dBi and dBd
Gain in dBi is measured against an ideal antenna that radiates equally in all directions (isotropic). Gain in dBd is measured against a half-wave dipole, which itself has 2.15 dBi. So dBd = dBi − 2.15, and ERP = EIRP − 2.15 dB.[1, 2] CompleTech states gain in dBi.[3] Check which one a competitor's datasheet uses before comparing.
Omni or directional
Mobile units want an omnidirectional pattern. Fixed links and corridors suit a directional antenna, and the extra gain can let you turn the transmitter down.[4] High gain is not automatically better: the beam gets narrower and has to be aimed.[4]
How CompleTech describes a pattern
Each ComAnt datasheet gives the gain, the beamwidth in the horizontal (H) and vertical (E) planes at the −3 dB points, and the front-to-back ratio (F/B). From the ComAnt catalog (March 2026):
| Family | Type | Gain | H −3 dB | E −3 dB | F/B |
|---|---|---|---|---|---|
| CAD | offset pattern dipole | 5 dBi | 179º | 74º | 6-10 dB, depending on mounting |
| CAC4 | offset pattern collinear | 11 dBi | 182º | 13º | 4-10 dB, depending on mounting |
| CAB2 | bidirectional broadside | 6 dBi | 71º | 69º | 0 dB |
| CAY++ | directional yagi | 10 dBi | 59º | 47º | 12 dB |
| CAS3 | directional stacked yagi array | 10 dBi | 173º | 20º | 11 dB |
| CAS2+++ | directional stacked yagi array | 13.5 dBi | 49º | 24º | 12 dB |
| CAR | reflector monopole | 12 dBi | 54º | 45º | 30 dB |
| CAN4 | cardioid pattern notch | 8 dBi | 229º | 23º | 30 dB |
Values as printed by CompleTech (ComAnt catalog, pp. 22–51)[3]. Read them as the vendor states them; the full pattern plots are in the catalog.
Two things to notice: the CAC4 collinear reaches 11 dBi by squeezing the vertical beam to 13º while keeping 182º around the mast, and the CAS2+++ reaches 13.5 dBi with both beams narrow, so it must be aimed.
Polarization
Polarization is the direction of the electric field. The antennas at both ends should match for the best result; outdoors on a line-of-sight link it matters most, indoors reflections make it less critical.[4] Many ComAnt yagis are listed as "vertical/horizontal". The cross-polarized yagis (CAX) are "dual feed", and CompleTech lists the CAX polarization as "circular/slanted". (ComAnt catalog)[3]
Downtilt
CompleTech's TP tilting plate "allows, depending on the mounting orientation, a mechanical down or up tilting up to 45 degrees. The tilting angle is continuously adjustable." (ComAnt catalog, p. 81)[3] Several stacked arrays also list "field adjustable pattern, optional beam tilting".[3]
Gain and the law
On US unlicensed bands, more antenna gain can mean turning the radio down.[5] See the 6 dBi rule.
CompleTech parts for this
- Yagis, yagi arrays and other directional antennas: directional: one direction, more gain, narrow beam
- Bidirectional broadside arrays: two opposite directions, e.g. along a pipeline or a road
- Offset-pattern collinears and dipoles: offset patterns: mostly around the mast with a bias
- Mounting, tilting and isolation kits: TP tilting plates for downtilt
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Request a quoteSources
- Texas Instruments application report SWRA048, ISM-Band and Short Range Device Regulatory Compliance Overview (May 2005)
- 47 CFR 27.4
- CompleTech ComAnt catalog, March 2026 (PDF, hosted by Gross Automation)
- Texas Instruments Application Note AN058, Antenna Selection Guide (SWRA161B)
- 47 CFR 15.247