New wideband RF amplifiers expand test capabilities

This article originally appeared in the June'22 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.

Fast-changing technology trends make it hard for RF equipment developers and test organisations to keep up with the pace. There is plenty of room for improvement in traditional tasks – let alone the complexities emerging from 5G mobile communications standards, eMobility with its assistance systems, emerging vehicle-to-vehicle communication solutions, and defence systems such as drone jammers. Moreover, there is increased demand for robust equipment to ensure high availability with low downtime for the customer.

These are some of the driving forces behind a major extension of Rohde & Schwarz’s RF test solutions portfolio, with the introduction of a new wideband RF amplifier platform – the R&S BBA300 family. New broadband amplifiers are a major advance on existing amplifiers for development and product validation tests in quality assurance and in the development and production of components as well as in EMC testing. This all-new design is more than just an extension of the existing R&S BBA130/BBA150 families. Not a replacement, either. The new broadband amplifiers ensure outstanding wideband RF performance, enabling dependable EMC test and measurement results. Key advances include high linearity, outstanding harmonic performance, and excellent noise characteristics.

The challenge of robustness in EMC tests

In EMC testing, especially immunity testing, strong, defined interference fields are generated by a generator-broadband amplifier-antenna system. The devices under test (DUT) are exposed to this electromagnetic interference field in EMC chambers and tested for susceptibility to interference. Modulated test signals of all types are swept over the entire frequency range of e.g. 380MHz - 6GHz. Cables, antenna, chamber and the DUT reflect the energy fed to the broadband amplifier as reflected power. The ratio of forward power to reflected power is represented by the voltage-standing-wave-ratio (VSWR). The excess energy generated by the reflected power must be dissipated as heat.

Robust wideband amplifiers provide the specified P1dB RF output power even with 50% reflected RF power (VSWR 6:1). Even in the event of a short circuit and open circuit at the RF output, these amplifiers deliver up to 50% of their nominal RF output power. Appropriately sophisticated cooling concepts ensure that the excess energy is dissipated.

An intelligent, modular mechanical concept ensures a very compact, flexibly configurable and service-friendly broadband amplifier.

High linear RF power for PIM tests

Another problematic emerging test requirement is for fast and accurate passive intermodulation measurements (PIM). At very high-power levels, PIM can occur in devices such as cables, connectors, and duplex filters. It is a major consideration for base station transceivers, where the frequency of PIM signals may coincide with the receiver path frequency of the duplex filter, hence degrading receiver sensitivity. Because of this, PIM testing of duplex filters during production is essential. Two tones need to be applied to the DUT, ideally swept in both power and frequency to achieve this.

High linear RF power for PIM tests Another problematic emerging test requirement is for fast and accurate passive intermodulation measurements (PIM). At very high-power levels, PIM can occur in devices such as cables, connectors, and duplex filters. It is a major consideration for base station transceivers, where the frequency of PIM signals may coincide with the receiver path frequency of the duplex filter, hence degrading receiver sensitivity. Because of this, PIM testing of duplex filters during production is essential.

Two tones need to be applied to the DUT, ideally swept in both power and frequency to achieve this.

A vector analyser with two internal sources is used, which can generate two frequency-shifted tones and receive, rapidly sample and evaluate them simultaneously. The two tones are applied to the linear R&S BBA300 broadband amplifiers with outstanding noise power density (as low as –110 dBm/Hz), and excellent harmonic performance (down to –25 dBc) to generate the required high power levels. Offering frequencies from 380MHz up to 6GHz and output power from 15W to 180W, these amplifiers are ideal for extremely fast, highly accurate and reproducible PIM measurements.

Coexistence – a growing problem for smart solutions

Today’s T&M environment brings another growing challenge: that of ensuring the performance of new and emerging smart-home devices. Wireless speaker systems, thermostats, home security and monitoring systems, domestic robots, smoke/CO detectors, lighting, home energy consumption monitors, door locks, refrigerators, laundry machines and water detectors. All these products come with an integrated wireless communication module that supports some form of WLAN, LPWAN or Bluetooth technology. The additional connectivity features bring particular challenges – not least meeting compliance requirements.

The issue here is wireless coexistence, which ensures high quality of service in real-world use, together with security and product compliance. The intended use-case for DUTs needs to be defined in order to identify the baseline electromagnetic environment and the corresponding functional performance of the wanted communications system. Based on the information, it is possible to define the worst-case RF scenario and later recreate it for testing.

Take the example of a smart washing machine connected to the home WLAN network. The appliance is in an area where the electromagnetic environment is mostly time-invariant and stable. The worst-case scenario occurs when the washing machine is located in an area with a very weak WLAN signal and a smartphone running an active Wi-Fi hotspot and Bluetooth application and transmitting at maximum power is placed on top of or next to the washing machine. What happens if a smartwatch is brought into the equation? The test challenge is to recreate this exact electromagnetic environment and test conditions inside an anechoic chamber in a repeatable manner. Here, due to its ultrawide bandwidth, the R&S BBA300 high power amplifier provides the perfect way to boost the signal level during radiated testing. A baseline functional performance test is performed and the results for all the relevant KPIs (such as throughput data rate, PER, BLER, video and audio performance) are recorded.

At a glance

The R&S BBA300’s all-new design extends through its mechanical aspects, software, and RF design, delivering flexible and robust RF performance. The family’s design and manufacture ensure excellent linearity, outstanding noise power density (as low as –110 dBm/Hz), and excellent harmonic performance (down to –25 dBc).

Rohde & Schwarz’s robust design and manufacturing provide resilience against all forms of mismatch. With self-protection built-in, the instruments are robust against RF mismatch up to VSWR of 6:1. Intelligent protection ensures high availability, even in the event of component failures. The amplifier runs as long as possible.

The amplifier design offers the flexibility to realise a broad array of customer system setups with multiple switch options, offering high flexibility, scalability, with upgradable frequency and power. The instruments’ upgradability makes it easy for customers to expand their systems, building upon their initial investment.

User changeable amplifier characteristics

The new broadband amplifiers come with a new software platform for amplifier control and monitoring. Different roles with graduated rights to be defined for configuration and operation. Dedicated access to the comprehensive parameter sets can be granted. The new operating concept gives users a modern, role-based operation supported by an optional 10" touchscreen (R&S BBA-B200), provides a unique user experience with straightforward operation on-site or remotely using a web GUI.

The models benefit from numerous smart settings and activation functions. Starting from the basic functionality, the user can unlock additional functions via keycode. This allows the amplifier's transmission characteristics (e.g. gain, operating point, power mode) to be adapted to the customer's requirements.

The user adjustable operating point gives the amplifiers high linearity in class A mode or faithful reproduction of pulsed signals in class AB mode. With the adjustable output power mode, the user has a choice between high mismatch tolerance for applications where the amplifier still has to deliver power under high VSWR conditions or higher output power, for applications where the amplifier is used in well matched set-ups. (Available with R&S BBA-K1 option).

Via a standard Ethernet interface, test sequences can be automated using remote control SCPI commands. The SNMP protocol can optionally be enabled for remote control. Rohde & Schwarz at embedded world: Hall 4, Booth 218