April 30, 2015
Engineers have used vector network analyzers (VNAs) for passive device testing for decades. Many applications require high-priced, high-performance, and full-featured VNA solutions while others only necessitate simple S-parameter and time domain measurements at the lowest possible cost. Unfortunately, engineers in these latter environments have had to use expensive, full-featured VNAs, because there were no alternatives. In today’s highly competitive world where low cost-of-test and fast time to market are necessities, the added – and unnecessary – cost and complexity associated with these high-end VNAs are unacceptable in many applications, such as testing antennas in mobile communications and automotive designs, as well as in university labs.
In each of these environments, a 1-port USB VNA (figure 1) can satisfy most test requirements. In fact, such a compact, easy-to-use VNA solution provides a number of economic and throughput benefits.
In today’s mobile devices, there are a minimum of four antennas – for cellular, Wi-Fi, Bluetooth, and GPS. A 1-port USB VNA solution can dramatically increase throughput during production of these devices compared to traditional test solutions featuring a 2-port VNA and a multi-port switchbox. Multiple USB VNAs can be connected to a single PC for simultaneous measurements, dramatically reducing test costs and increasing throughput versus waiting for a switchbox to test devices serially.
There are other advantages with a 1-port USB VNA when testing mobile devices. Conventional (VNA+switchbox) test solutions are more prone to production downtime because a failure or calibration drift in either the VNA or switchbox will bring the entire production line to a halt. In addition, the switchbox is an electro-mechanical device with a limited life and repeatability. Therefore, it will need to be replaced over time, bringing with it unpreventable cost.
A third advantage of a 1-port USB VNA is that it can be directly connected to the device under test (DUT), avoiding the need of costly RF cables that can negatively affect RF performance and stability. RF cables can also further add complexity to the test configuration, something that is particularly unwanted in a production environment.
Similar benefits are also realized when testing base station antennas on the manufacturing line. Multiple 1-port USB VNAs connected to a laptop create a multi-port solution that can conduct all the required measurements, including VSWR, to verify performance.
Today’s automobiles feature multiple antennas and RF cables to accommodate the various technologies and communications systems. Testing these devices is not only challenging because of the variety of frequencies ranging from AM/FM and satellite to WiFi and cellular, but the accessibility of these devices in the car. Using a 1-port USB VNA allows engineers to conduct the necessary measurements much more simply. A direct connection to the DUT can be established, for more stable measurements. Because the 1-port USB VNA is integrated with a laptop, testing is convenient, as engineers can perform measurements and view results on a large display while sitting in the car seat.
Engineering schools are always in search of a low-cost laboratory tool for teaching students how to conduct VNA measurements. A 1-port USB VNA is a perfect solution, as its economical price fits most university budgets and it provides the necessary measurement capability for students to gain an understanding of VNA concepts.
This post outlined some of the applications in which a 1-port USB VNA can be advantageous. If you are interested in learning about additional VNA applications requiring more robust VNA capabilities, such as radar, on-wafer and signal integrity, you can download a free application note.