How do I design a wideband antenna for a radar warning receiver covering 2 to 18 GHz?
RWR Wideband Antenna Design
The RWR antenna is a critical component whose performance directly impacts the system's sensitivity, AoA accuracy, and probability of intercept.
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
- Interface compatibility: verify impedance, connector type, and mechanical form factor match the system architecture
- Margin allocation: include sufficient design margin to account for manufacturing tolerances and aging effects
Frequently Asked Questions
Why circular polarization?
Threat radars can be: horizontally polarized (most ground-based surveillance radars), vertically polarized (some naval radars, some missile seekers), or slant-polarized (some fighter radars). A linearly polarized RWR antenna would suffer 3 dB loss when receiving a cross-polarized signal and potentially 20+ dB loss when perfectly cross-polarized. A circularly polarized spiral antenna receives any linearly polarized signal with at most 3 dB loss (since any linear polarization decomposes into equal RHCP and LHCP components, and the spiral captures one). This polarization-independent reception ensures that the RWR detects threat signals regardless of their polarization.
How is the AoA determined?
Amplitude comparison DF: the RWR has 4-6 antennas pointing in different directions (typically 60-90° beamwidth each). The same pulse is received by multiple antennas at different amplitudes. The antenna with the highest amplitude indicates the approximate bearing. The amplitude ratios between adjacent antennas provide a more precise bearing estimate: AoA = f(amplitude_1, amplitude_2, ... amplitude_N). Accuracy: ±5-15° (adequate for threat warning and countermeasure cueing). For more precise DF: use an interferometric approach (phase comparison between antennas) for ±1-5° accuracy. This requires coherent receivers on each antenna.
What about conformal antennas?
For aircraft: the RWR antennas must be conformal (flush-mounted on the aircraft skin) to avoid aerodynamic drag. Conformal spiral antennas: the spiral is printed on a flexible substrate and conformed to the aircraft surface curvature. The curvature affects the pattern (distorting the beam shape and shifting the phase center), but: for the broad beamwidths used in RWR (60-90°), moderate conformal distortion is acceptable. Blade antennas: some RWR installations use small blade antennas (protruding a few cm from the skin) that provide omnidirectional coverage but lower gain. The blade's small size limits the low-frequency coverage.