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Abstruct-Using a two-port network and geometrical interpretation of equations involved in antenna scattering, it can be derived that antenna characteristics may be determined in properly designed scattering measurements. As an alternative to this approach it is shown that measurement procedures for gain and radiation pattern can be developed from simple considerations of the receiving, transmitting, and scattering properties of antennas. The main advantages of the technique are that no gain standard is required and a disturbing feedline to the antenna can be avoided. In addition to this the technique seems to be highly accurate. These general conclusions are well corroborated by experimental data on a standard gain horn. Sources of errors are outlined and compared with sources of errors in conventional techniques. D

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Abstmcf

A cavity backed coplanar waveguide (CPW) to coplanar strip (CPS) -fed logarithmic uniplanar spiral antenna, which covers a 9 to 1 bandwidth with a return loss better than I O dB from 0.4 to 3.8 GHz is presented. A wideband balun is used to accomplish the transition from the unbalanced CPW transmission line to the balanced CPS transmission line. The balun exhibits an insertion loss of less than 3 dB in a frequency band from sub 100 kHz and up to a frequency of 3.85 GHz. The numerical results presented are based on simulations using the lE3D Version 6.03 for Windows 98 on an INTEL Celeron 338 MHz computer. The obtained numerical results are in good agreement with experimental data. The spiral antenna is designed and prototyped for the FR-4 substrate. By placing the antenna on the FR-4 substrate it yields a low cost solution, which indeed is an advantage. Simulations have shown that the input impedance remains essentially constant over a bandwidth, which is larger than 1 1 to 1. The simulated as well as the measured input impedance for the spiral antenna is 80 R. Measurements in an anechoic chamber have been made in order to measure the radiation pattern and the directivity of the antenna. The cavity backed spiral antenna exhibits a unidirectional radiation pattern, due to the absorbing material. It is noted that only half of the input power is transformed into radiated power due to the presence of the absorber. The simulated performance of the spiral antenna is very promising. The simulations indicated that the antenna has a radiation efficiency of more than 70 % and an axial ratio and a return loss better than 3.5 dB and I O dB, respectively, in the frequency band from 0.4 to 3.8 GHz, i.e., a 9 to 1 bandwidth.