Transmission lines are a foundational part of every phased array. They are used to transport the communication or radar signals used by the phased array antenna. It would be nearly impossible to understand phased arrays without knowing these four transmission line types.
A summary of the four transmission lines is in Figure 1. It shows an illustration of the transmission line, its benefits, drawbacks, and typical uses. In the first column of the table, the green features of the transmission line illustrations are dielectric material such as Teflon, aluminum oxide, or similar material. The black sections connected to the dielectric is metal–Usually thin copper or gold that is etched or printed in a pattern.
It is important to note that all these transmission lines are useful for phased arrays. In fact, most phased arrays will use at least three of the transmission line types. This blog will describe each of these.
Transmission Line #1: Coaxial Line
Coaxial transmission line will be familiar to many since it is the type that is used in cable TV and satellite TV. They are often white or black cables that are connect to the cable or satellite box near your TV. Coaxial line has two conductors. One is the center conductor and the other is the ground shield. The two conductors are typically separated from each other by a dielectric.
Transmission Line #2: Microstrip Line
One of the most commonly used transmission line type types in modern phased arrays is microstrip. It has a dielectric with a lower ground metal and a top strip of metal. This transmission line is used as the interconnect between integrated circuits.
Transmission Line #3: Stripline
The center conductor of Stripline is buried within a dielectric and ground metal is placed over the top and bottom as illustrated in the table. Stripline can have high isolation to adjacent circuits when the top and bottom grounds are properly connected together (usually using vias of metal).
Transmission Line #4: CPW
Coplanar Waveguide (CPW) with ground is an attractive transmission line to use in some phased array applications since it can provide more isolation to adjacent circuits compared to microstrip. In most applications, it does require the topside grounds to be connected to the bottom side grounds using vias of metals.
This blog provides essential information about four transmission lines that are necessary for phased arrays. Table 1 can be used when making a decision on which transmission line type to use.
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