A study on jig using semi-rigid cable for the S-parameter method

Recently, the S-parameter method using a vector network analyzer was proposed whereby the differential input impedance of a balanced-fed antenna were obtained. To improve measurement accuracy of the S-parameter method, the dependence on thickness of the semi-rigid cable used for the measurement jig is obtained from the results of calculations using the FDTD method. Three types of jigs each made from semi-rigid cables of differing thickness were fabricated, and the input impedance of the dipole antenna calculated using the S-parameter method. The impedances were compared with those obtained from the available theories by King. Results from the S-parameter method agree with the available theories by King, over a range of about 5 GHz or less.