Making Fast and Accurate Antenna Measurements

7/28/13

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October 27, 2008 1. Antenna Measurements, RCS and Range 2. A Faster, More Accurate Measurement Receiver 3. Antenna Applications 4. Conclusion 5. Contacts 6. Related links for more information Advanced technology improvements and new architectures are enabling increasingly complex antennas for a range of applications including radar and satellite communications in the aerospace and wireless industries. Complex antennas like the phased array beam-steering antenna, for example, can dramatically increase the amount of data necessary to fully characterize complex arrays and also increase overall test time. It is the antenna test engineer's responsibility to ensure that the antenna is accurately characterized and meets specification, but doing so quickly and accurately given this complexity can be challenging. It requires a solution that is fast, accurate, highly measurement sensitive, and able to handle large amounts of data.

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Antenna Measurements, RCS and Range When testing an antenna, the antenna test engineer must typically measure a number of parameters such as the radiation pattern, gain, impedance, or polarization characteristics. One of the techniques used to measure antenna patterns is the far-field range where an antenna under test (AUT) is placed in the far-field of a transmit range antenna. A second technique is the near-field range where the AUT is placed in the near-field and then the data is mathematically transformed to the far-field. Radar crosssection (RCS) measurements are used to measure the angle-dependent echo characteristics of radar targets. Depending on the antenna and the application, a nearfield, far-field or RCS range will be the preferred technique to properly determine the amplitude and/or phase characteristics of an AUT.

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Figure 1: Shown here is a simplified far-field antenna range example with MXG source and PNA-X Measurement Receiver with LO source. A typical antenna-range measurement system can be divided into two separate parts: the transmit site and the receive site (see Figure 1). The transmit site consists of the microwave transmit source, optional amplifiers, transmit antenna, and communications link to the receive site. The receive site consists of the AUT, a reference antenna, receiver, LO source, RF downconverter, positioner, system software, and a computer. On a traditional far-field antenna range, the transmit and receive antennas are typically separated by enough distance to simulate the intended operating environment. The AUT is illuminated by a source antenna at a distance far enough away to create a nearplanar phase front over the AUT's electrical aperture. Far-field measurements can be performed on indoorand outdoor ranges. Indoor measurements are typically made in an anechoic chamber specifically designed to reduce reflections off the walls, floor and ceiling. Measurement of an object's RCS is performed at a radar reflectivity range or scattering range. The first type of range is an outdoor range where the object is positioned on a specially shaped low-RCS pylon some distance down range from the transmitters. As with indoor far-field antenna measurements, an anechoic chamber is also commonly www.agilent.de/about/newsroom/tmnews/background/2008/27oct2008_pna-x_receiver.html

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used. Here the object is placed on a rotating pillar in the center of the chamber. The walls, floors and ceiling are covered by radar absorbing material to prevent corruption of the measurement due to reflections.

A Faster, More Accurate Measurement Receiver The new PNA-X Measurement Receiver from Agilent Technologies offers the speed, accuracy, sensitivity, and flexibility required for near-field, far-field antenna or RCS measurements (see Figure 2). Featuring a 30 percent faster data acquisition speed than any other antenna receiver on the market (400,000 data points per second simultaneously on each of five receiver channels), it sets a new industry standard for antenna test applications. In addition to its fast data acquisition speed, an optional Fast-CW mode enables a 500-million-point data buffer which allows users to stream infinite amounts of data directly to the network. It also provides 20 dB better receiver dynamic range than existing antenna receivers (134 dB @ 10 Hz IFBW), with up to 5 channels/unit.

Figure 2: The PNA-X measurement receiver is the fastest measurement receiver for antenna and radar cross-section measurement applications for radar and satellite communications where large volumes of data are required to fully characterize complex www.agilent.de/about/newsroom/tmnews/background/2008/27oct2008_pna-x_receiver.html

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antenna arrays. The PNA-X Measurement Receiver features an optional, built-in 26.5-GHz LO source with +10 dBm of output power which can be used as a signal source for remote mixers or frequency converters. It is also compatible with Agilent's MXG/PSG signal sources, existing 85309A distributed frequency converter and 85320A/B mixers. Combining the receiver with an MXG source typically results in a system speed improvement that is 10 times faster. The PNA-X Measurement Receiver is built on the Agilent PNA-X network analyzer technology platform and therefore provides a number of key benefits for antenna test applications, including: High Sensitivity The PNA-X Measurement Receiver is the direct 8530A replacement with fast throughput and low noise floor. Engineers can select from a minimum of 29 different IF bandwidths, optimizing sensitivity versus measurement speed to fit a particular measurement and application requirement. Increased Speed COM/DCOM features help the PNA-X realize extremely fast data transfer rates, while LAN connectivity through a built-in 10/100-Mbps LAN interface enables the PC to be distanced from the test equipment. These features enable remote testing as well as reduced test time. Flexibility and Accuracy For maximum flexibility, the PNA-X Measurement Receiver provides up to five simultaneous test receivers (A, B, C, D, and R); with each receiver capable of measuring up to 400,000 points of data. Further enhancing performance and improving measurement accuracy, the PNA-X Measurement Receiver supports synchronization with external signal generators. Security For secure environments, the PNA-X features a removable hard drive to completely ensure the security of the data it acquires.

Antenna Applications With its array of features and key benefits, the PNA-X Measurement Receiver can be easily integrated into near-field, far-field and RCS measurement systems. For far-field or large near-field antenna applications, the PNA-X Measurement Receiver-based system incorporates Agilent's 85320A/B broadband external mixers and 85309A distributed frequency converter (see Figure 3). Its optional, built-in 26.5-GHz synthesized source is used as the LO source for the 85309A LO/IF Distribution Unit.


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Figure 3: Depicted here are typical frequency converter and remote mixing configurations. The PNA-X Measurement Receiver's ability to obtain more than 400,000 points of data per second, makes it ideal for far-field antenna range applications. Extremely fast data processing is particularly useful in applications where ranges include active array antennas and data acquisition is therefore quite intensive. With faster data acquisition speeds, the IF bandwidth can be narrowed; significantly improving measurement sensitivity without increasing total measurement times. High-power pulses are often used in RCS measurements to overcome losses due to low device reflection and two-way transmission path loss. Receiver gating may therefore be required in a PNA-X RCS configuration to avoid overloading the receiver during the transmission of the pulsed-RF signal (see Figure 4).


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Figure 4: Typical RCS measurement configuration using a PNA-X network analyzer. Other features which make a PNA-X RCS configuration compelling include: Having the source and receiver integrated into the same instrument, with a choice of frequency ranges, is very cost effective in RCS applications. 100,000 data points are available per measurement trace. This provides extremely long alias-free down-range resolution for RCS measurements. The PNA-X has a removable hard drive to comply with data security requirements.

Conclusion Given today's increasingly complex antenna architectures and technologies, quickly and accurately characterizing an antenna and ensuring that it meets specification can be quite challenging. Agilent's PNA-X Measurement Receiver offers the speed, accuracy, measurement sensitivity, and flexibility required to accomplish this task. It's these capabilities which make the receiver so well suited for near-field, far-field antenna and RCS measurement applications. As a result, Agilent's PNA-X Measurement Receiver is quickly becoming an essential tool for ensuring today's antenna test engineer.

About Agilent Agilent Technologies Inc. (NYSE: A) is the world's premier measurement company and a technology leader in communications, electronics, life sciences and chemical analysis. The company's 19,000 employees serve customers in more than 110 countries. Agilent had net revenues of $5.4 billion in fiscal 2007. Information about Agilent is available on the Web at www.agilent.com. www.agilent.de/about/newsroom/tmnews/background/2008/27oct2008_pna-x_receiver.html

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Contacts Janet Smith +1 970 679 5397 [email protected]

See the following related links for more information Press Release: Backgrounder: Photos:

Agilent Technologies Introduces Industry’s Fastest Antenna Test Receiver - 30 Percent Faster than Existing Solutions (2008-October-27)

Defining A New Generation of Network Analyzers (2007-February-01)

PNA-X Measurement Receiver Photos: www.agilent.com/find/PNA-X-Receiver_images Agilent Documents: For more information, go to www.agilent.com/find/antenna or www.agilent.com/find/N5264A > More Press Releases > More Backgrounders

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Making Fast and Accurate Antenna Measurements

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