This paper proposes and presents, for the first time, a fundamental and important concept for designing and making radio-frequency (RF) and millimeter-wave integrated circuits (ICs). This is made possible with the integration of two dissimilar but complementary structures on the same substrate, namely, planar circuits—such as microstrip line—and non-planar waveguides that are synthesized in planar form compatible with conventional planar fabrication.

“This work reports a class of simple and high performance transitions which have widely been adopted by the scientific and engineering community pursuing research on the SIW concepts and applications.”

This synthesized non-planar structure reported in this work is called "Substrate Integrated Waveguide (SIW)," which is part of the family of substrate integrated circuits (SICs). This is a primordial component in the design of highly integrated microwave and millimeter-wave circuits and systems. The key to integration is related to the transition between those two structures. This work reports a class of simple and high-performance transitions which have widely been adopted by the scientific and engineering community pursuing research on the SIW concepts and applications.

The SIW concept with the integration of planar and non-planar structures on the same substrate or layer, including the transition proposed in this paper, brings a completely new possibility in GHz and THz electromagnetic circuit and system integration. This novel structure has a unique capability to significantly reduce the manufacturing cost of millimeter-wave circuits and systems and also enhance their performances. Moreover, it opens up a revolutionary way towards a completely different integration scheme in which all components and devices are integrated and fabricated on the same platform.

Low-cost, mass-producible, high-performance and high-yield RF, microwave and millimeter-wave technologies, are critical for developing successful commercial circuits and systems. At millimeter-wave frequencies, in particular, circuit-building blocks are closely related to each other, which should also involve antenna parts.

In this case, the circuit design should be made with a global system consideration. Unfortunately, the current RF and millimeter-wave technologies are unable to meet such stringent requirements and a new generation of ICs is highly needed.

The technical breakthrough of the proposed SIW concept in our work is to synthesize a non-planar (rectangular waveguide) structure with a planar dielectric substrate or layer and make it in planar form, which is completely compatible with other planar structures and their fabrication processes. In fact, this SIW presents just a series of "planarized" waveguiding structures that belongs to the SICs family.

Naturally, the resulting planar waveguide has much better loss characteristics than its planar counterparts. And also, there are many interesting features in connection with the SIW concept and its integration with other planar circuits. This new concept has unified the hybrid and monolithic integrations of various planar and non-planar circuits that are made in single substrate and/or multilayer platforms. With this concept, the cost of fabrication of a RF and millimeter-wave system can be reduced in a very significant way as compared with the current technologies.

This revolutionary SIW technology is still in its infancy and its potential needs to be explored and demonstrated even though there are many practical SIW examples that were implemented.

Since this technology is compatible with many fabrication processes, we can expect strong and growing interests in it for many high-frequency applications. In addition, emerging technologies will push forward the development of SIWs at an unprecedented pace, which include nano-technologies, new low-loss/smart materials, photonic and optoelectronic ICs, millimeter-wave system-on-chip, terahertz technologies, and many others.

The whole concept stemmed from our early technological problems encountered in circuit and system integration for millimeter-wave applications. At that time, we were looking at different means to integrate all the building-blocks together with a low-cost fabrication process. This was the point of thought where we started and developed the concept of a new generation of high-frequency integrated circuits called "Substrate Integrated Waveguide" or "Substrate Integrated Circuits" to a large extent. This becomes, nowadays, the most important technique for designing substrate ICs and systems.

We hope that this research will generate a huge impact on high-tech industries through the development of highly integrated, low-cost, and high-performance wireless and wireline systems in upcoming decades. This should generate positive changes in our society.