Abstract: An image spatial filter comprises back-to-back image cavities with means for coupling energy from one cavity to the other. Large angle of incidence energy is attenuated by each image cavity successively, thus providing a high degree of attenuation. Two quarter wavelength dielectric sheets with a ground plane between them and spaced from each by one-half wavelength form the image cavities. Slots in the ground plane provide coupling from one cavity to the other. Image spatial filters are not substantially more expensive than multi-layer dielectric spatial filters and are as easily fitted to existing antennas. But image spatial filters substantially reduce large angle passbands caused by the Brewster effect and by cavity resonance in dielectric spatial filters.

Abstract: Image element antennas are well known for their relatively small size and highly directive radiation patterns. Such antennas, however, have an inherent disability in that the mechanism responsible for high directivity is inoperable at a certain angle, thereby producing a sidelobe into which relatively large amounts of power are radiated. The present invention involves an improved element for use in image element antennas which avoids radiating any substantial amounts of power into this sidelobe. A preferred embodiment of the invention provides a doublet element having a minimum of radiated power at the angle of the sidelobe, thus avoiding the need for the multiple reflection-transmission mechanism which fails at this angle.

Abstract: A first disk having radiating elements formed thereon, a second disk having radiating elements formed thereon and overlying the first disk, an electromagnetic energy reflecting disk overlying the second disk and having a first plurality of parallel slots aligned with some of the radiating elements and a second plurality of parallel slots, perpendicular to the first slots, aligned with the remainder of the radiating elements, a nonconducting, spacing layer overlying the reflecting disk and a partially reflecting disk overlying the spacing layer so that the radiating elements form slot sources in the reflecting disk with part of the energy from the slot sources passing through the partially reflecting disk and part being reflected back to the total reflecting disk to form a dual polarized image element antenna array. A second embodiment illustrates different energy radiators.

Abstract: First and second elements mounted in parallel spaced apart relation with one end shorted to form a quarterwave transmission line at a base frequency and a halfwave transmission line at an even harmonic thereof, with the spacing being .lambda./8 at the base frequency and .lambda./4 at the harmonic and a feedline being connected between the elements and positioned so the impedance of the antenna matches the impedance of the feedline at the base frequency and the diameter of the feedline being adjusted so the impedance of the antenna matches the impedance of the feedline at the harmonic frequency.