Main lobe (peak gain, where the radar looks), side lobes (unintended sensitivity off boresight), and the back lobe (small lobe pointing roughly opposite the main lobe).
Energy arriving through a side lobe still reaches the receiver. A jammer nowhere near the main beam can inject energy through a side lobe and degrade the radar.
Half-power beamwidth: the angular width between the two points where gain falls 3 dB below the peak. It quantifies how tightly the beam is focused.
About \(-13.2\) dB relative to the main lobe — the textbook constant for uniform illumination.
It lowers the side lobes (good for EP) at the cost of a wider main beam (larger HPBW). Lower SLL trades against beamwidth — no free lunch.
\(\theta_{\text{HPBW}} \approx 70\,\lambda/D\) degrees, and \(G \approx 30{,}000/(\theta_{\text{az}}\cdot\theta_{\text{el}})\). Bigger aperture in wavelengths → narrower beam and higher gain.
By applying a progressive phase step \(\Delta\phi = (2\pi/\lambda)\,d\,\sin\theta_s\) across the elements. The contributions add in phase at \(\theta_s\), so the main lobe points there — no moving parts.
Full-strength copies of the main lobe in unwanted directions, appearing when element spacing \(d > \lambda/2\) (the angular-domain Nyquist limit). Keep \(d \le \lambda/2\) to suppress them at broadside.
An ESA steers the beam with phase shifters. An AESA (active ESA) gives every element its own transmit/receive module.
Microsecond beam pointing (interleave search and track), graceful degradation (dead modules cost a little gain, not the radar), and multiple simultaneous beams. (Also: LPI waveforms from precise phase control.)
Effective aperture shrinks as \(\cos\theta_s\) and HPBW broadens as \(1/\cos\theta_s\). Steering to \(60^\circ\) doubles the HPBW and costs about 3 dB of gain.
Side-lobe cancellation (an auxiliary antenna subtracts the side-lobe signal) and side-lobe blanking (an omni reference rejects strong pulses outside the main beam). Low-SLL (tapered) antenna design also helps.