Key focus: Phased Array Antenna, employs simpler elemental antennas to configure a complex system, has many interesting features and capabilities.
Articles in this series
- Phased Array Antenna – an introduction (this article)
- Electronic Scanning Arrays
- Grating lobes in electronic scanning
- Array pattern multiplication
Since the latter half of previous century, a class of antenna technology called the ‘Phased Arrays’ has witnessed phenomenal progress in design, engineering and applications. Concurrent progress in solid state material has enabled active antenna elements to be packed as arrays in many different geometries- linear, planar and conformal shapes. Though started as the solution for various taxing military needs, this technology has since entered many civilian domains, the space applications being one of the prominent usage in the present times.
Phased Array, which employs simpler elemental antennas to configure a complex system, has many interesting features and capabilities. The first one that appeals to a designer, is the ability to address the design problem by reaching at the elemental level for control. Theoretically, it is possible to control at each element, the amplitude and phase of the signal being fed. This gives rise to a dynamic control of antenna beam shape, electronic scanning, sidelobes and their placement-all leading to a variety of applications from the same system.
Though amplitude and phase control are possible at element level, it is generally seen that the designers use the amplitude control to set the illumination function of the elements and deal with the dynamic requirements by phase shifter switching. Presently, phase shifters are capable of being engineered in small form factor, incorporating the solid state source, the connecting geometry and the radiating element. Digital and modular technology make it feasible for mass production and for maintainability and reliability in severe environmental condition.
The phase shifters employed in such systems use solid state devices and electronically controlled ferrites for switching. They are typically controlled with 4 to 5 bits digital accuracy which give enough phase states to design for. The setting accuracy of a phase state has also considerably advanced in that a designer can plan for dynamic beam shaping with confidence. By dividing the entire R.F. source among many elements, the power management and heat dissipation of the system get distributed to manageable engineering practice. Hence such a level of sophistication on phase control has finally evolved an array system, justifiably called the ‘Phased Array Antenna’.
In the succeeding pages, effort has been made to describe what is the unique specialty of Phased Arrays- ‘the electronic steering’ –its value and also the limitations, so that a balanced view is derived. The idea is to employ simple examples to start with and build on this initial strength to move onto more intricate antenna functions. The emphasis will be on the design concepts and their practical utility. No deeper background in EM theory, RF-Microwave practices are required at present; but essential knowledge of antennas and their different operating frequency environments are already visible to everyone in today’s technology bound world.
It is presumed that readers are familiar with many of the antenna concepts and parameters, like antenna gain, beamwidth, sidelobes, field and power patterns, reciprocity in antenna for transmitting and receiving; and allied engineering mathematical concepts like Fourier Transform, geometric series and their summation, and the need for logarithmic compression in the plotting of antenna patterns. Such an initial preparation will help in assimilating the text and graphics which follow.
Continue reading the discussion on electronic scanning arrays… (not yet published! Monitor this place for the follow-up article)
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