Abstract: The present invention relates to a multi-mode filter comprising a carrier on which is mounted a dielectric resonator having a covering of an electrically conductive material in which there is provided an aperture and a coupling structure for coupling input signals to the dielectric resonator or for extracting filtered output signals from the dielectric resonator. The carrier is provided with an enclosing formation of electrically conductive material, which enclosing formation is electrically coupled to the electrically conductive covering of the dielectric resonator, such that the covering and the enclosing formation together form an electrically conductive enclosure for the dielectric resonator. The enclosure formed from the covering of the dielectric resonator and the enclosing formation increases the isolation of the filter and reduces leakage. The filter of the present invention is particularly suitable for use in cascaded resonator filter arrangements, and in duplex/diplex filters.

Abstract: The present invention provides multi-resonator cavity filters in which one or more patch elements are introduced into the coupling apertures between resonators, reducing the strength of the electric field in the aperture gap while maintaining the coupling strength from resonator to resonator. This reduced field strength reduces the sensitivity of the resonators to gap-thickness variations, and allows use of the filter in high-power applications.

Abstract: The present invention provides multi-resonator cavity filters in which one or more patch elements are introduced into the coupling apertures between resonators, reducing the strength of the electric field in the aperture gap while maintaining the coupling strength from resonator to resonator. This reduced field strength reduces the sensitivity of the resonators to gap-thickness variations, and allows use of the filter in high-power applications.

Abstract: A predistorter arrangement for linearizing an amplifier. The predistorter arrangement is designed to compensate for IMD distortion in an amplifier using polynomial approximation techniques. The predistorter arrangement also includes pilot based feedback circuitry for controlling the operation of the predistorter.

Abstract: A Cartesian loop transmitter for transmitting baseband signals is disclosed. The disclosed Cartesian loop includes a forward path having a first input for receiving the baseband signals and a second input and a feedback path having an input from the forward path. The forward path including an upconverter to upconvert the input signals to a signal to be transmitted, an attenuator having selectable attenuation and a plurality of power amplifier stages. The feedback path including a pin diode attenuator having selectable attenuation and a downconverter to downconvert the input from the forward path. The feedback path provides an error signal indicative of the non-linearity of the forward path to the second input of the forward path.

Abstract: A system for creating multiple subchannels in a single two-way radio channel and a power control system for a mobile radio transmitter are described. Each subchannel in the system is capable of carrying voice or data. Each subchannel is split into an upper and a lower band with the upper band placed in a particular frequency range above the center of the channel and the lower band is placed in a corresponding frequency range below the center of the channel. Either one or two pilot tones placed at or adjacent to the center of the channel are used to provide a reference for all of the subchannels to allow for correction of distortions when the signal is received. The system includes base station with a transmitter and receiver and a plurality of mobile units each with a transmitter and a receiver. The base station transmits a signal which is the sum of all the subchannels. The mobile unit receives the signal, separates and processes the particular subchannel for that mobile unit.

Abstract: The invention provides methods and apparatus for substituting a reference spread spectrum signal for a pilot tone or providing a reference spread spectrum signal where no pilot tone has been used. The invention has particular relevance when a large number of input channels are required for a broad band linear amplifier and when an omni-directional antenna is required for a repeater which may be prone to instability.

Abstract: Broadband amplifiers which are intended to be linear suffer from distortion and although many techniques have been devised to overcome this problem significant improvements are required especially at frequencies above 100 MHz. An error signal is formed from the output of the amplifier 4 by comparison in a subtractor 11 with its input and the error signal is combined in a coupler 17 with the amplifier output to reduce distortion. The present invention provides automatic amplitude and phase control of the signals forming the error signal by means of components 24 and 25 in a multi-channel input and in the error signal by means of components 13 and 14. These components receive control signals from feedback networks 18' and 20' which each process two of three input signals from: couplers 34, 36 before the subtractor 11, a coupler 22 which passes the error signal and a coupler 21 after the coupler 17.

Abstract: Broadband amplifiers which are intended to be linear suffer from distortion and although many techniques have been devised to overcome this problem significant improvements are required especially at frequencies above 100 MHz. An error signal is formed from the output of an amplifier by comparison in a subtractor with its input and the error signal is combined in a coupler with the amplifier output to reduce distortion. The present invention provides automatic amplitude and phase control of the signals forming the error signal by two groups of adjustment means, one group in a multi-channel input path and one group in the error signal path. These groups receive control signals from respective feedback networks which each process two of three input signals from: couplers before the subtractor, a coupler which passes the error signal and a coupler situated after the coupler which combines the amplifier output signal and the error signal.