Tag: Side

Array pattern multiplication – phased array antenna

Articles in this series

Array pattern multiplication

If the element pattern of an array is very broad (as in an Omni directional antenna element) the pattern of the array is mostly the Array Factor since it is more directional. However, if the element pattern has some distinctive features by employing specific illumination function, then the composite radiation pattern is obtained by the principal of pattern multiplication. If Farrayis the Fourier transform of the array field and Felement is the Fourier transform of the element field, the combined pattern is given by the pattern multiplication

Composite antenna pattern = Farray × Felement

Example:

  1. Uniformly illuminated array produces a first sidelobe level of -13.5 dB [=20×log10 (field amplitude)]. Due to the vast difference in levels between major and minor lobes, logarithmic (dB) scale is preferred in such measurements to provide the required dynamic range. This illumination function produces a better aperture efficiency (gain), sharper beamwidth but at the cost of near sidelobes getting elevated.
Radiation pattern with uniform aperture illumination
Figure 1: Radiation pattern with uniform aperture illumination

2. The cosine aperture distribution on a pedestal attempts to deal with a maximized gain along with control on the sidelobe levels. The accompanying figure below is the array pattern with illumination function of the type f(x) =0.9×cos(x) +0.1, where x refers to the linear position of the element.

Figure 2: Radiation pattern with cosine aperture illumination

Instead of tapering the edge illumination to zero, the cosine function sits on a pedestal to provide a constant illumination, but at a lower percentage level, at the peripheral geometry of the radiating element. The main beam is broadened but the first sidelobes are at -23.5dB level, an order of improvement on the -13.5 dB level of the previous case.

Several sophisticated illumination functions are available to the designer now to optimize array design.

Concluding remarks

It should be stressed that a Phased Array produces huge opportunity for designers to exploit its dynamic properties; but at the same time, it challenges us with system engineering and integration complexity, maintainability and finally in the cost factor. In an evolving era of technology, limitations in engineering and operation, would always witness a better tomorrow, provided the basic scientific validation and sustainability are present in all of the newer innovations. 

Rate this post: Note: There is a rating embedded within this post, please visit this post to rate it.

Phased Array Antenna – an introduction

Key focus: Phased Array Antenna, employs simpler elemental antennas to configure a complex system, has many interesting features and capabilities. 

Articles in this series

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)

Rate this post: Note: There is a rating embedded within this post, please visit this post to rate it.