Abstract: A cellular-type wireless communications system, comprising: an airborne platform that reflects wireless communication signals; and a centralized base station associated with at least one cell, each cell corresponding to a geographic area, the centralized base station configured to send wireless communication signals to the airborne platform and receive wireless subscriber signals which have reflected down off of the airborne platform.

Abstract: A control system comprising an electrical circuit that produces distortion where the electrical circuit has a frequency band of operation. A pilot modulated carrier signal is frequency hopped about the frequency band of operation. The hopping pilot modulated carrier signal does not interfere with any signal applied to or generated by the electrical circuit as it is not at any time located within the frequency band of operation. Information obtained from the hopping pilot modulated carrier is provided to the control system which uses such information to cancel the distortion produced by the electrical circuit.

Abstract: A cellular-type wireless communications system, comprising:

Abstract: An inexpensive RF test probe provides consistent monitoring of an RF signal while having minimal effect on the circuit under test. In one embodiment, an RF test probe comprises a return conductor and a probing conductor. The probing conductor is positioned within an insulator and a termination such as a 50 ohm resistor is electrically positioned between the ground conductor and probing conductor. The probe is used by placing a portion of the insulating material surrounding the probe conductor in contact with a circuit such as an RF microstrip carrying an RF signal to be monitored.

Abstract: A control system comprising an electrical circuit that produces distortion where the electrical circuit has a frequency band of operation. A pilot modulated carrier signal is frequency hopped about the frequency band of operation. The hopping pilot modulated carrier signal does not interfere with any signal applied to or generated by the electrical circuit as it is not at any time located within the frequency band of operation. Information obtained from the hopping pilot modulated carrier is provided to the control system which uses such information to cancel the distortion produced by the electrical circuit.

Abstract: A control system comprising an electrical circuit that produces distortion where the electrical circuit has a frequency band of operation. A pilot modulated carrier signal is frequency hopped about the frequency band of operation. The hopping pilot modulated carrier signal does not interfere with any signal applied to or generated by the electrical circuit as it is not at any time located within the frequency band of operation. Information obtained from the hopping pilot modulated carrier is provided to the control system which uses such information to cancel the distortion produced by the electrical circuit.

Abstract: A gain and phase control system performs a gain (or phase) adjustment based on the results of a previous gain (or phase) adjustment after an intervening phase (or gain) adjustment. A gain adjustment is based on the results of a previous gain adjustment rather than on the results of an intervening phase adjustment. A phase adjustment is based on the results of a previous phase adjustment rather than the results of an intervening gain adjustment. As such, the above-mentioned increase in error signal does not occur because a gain adjustment is based on the results of the previous gain adjustment, and a phase adjustment is based on the results of the previous phase adjustments.

Abstract: A frequency mixing system provides an expanded dynamic range when compared to the dynamic range(s) of an individual mixer(s) that make up the arrangement. The frequency mixing system uses a feed-forward arrangement to reduce the distortion emanating from a single mixer due to a signal power level which would result in a frequency converted signal outside the dynamic range of the mixer. For example, the frequency mixing system splits an input signal onto a first path and a second path. On the first path, a first mixer frequency mixes the signal to produce a frequency converted signal with distortion, such as intermodulation distortion. On the second path, the amplitude of the signal is attenuated then frequency mixed by a second mixer to produce a frequency converted signal with a low and/or insignificant level of distortion.

Abstract: Method and apparatus for substantially eliminating distortion produced by a processing circuit where the distortion produced by a first circuit with similar characteristics as the processing circuit is modified and the modified distortion is applied to the processing circuit. The distortion produced by the first circuit is modified based on information derived from distortion produced by the processing circuit. The modified distortion, when applied to the processing circuit, combines destructively with distortion produced by the processing circuit.

Abstract: A frequency mixing system that provides an expanded dynamic range when compared to the dynamic range(s) of an individual mixer(s) that makes up the frequency mixing system. The frequency mixing system adjusts the amplitude of an input signal to be frequency mixed to produce a frequency converted signal with an acceptable and/or lower (when compared to the amplitude of intermodulation distortion produced by mixing the input signal without amplitude adjustment) amplitude of intermodulation distortion. If the input signal were frequency mixed without the amplitude adjustment, an unacceptable and/or higher level of intermodulation distortion would result (when compared to the corresponding intermodulation distortion if the amplitude-adjusted signal were mixed by an individual mixer). Adjusting the amplitude of the input signal creates an adjusted signal with signal distortion on the first path.

Abstract: A wireless telecommunications system with a base station positioned on an airborne platform is provided. The system utilizes a ground-based wireless switching center which communicates via a microwave link with a plurality of airborne base stations positioned above a geographic area being serviced by the telecommunications system. The base stations are supported on an airborne platform having a propulsion system designed to maintain the platform and the base stations in position above the geographic area being serviced. Advantageously, the platform may be positioned in the stratonull which is generally very stable and is located above the troposphere, wherein weather variations occur.

Abstract: An adaptive gain and/or phase control system adapts the gain and/or phase adjustment resolution to provide improved performance. For example, the adaptive gain and/or phase control system can dynamically adjust the adjustment resolution for gain and/or phase adjustments as a function of the error signal(s). In response to a large error signal(s) (far from the null), the adaptive gain/or phase control system decreases the adjustment resolution, resulting in a faster convergence rate. In a feed forward distortion reduction system, decreasing the adjustment resolution improves the transient response of the amplifier (for example, given any set of operating conditions, how quickly the amplifier responds to a changing input). As phase or gain adjustments are made to approach the null, the error signal reduces, and the adaptive distortion reduction system increases the adjustment resolution.

Abstract: A pilotless feed forward distortion reduction system uses phase and gain control based on the phases and amplitudes of combining signals prior to a distortion isolation point to maintain the relationship between the phase and amplitudes of combining signals. For example, the feed forward arrangement receives a signal to be amplified on a main signal path and replicates the signal onto a main signal path and a feed forward path. The signal on the main signal path is applied to a gain & phase circuit. The output of gain & phase circuit is applied to the amplifier whose output comprises the amplified signal and distortion signals produced by the amplifier. A portion of the output of the amplifier is placed on a coupling path and combined at the distortion isolation point with a delayed version of the signal on the second path to isolate the distortion produced from the amplifier.

Abstract: A method for reducing the level of an undesired signal, generated through a frequency converter device, by implementing a local oscillator (hereinafter "LO") leak cancellation circuit. A feedback correction loop, for a radio frequency (RF) transmitter or receiver, reduces an undesired local oscillator leak generated through a single input frequency converter device, such as a mixer, by a unique detection circuit. A unique nulling circuit is also implemented for a multiple input frequency converter device, such as a quadrature modulator.

Abstract: A control system comprising an electrical circuit that produces distortion where the electrical circuit has a frequency band of operation. Double side band pilot signals are located slightly outside the boundaries of the frequency band of operation so as not to interfere with any signals within the frequency band of operation, but still provide information that the control system uses to substantially cancel the distortion.

Abstract: A nested feed forward distortion reduction system, which reduces the distortion from a main amplifier on a main signal path, uses a nested feed forward arrangement for the correction amplifier to reduce the distortion produced from the correction amplifier. In reducing the distortion from the correction amplifier(s) and using progressively higher quality correction amplifier(s), the nested feed forward arrangement produces an improved, more stable representation of the distortion from the main amplifier, thereby alleviating the need for variable gain and/or phase control in producing amplified signal with reduced distortion.

Abstract: An A/D system provides an expanded SFDR when compared to the SFDR of individual A/D(s) that make up the A/D system. In response to an analog input signal whose amplitude would result in an narrower SFDR for a first A/D, the A/D system uses an amplitude adjuster which receives the analog input signal and produces an amplitude-limited signal with resulting signal distortion to the first A/D. By amplitude-limiting the analog input signal, the A/D system produces the resulting signal distortion but reduces or "clips" the amplitude of the analog input signal, thereby improving the SFDR performance of the first A/D by reducing the spurious distortion produced by the first A/D. The signal distortion resulting from the amplitude adjustment is routed to a second A/D. The first A/D converts the amplitude-limited analog signal to a digital signal with an expanded SFDR due to the lower amplitude of the adjusted analog signal.

Abstract: The present invention provides an improved pilot detection technique for a control system comprising an electrical circuit that produces distortion and which applies the pilot signal to the electrical circuit and uses information obtained from the pilot signal to cancel the distortion from the electrical circuit.

Abstract: The present invention is a method and a feed forward circuit incorporating an automatic gain and phase controller for controlling amplitude gain and phase shift being applied to an input signal of an amplifier undergoing changing conditions. The automatic gain and phase controller is configured to monitor the amplifier output signals and manipulate the amplitude and phase of the amplifier input signal (via a gain and phase adjuster) such that the amplitude and phase of the amplifier output signals are substantially identical to those of previous amplifier output signals.

Abstract: The present invention is a method and an apparatus for measuring phase differences between signals A and B using an absolute voltage value for each phase difference between .+-.180.degree.. This is accomplished using a third signal C, which is a signal having a phase approximately equal to the average phase between signals A and B. Signals C and A are subsequently amplitude limited and mixed to produce a fourth signal D, which is a signal having associated an absolute voltage value for each degree of phase difference between .+-.180.degree. for signals A and B.