as the space between antenna elements becomes constrained, the packaging size for processing components for each antenna element must be reduced. For example, millimeter wave, i.e. extremely high frequency (EHF), phased array antennas may be complex and costly to manufacture. Furthermore, these phased array antennas may be limited in bandwidth and the number of beams.
One approach to the phased array antenna is disclosed in U.S. Pat. No. 5,999,128 to Stephens et al. This phased array antenna includes a plurality of antenna elements, and a plurality of optical paths with varying lengths coupled to the respective antenna elements. The phased array antenna comprises a plurality of phase coherent sources, and a plurality of combiners coupled downstream for the phase coherent sources for providing a signal to the optical paths.
In view of the foregoing background, it is therefore an object of the present invention to provide a phased antenna array that can operate effectively at high frequencies.
This and other objects, features, and advantages in accordance with the present invention are provided by a phased antenna array comprising an array of antenna elements, and an electro-optic (EO) readout circuit coupled to the array of antenna elements. The EO readout circuit comprises an optical source configured to generate an optical carrier signal, a first EO modulator configured to modulate a signal from at least one antenna element based upon the optical carrier signal, and an optical-to-electrical converter coupled downstream from the first EO modulator. Advantageously, the phased antenna array converts the electrical signal from the antenna elements to the optical domain for more efficient processing.
More specifically, the EO readout circuit may comprise a local oscillator, and a second EO modulator coupled to the local oscillator and between the optical-to-electrical converter and the optical source and configured to generate a local oscillator optical carrier signal. The EO readout circuit may comprise an optical coupler coupled between the first EO modulator and the optical-to-electrical converter. The optical-to-electrical converter may be configured to downconvert the modulated optical signal from the first EO modulator based upon the local oscillator optical carrier signal.
In some embodiments, the EO readout circuit may comprise a band pass filter coupled between the second EO modulator and the optical coupler and configured to select at least one harmonic of the local oscillator optical carrier signal. For example, the optical-to-electrical converter comprises first and second optical detectors coupled to the optical coupler, and a combiner coupled to the first and second optical detectors.
Another aspect is directed to a method of operating a phased antenna array comprising an array of antenna elements, and an EO readout circuit coupled to the array of antenna elements. The method comprises using an optical source to generate an optical carrier signal, using a first EO modulator to modulate a signal from at least one antenna element based upon the optical carrier signal, and converting the modulated optical signal with an optical-to-electrical converter downstream from the first EO modulator.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments.
Referring initially to
The phased antenna array system 10 illustratively includes an EO readout circuit 12a coupled to the array 11 of antenna elements, and a digital processor 13 coupled downstream therefrom. The EO readout circuit 12a is configured to receive the signals from the array 11 of antenna elements. Shown with dashed lines, the phased antenna array system 10 may also include a second EO readout circuit 12b cooperating therewith to receive and process the signals from the array 11 of antenna elements. In particular, each EO readout circuit receives signals from a group of antenna elements 14a-14n. For example, the phased antenna array system 10 may include a plurality of summers (not shown) upstream of the EO readout circuits 12a-12b for summing the electrical signals from the respective groups of antenna elements 14a-14n. In other embodiments, the phased antenna array system 10 may include individual EO readout circuits for each antenna element 14a-14n, which would provide advantageous beam steering and beam shaping, flexibility, and greater bandwidth.
Referring now additionally to
The antenna component module 20 illustratively includes a pair of antenna elements 14a-14b, i.e. dual polarity vertical and horizontal oriented antenna dipole elements. In the illustrated embodiment, the antenna component module 20 comprises an integrated component including the antenna elements 14a-14b, a pair of amplifiers 21a-21b (e.g. low noise amplifiers) coupled downstream from the antenna elements, and a pair of first EO modulators 22a-22b configured to modulate a signal from the antenna elements based upon the optical carrier signal. In other embodiments, the antenna element may comprise a separate component and the antenna component module 20 would be installed directly adjacent the antenna element. As will be appreciated by those skilled in the art, the modulated optical signals coming out of the pair of first EO modulators 22a-22b each have a frequency spectrum including the carrier frequency and a pair of sidebands, i.e. the spectrum of the signal from the antenna elements 14a-14b.
Nevertheless, the antenna component module 20 is relatively small compared to those of the prior art, which may reduce difficulty in manufacturing the phased antenna array system 10 for high frequencies. Moreover, since the antenna signals are promptly converted to the optical domain, the optical coupling to the output of the antenna component module 20 (e.g. optical fiber, optical waveguide, etc.) can of significant length and without the typical losses of a typical electrical connection. Indeed, the circuitry downstream from the antenna component module 20, discussed below, can be remote to the antenna array 11. As will be appreciated by those skilled in the art, the EO readout circuit 12 may span several miles.
The EO readout circuit 12 comprises a pair of time delay modules 23a-23b coupled downstream from the pair of first EO modulators 22a-22b, i.e. for analog time delay beam forming. Of course, in other embodiments, the time delay modules 23a-23b may be omitted and any needed time delay operations may be accomplished digitally by the digital processor 13.
The EO readout circuit 12 comprises a pair of optical couplers 24a-24b coupled downstream from the time delay modules 23a-23b. The pair of optical couplers 24a-24b combines the modulated optical signals from the pair of first EO modulators 22a-22b, and provides a pair of combined outputs with 180° of phase difference.
The EO readout circuit 12 also illustratively includes a pair of optical-to-electrical converters 25a-25b coupled downstream from the optical couplers 24a-24b, and a pair of analog-to-digital converters 26a-26b coupled to the pair of optical-to-electrical converters and configured to produce a digital output signal. For example, each optical-to-electrical converter 25a-25b may comprise first and second optical detectors (e.g. balanced photodiodes) coupled to the optical coupler 24a-24b, and a combiner coupled to the first and second optical detectors.
The EO readout circuit 12 comprises a local oscillator 32, and a second EO modulator 30 coupled to the local oscillator. The second EO modulator 30 is configured to generate a modulated optical carrier signal commensurate of the LO frequency. The EO readout circuit 12 illustratively includes a band pass filter 33 coupled between the second EO modulator 30 and the pair of optical couplers 24a-24b and configured to select at least one harmonic of the local oscillator optical carrier signal. The pair of optical couplers 24a-24b is configured to combine the modulated optical signal from the pair of first EO modulators 22a-22b and the modulated local oscillator optical carrier signal. These two combined modulated signals interact and mix in the optical-to-electrical converters 25a-25b to form the intermediate output frequency in the electrical domain. The local oscillator 32 may be configured to provide flexibility in the optical conversion to the intermediate frequency signal. Advantageously, the photonic frequency conversion may generate intermediate frequency signals with wide bandwidth with the advantage of significantly lower undesired mixing spurious signal levels than that encountered in typical RF frequency downconversion systems.
In the illustrated embodiments, the EO readout circuit 12 includes individual paths for each polarized antenna element (horizontal and vertical). Advantageously, this provides isolation for the horizontal and vertical polarizations. Nevertheless, in other embodiments, a group of polarized antenna elements may be coupled to the EO readout circuit 12. In particular, in these embodiments, the signals from the antenna elements 14a-14b would be combined via a polarization combiner and fed into the EO readout circuit 12. Of course, these embodiments exchange phased antenna array system 10 beam steering and beam shaping flexibility and bandwidth for reduction in components.
Advantageously, the EO readout circuit 12 may provide for a widely tunable front end (i.e. universal frequency converter) that can be coupled to a low-speed, digital beam former back end. In other words, the digital processor 13 may have less computational resources than in typical approaches.
Referring now to
The MLL 29′ is configured to generate an optical carrier signal comprising a plurality of beam carrier wavelengths. In other words, each of the locked frequency modes of the MLL 29′ is modulated with the signals from the antenna elements. In other embodiments, the EO readout circuit 12′ may include optical filters upstream of the pair of modulators 22a′-22b′ and upstream of the optical couplers 24a′-24b′ to address dispersion over wavelength in the modulators or optical components that could add signal jitter to the signal at the optical-to-electrical converters 25a′-25b′. Moreover, each of these beam carrier wavelengths is worked through the entire path to digital conversion at the pair of analog-to-digital converters 26a-26b. To this point, each of the locked frequency modes (frequency comb) of the MLL 29′ are modulated by the pair of modulators 22a′-22b′. Advantageously, the MLL 29′ provides for low phase noise and potentially a large number of beams.
In particular, the digital processor 13 (
Referring now to
The antenna component module 40 includes a pair of antenna elements 49a-49b, a pair of amplifiers 41a-41b coupled downstream from the pair of antenna elements, a pair of first EO modulators 42a-42b configured to modulate signals from the antenna elements based upon the optical carrier signal, and an optical splitter 67 configured to deliver the optical carrier signal to each first modulator 42a-42b. As in the embodiments above, the pair of first EO modulators 42a-42b creates frequency sidebands for each beam carrier wavelength.
The EO readout circuit 70 illustratively includes a pair of second WDMs 43a-43b coupled downstream from the pair of first EO modulators 42a-42b, first and second time delay module pluralities 44a-47a, 44b-47b coupled downstream from the pair of first EO modulators, first and second optical coupler pluralities 48a-51a, 48b-51b coupled downstream from the time delay modules, and first and second optical-to-electrical converter pluralities 52a-55a, 52b-55b coupled downstream from the optical couplers. The pair of second WDMs 43a-43b is configured to multiplex each modulated beam carrier wavelength to a respective optical-to-electrical converter 52a-55a, 52b-55b. Each time delay module 44a-47a, 44b-47b may be independently controlled. Advantageously, this enables the phased antenna array system 10 to have independent steering for each beam.
The EO readout circuit 70 illustratively includes a local oscillator 65, and a second EO modulator 64 coupled to the local oscillator and the optical source 61. The second EO modulator 64 is configured to generate a local oscillator optical carrier signal comprising a plurality of intermediate beam carrier wavelengths. The EO readout circuit 70 illustratively includes a third WDM 74 coupled between the second EO modulator 64 and the first and second pluralities of optical couplers 48a-51a, 48b-51b and configured to multiplex each intermediate beam carrier wavelength to the respective optical-to-electrical converter 52a-55a, 52b-55b.
The EO readout circuit 70 includes an optical amplifier 63 configured to generate the optical carrier signal from the optical source 61, and an optical splitter 66 coupled between the optical amplifier and the antenna module 40. As in the embodiment of
More specifically, this EO readout circuit 70 uses the first and second time delay module pluralities 44a-47a, 44b-47b to perform optical beam forming. Moreover, in the illustrated embodiment, there are four separate beam signals, but in other embodiments, the number of beams can be increased. Of course, in other embodiments, the first and second time delay module pluralities 44a-47a, 44b-47b may be omitted and replaced with digital beam forming in the digital processor 13.
Referring now to
Moreover, the optical splitter 66′ comprises a reconfigurable wavelength-selective switch/wavelength blocker configured to send signal wavelengths to the aperture and local oscillator wavelengths to the downconverter. In particular, the optical splitter 66′ will select the appropriate locked frequency mode (beam carrier wavelength) and output it to the third WDM 74′. Advantageously, the above disclosed EO readout circuits 12, 12′, 70, 70′ each provides enhanced multi-beam capabilities for the phased antenna array system 10 at greater frequencies than the typical phased antenna array. Other advantages may include lower beamforming signal losses than typical high frequency array and the ability to un-constrain the beam steering and beamforming component packaging density requirements of high frequency arrays.
Other features relating to phased antenna arrays are disclosed in co-pending applications “PHASED ANTENNA ARRAY WITH EO READOUT CIRCUIT WITH MLL AND RELATED METHODS,” Attorney Docket No. GCSD-2475 (61832); “PHASED ANTENNA ARRAY WITH EO READOUT CIRCUIT WITH MULTIPLEXING AND RELATED METHODS,” Attorney Docket No. GCSD-2476 (61833); and “PHASED ANTENNA ARRAY WITH EO READOUT CIRCUIT WITH MULTIPLEXING AND MLL AND RELATED METHODS,” Attorney Docket No. GCSD-2477 (61834), all incorporated herein by reference in their entirety.
Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.
