The present invention relates to the field of antennas and, more particularly, to low profile antenna arrays for airborne applications.
Antenna systems are an important part of electronic warfare (EW) and radar applications for jamming and electronic attacks. Such antenna systems need low profiles when installed on airborne platforms. For low profile requirements, conventional antenna designs have used patch radiating elements, which are thin and low profile.
FIGS. 1A, 1B, and 1C depict patch antenna configurations. FIG. 1A schematically depicts a cross section of a typical patch antenna 10. A patch element 12 is located above a ground plane 14. The patch element 12 is fed by a probe 16 that is isolated from the ground plane 14. Antenna radiation occurs at ends 18a, 18b. FIG. 1B depicts an alternative patch antenna 20, which is similar to that depicted in FIG. 1A, but with a patch element 12′ having an end 18c connected to the ground plane 14. The ground plane connection occurs at a distance λ/4 from the probe 16, where λ is a wavelength of radiation with which the antenna is used. This configuration provides for radiation only from end 18b. FIG. 1C depicts yet another patch antenna arrangement wherein multiple patch antennas, for example, those of FIG. 1B, are in an array 30 with each of the radiating ends facing in a same direction 32. This array arrangement takes advantage of the array factor gain (G (db)=10 log N, where N is the number of array elements) for improved radiation strength.
In military applications such as detecting targets under trees, road side bombs, land mines, and border tunnels, low band (VHF, UHF) antennas are typically used. However, radiating elements at these frequencies are typically very long and pose a problem for airborne platforms. While patch antenna elements may be thin, they have a very limited 5% bandwidth and are not suitable for systems that require 20% bandwidth. Furthermore, some EW missions require high power (45 kW) transmit antennas operating at VHF (150 MHz) for jamming and attacks. Such capabilities are not readily available, so there has been a critical need to develop a low profile VHF antenna with sufficient bandwidth for high power applications.
Patch antenna configurations generally have very limited bandwidth (for example, 5%) and, as a result, are not suitable for EW and radar applications that require a large bandwidth (for example, 20%) and high power for jamming and electronic attacks. As such, there is a need for a low-profile antenna that provides 20% bandwidth at VHF (150 MHz) and supports high power (3 kW per element) applications.