The satellite communication industry is now in the middle of a major transition. For many years, VSAT networks have been built mainly on GEO (Geostationary Earth Orbit) satellites located about 36,000km above the equator. However, LEO (Low Earth Orbit) constellations operating at an altitude of only 500 to 1,200km are expanding very rapidly.
As of July 2026, SpaceX Starlink has more than 10,700 satellites in orbit, and Amazon has started deploying its own constellation “Amazon Leo” (formerly Project Kuiper), with initial service planned within this year. Eutelsat OneWeb is also operating a constellation of about 600 satellites for enterprise and government users.
This rapid growth of LEO constellations does not mean the end of GEO VSAT. GEO satellites are still essential for broadcasting, maritime, backhaul and government networks. Instead, ground segment operators are now required to design and operate both GEO and LEO earth stations, and in many cases hybrid networks. In this column, we would like to explain how the LEO era changes the requirements for VSAT components such as BUC (Block Up Converter), LNB (Low Noise Block down converter) and reference oscillators, and what should be considered when selecting them.
How LEO Changes the Requirements for the Ground Segment
From the component point of view, the difference between GEO and LEO is not only the orbit altitude. The table below summarizes the main differences that affect the earth station design.
| Item | GEO VSAT | LEO Earth Station / Gateway |
|---|---|---|
| Satellite position | Fixed (one satellite, fixed pointing) | Moving (satellite passes in 5 to 15 minutes, continuous tracking and handover) |
| Round trip latency | Approx. 500ms | Approx. 20 to 50ms |
| Doppler shift | Negligible | Large and continuously changing (up to several hundred kHz at Ku/Ka-band) |
| Frequency band | C-band, Ku-band, Ka-band | Mainly Ku-band and Ka-band, wide channel bandwidth |
| Ground stations | Small number of large hub stations | Large number of gateway stations distributed worldwide |
| Duty cycle of equipment | Continuous operation with one link | Frequent handover, continuous operation with changing link conditions |
These differences directly affect the selection of RF components and timing devices. Below, we would like to look at each key component.
1. BUC Selection: Linearity, Efficiency and Wide Bandwidth
In LEO systems, the modulation schemes are generally higher order (16APSK, 32APSK and higher) to make maximum use of the limited pass time of each satellite. Higher order modulation requires better linearity of the transmit chain. Therefore, ACPR (Adjacent Channel Power Ratio) and P1dB with sufficient back-off margin become more important than simple saturated output power when selecting a BUC.
Also, LEO gateway networks require a large number of ground stations. Power consumption, size and weight of each BUC directly affect the total operating cost of the network. High efficiency GaAs and GaN based BUCs are strongly preferred for this reason.
We are handling the Nisshinbo Micro Devices (former New Japan Radio, NJRC brand) BUC lineup, which has a long track record in VSAT networks worldwide:
| Model | Band | Output Power | Feature |
|---|---|---|---|
| NJT8304 series | Ku-band (13.75 to 14.5GHz) | 4W (P1dB +36.0dBm min.) | High efficiency, compact 0.5kg housing, ACPR -29dBc typ. |
| NJT8306 series | Ku-band (13.75 to 14.5GHz) | 6W Linear | Slim type, reduced power consumption from the previous model |
| NJT8336 series | Ku-band | 16W | New generation GaN 16W class for high throughput terminals |
| NJT8371 series | Ku-band | 40W Saturation (+46dBm) | GaN based, for hub and gateway stations |
| GaN HEMT X-band BUC | X-band | Under development | GaN based high efficiency design (evaluation prototype available) |
For the details of each model, please refer to our previous articles or contact our sales department.
2. LNB Selection: PLL Type with External Reference is Becoming Standard
For the receive side, the selection between DRO (Dielectric Resonator Oscillator) type and PLL (Phase Locked Loop) type LNB becomes much more important in the LEO era.
A DRO type LNB is low cost, but its local oscillator frequency stability is typically +/-500kHz to +/-1MHz or more over temperature. In a GEO link with a fixed satellite, this can be acceptable for wideband carriers. However, in a LEO link, the received frequency is already moving continuously due to the Doppler shift. If the LNB local oscillator also drifts, the modem must compensate both at the same time, and carrier acquisition becomes difficult, especially for narrowband carriers.
A PLL type LNB locks its local oscillator to a stable reference (internal crystal reference, or external 10MHz reference supplied through the IF cable). The frequency stability improves to the ppm order, and the phase noise characteristic is also well defined. For LEO earth stations and for modern GEO networks using high order modulation, we recommend PLL type LNBs with an external reference input, so that the whole station (BUC, LNB, modem) can be synchronized to one high quality 10MHz reference.
As our lineup, we have introduced the flange type C-band PLL LNB NJS8496 series (RF 3.4 to 4.2GHz full C-band) in a previous article, and Ku-band PLL LNB models are also available. Please contact us for the details.
3. Reference Oscillator: The Timing Backbone of the Earth Station
In the LEO era, the most easily overlooked, but in fact the most fundamental component is the reference oscillator that supplies the 10MHz (or 100MHz) reference to the BUC, LNB, frequency converters and modems.
The phase noise of the reference oscillator is multiplied up to the RF frequency. For example, when a 10MHz reference is multiplied to a 14GHz Ku-band carrier, the phase noise is degraded by 20log(1400) = approx. 63dB. This means that the phase noise of the reference directly limits the EVM (Error Vector Magnitude) of the whole link. As higher order modulation such as 32APSK and 64APSK is used, the requirement for the reference phase noise becomes more severe.
In addition, LEO gateway stations must keep precise frequency and time synchronization for Doppler pre-compensation and beam handover. GNSS disciplined configurations are common, but the holdover performance during GNSS interruption depends on the stability of the local OCXO.
For these requirements, we can offer the following crystal device solutions:
| Product | Typical Application | Feature |
|---|---|---|
| Ultra-Low Phase Noise Crystal Oscillator | Station reference, up/down converter reference | Phase Noise less than -160dBc/Hz (10kHz offset class) |
| OCXO AXK-OLP series | Gateway reference, GNSS holdover | Low phase noise and high frequency stability over temperature |
| Low Jitter CMOS VCXO (AOK-C9070LP etc.) | Modem and FPGA clock, jitter cleaner reference | 50.000MHz to 156.250MHz, low jitter CMOS output |
| Wide Temperature Range Crystal Resonators / TCXO | Outdoor unit (ODU) built-in reference | Stable operation in -40 to +85deg C outdoor environment |
Since the antenna outdoor unit is exposed to severe temperature conditions, wide temperature range and aging characteristics are also important selection points for the built-in crystal devices of BUCs and LNBs. We can propose the suitable crystal resonator, TCXO, VCXO and OCXO according to your required frequency, stability and phase noise. Custom specifications are also welcome.
Summary: Selection Points for the LEO Era
To summarize, we recommend to check the following points when selecting VSAT components for LEO and GEO/LEO hybrid systems:
- BUC: Check ACPR and linear output power (not only saturated power), power efficiency, and size/weight for multi-site deployment.
- LNB: Select PLL type with external reference input for stable carrier acquisition under Doppler shift. Check phase noise specification, not only noise figure.
- Reference oscillator: Check phase noise at the multiplied RF frequency and holdover stability. The reference quality limits the performance of the whole station.
- Environment: Confirm wide temperature range operation (-40 to +85deg C class) for outdoor units.
The LEO constellation era is a big opportunity for the ground segment industry, and the number of earth stations and terminals will continue to increase. If you are developing or procuring equipment for LEO gateways, GEO VSAT or hybrid networks, we will be pleased to support your component selection — from BUC and LNB to the crystal devices inside them.
For specification details, please feel free to contact our sales department. If you inquire about the specifications you want, we will review with our technical department.
*Specifications, designs and service contents described are subject to change without notice. Please confirm the details to our sales.*