Since 1979, the 71-76 GHz and 81-86 GHz bands have been available for worldwide use [1]. Recently, these frequencies, known as the E-band, have garnered interest based on the possibility of very high data rates that they can easily accommodate. Since each band has a width of 5 GHz, the total frequency allocation represents 50 times the bandwidth of the entire cellular spectrum, shown in Figure 1. Other benefits of using high frequency millimeter wave communications are the use of smaller reflector antennas and greater directivity. Challenges arise due to the higher quality of electronics needed for millimeter wave systems, along with increased path loss due to atmospheric effects at these frequencies. This project responds to the proposal given by the Air Force Research Laboratory, and addresses some of these technical challenges in detail. The proposal can be found in its entirety below.

Figure 1: FCC frequency allocation, with E-band offering a large portion of the bandwidth [1].

Since the E-band has seen little use until recently, there are still questions to be answered about the propagation effects that characterize the frequency range. Atmospheric phenomena such as polarization shift, distortion, and attenuation are only known in a theoretical capacity at these high frequencies. The beacon component of this project seeks to operate a transmitter in a geostationary orbit that will transmit a known signal repeatedly, utilizing a low bandwidth. The ground receiver will be used to measure this signal, and note any propagation effects that occur. The goal for beacon mode was a link margin of 36 dB, with three tones between 71 and 76 GHz. This data will be used for the production of future military satellite communication systems. The orbit will be over approximately 100° W longitude, which corresponds to the continental United States. For this project, the Earth Station was assumed to be in Atlanta, GA, USA.

The transponder portion of the project seeks to characterize a communication link at the frequencies of 71-76 GHz (downlink) and 81-86 GHz (uplink). The objective is to determine statistics such as bit error rate (BER), data rate, link margin, and availability. The design goal for the transponder mode was a 10 Mbps data rate. The BER is dependent on the carrier to noise ratio (CNR) at the receiver. Cryogenically cooled Low Noise Amplifiers (LNAs) were used at the earth station in order to minimize the noise temperature. The availability will be determined by changes in atmospheric phenomena that can vary with the geography of the region. Rain attenuation may be a limiting factor at these high frequencies due to the very short wavelength of the signals. The clear day link margin was limited by power capabilities of the satellite antenna, along with the losses experienced due to the on-board electronics. Lastly, data rates are dependent on bandwidth and modulation. Since increasing bandwidth will also increase noise power, the minimum bandwidth to meet data rate requirements was used. Higher order modulations can also degrade BER since the signal constellations are more confined, so a compromise had to be met with this parameter as well.

[1] F. Versluis. "Millimetre wave radio technology." Microwave Engineering Europe. November 2008.