Error correction method of wideband multi-port reflectometer using least mean square

Abstract

The microwave imaging applications have a great demand in recent years by having considerable interest such as in medical, industrial and military aspects. Particularly, in most research of microwave imaging applications, Vector Network Analyzer (VNA) is frequently been used to act as transmitter and receiver to allow the measurement of complex ratio between two microwave signals and also provide accurate measurement of reflected and scattering parameters, but it is bulky and expensive. Therefore, in this research, a portable low-cost measurement device namely multi-port reflectometer is proposed as an alternative to VNA in the imaging system. The configuration of this device is formed by four couplers and two power dividers over the operating wideband frequency range between 1 and 6 GHz. The investigation of the characteristics and operation of such reflectometer are accessed via simulation using existing components in Agilent’s Advance Design System (ADS) software and measurement of real components in the laboratory. The real components used are Krytar 90º hybrid coupler and Aeroflex two-way in-phase power divider. Each component constituting the multi-port reflectometer is not operated in error-free state in wideband frequency range. Thus, in order to offer accurate measurement of any Device Under Test (DUT) using wideband multi-port reflectometer, a suitable error correction procedure or known as calibration is implemented. A variety of loads have been used as DUT in order to verify the proposed error correction method. A one-port error model with three standards and Least Mean Square (LMS) technique have been applied to the proposed multi-port reflectometer. Through that, any imperfect operation of the wideband multi-port reflectometer is removed. By implementing the proposed error correction method, the imperfect operation of the multi-port reflectometer has successfully been corrected and an accurate wideband performance with fully error correction can be offered. Therefore, the multi-port reflectometer achieves the desired value of its operation.