Microstrip array with semiconductor phase shifter

Interest in land mobile satellite communications has grown in recent years and high data rate services such as GBS, have been identified as prime applications. Phased array technology is well suited to tracking satellites as vehicles move through uneven terrain. However, electronically steered arrays are expensive compared to reflector antennas and one of the critical issues with phased arrays in mobile communication applications is the cost of the phase shifters. Ferrite phase shifters have been extensively used for phased arrays mainly in military applications because their weight is low and their size is small. However, their extremely high cost has prevented more widespread use and they may not be practical in mobile SATCOM applications which require a low unit cost. Recently, ceramic phase shifters have drawn much attention in the antenna community because of their relatively low cost and reliable performances. Ceramic materials, however, have very high dielectric constants, thus causing a complex impedance matching problem and subsequent low efficiency. Due to the complexity of impedance matching, the size of the ceramic device may be too large for mobile SATCOM antennas. The proposed semiconductor phase shifter is similar to the ceramic phase shifters presently in operation. The phase shift is achieved by varying the effective dielectric constant of the microwave medium. With a properly doped semiconductor substrate, the dielectric constant is altered by an applied DC bias voltage. The attractive feature of the proposed device is that the applied DC bias is negligible and a high DC bias field can be applied without causing dielectric breakdown. The new device is inexpensive to fabricate and easy to implement in a cost-slaving monolithic environment. A compact low cost phased array antenna is anticipated by integrating the newly developed phase shifters with radiating microstrip patch elements on a single semiconductor chip.