Testers Mimic Propagation Losses To 13.25 GHz

This family of attenuator- and coupler-based microwave path simulators can introduce controlled amounts of signal loss to emulate the conditions in communications links.

Signal losses and fading in communication links result from atmospheric losses, reflections from terrain, and multipath distortion. To recreate the effects of those signal losses, ARRA, Inc. (Bay Shore, NY) offers their model AR39XX and AR40XX series of Microwave Path Simulators for evaluating communications equipment and components from 1.7 to 13.25 GHz in bands. Based on a combination of precision variable attenuators and couplers, the path simulators allow users to dial in as little or as much signal attenuation as needed to find such parameters as system sensitivity and threshold points where bit-error-rate (BER) performance is degraded. The path simulators typically offer a minimum dynamic attenuation range of 100, and achieve total attenuation to a maximum of 140 dB when all dials are set at maximum.

One example of the product line is the AR3987-1, an eight-port path simulator that operates from 10.70 to 13.25 GHz (see figure). Six- and four-port versions are also available. The rack-mountable unit features an attenuation range of 0 to 100 dB (as much as 140-dB attenuation considering total losses through the simulator). The simulator leverages the company's expertise in attenuator technology to provide low VSWR at all direct and coupled ports. The VSWR at ports A, B, and C, for example, is less than 1.15:1. The VSWR at coupled ports M and M´ is less than 1.80:1.

The simulator provides three calibrated dials and one uncalibrated dial to control the amount of attenuation (signal loss) when simulating transmission propagation losses. The first calibrated dial features an attenuation range of 80 dB while the other three dials control attenuation ranges of 20 dB each. The resolution for any dial setting is less than or equal to 1 dB, while the resettability at any dial setting is less than or equal to 0.5 dB. The accuracy of these attenuation settings is ±1 dB. The path simulators are calibrated by means of intermediate-frequency (IF) substitution techniques at fixed frequencies, with attenuation measurements made incrementally from 0 to 10 dB, then 10 to 20 dB, then 20 to 30 dB, and so on until the highest attenuation setting.

The cumulative frequency response of the AR3972-1 Microwave Path Simulator is better than 0.5 dB for narrowband (50 MHz or less) applications and less than 2 dB from 10.70 to 13.25 GHz. The level balance between various output ports is better than 2 dB. Isolation between adjacent ports is at least 25 dB (from port B to port C and from port B´ to port C´) and as much as 28 dB or more (from port A to port B and from port A´ to port B´).

Since the AR3987-1 is a passive system, the couplers, attenuators, connectors, and transmission lines exhibit some insertion loss even when all attenuators are set to zero. For example, the through-path losses from port A to A´ or from A to B´ is less than 38 dB, while the worst-case through-path losses, from port B to A´, B´, or C´ or from port C to A´, B´, or C´, is less than 46 dB.

The model AR3987-1 Microwave Path Simulator is designed for use with additional test equipment and hardware, including a scalar network analyzer, signal generator, a set of attenuators, adapters, and a VSWR bridge. The company verifies performance of its simulators (see table) over temperatures from +32 to +125°C. ARRA, Inc., 15 Harold Court, Bay Shore, NY 11706; (631) 231-8400, FAX: (631) 434-1116, e-mail: [email protected], Internet: www.arra.com.

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