How do I design a log-periodic dipole array for a wideband measurement antenna?
Log-Periodic Dipole Array Design
The LPDA is the standard wideband measurement antenna for EMC testing, spectrum monitoring, and antenna range illumination. Its frequency-independent properties make it invaluable for applications requiring a single antenna to cover a wide frequency range.
| Parameter | Low Gain | Medium Gain | High Gain |
|---|---|---|---|
| Gain Range | 2-6 dBi | 6-15 dBi | 15-45 dBi |
| Beamwidth | 60-360° | 15-60° | 1-15° |
| Typical Types | Dipole, monopole, patch | Yagi, helical, horn | Parabolic, array, Cassegrain |
| Bandwidth | Narrow to wide | Moderate | Narrow to moderate |
| Complexity | Low | Medium | High |
- 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
Frequently Asked Questions
What gain can I achieve?
LPDA gain depends on tau and sigma: tau=0.8, sigma=0.15: G approximately 6 dBi (fewest elements, shortest boom). tau=0.9, sigma=0.15: G approximately 8 dBi (moderate). tau=0.95, sigma=0.18: G approximately 10 dBi (most elements, longest boom). Higher gain requires more elements and a longer boom. For comparison: a Yagi antenna provides 10-15 dBi but only over a narrow bandwidth (approximately 5-10%). The LPDA trades peak gain for bandwidth.
What measurement antennas are commercially available?
Commercial LPDA measurement antennas: ETS-Lindgren 3147 (200 MHz-2 GHz, 7 dBi, the industry standard for EMC emissions testing). Schwarzbeck VULB 9160 (80 MHz-3 GHz, 6-8 dBi, precision measurement antenna). A-INFO JXTXPZ-100180 (1-18 GHz, 6-7 dBi, compact wideband). Aaronia HyperLOG series (380 MHz-6 GHz, 5-8 dBi, affordable). Prices: $500-5000 depending on the frequency range, precision, and calibration. Most come with calibration data (antenna factor or gain vs. frequency).
How does the LPDA compare to other wideband antennas?
vs. horn antenna: horn has higher gain (10-25 dBi) but narrower bandwidth (typically 1.5:1). Horn is the preferred wideband antenna above 1 GHz where size permits. vs. ridged horn: ridged horn extends the horn's bandwidth to 2-3:1 with 6-10 dBi gain. Similar performance to LPDA but more compact at higher frequencies. vs. spiral antenna: spiral provides wideband CP (circular polarization) with 2-5 dBi gain over a 10:1+ bandwidth. Used for DF and ESM where CP is needed. vs. discone: discone is omnidirectional with approximately 0-2 dBi gain over a 10:1 bandwidth. Used for monitoring and scanning. The LPDA is preferred when: directional gain with linear polarization is needed over a wide bandwidth.