Randtron Antenna Systems Microstrip Patch Technology

Randtron Antenna Systems is fully capable of designing and manufacturing patch antennas and arrays of patches for any application that is appropriate to this technology. Microstrip patch antennas are often chosen for applications that require a very thin design conformally surface mounted on its platform. Production costs are minimized due in fact to relatively simple fabrication processes of these antennas. Another characteristic advantage of the microstrip approach is the rugged antenna structure, typically a solid laminate of copper-clad microwave substrate materials. The primary limitation of this type of antenna is the bandwidth, which is less than 5% for most single substrate designs. However, a second substrate can be added to create a dual band design or a broadband design with a bandwidth of up to 35%.

The flat plate array is designed for a C-Band satellite application (above). The 50 elements of this array are combined to provide a precisely controlled beam shape, not to maximize directivity. The beam shape is optimized for nearly constant amplitude coverage across the surface of the earth from a low-earth orbit. The antenna radiates both right-hand and left-hand circular polarizations with very good isolation between the two. It has a 4% bandwidth.

An example of a conformal patch array for an airborne application is the four by eight rectangular array . This antenna is designed for a C-Band data link with a 13% bandwidth. The larger bandwidth requires the use of a coupled patch on top of the driver patch, and the circuits for both of these layers are shown in the photograph (above right). The four element columns of the array are fed in microstrip on the lower circuit layer, and the columns are then combined in an external beam former. Alternatively, the entire feed circuit could be integrated onto a single substrate.

We have also developed a single element antenna for portable land use. The unique feature of this product is that it radiates efficiently at 265 MHz and yet is only five inches square. The effective cavity under the patch is primarily filled with air so that losses are minimized and the antenna is very light. A resonance at 265 MHz is achieved with capacitive loading on the edges of the patch. Bandwidth for a single layer patch is proportional to cavity volume and is only about 1 MHz for this design. The antenna radiates a nearly hemispherical, circularly polarized, radiation pattern.

LO Patch Radiating Element

For low RCS platforms that require GPS guidance, the radar cross section (RCS) of a conventional patch antenna is often too high to be acceptable. A standard technique that is used to reduce the RCS of a conventional patch is to cover the patch with magnetic radar absorbing material. Unfortunately, this type of treatment reduces the antenna gain by several decibels or more.

An antenna element that has full aperture gain (>80% efficiency) of an untreated patch and much lower RCS is Randtron's patented LO Patch radiating element. There are numerous advantages of this element over a conventional patch. One advantageous feature is that the element diameter is less than a quarter of a wavelength which provides an electrically smaller element for a given frequency, which is useful when the element is arrayed, as it allows a wider edge-to-edge separation for a given center-to-center spacing. The element is flush mounted conformal to a flat or curved surface. The required cavity depth behind the element is less than 0.25" for GPS applications. In addition to this size reduction, the element shorts out all higher order resonant patch antenna modes. Thus reducing the RCS by 5 to 20 dB compared to that of a conventional patch antenna while maintaining the full aperture gain. It can be used in a wide variety of Controlled Radiation Pattern Antenna (CRPA) geometry's and interfaces with most all GPS anti-jam nulling receivers.

Randtron Antenna Systems will design and manufacture a patch antenna to meet your specific requirements using our patented LO patch radiating element.