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Radar systems of the future: fixed phase array radar rely on fast, efficient signaling for beam steering.

Twentieth Century warfare gave rise to the saturation attack --a tactic in which multiple missiles and aircraft come from all directions at the same time toward a single target. Like a blitz in football, it is designed to overwhelm defenses by sheer number and volume to increase the chance of success against any countermeasures that are used to protect the given target. Radar, with its ability to detect and track planes and missiles, is an obvious defense option. However, to effectively provide accurate information in the event of a saturation attack, radar systems need optimal data handling capabilities.

Depending on how planes and missiles need to be detected, the high speeds and the near-simultaneous convergence of the incoming targets, radar must process information at a corresponding pace so personnel can return fire in a counterattack.

Traditional mechanical radar isn't very effective when it comes to saturation attacks. Each radar rotation is called a sweep. During a sweep, the radar sends a microwave signal out to a target and waits for a portion of the signal to travel back so the data to be processed. Rotating the radar faster decreases the range signals can cover. Because signals would be limited to the distance they could travel before the next sweep, a faster rotation results in a smaller range in which to detect an object. When the signal detects an object, radars wait an additional second to perform another sweep and correlate the two echoes while processing information about that target. The reduced range coupled with the added verification time means less time to respond to threats and less-detailed returns for stealthier or more sophisticated targets.

Phased array solutions rival mechanical radar

Phased array radar is now widely used in military environments because it can track hundreds of targets and is not susceptible to mechanical failure, like malfunctioning motors in rotational radar. A phased array system is comprised of several antennae spread evenly apart in a panel. Each antennae sends out RF signals in all directions and angles. These signals incorporate a phase shift to change the effective radiation pattern to point to a specific direction, and bypass other directions in just a fraction of a second.

By relying on electronic signals instead of a rotating sweep, phased array radar is able to send out different sized beams to perform specific functions, such as an individual search beam, and others for object tracking and altitude--all in one system. Therefore, it can track multiple targets and perform multiple tasks at the same time.

Power dividers handle the steering

Steering a radar's beam digitally to scan one direction is known as beamforming, and power dividers are used to emit signals of varying phase and amplitude to the antennae. "The power that comes out from the antenna elements can be made such that it varies along the same surface," says Anuj Srivastava, president and CEO at Renaissance Electronics & Communications, which provides high-reliability RF, microwave, and millimeter wave products for military commercial applications, including power dividers for fixed phase array radar systems. "With time we vary the power that goes, let's say right to left, on this antenna panel. It is similar to scanning the antenna and moving it, because in any direction the power is now changing and it goes from high to low. The signal received coming back can be put together, and it gives information about the target's speed and location."

Power dividers couple electromagnetic power in a transmission line to a port to be used in another circuit. In a fixed phase array radar system, the input signal is divided into two or more signals, which are then altered to different power levels using attenuators. The altered signals are sent from the output ports at specific amplitudes into the antenna array panel, which creates the radiation pattern that steers the beam in the desired direction.

Since phased array radar systems are positioned in tight spaces on ships and, increasingly, aboard jet planes, designers of these systems are concerned about keeping them as small and lightweight as possible. Today's power divider vendors are responding with units that do not require attenuators. Attenuators add size and weight to the system and consume additional power. One divider that does not require attenuators is an eight-way unit that can divide power from 6 dB to 18 dB across its output ports, and handle 350 W peak and 35 W (continuous wave) while operating between 1,100 MHz and 1,500 MHz. Its 8" x 5" x .5" footprint makes it appropriate for space constrained environments often found in the military.

An eight-way power divider can be customized for unequal outputs at the ports. Instead of an even split at two ports, for example, output can also be "tapered" depending on the movement of an object --or several objects. For a fast-moving object that is at the outer end of the radar's range, the centermost ports can output the maximum power necessary to track the object. When the object gets closer to the radar and needs less power to track, the divider can switch to a weaker signal at its outermost edge. This enables a fixed phase radar system to track an object as fast as possible while optimizing power efficiency.

Electronics take control

Engineers looking to maximize the radar operator's ability to quickly respond to threats need to ensure reliability throughout the system. That means the radar system should be designed with as little mechanical motion as possible, and the systems intended for scanning purposes--especially the antenna and beam steering elements--should be controlled electronically. In addition, typical military requirements must apply: resistance to shock (up to 1,000 g), and an operating temperature range from -40[degrees]C to +85[degrees]C. Cutting edge power dividers are now able to withstand as much as 400 W peak with 40 W average power.

When specifying power dividers for fixed phase array radar systems, consider the maximum broadband capabilities. Srivastava believes future power dividers will be able to cover 500 MHz to 20 GHz and have the same capabilities at those bands as L-band devices can provide. He also emphasizes their ability to handle reflected power and mismatch between any two channels. "They should be correctly designed and selected to withstand the reflective power, and also have a little bit of margin built into them so that when the power divider goes through some of the temperature extremes, it will still perform without failing," he says.

The goal for radar system designers is to enable operators to see in all directions and to counter attacks instantaneously. Today's power dividers provide fast, efficient signaling necessary for fixed array radar to efficiently scan multiple targets across an increasingly longer range with the resolution that is needed to reduce the chance of penetration by an otherwise overwhelming, coordinated attack from the sky.

By Chris Warner, Executive Editor
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Title Annotation:Military
Author:Warner, Chris
Publication:ECN-Electronic Component News
Date:Sep 1, 2014
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