VSAT Antenna Size Selection: 0.75m, 1.2m, 1.8m, or Larger?

Published by Bravosatcom · VSAT Engineering Series

Antenna diameter is the single most consequential hardware decision in a VSAT installation. It sets your gain, drives your BUC power requirement, determines your pointing tolerance, and dominates the cost of the mount and foundation. Oversize the dish and you pay for steel, shipping, and civil works you did not need. Undersize it and the link never closes — and no amount of BUC power will fully compensate.

This guide covers how antenna size actually affects performance, what the standard sizes deliver at Ku- and C-band, and how to select a diameter from your link budget rather than from habit.

Why Diameter Drives Everything

A parabolic antenna concentrates RF energy. The larger the reflector, the more energy it collects on receive and the more tightly it focuses on transmit. The relationship is governed by:

G = 10 · log₁₀( η · (πD/λ)² )
Where G is gain in dBi, η is aperture efficiency (typically 0.60–0.70 for a quality offset-fed VSAT antenna), D is diameter in metres, and λ is wavelength in metres.

Two consequences follow directly from the D² term:

Doubling the diameter adds 6 dB of gain. A 2.4m dish has 6 dB more gain than a 1.2m at the same frequency. That 6 dB applies on both the transmit and receive path.
Gain rises with frequency for a fixed diameter. A 1.2m dish has roughly 6 dB more gain at Ku-band than at C-band, which is why C-band sites need much larger reflectors for equivalent performance.

The practical effect on the link budget is that antenna gain is the cheapest dB you can buy. Going from a 1.2m to a 1.8m antenna adds about 3.5 dB — achieving the same uplink improvement with BUC power alone would require more than doubling the amplifier.

Gain by Diameter and Band

Figure 1 — Antenna gain by diameter at Ku-band. Every doubling of diameter adds 6 dB on both the transmit and receive path.

At 65% aperture efficiency, the standard sizes deliver:

Diameter	Ku Rx (11.7 GHz)	Ku Tx (14.25 GHz)	C Rx (3.95 GHz)	C Tx (6.175 GHz)
0.75 m	37.4 dBi	39.1 dBi	—	—
0.98 m	39.7 dBi	41.4 dBi	—	—
1.2 m	41.5 dBi	43.2 dBi	—	—
1.8 m	45.0 dBi	46.7 dBi	35.6 dBi	39.4 dBi
2.4 m	47.5 dBi	49.2 dBi	38.1 dBi	41.9 dBi
3.8 m	51.5 dBi	53.2 dBi	42.1 dBi	45.9 dBi

Note the C-band columns start at 1.8m. Below that diameter, C-band gain is too low and the beamwidth too wide for practical use on a commercial network.

Beamwidth: The Hidden Cost of a Bigger Dish

Higher gain comes with a narrower beam. The 3 dB beamwidth is approximated by θ ≈ 70 · λ / D (degrees). This matters operationally: a 3.8m antenna must be pointed roughly five times more precisely than a 0.75m to achieve the same fraction of peak gain.

Figure 2 — Beamwidth narrows and wind area grows as diameter increases. Pointing tolerance is roughly 10% of the 3 dB beamwidth.

A large dish is far less tolerant of mount flex, thermal movement, and foundation settling. If you specify a 2.4m or larger antenna, you must also specify a mount and foundation rigid enough to hold ±0.08° through wind and temperature cycling — otherwise the extra gain is simply lost to pointing error.

Wind Loading and Structural Cost

Wind force on a dish scales with reflector area, which scales with D². The structural consequences compound quickly:

A 1.2m antenna presents about 1.1 m² of area and typically mounts on a non-penetrating roof frame with ballast, or a light wall bracket.
A 2.4m antenna presents about 4.5 m² — four times the force — and generally requires a concrete foundation with anchor bolts.
A 3.8m antenna presents about 11 m² and needs an engineered foundation sized for the site’s design wind speed.

Most commercial VSAT antennas specify operational wind (full performance, typically 65–80 km/h), degraded-operation wind, and survival wind (stowed, typically 200 km/h). In the GCC, the design driver is usually a combination of sustained summer heat and shamal wind events. Confirm the survival rating and the foundation loading figures from the manufacturer’s structural datasheet before pouring concrete — retrofitting a foundation is far more expensive than sizing it correctly the first time.

Selecting Size from the Link Budget

The correct workflow is to size the antenna from the required EIRP and G/T, not from a rule of thumb:

Obtain the link budget from your satellite operator. It will state the required station EIRP in dBW and the required receive G/T in dB/K for your specific site location and service plan.
Calculate available EIRP for each candidate size. EIRP = BUC output power (dBW) + antenna transmit gain (dBi) − IFL and feed losses (dB).
Calculate G/T for each candidate size. G/T = antenna receive gain (dBi) − 10·log₁₀(system noise temperature in K). System noise temperature is dominated by the LNB noise figure and antenna sky noise.
Select the smallest diameter that meets both requirements with margin. Target 1–2 dB above the operator’s stated minimum to allow for ageing, pointing drift, and manufacturing tolerance.
Sanity-check the mount and foundation. If the selected size requires civil works the site cannot support, revisit the BUC power or the service plan rather than under-sizing the antenna.

Do not size for clear sky alone. The link budget must include rain fade margin appropriate for your region and availability target. In the Gulf, Ku-band rain margin of 4–6 dB for 99.5% availability is typical; tropical sites need considerably more, which is a large part of why C-band remains common in sub-Saharan Africa.

Practical Size Recommendations

Figure 3 — Size selection matrix by application. Note how the mounting requirement escalates faster than the diameter.

0.75m – 0.98m (Ku-band only)

Consumer and light-commercial broadband, temporary deployments, and flyaway systems where portability dominates. Adequate for a few Mbps on a strong HTS spot beam. Not suitable for edge-of-beam locations or any application with a high availability requirement.

1.2m (Ku-band)

The workhorse size for fixed commercial VSAT in the GCC and most of the MENA region. Good balance of gain, manageable wind loading, and straightforward mounting. Suits typical office, retail, and small remote-site connectivity of 2–20 Mbps.

1.8m (Ku-band or entry C-band)

Specified when the site is toward the edge of the satellite footprint, the availability target is above 99.5%, or throughput requirements are high. This is also the practical minimum for C-band remote terminals. Requires a proper foundation.

2.4m (Ku or C-band)

Oil and gas sites, mining camps, broadcast contribution, and any location where an outage is expensive. The extra 2.5 dB over a 1.8m buys meaningful rain margin. Expect a concrete pad and a crane or lifting equipment for installation.

3.8m and larger

Hub stations, teleports, and high-value contribution links. At this size the antenna is an engineered installation, not a field deployment — factor in structural design, access for maintenance, and de-icing or heating in relevant climates.

Frequently Asked Questions

Can I use a smaller antenna and a bigger BUC to compensate?

Only on the transmit path, and only up to a point. A larger BUC increases EIRP, so it can substitute for transmit gain. But it does nothing for the receive path — G/T depends on antenna receive gain and LNB noise figure, and no amount of transmit power improves your downlink. If the link budget fails on G/T, you must increase antenna size. There is also a practical ceiling: satellite operators specify maximum off-axis EIRP density to limit interference into adjacent satellites, and a small dish with a large BUC can exceed it because the wider beam spills more energy toward neighbouring orbital slots.

What aperture efficiency should I assume if the datasheet does not state gain?

Use 0.65 for a quality offset-fed antenna from an established manufacturer, and 0.55–0.60 for a budget or unbranded reflector. Efficiency accounts for feed spillover, surface accuracy, blockage, and illumination taper. If a manufacturer quotes gain that implies efficiency above 0.70, treat the figure with caution and ask for a measured antenna pattern.

Does the antenna size need to match on transmit and receive?

It is the same reflector, so yes — one diameter serves both paths. The gain differs between them only because the frequencies differ. When you evaluate candidate sizes, check the transmit gain against the EIRP requirement and the receive gain against the G/T requirement separately, because one of the two will usually be the binding constraint.

How much does surface accuracy matter?

Significantly at Ku-band and above. Reflector surface errors cause phase errors across the aperture, reducing efficiency. The tolerance scales with wavelength, so a surface deviation that is negligible at C-band can cost real gain at Ku- or Ka-band. This is the main reason a cheap reflector often underperforms its published gain figure — and why it is worth requesting the manufacturer’s surface accuracy specification for antennas 2.4m and above.

Should I oversize the antenna to future-proof the site?

Modestly, yes. Moving up one size at initial installation is far cheaper than replacing an antenna and foundation later, and the extra margin protects against service plan upgrades, satellite changes, and gradual performance degradation. But the cost curve steepens sharply above 2.4m, and the pointing and structural requirements grow with it. Going one size up is prudent; going two is usually not.

Selecting an Antenna for Your VSAT Site?

Bravosatcom supplies VSAT antennas from 0.75m to 3.8m, with matching mounts, feed assemblies, BUCs, and LNBs for installations across the GCC and MENA region.

Talk to our technical team →