Non-Invasive Near-Field Scanning Using NeoScan

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Non-Contact Ultra-Near-Field Scanning

One of the most unique features of the NeoScan system is the very small size of its field probes and the absence of any metallic parts at the probe tip. As a result, you can position a NeoScan field probe very close to the device under test (DUT) without perturbing the ambient electric or magnetic fields. In addition to the very small footprint of the EO probe, its true spatial resolution is driven by the spot size of its laser beam, which is less than 10μm. These aspects of the NeoScan system, i.e. non-invasiveness and very high spatial resolution, are very critical for probing and characterizing the fields on the surface of microwave and millimeter wave active or passive devices.

VIDEO: Mapping the fields of a CPW thru line.

When mounted on a computer-controlled XY positioner, the probe can scan the surface of your device and create a field map in real time. You can generate maps of the tangential and normal components of the field displaying the amplitude and phase of the respective field components over the entire scanned area. The turnkey NeoScan system comes with a precision computer-controlled XY translation stage and probe holder fixture. A visual software interface allows you to easily set up the scan area and run a near -field scan, or control the probe motion at your discretion point to point. You can observe and monitor the evolution of the field maps on the screen as the probe step through the designated scan surface. At the end of a field scan, you can save, plot and manipulate the collected field data.

NeoScan field probe scanning the surface of a coplanar waveguide (CPW) thru line.
A close-up picture of the NeoScan field probe scanning the surface of a CPW thru line. Pay attention to how narrow the CPW slots are and how close the probe tip has been placed above the line.

Thanks to their optical nature, NeoScan probes provide a very large operational bandwidth. Using the same EO probe, you can measure fields at very low frequencies down to 20MHz or at very high frequencies up to 20GHz. This offers a significant advantage over the conventional near-field scanning systems which require a large set of metallic probes of different types and sizes to cover different frequency bands. The figure below shows the measured field maps of a CPW thru line at three different operational frequencies: 1Ghz, 5GHz and 10GHz, using the same probe and DUT setup. All you need to do is to change the frequency of the RF signal generator feeding the DUT.

The field maps along the CPW thru line measured at different frequencies.

An Indispensable RF Diagnostic Tool

NeoScan provides detailed field maps of passive and active devices and circuits including RFICs and MMICs. Such invaluable information can be used for effective design validation, performance evaluation and fault isolation at various parts of your RF system.

Detecting Field Emissions & Device Package Evaluation

NeoScan can be effectively used to detect and measure spurious field emissions. Therefore, it can be utilized as part of EMC/EMI testing and certification for many electrical and RF products. Our miniaturized field probes will be a surprising delight to RF test and evaluation (T&E) engineers, who are typically accustomed to very large and bulky field probe or booms, or have to use large log-periodic or horn antennas for ultra-wideband measurements.

Another important application of field emission measurement is diagnostics of packaged RF and electronic devices. Device packages and shielding are usually designed using computer simulation or based on experience, rules of thumb and accepted practices. The device designers typically evaluate the effectiveness of their packages based on the measured port characteristics of their devices. If the performance is not desirable, there is very little they can do to diagnose the cause of the problem. This usually leads to lengthy and costly design iteration cycles. NeoScan can shed light on the performance of your device package by measuring the radiated field penetrating outside of the shielding. High resolution field map can indeed identify and locate all the hot spots accurately without perturbing the emitted field distribution outside the package. The figure below shows the field maps of two packaged RF switches at three different frequencies. The field maps on the left were measured on the surface of the original packaged device. They show strong unwanted field emissions through the shielding package. The field maps on the right correspond to an improved package design for the same switch device.

Using NeoScan field maps to identify and locate RFIC package emissions and leakage.

Near-Field Scanning of Active Phased Arrays

Conventional near-field scanning systems are often used to measure the radiation patterns of active phased arrays. As long as the metallic probes of such systems are kept far away from the surface of the radiating array, quite accurate measurements can be performed typically in conjunction with complex error correction algorithms. These so-called near-field scanning systems, however, cannot provide "true aperture-level" near-field maps of the active phased array under test. Diagnostics of active phased array systems is usually a very challenging task because any external probe approaching the array's aperture would easily perturb its fields and will interfere with its operation.

NeoScan's non-invasive RF-transparent probes, on the other hand, can be placed very close to the surface of an active phased array without perturbing the aperture fields. The figure below on the left shows the aperture-level field map of an active transmit phased array. It is easily seen that one of the radiating elements is malfunctioning and is not putting out any power. Information like this can never be acquired without probing the fields very close to the surface of the array aperture. Using NeoScan, you can also investigate an antenna array's inter-element coupling effects by exciting a single element and mapping the aperture fields over its neighboring elements. Such information can be effectively utilized as part of the array design process to achieve very demanding specifications.

NeoScan systems are particularly useful for phase characterization and calibration large phased array antenna systems.

Diagnosing malfunctioning elements of an active phased array.
Characterizing and quantifying the inter-element coupling effects in an active phased array.

Verification & Validation of Simulation vs. Measurement

Users of electromagnetic simulation tools are often haunted by a very important question: "How do I know if my simulation results are correct and represent the reality?" The primary solutions of most electromagnetic solvers are electric and/or magnetic fields in the given computational domain. All the secondary quantities such as the S/Z/Y parameters, radiation patterns and other characteristics are derived from the primary field quantities. In a similar vein, the NeoScan system measure the actual electric and/or magnetic fields at a given point or on a specified surface.

Using these measured field profiles, one can compute all the other secondary quantities of interest. You can use the NeoScan field maps as an effective means of verification and validation (V&V) of your modeling and simulation tools. Similarly, you can use our electromagnetic analysis tools such as EM.Cube to verify and validate the field measurement results.

Click here to read a web article entitled "Using EM.Cube and NeoScan System Together for Antenna Design" describing an extensive V&V case study.

A comparison between the simulation and measurement results for the amplitude and phase of the three field components of a patch antenna.

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