Six-port technique at millimeter-wave band - Principles and applications

Over the past few decades, wireless telecommunications systems, such as satellite communications, digital radio and television, home automation, and mobile telephony, have experienced spectacular growth. These telecommunications systems have brought a new dimension to our society, with significant technological, economic, environmental, and sociological implications.

All these wireless applications require robust and reliable communication systems with simplified structures, low power consumption, and reduced costs. Indeed, the conventional receivers used in most current communication systems employ active mixers that require considerable local oscillator power. In addition, manufacturing imperfections inherent in high frequencies generate amplitude and phase distortions in RF signals, leading to deterioration in receiver performance and transmission quality.

To overcome these problems, the concept of direct conversion receivers using multiport (six-port) reflectometers was introduced, extensively studied, and implemented in 1995 at the Poly-Grames Research Center at the École Polytechnique de Montréal. In fact, the proposed architecture of the six-port reflectometer in this research is quite similar to the original approach introduced by Dr. G.F. Engen of the National Bureau of Standards in the United States in the 1970s, where calibration and a reference port were essential for measuring circuit dispersion parameters.

Since 2001, various six-port topologies that do not require calibration, mainly in the Ka band, have been developed, making the six-port concept more accessible and easier to implement. Thus, I/Q signal demodulation can be performed either analogically or digitally.

Today, the six-port concept represents more of an alternative solution in the design of radio frequency front ends dedicated to future emerging wireless applications, particularly in millimeter wave frequency bands. These applications include, but are not limited to, direct demodulation of quadrature signals (I/Q), high-precision radar detection, and estimation of directions and angles of arrival.

This article will consist of three chapters. The first will be devoted to the fundamental principle of operation and analysis of the six-port device. We will begin by presenting the use of the six-port in millimeter wave receivers, as a low-power RF mixer and as an I/Q demodulator of RF signals. It will also describe the design and implementation of the six-port circuit in the millimeter band using MHMIC (Miniaturized Hybrid Microwave Integrated Circuits) technology, as well as the experimental characterization, while presenting the calibration standards and test bench used. Some measurement results of S parameters and...