Principle of Anti-Jamming Antenna

While walking by a lakeside, if two waves are generated at two nearby points, the ripples spread outward continuously and eventually overlap, forming the pattern shown below.

It can be observed that the waves strengthen in some areas and weaken in others, with these regions distributed alternately. This effect is most noticeable in the narrow central region.

When a crest meets another crest, or a trough meets another trough, their energies add together, making the crest higher and the trough deeper. This is called constructive interference.

Conversely, when a crest meets a trough, they cancel each other out, and the vibration fades into calmness. This is called destructive interference.

Main Lobe, Side Lobes, and Nulls

At the midpoint between the two feed sources, constructive interference results in the strongest energy, forming a directional beam known as the main lobe. On both sides, destructive interference cancels the energy, creating nulls. Further outward, constructive interference occurs again but with weaker intensity than at the center, forming what are known as side lobes.

Nulling technology forms nulls in the direction of interference while ensuring that the main lobe remains undistorted or has minimal distortion. Its goal is to align the main lobe with the desired signal and the nulls with the interference sources, thereby minimizing the degradation of signal-to-noise ratio caused by interference. This means that nulling technology must not only enhance the reception of the desired signal but also effectively suppress interfering signals.

Principle of Beamforming Antenna

Inside the antenna, a series of electromagnetic radiating elements are arranged, known as radiators or antenna elements. These antenna elements also use the principle of interference to form directional beams.

From the figure above, it can be seen that the more antenna elements arranged vertically, the more energy can be concentrated in the central direction, resulting in a narrower beam. However, this is only a vertical cross-section. In reality, the full beam is three-dimensional in space, and its horizontal and vertical beamwidths may be completely different.

The figure below shows the arrangement of the antenna elements and the three-dimensional distribution of the radiated energy.

It can be seen that the radiating elements in the antenna above are arranged vertically, with very few elements in the horizontal direction. As a result, the beam energy is concentrated in the vertical direction, while the horizontal beamwidth remains relatively wide, resembling a thin pancake.

If we change the arrangement of these antenna elements into a rectangular array, the radiated electromagnetic energy will form a much thicker main lobe at the center, with a ring of side lobes surrounding it—this begins to resemble beamforming.

To make the beam narrower and the energy more concentrated, the antenna elements need to be greater in number and more densely packed, with both the horizontal and vertical dimensions taken into account. The original antenna thus evolves into a large-scale antenna array.

With this, the generated beam becomes much sharper, enabling large-scale antenna arrays to support beamforming.

However, there is still a problem: the main beam is located at the center and propagates perpendicular to the antenna array, while satellites continuously orbit the Earth and their positions are not fixed. Even if the main beam is sharp, it is useless if it cannot be directed toward the satellite.

So, is it possible to steer the beam by a certain angle and aim it at the satellite to enhance its signal? First, let’s look at how the central main beam is formed: when multiple waves have the same phase—meaning their crests and troughs align at the same time—they can undergo constructive interference when they reach the antenna, and the signal is strengthened through superposition.

If the satellite and the antenna array form a certain angle, the phases of the signals received by the array elements can no longer align properly. A crest may meet a trough, or the waves may superimpose at other phase offsets, making it difficult to achieve constructive interference and therefore preventing effective signal enhancement.

What should we do then? We certainly can’t rotate the entire antenna just to make the beam follow the satellite.

In fact, periodicity is one of the most fundamental characteristics of waves. Different phases appear repetitively—if one crest is missed, the next crest will arrive—therefore, the phase can be adjusted.

By adjusting the amplitude and phase (weights) of the signals received by different antenna elements, the signals can be made to align in phase in the direction of the satellite, even if their propagation paths differ. This allows the signals to combine constructively, effectively steering the array’s gain toward the satellite.

The figure below provides an example, showing how the antenna array adjusts the phases of the received signals to steer the beam by an angle of θ, enabling precise alignment with the satellite for signal reception.

This shows that the key to beamforming lies in controlling the phases of the antenna elements, which essentially depends on the processing of the antenna weights.

Depending on where and how the beamforming processing is performed, it can be classified into three types: digital beamforming, analog beamforming, and hybrid beamforming.

Analog beamforming refers to adjusting the antenna phase by manipulating the RF signal weights using phase shifters, with the processing taking place relatively early in the signal chain.

A key characteristic of analog beamforming is that the number of baseband processing channels is far smaller than the number of antenna elements, which limits overall capacity. In addition, the beamforming relies entirely on hardware implementation and is affected by component precision, which places constraints on performance.

Digital beamforming, on the other hand, processes the antenna weights at the baseband stage, where the number of baseband channels equals the number of antenna elements. As a result, a complete RF chain must be provided for each data path.

The advantages of digital beamforming include high beamforming accuracy, flexible implementation, and fast response to antenna weight adjustments. Its disadvantages are the high requirements on baseband processing capability, increased system complexity, larger equipment size, and higher cost.