Abstract: In a multi-stage, varactor-tuned bandpass filter utilizing electromagnetic field coupling between successive filter stages, the effective area of a coupling window provided in the RF shielding separating the filter stages is varied as a function of the varactor tune voltage to provide a flat frequency response over the filter frequency range. The bias current through a PIN diode connected across the coupling window is controlled by varactor tune voltage to effectively decrease the window area with increasing filter frequency.

Abstract: A multi-function, general purpose apparatus includes various instrument modules configured to perform a number of functions controlled by an internal processor, stored programs and user selected inputs. A five-port RF signal interface couples the apparatus to user equipment under test to allow a wide range of RF signal measurements over a wide range of test signal levels. The RF signal interface buffers the user equipment from the apparatus internal modules while providing a uniform attenuation of an RF test signal over the RF path to the desired internal module. Antenna, RF Input and Duplex ports provide apparatus connection to user equipment while signal generator and receiver ports provide internal apparatus connections. An apparatus internal processor is user and software controlled to provide automatic sweep tuning of RF interface filter sections and automatic sensitivity settings for the interface amplifier and attenuator sections.