Filter unit, mobile communication terminal test system, and mobile communication terminal test method

A filter unit which is used in a mobile communication terminal test system and attenuates a desired signal in a frequency band for mobile communication, comprising:

• first and second variable filters which are individually tunable and connected to each other in series, respectively have YIG elements to vary tuning frequencies, and attenuate the desired signal within predetermined bandwidths having centers of the tuning frequencies, wherein the tuning frequency of the first variable filter and the tuning frequency of the second variable filter are controlled to be the same as each other or around each other so that the desired signal is included in the predetermined bandwidth of both of the first variable filter and the second variable filter to increase attenuation of the desired signal when the desired signal is located at a low frequency band side of the communication frequency band,
• wherein the tuning frequency of the first variable filter and the tuning frequency of the second variable filter are controlled to be different such that the desired signal is included in a connected bandwidth, which is formed from a concatenation of the predetermined bandwidths of the first and second variable filters and wider than any of the predetermined bandwidth of the first variable filter and the predetermined bandwidth of the second variable filter individually, when the desired signal is located at a high frequency band side of the communication frequency band,
• wherein the filter unit is used in a band stop filter of the mobile communication terminal test system and attenuates a signal of a frequency band corresponding to a base station signal from an interference wave, and
• wherein the mobile communication terminal test system performs communication between a mobile communication terminal and a pseudo base station which perform communication using a frequency band of one of a plurality of frequency bands specified by a communication standard and tests the influence on the mobile communication terminal by the interference wave, the mobile communication terminal test system comprising:
• the pseudo base station including a signal transmission unit which transmits the base station signal and a signal reception unit which receives a response signal transmitted by the mobile communication terminal in response to the base station signal;
• a signal generator which outputs the interference wave;
• the band stop filter;
• a directional coupler which couples the base station signal to the interference wave from the band stop filter and outputs a coupled signal to the mobile communication terminal;
• and
• a reception signal measurement unit which measures the response signal received by the signal reception unit from the mobile communication terminal.