X-Band Radar: Block Diagram & Working Principle

Introduction: X-band radar systems operate in a high frequency microwave band that strikes a balance between resolution and range, making them invaluable for applications such as airborne surveillance, maritime navigation, weather monitoring and target tracking. In this tutorial, we will describe how X-band radar works, its advantages and limitations.

How X-Band Radar Works?

• Modern X-Band radars (operating between 8–12 GHz) rely on Active Electronically Scanned Arrays (AESA). Instead of a single large tube and a spinning dish, these radars use thousands of tiny, integrated chips called Transmit/Receive (T/R) Modules.

• By adjusting the phase (timing) of the signal leaving each tiny module, the radar can steer the beam left, right, up or down instantly without physically moving the antenna.

• The system sends out high energy chirps and listens for the echo. Digital signal processing (DSP) then converts these echoes into a high-resolution 2D or 3D map.

X-Band Radar & functions of its components

Transmitter Chain:

• The signal to be transmitted is initially baseband signal at lower frequency and generated by waveform generator.
• The signal is converted to analog form by DAC (Digital to Analog Converter).
• The low frequency analog signal is up converted to higher frequency (8-12 GHz) using RF mixer and LO (Local Oscillator).
• The up-converted RF frequency is amplified using PA (Power Amplifier). GaN technology is used for PA to achieve better efficiency.

Image Courtesy : QorVo, Inc.

Beamforming and Control:

• Phase Shifter : This component delays the radio signal by a specific fraction of a wavelength at each individual antenna element. By slightly changing the timing (phase) of the signal across the array, the collective radar beam can be steered left, right, up, or down electronically. This allows the radar to track multiple targets instantly without mechanical movement.
• Digital Step Attenuator : It controls the amplitude of the signal with high precision. It is used for Beam Tapering to reduce side lobes. This reduces false alarms and makes the radar harder for enemies to detect.

T/R Switch: This high speed switch toggles the antenna connection between the PA (Transmit path) and the LNA (Receive path). It provide isolation to protect sensitive receiver components from high power transmission from PA.

Receive Chain:

• After the pulse is sent, the switch flips to receive mode to listen for tiny echo bouncing off a target.
• Limiter : A protection circuit placed immediately after the antenna. It “clamps” or limits the power entering the receiver.
• LNA (Low Noise Amplifier) : It amplifies the incredibly weak return signal (echo) while adding as little electronic noise as possible.
• Filters : It blocks all the frequencies which are not part of radar’s operating range.
• ADC : It is interface between physical world (i.e. analog voltages) and computational world (i.e. binary data). X-Band radars often use wide bandwidths (e.g., 500 MHz) to achieve high resolution. The ADC must sample extremely fast (High Sampling Rate) and have a high Dynamic Range to detect tiny echoes that might be hiding next to massive echoes (like a mountain).
• Pulse compression : In radar physics, to get Long Range, you need a long pulse (more energy on target). But to get High Resolution (seeing detail), you need a short pulse. Radar transmitter uses long pulse to achieve long range. At receiver, pulse compression compresses it to short pulse to achieve high resolution.
• Doppler processing : This block analyzes the frequency shift of the returning signal. It uses FFT. If the target is moving toward the radar, the frequency increases; if moving away, it decreases.
• Detection : In a basic system, any signal above a fixed voltage line is a target. However noise levels change this. Modern systems use CFAR (Constant False Alarm Rate) logic. The detector looks at the noise level in the cells surrounding the target and dynamically raises or lowers the threshold. This ensures the radar detects targets in storms without flooding the screen with false alarms.
• Tracking & parameter estimation : Once detection is made, data is still coarse. Tracking happens over time. Various parameters of the target are estimated which include speed, target ID, heading etc.

Comparison between X-Band Vs. Lower Bands (L/S)

Advantages of X-Band Radar

Following are some of the benefits of X-Band Radar compared to low frequency radars.

1. Can clearly distinguish three separate objects. This makes it essential for Fire Control Systems (guiding munitions) and Air Traffic Control.
2. X-Band antenna array can be significantly smaller and lighter.
3. X-Band is highly sensitive to targets with a low Radar Cross Section (RCS). It is excellent at detecting stealthy or non metallic objects that do not reflect radio waves strongly.

Disadvantages of X-Band Radar

Following are some of the limitations of X-Band Radar.

1. The same physics that allows X-Band to detect rain droplets also makes it vulnerable to them. In heavy storms, X-Band signals can be absorbed or scattered by rain, snow and moisture in the air.
2. Above mentioned characteristics cause signal loss (attenuation) which reduces radar’s effective range during bad weather compared to lower frequencies like L-Band.
3. Higher frequency signals generally travel shorter distances than lower frequency signals for same transmit power.
4. Dense packing of high power components into small compact X-band array creates immense heat. Designing the cooling systems to prevent these chips from overheating is a major engineering challenge.

Summary: X-band radar delivers powerful capabilities such as high resolution, compact antenna size and precise target tracking which make it ideal for many modern radar applications, from maritime navigation to airborne surveillance.