As can be seen by (4), the bandwidth needed to scan from
broadside to endfire is reduced as is increased, while hollow
waveguides would require very large bandwidths to
approach angles close to endfire, thus limiting the scanning
range in practice. On the other hand, dielectric-filled LWAs
have higher losses associated with the dielectric medium, and
they suffer from higher changes in the beamwidth as frequency
is varied [1]. For these reasons, it would be desirable to create
an LWA based on a hollow waveguide to minimize the dielectric
losses and beamwidth dispersion, but with increased frequency
sensitivity to perform the scanning in the minimum bandwidth.
With this main objective in mind, we present a new LWA based
on a hollow rectangular waveguide with its top narrow wall
replaced by a partially reflective surface (PRS) (as described
in [7]) by adding a high-impedance surface (HIS) [8] in the
bottom narrow wall, as illustrated in Fig. 1. In Section II, the
effect of the HIS on the leaky-mode frequency dispersion will
be theoretically studied by using an efficient transverse equivalent
network (TEN) developed in [7], illustrating how the HIS
increases the frequency sensitivity of the original hollow-waveguide
LWA. Experimental results on manufactured prototypes
are reported in Section III, validating the proposed mechanism
to improve the LWA frequency-scanning response. Finally,
Section IV presents the conclusions of this work.