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In 2003 Focus Microwaves introduced its iTuner computer-controlled electro-mechanical microwave tuner product line. At the time it featured a frequency range of 0.2 to 18 GHz, and was completely self-contained and fully calibrated as a result of the powerful internally housed micro-controller. This innovative new device revolutionized production testing of microwave devices that traditionally had been tested under matched conditions within relatively narrow VSWR ranges using isolators to embed the systems. These mechanical tuners were able to maintain constant VSWR settings over a wide frequency range without operator intervention and are automatically calibrated in order to de-embed the test results to the device reference plane.
A new iTuner mechanical tuner has now been introduced that is capable of handling power levels up to 300 W and covering the frequency range from 100 MHz to 1 GHz. This new mechanical tuner is comprised of a 64" long high power, low loss slab line with a 0.235" wide by 0.800" high stripline center conductor that has been machined with less than a 1 mil overall tolerance. The slab line is machined from a solid 3" × 3" piece of 7075–T6 aluminum with a 0.9" wide and 2.5" deep slot. The tuning carriage travels on an ultra-high precision rail guide and is driven by a high speed micro-stepping motor, thus allowing a full 360° phase sweep at 100 MHz in less than 15 seconds. Figure 1 shows the new tuner’s typical return loss vs. frequency at minimum (50?) and maximum reflection.
Other features of the new 100 MHz tuner include an internal microprocessor with 512K random access memory (RAM) and 512K Flash memory with a TCP/IP and RS232 interface. Its firmware is field upgradeable via its serial port and it has a 64M Flash card to store calibration data. The unit contains an electronically eraseable programmable read-only memory (EEPROM) to store tuner configuration and operation parameters such as speed, acceleration/deceleration profile and motor current. There is an ASIC chip for the stepper motor control with a programmable acceleration/deceleration profile. Its microstepper control is capable of high phase resolution (0.1° at 100 MHz) and the tuner carriage is belt driven for fast tuning (15 seconds for 360° at 100 MHz).
The new high power, high speed 100 MHz tuner operates no different than its higher frequency counterparts. It is a self-contained unit requiring only a computer interface and appropriate test measurement equipment. When the tuner is initialized it has very low loss and behaves like an ordinary transmission line, thus only the phase of the test signal going to the test equipment is modified. The additional loss, caused by the tuner, is taken into account when performing the system calibration. Mechanical slide-screw tuners, such as this one, are low pass and very wideband, and do not interfere abnormally with out-of-band signals, such as intermodulation products and spurious oscillations that may have to be detected and measured.
The iTuner is controlled via a TCP/IP connection to the host computer. The TCP/IP interface is compatible with almost any operating system (Windows, Unix, Linux, MAC) and programming language (MS C++, Borland Builder, Delphi, LabView, Agilent VEE). No additional hardware beyond a network card in the controlling computer and a RJ-45 network cable is required to operate the tuner. Each tuner has its own user-settable IP address, thus multiple tunes can be controlled simultaneously by using an Ethernet hub.
Specifications and test conditions are generally defined in the device under test (DUT) input or output reference plane, and the test setup is calibrated to allow correction of the raw test results measured with standard microwave test instruments, such as a power meter.
Although the iTuner is fully calibrated with respect to its input and output port, the VSWR reference plane for testing is located at the output of the DUT. The iTuner firmware has been extended to allow such reference plane shifting. Further, a non-perfect load impedance is also taken into account when adjusting the VSWR value in the DUT reference plane.
This new high power, high speed 100 MHz tuner brings the same testing capability that the previous iTuner instruments offer at the higher microwave frequencies to a lower frequency range and the higher power capability makes testing high power transmitting devices possible below 1 GHz. Additional information and availability may be obtained from the company’s Web site.
Dollard-des-Ormeaux, Quebec, Canada
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