Optimised Via Design and Modeling for a Radio Astronomy Receiver

Measurements performed on a Ku-band radio astronomy receiver brought to light significant passband ripple and poor return loss, limiting the scientific usefulness of the receiver. Investigation revealed that coupling to the high-Q bandpass filter through the PCB via structure accounted for the majority of the poor performance. This paper investigates and compares two via modeling strategies, namely the 4-pair two wire and coaxial model. The impedance profiles of these models are theoretically evaluated and validation is performed using a fullwave electromagnetic field solver. Partial agreement is achieved for the two wire model, but good agreement is noted for the coaxial model. The image reject filter input and output coupling is re-designed based on the coaxial via design graphs resulting in a significant performance improvement for the gain and ripple of the receiver.