| Antenna Definition | Dual-reflector parabolic antenna | A Cassegrain antenna uses a large primary reflector and a smaller convex subreflector. The feed is positioned near the center or rear of the primary reflector, while the subreflector redirects electromagnetic energy toward the main reflector. | Choose this architecture when high gain, a compact feed arrangement, low spillover, and accurate beam control are more important than the simplest mechanical design. |
| Operating Principle | Reflector-based aperture focusing | During transmission, the feed illuminates the subreflector and primary reflector, which transform the spherical wavefront into a narrow beam. During reception, the same reflector path concentrates incoming energy onto the feed. | Verify that the reflector profile, subreflector shape, and feed position are optimized for the intended frequency band rather than relying only on the stated dish diameter. |
| Operating Frequency | Commonly 1–40 GHz; higher bands are also possible | Frequency determines wavelength, electrical aperture size, surface accuracy requirements, atmospheric loss, achievable beamwidth, and feeder or waveguide compatibility. | Select an antenna whose specified frequency range fully covers the lowest and highest operating frequencies, including required guard bands and frequency-dependent performance. |
| Primary Reflector Diameter | Approximately 0.6–12 m for many precision microwave applications | A larger aperture generally provides higher gain and a narrower beam. The approximate directivity relationship is proportional to (πD/λ)², where D is reflector diameter and λ is wavelength. | Increase diameter when link margin, spatial resolution, or interference rejection is critical. Check transport, foundation, wind loading, and installation constraints. |
| Gain | About 30–65 dBi, depending on frequency and aperture size | Practical gain is lower than ideal aperture gain because of reflector illumination, spillover, blockage, surface errors, polarization loss, and manufacturing tolerances. | Compare gain at the exact operating frequency. For link-budget work, use the measured or guaranteed value rather than a theoretical value calculated from diameter alone. |
| Aperture Efficiency | Typically 50–75% for well-designed dual-reflector systems | Aperture efficiency represents how effectively the physical reflector area produces useful radiation. It includes illumination efficiency, phase efficiency, spillover, blockage, polarization, and surface effects. | Prefer higher efficiency when physical size, transmit power, or receiver sensitivity is limited. Ask whether the stated efficiency applies across the complete frequency band. |
| Half-Power Beamwidth | Approximately 0.5°–8°, depending on D/λ | Beamwidth decreases as the electrical aperture becomes larger. A commonly used engineering approximation is beamwidth ≈ 65λ/D degrees, although the exact value depends on aperture illumination and reflector geometry. | Choose a narrower beam for point-to-point links, tracking, and interference rejection. Allow adequate pointing accuracy and structural stiffness for narrow-beam operation. |
| Polarization | Linear, dual-linear, circular, or dual-circular | The feed establishes the polarization state. Cross-polarization performance depends on feed symmetry, subreflector geometry, reflector accuracy, and alignment. | Match the antenna polarization to the radio system. For polarization reuse or dual-polarized links, specify cross-polar discrimination at the operating angles. |
| Voltage Standing-Wave Ratio | Common target: ≤1.25:1 or ≤1.5:1 across the specified band | VSWR indicates impedance matching between the feed and transmission system. Lower VSWR reduces reflected power and helps preserve transmitter efficiency and receiver noise performance. | Confirm the VSWR or return-loss specification at the feed interface and across all required channels, not only at the center frequency. |
| Side-Lobe Level | Often below −17 to −25 dB for precision designs | Side lobes are unwanted radiation away from the main beam. They are influenced by feed taper, subreflector size, edge diffraction, reflector shaping, and blockage. | Specify side-lobe limits when the antenna operates near other links, satellites, radar systems, or regulated spectrum users. |
| Cross-Polarization Discrimination | Common target: ≥30 dB; higher values may be required | Cross-polarization discrimination measures how well the antenna rejects the orthogonal polarization. Poor performance can cause channel leakage and polarization interference. | Use a higher target for frequency-reuse systems, dual-polarized communications, radio astronomy, and precision measurement applications. |
| Surface Accuracy | Typically better than λ/16 RMS for high-performance operation | Reflector surface errors create phase errors that reduce gain and increase sidelobes. The impact becomes more severe as wavelength decreases. | At millimeter-wave frequencies, require tighter manufacturing and alignment tolerances. Consider thermal expansion, gravity deformation, rain, ice, and wind-induced distortion. |
| Pointing Accuracy | Typically about 0.01°–0.2°, depending on beamwidth and application | Pointing error reduces received power when the antenna boresight is displaced from the target. Narrower beams require more accurate mounts, encoders, and tracking systems. | A practical design target is usually a pointing error significantly smaller than the half-power beamwidth. Include installation alignment and wind effects in the error budget. |
| Feed and Subreflector Blockage | Minimize projected blockage; exact value is geometry-dependent | The subreflector and support struts can obstruct part of the primary aperture, causing gain loss, diffraction, and increased sidelobes. | Compare blockage ratio, support-leg design, and measured radiation patterns when gain, sidelobe control, or low-noise reception is important. |
| Environmental Protection | Outdoor-rated enclosure; commonly IP or equivalent protection | Radomes, feed covers, seals, corrosion-resistant materials, and drainage features protect the RF path and mechanical alignment from weather exposure. | Specify wind speed, temperature range, humidity, salt fog, solar radiation, icing, and rain attenuation requirements for the installation site. |
| Mechanical Stability | Low structural deflection under operational wind load | Mechanical deformation changes reflector shape and boresight direction, producing gain reduction, beam pointing error, and phase distortion. | Review stiffness, mount backlash, encoder resolution, foundation design, and wind-load data together with the RF specifications. |
| Transmit Power Handling | Determined by feed, waveguide, connectors, cooling, and duty cycle | Power capability is limited by electric-field breakdown, dielectric heating, conductor loss, thermal dissipation, and continuous-wave or pulsed operating conditions. | Confirm average power, peak power, pulse width, duty cycle, altitude, and allowable temperature rise before finalizing the feed and transmission interface. |
| Typical Applications | Point-to-point links, satellite ground stations, radar, tracking, and radio astronomy | The combination of high gain, narrow beamwidth, compact feed placement, and accurate reflector control supports long-distance and high-resolution microwave applications. | Define the application first, then prioritize gain, beamwidth, sidelobes, polarization, pointing accuracy, environmental rating, and maintainability in that order of importance. |
| 2026 Selection Checklist | Frequency, gain, beamwidth, efficiency, polarization, VSWR, mechanics, compliance | Antenna performance is a system-level result. RF specifications, installation geometry, tracking control, weather conditions, and regulatory requirements interact with one another. | Request a complete datasheet, radiation patterns, test conditions, mechanical drawings, environmental limits, calibration information, and acceptance-test criteria before purchase. |
