History of Microwave Circuits (II)

4 Development trend of microwave circuits

In recent years, with the development of microwave technology, microwave circuits have made great progress in many technologies. The main development trends of microwave circuits in recent years are:

4.1 Interconnection and manufacturing technology of microwave circuits

The use of microwave technology and microwave circuit interconnection and manufacturing technology with a frequency above 1 GHz is rapidly developing and widely used. In modern information systems and military electronic equipment such as radar, navigation and communication equipment, microwave circuits are the "aorta" of high-speed information. Therefore, microwave circuits and their interconnection and manufacturing technologies are a major key technology in the development and production of information systems and military electronic equipment. Microwave circuit interconnection and manufacturing technologies include: microwave circuit substrate material and manufacturing technology, microwave circuit design and manufacturing technology, microwave device or component packaging and assembly technology, microwave component or system interconnection and debugging technology. It involves many disciplines such as microelectronics, materials science, computer application technology, and electromechanical engineering; it is a multidisciplinary and comprehensive science and technology. It has the characteristics of high technology content, high technical difficulty, fast development speed, wide application and great role in information systems and military electronic equipment.

With the rapid advancement of science and technology such as microelectronics technology, component technology, materials science, computer-aided design and manufacturing, new technologies and technologies for microwave circuit interconnection and manufacturing are also emerging. For example, multi-layer microwave integrated circuits and three-dimensional microwave integrated circuits (3DMMIC), low-loss transmission lines and shielding film microstrip (SMM) circuits, multi-chip microwave modules, microwave circuit micro-electromechanical systems (MEMS) interconnection and manufacturing technology, new Resin microwave PCB technology, new microwave circuit protection coating technology, 3D circuit simulation technology applied to microwave circuit design, microwave circuit CAD and optimization technology based on intelligent method, etc.

4.2 Photonic band gap structure of microwave circuit

In 1987, Yablonovitch proposed a sub-bandgap (PBG) structure, which was originally applied to the field of optics and has been introduced into the microwave band in recent years, which has attracted widespread attention. When electromagnetic waves propagate in a material with a periodic structure, they are modulated to produce a photonic band gap. When the operating frequency of the electromagnetic wave falls in the band gap, no transmission state exists. The sub-bandgap structure is applied to the microwave band, which can make electromagnetic waves in a specific frequency band completely unable to propagate therein. At the same time, the photonic band gap structure will also change the propagation constant in the pass band, which is a slow wave structure. Due to the above characteristics of the photonic bandgap structure, it is widely used in band resistance, suppression of higher harmonics, improvement of efficiency, increase of bandwidth, and reduction of size. The photonic bandgap structure can be implanted into the substrate material using metal, dielectric, ferromagnetic or ferroelectric materials, or can be directly arranged by various materials. The microwave photonic bandgap structures proposed at home and abroad are various, and currently develop from three-dimensional structures to one-dimensional and two-dimensional structures. Due to the ease of implementation and ease of integration, the research of photonic bandgap structures has been developed into the fields of electronics and communication. Nowadays, the unit shape of the photonic band gap structure, the periodic conditions, the combination of various periodic structure deformation bodies and the development of materials are all hot research topics.

A subcrystal is an artificial crystal formed by periodically arranging a medium in another medium. The basic characteristics of a photonic crystal are photonic band gaps, and electromagnetic waves whose frequencies fall in the band gap are prohibited from propagating. The unique properties of photonic crystals, originally used in the field of optics, have since rapidly expanded into other fields, and are now being studied and applied in the microwave band. At present, a variety of microwave photonic band gap structures have been proposed at home and abroad. The initial microwave photonic bandgap structure is composed of three-dimensional medium periodic arrangement. Due to the complexity of three-dimensional structure processing and analysis, the research and production of microwave photonic bandgap structure are concentrated. On the plane structure. The emergence of planar photonic bandgap structure has changed the traditional design method, providing a new way to design high-performance, highly integrated circuits, bringing a revolution in microwave integrated circuit design ideas. Because the one-dimensional and two-dimensional planar bandgap structures are flexible, easy to implement and easy to integrate, they have been widely used in microwave circuits, and have led to the rapid development of microwave integrated circuits.

4.3 MEMS switch for microwave circuits

According to the latest definition of MEMS, it is a miniaturized device or array of devices that combines electrical and mechanical components and can be fabricated in batches using IC processes. Although the traditional IC fabrication process and the MEMS fabrication process have great similarities, the former is planar technology and the latter is three-dimensional technology. Currently widely used MEMS fabrication technologies are: bulk micromachining technology, surface micromachining technology, bonding micromachining technology and LIGA technology (lithographic electroforming technology).

The switch is a key component of the microwave signal transformation. Compared with traditional p2i2n diode switches and FET switches, today's RFMEMS switches have superior microwave characteristics and inherent advantages of light weight, small size, and low power consumption. With the development of MEMS fabrication technology and process theory, after overcoming the shortcomings of short working life and low switching rate of MEMS switches, RFMEMS switches will surely achieve greater development in microwave systems. Currently, RFMEMS switches have been used in front-end circuits, digital capacitor banks, and phase shifting networks for some microwave systems.

4.4 lumped componentization of microwave circuits

Another trend in microstrip circuits is the use of lumped components. In the past, the lumped element size was comparable to the microwave wavelength and could not be used for microwave frequencies. With the development of lithography and thin film technology, the size of lumped components (capacitors, inductors, etc.) is greatly reduced, so that the J-band can always be used. The assembly of the lumped elements on the dielectric substrate with the semiconductor devices in the form of chips is a completely new approach for microwave integrated circuits. In addition to reducing the size, another advantage of the lumped components is that some of the most useful techniques and optimization techniques in low-frequency circuits can now be used directly in the microwave field.

4.5 Two-dimensional planarization of microwave circuits

In addition to lumped elements and one-dimensional transmission line elements, two-dimensional planar elements for microwave circuits have also been proposed. These components are compatible with stripline and microstrip lines, which provides a very useful alternative for microwave circuit design.

At present, the realization of two-dimensional planar circuits mainly has three modes: three-element structure, open-structure structure and cavity structure. Compared with the strip line circuit, it has the advantages of high degree of freedom and low input resistance. Compared with the waveguide circuit, it is easier to analyze and design. With the powerful computing power of the high-speed computer, it can be used for any shape according to requirements. The planar circuit is analyzed to greatly improve work efficiency. I believe that in the near future, its application will become more and more extensive.

4.6 New generation MIC

The new generation of MICs may be monolithic microwave integrated circuits on semiconductor substrates using high resistivity silicon, high resistivity gallium arsenide, and low resistivity silicon with a silicon dioxide layer. There are two technical difficulties. First, there is no general manufacturing method for various microwave semiconductor devices used therein, and secondly, passive distribution elements (transmission line segments) require a large-area substrate. However, recent trends indicate that the gallium arsenide process is the key to microwave monolithic integrated circuits. Gallium arsenide metal-semiconductor field-effect transistors (MESFETs) dominate the gigahertz bandwidth analog amplifiers and gigabit-rate digital integrated circuits. Whether it is a hybrid or a monolithic microwave integrated circuit, its advantages are basically the same as those of a low frequency integrated circuit, that is, the system has high reliability, volume, and weight. In the case where a large number of standardized components are required, the cost is ultimately reduced. Like low-frequency integrated circuits, MIC has great potential to expand existing markets and open up many new applications, including large numbers of civilian projects.

5 Conclusion

This article focuses on the origin of the microwave circuit, as well as a summary of the status quo and the introduction of cutting-edge technology. The rise of microwave circuits in the 1940s, and the emergence of microstrip circuits in the 1960s, microwave circuits have advanced at an unprecedented speed. With the popularity of various integrated circuits, the development of microwave circuits is bound to have a good prospect forecast.