Time Domain Antenna Measurement Research Articles

Modeling the Transient Radiated and Received Pulses of Ultra-Wideband Antennas

In this paper, we propose a method for modeling the transient radiated and received pulses of ultra-wideband (UWB) planar aperture antennas. The proposed method is able to analytically model the angle-dependent pulse distortion of the antennas. The method relates the input pulse of an antenna to its transient radiated fields, and the incident transient fields to its output pulse. This method needs to estimate the antenna's aperture field distribution from time-domain antenna measurements. Using the proposed method, the received pulses from three different antennas-a ridged-horn, a dielectric loaded horn, and a Vivaldi antenna-are modeled and compared with the measured received pulses. A comparison of pulse shape, amplitude, and energy shows very good agreement. Different input pulses are also examined for the experimental evaluation of the proposed method. The method allows designers to analytically estimate the antenna effect on transmitted pulse enabling the inclusion of pulse distortion by the antenna into the ultra-wideband transceiver design.

Compact antenna test range without reflector edge treatment and RF anechoic chamber

There are several types of CATRs (compact antenna test ranges) used in antenna-pattern measurements. An offset reflector is generally used to generate the quiet zone of a CATR. Serrated edges, rolled edges, or R-cards are generally chosen along the reflector's edge to reduce the edge-diffraction field inside the quiet zone of the CATR. In order to reduce stray signals from the environment, a high-quality RF anechoic chamber is required for a CATR. In this paper, a new type of CATR, without either a reflector edge treatment or an RF anechoic chamber, is developed. A commercially available DBS (direct-broadcast satellite) reflector antenna, without edge treatment, is used as the reflector antenna of the CATR to generate the quiet zone of the antenna test range. In order to improve the quiet zone's performance, the fields due to feed spillover, edge diffractions, and other stray signals are gated out by the ITDAMS (impulse time-domain antenna measurement system). The RF interference in the environment can also be reduced by time synchronization and pulse integration of the impulse time-domain antenna measurement system. In order to verify the capabilities of the proposed CATR, three kinds of antennas (a low-directivity horn antenna, a high-directivity 60 cm direct-broadcast satellite reflector antenna, and a 25 cm Ka-band Cassegrain LMDS - local microwave distribution system - antenna) were measured by the proposed CATR. The antenna-pattern results agreed quite well with those of a near-field range and a far-field range.

Analysis of gating errors in time domain antenna measurements

Although relatively new, the principle of measuring the radiation pattern of an antenna using the time domain rather than frequency domain is well known and relies on gating out unwanted reflections. Time domain measurements on horn and spiral antennas illustrate the need for error criteria and in this paper the nature of the gating error, and its relationship to the anti-interference enclosure size and the antenna frequency response, are investigated by both analytical and computer simulation methods. The results show that a lower frequency antenna can be expected to require a larger enclosure for a given gating error and that, for small enclosures, the time domain method has advantages over the conventional frequency domain method. The practical implementation of time domain measurement involves other factors such as the effects of aliasing, the need for a high quality reference channel for calibration, matching and noise levels. It is concluded that, in the time domain method, the amount of absorbent material in a chamber may be reduced but at the expense of a fast signal processing facility and, to some extent, a more critical equipment installation.

Time domain sensors for radiated impulsive measurements

Discussion of various sensors and radiators commonly used for time domain antenna measurements is presented. The sensors and radiators discussed here are passive and analog devices which convert the electromagnetic quantity of interest to a voltage or current at their terminal ports. Moreover they are primary standards in the sense that their transfer functions can be calculated from their geometries and are flat (constant) across a wide frequency range. One of the major requirements for these sensors and radiators is that the electromagnetic far field, transmitted or received, is a replica or high fidelity derivative of the original pulse. Note that the transmitting transfer function of an antenna is proportional to the time derivative of the receiving transfer function of the same antenna, which follows from the reciprocity theorem. For electric field strength measurements, linear antennas loaded nonuniformly and continuously with resistance, or with both resistance and capacitance are discussed. Also, a conical antenna and an asymptotic conical antenna are discussed from the standpoint of improved characteristics. For an improved directivity, various types of transverse electromagnetic (TEM) horns are considered, e.g., a conducting TEM horn, and a resistively loaded TEM horn.