What changes in real installations?

In practice, the difference between active vs passive GPS antennas is not just about gain; it’s about how well the system handles real-world losses.

A passive antenna works well when:

• The antenna is placed directly on the PCB
• The RF path to the receiver is very short
• There is a clear view of the sky

However, performance can degrade quickly if:

• The antenna is inside an enclosure
• The ground plane is limited
• The environment introduces attenuation or interference

An active antenna helps compensate for these losses by amplifying the signal early in the signal chain. This improves the signal-to-noise ratio (SNR) at the receiver input and helps maintain reliable satellite tracking.

Power and integration considerations

Active antennas require a DC supply, usually delivered via the RF cable (bias tee).

• Typical operating voltage: 3.3 V to 24 V
• Without power, the LNA becomes a loss element
• Performance may drop below that of a passive antenna

This is a common integration issue in GNSS designs.

Selection flow chart for choosing between active and passive GNSS antennas

The post Active vs passive GPS antennas: What’s the Difference? appeared first on Siretta Limited.

In dense urban environments, often referred to as urban canyons, this effect becomes more pronounced. The receiver may only see a limited number of satellites, and some of those may be reflections rather than true line-of-sight signals. Although modern receivers attempt to mitigate this in software, they cannot fully correct poor signal conditions at the antenna.
In practice, this shows up as position drift, slow fix times, or large jumps in reported location, particularly when moving between open areas and built-up streets.

Direct and reflected GNSS signals in urban environments. Buildings block line-of-sight signals and create delayed reflections, leading to positioning errors.

How to improve GPS accuracy in urban environments

1: Antenna placement

The antenna location has the biggest impact on performance.

It should be positioned as high as possible with a clear view of the sky. Mounting low down, inside an enclosure, or close to vertical metal surfaces will increase reflections and reduce direct signal reception. In vehicle applications, a roof-mounted antenna will consistently outperform one placed on a dashboard or inside the cabin.

Keeping distance from nearby metal surfaces is also important. Vertical conductive surfaces act as reflectors and can significantly increase multipath errors if the antenna is mounted too close to them.

2: Antenna type

For static installations, a patch antenna with a suitable ground plane is generally preferred. The ground plane helps maintain a stable radiation pattern and reduces sensitivity to low-angle reflected signals.

For mobile applications, external active antennas are typically used. Antennas such as the Mike 19 provide a practical balance of gain and radiation performance for vehicle or asset tracking, particularly when mounted with a clear view of the sky.

In embedded designs where the antenna must be located inside the product, ground plane size and placement become limiting factors. In these cases, compact active antennas such as the Echo 52 are designed to operate with reduced ground planes while maintaining acceptable polarisation and performance.

3: Antenna gain and noise

GNSS signals are very weak when they reach the earth, so an active antenna with a low-noise amplifier is typically required.

Lower noise figure improves signal quality, but gain must be considered in the context of the full system. Too little gain will result in poor tracking, while excessive gain can raise the noise floor or make the system more susceptible to interference from nearby radios.

4: Cabling

Cable losses can significantly affect performance, particularly at GNSS frequencies.

Where possible, the cable between the antenna and receiver should be kept short. If a longer cable is required, a low-loss coaxial cable should be used and the antenna gain selected to compensate for the additional attenuation.

5: GNSS receiver capability

Using a receiver that supports multiple constellations such as GPS, GLONASS and Galileo can improve performance in urban environments by increasing the number of available satellites and improving positioning geometry.

Multi-frequency operation can also help reduce certain error sources, although it does not eliminate multipath caused by reflections from nearby buildings.

Summary

Poor GPS accuracy near buildings is usually caused by a combination of signal blockage and multipath reflections, rather than an issue with the receiver itself. The most effective improvements come from optimising antenna placement, ensuring a clear view of the sky, and selecting an antenna suited to the installation.

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Improved data throughput in combination with signal quality are two essential requirements for modern cellular networks such as LTE-A and 5G. The original release of LTE in the 3GPP release 8 went some way to meeting these needs by supporting flexible bandwidths. It was release 10 and the utilisation of carrier aggregation and MIMO (Multiple-input-multiple-output) antennas which support high data rates in both the uplink and downlink channels that addressed the requirements more fully.

Minimised fading and supporting higher data throughput required a different type of modulation. Traditionally four types of modulation were used PSK (phase shift keying), FSK (frequency shift keying), ASK (amplitude shift keying) and QAM (Quadrature amplitude modulation). LTE needed a different approach and implemented OFDM (Orthogonal frequency division multiplexing) in the downlink and SC-FDMA (single carrier frequency division multiple access) in the uplink. OFDM is the basic signal format used in LTE giving the highest data rates and allowing for higher modulation techniques that the historical forms of modulation could not achieve. The OFDM carrier signal is the sum of several orthogonal sub-carriers with baseband data on each sub-carrier being independently modulated with QAM. This baseband signal is typically used to modulate a main RF carrier which can be referred to broadly as the channel.

OFDM

OFDM gives a method of encoding digital data transmission using many closely spaced sub-carriers modulated with a low-rate data stream. These signals are phased differently to reduce interference with other signals, eliminating fading and noise.

In LTE, OFDM has a maximum of 2048 different sub-carriers at 15kHz spacing, the 3GPP specification defines that all mobile devices have all 2048 sub-carriers however that is not the requirement for base stations with most currently offering 72, there will be a move towards 2048 as part of future infrastructure deployments.

QAM (Quadrature amplitude modulation) in LTE

There are four different modulations available QPSK / 16QAM / 64QAM / 256QAM by combining OFDM with the maximum number of carriers and utilising QAM256 you will achieve the highest data rate throughput. The LTE modulation is negotiated by the equipment depending upon the conditions. When there is a greater signal to noise ratio the higher order modulation QAM256 can be used and enhances data throughput. When lower signal to noise ratio is experienced, it makes it more demanding to extract the sub-carrier’s modulation and lower modulation rates are used. The Lower the modulation rate the less bits per transmission can be achieved and therefore the less bandwidth is available to transmit data across the channel.

Single-carrier FDMA (SC-FDMA)

SC-FDMA is a frequency-division multiple access scheme. This scheme enables multiple users to communicate with a single base station. SC-FDMA is a popular method in uplink communications in LTE where lower peak-to-average power ratio (PAPR) benefits the mobile terminal in terms of transmit power efficiency and reduced cost of the power amplifier.

The performance gap between SC-FDMA and OFDMA is small but SC-FDMA’s low PAPR means it is preferable in uplink transmission, where transmitter power efficiency is of paramount importance.

MIMO enhancing signal strength

MIMO (multiple input, multiple output) is an antenna technology used in wireless communications where the capacity and signal strength for both transmit and receive signals are enhanced through the use of multiple antennas improving spectral efficiency. This approach is adopted in LTE to further increase reliability and to improve the signal to noise ratio. Greater signal to noise ratios allows for higher modulation rates, improving data throughput by maximising the quadrature amplitude modulation being used. These types of antennas are available from Siretta in their MIMO antenna ranges.

MIMO Antennas to support higher data rates

3GPP release 13 specified MIMO modes for up to 16 transceivers at the base station, release 14 however is expected to allow as many as 64 bringing efficiency gains for downlink transmissions by utilising various antenna groups (2×2 through 4×4 up to 8×8 and so on to 64×2). As an example, you can expect a 2.5x gain in spectral efficiency using a 16×2 antenna configuration compared to a 2×2 antenna configuration, while 64×2 configuration shows a 3x gain.

The gain available from a 64×2 configuration compared to 8×2 is 50 percent. Some transceiver configurations have four or eight columns of polarised antenna elements, while the 2×2 transceiver configuration has only one column of polarised antenna.

Aggregation of Antenna Signals

You can have up to 2048 sub-carriers so by combining more of these together, either in the same or different bands it is possible to increase the bandwidth available and, in this way, increase the capacity of the link.

The target figures for data throughput in the downlink channel is 1Gbps for 4G LTE. Even with advanced efficiency it is impossible to achieve this throughput. The only way to achieve the higher data rates is to also increase the overall bandwidth used. Various methods of Carrier aggregation can aid this:

Contiguous: The Intra-band contiguous carrier aggregation is the easiest form of LTE carrier aggregation to implement. Here the carriers are adjacent to each other. The aggregated channel can be considered as a single enlarged channel from the RF viewpoint, only one transceiver is required within the terminal, whereas more are required where the channels are not adjacent.

Non-contiguous: Non-contiguous intra-band carrier aggregation is more complicated. No longer can the multi-carrier signal be treated as a single signal and therefore two transceivers are required.

3GPP allows for up to five 20MHz carriers to be aggregated enabling a maximum bandwidth of 100MHz, although in practice the practical limit is two or three. These aggregated carriers can be transmitted in parallel to or from the same unit, thereby enabling a much higher throughput to be obtained.

Conclusions for Enhancing LTE and 5G Data Rates

LTE and 5G were designed to enable higher data rates, with multiple carriers, additional carrier aggregation and the ability to use multiple antenna paths for both transmit and receive which all go to producing a high-quality wireless link. The use of MIMO antennas combines signals and improves signal quality whilst enhancing data rates. Channel aggregation enhances bandwidth by combining multiple frequency carriers.

Historical limitations exist with some base stations only operating at the lower QAM, however, in time all cells will be upgraded to allow the highest rates. Geographic data and local population will influence this upgrade process.

When designing your application, it is possible to improve the data rates and operating performance of the entire system using MIMO in your design and Siretta can help you to select the best fit commercially for your end application from our extensive range of products and solutions.

Siretta understand the challenges faced and have developed their own Antenna selector tool www.siretta.com/products/antennas/antenna-selector/ to reduce time to market. Stretta’s portfolio includes cellular modems & terminals, routers, cellular network analysers, RF antennas including MIMO antennas and solutions for WLAN, LoRa and Sigfox. Siretta offer RF cable assemblies and RF accessories. Frequencies are typically within the 75MHz – 5.8GHz range covering the HF, VHF, ISM, Cellular, GNSS frequencies.

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What do you do when you want to represent a wireless IoT supplier with unrivalled product offering?

You choose Siretta.

Across Europe, dedicated design-in distributors see Siretta as a reliable supplier they can work with… but why?

At Siretta we design and manufacture our cellular wireless product range to the highest standard and offer an unmatched range of products.

From low-cost solutions to products that include GPIO and GPS, our range of 2G, 3G and 4G standard modems cover a host of features. For a more advanced solution, our range of intelligent managed modems enable customers to transfer data over cellular network, without having to write their own software or have knowledge of how the technology operates.

Our range of 3G and 4G routers with Ethernet, WiFi and GPS options are also designed with the industrial applications in mind.

To further extend our offering, our range of antennas in the most popular wireless technologies and mounting types and variety of connectors is unrivalled. From small PCB type antennas for embedded applications to outdoor types in low signal locations with low loss cable extensions, we have solutions that help our customers get the optimum use from their wireless products.

Finally, if our customers want to test the signal strength levels for their products prior to choosing the most suitable SIM card, our SNYPER family of 3G and 4G signal strength analysers are easy to operate and provide the confidence you need when choosing a provider that will give you the best service.

So, quite simply, that is why all major component broad-line distributors have chosen Siretta as their wireless IoT supplier of choice.

Our distributors have made their choice, now it’s your turn!

The post Distributors choose Siretta as their IoT supplier of choice appeared first on Siretta Limited.

I had a call from a customer the other day saying a competitor’s cellular Yagi antenna was no good, even though they claim it is very high gain. As Siretta offer a number of good quality Yagi antennas, I thought this would be a sales opportunity. I asked few more questions only to find out he had installed his antenna facing the building. I explained Yagi antennas are good… but not that good and he should really install his antenna in as clear a line of sight to the base station as possible to get a good result. A couple of days later he called back thanking me. It seems I can spot a good sales opportunity but not the sales.

Anyhow, the question of whether to use a Yagi or an omnidirectional antenna is a valid one.

In many situations where signal strength is weak (long range – cellular or short range – ISM) many users assume that using a high gain Yagi (directional) antenna will solve their problem.

However, there are a few points to take into consideration:

• Yagi antennas – by definition – are tuned to a very narrow receiving angle, meaning that if not correctly positioned they will not perform well, whatever the gain.
• RF signals will only go in a straight line if there is nothing blocking them. Therefore, if there are high buildings around, signals will bounce, providing multipath signal. A Yagi antenna with its narrow receiving angle will not necessarily receive these signals.
• In many cellular (2G, 3G, 4G) applications users automatically assume that the nearest base station will provide the strongest signal. This is not necessarily the case and users should try pointing their antenna to other available base stations and test.

On the other hand, omnidirectional antennas have lower gain as they cover a greater area, but they might be what is needed if you can’t avoid obstacles in your application.

So, what is the best antenna to use? The answer is I don’t know, and the users will not know either unless they try different types of antennas. This may be more time consuming and costly to start with but will save time and money in the long run. The best practice is to place your antenna as high as possible to avoid large constructions such as buildings and trees, in which case the higher up they are there will be more losses through the cable.

This means you should use low loss cables, and as it happens, Siretta manufacture a good number of low loss cables with different cable lengths and vast array of connector combinations. Try them, they are good.

If your equipment is in an area with lots of buildings, then the best type of antenna to use is an omnidirectional one. If there is a clear line of sight to the transmitting modem, then a Yagi antenna may be the best.

At Siretta we have a number of high quality directional and omnidirectional antennas for outdoor use (Oscar Family) manufactured with low loss cables and covering a wide variety of frequencies. They are used by companies that install routers, meters (utility and industrial), security companies, car parks and many others.

The post Yagi or not Yagi – that is the question appeared first on Siretta Limited.