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A new frontend for APERTIF

Submitter: Mark Ruiter on behalf of the APERTIF team
Description: This image presents the completely redesigned APERTIF element assembly. Each Phased Array Feed that will be installed in the WSRT will consist of 121 of these active antenna elements.

The element combines several functions, such as the antenna, low noise amplifier, limiters to protect gain stages for nearby GSM, an equalizer to correct gain slopes, filtering and a lot of gain. This gain is required to compensate for losses and hide the noise contribution of the A/D converter.

The hostile RFI environment at the WSRT posed the largest design challenge. A very strong suppression of out-of-band signals is required, especially of the digital television transmitters (DVB-T) from Smilde. The OFDM modulation scheme of only one such transmitter produces more than 2000 carriers in an 8 MHz band. If not sufficiently suppressed, these pseudo noise like modulations will mix with other transmitters and cause wide-band interference over almost the entire APERTIF band. The presented design realizes more than 100 dB of suppression and successfully mitigates the DVB-T issue. The board has a gain of 50 dB and a noise temperature of 45 K for a single active element. The design is built using modular blocks. By measuring and simulating these blocks, a good control of the overall complex design is maintained. It also gives possibility to reuse the blocks in another design or project.

For APERTIF, around 1,500 of these elements will be needed. This makes that the board must be mass producible. So all manufacturing details must be correct. For example, the component pad shapes must be designed according the IPC standard. The design itself is evaluated using statistical simulations and a number of boards are going to be thoroughly tested to see how they perform under (eg. thermal) stress.
Copyright: ASTRON
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