the theoretical results of Fig. 2 of [I] show that for LJ =-I 2pm, there are two values of L, at which minimum second-harmonic distortion can be achieved. This cannot be predicted from eqn. 7. Furthermore, for M,, = O S the approximation of the term (d(l-mJ d(l+mJ) using eqn. 6 results in an error of the order of' 3.5%. Such an error cannot reliably yield harmonic distortions of the order of-81dB. It appears, therefore, that eqn. 6 of [l] the harmonic performance of the second cell.

An active aperture-coupled leaky-wave antenna (LWA) with excellent dual-beam scanning capability is presented. An X-band varactor-tuned HEMT VCO is integrated on the other plane through an aperture with the LWA. This antenna has the advantages of multi-functionability, interference shielding, and a scanning main beam. The measured main beam in the elevation plane can be continuously scanned for 20" for each beam as the HEMT VCO frequency is vaned from 8.97 to 9.5GHz. An effective isotropic radiation power of 18.89dBm for the right beam and 19.06dBm for the left beam is achieved. Introduction. Recently, leaky-wave antennas (LWAs) have become popular, and there is a growing interest in the use of various types of leaky-wave antennas as frequency-scanning elements [ 1, 21. Leaky-wave antennas possess the advantages of a low profile, fabrication simplicity, ease of matching, a narrow beamwidth and frequency-scanning capability. The aperture-fed structure was

A frequency‐scanning leaky‐wave antenna with an aperture‐coupled feeding structure is presented. The aperture‐fed structure is used to excite the microstrip first higher mode. In order to suppress the dominant mode, we add a sequence of covered wire in the center of this antenna. The measured H‐plane main beam is a pencil beam, and is continuously scanned 12° as the frequency varies from 9.85 to 10.27 GHz. This feeding structure is very suitable for active phase antenna array applications. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 5–8, 1999.