The satellite transceiver design focused on maximizing received SNR while also decreasing the size and weight of the system by using as few components as possible. To this end, wideband equipment is used where feasible, and the system is designed to share oscillators between the transmit and receive chains.

The satellite uses a single antenna for transmitting and receiving, in both beacon and transponder modes. Due to the wide range of operating frequencies (71-76 GHz downlink, 81-86 GHz uplink), a circulator is too narrowband to effectively isolate the transmit and receive signals. Instead, a number of SPST RF switches are used to connect the appropriate transmit and receive paths when desired. These switches provide relatively low insertion loss (~2 dB) while maintaining high isolation between the transmit and receive paths (~30 dB).

Receive Chain

A two-stage superheterodyne receiver is used due to both the high operating frequency and to improve image rejection. A high gain LNA is used to counteract the high path losses and provide the best possible SNR, in order to accommodate the desired data rates of 10 Mbps. The first local oscillator is a high-frequency voltage-controlled Gunn oscillator, allowing a single oscillator to be used in both the receive and transmit chains by switching the frequency between 65 GHz and 75 GHz. The second LO is provided by a more precise voltage-controlled oscillator (such as a PLL-controlled oscillator) to mix the signal down to the final IF for sampling and demodulation.

The key parameters of the receiver chain are given in Table 1, and detailed noise figure calculations can be found in the Link Budget Worksheet file.

Table 1: Satellite Receiver Key Parameters

Transmit Chain

For the satellite downlink, a two-stage transmitter is likewise used due to the high operating frequency. The same LOs are used as in the receive chain, requiring fewer parts and decreasing cost and weight. The transmitter will be switched between horizontal linear polarization and vertical linear polarization in beacon mode in order to characterize Faraday rotation in the W-band, and vertical polarization will be used in transponder mode to minimize rain attenuation.

Table 2 shows the key parameters of the transmitter.

Table 2: Satellite Transmitter Key Parameters

Figure 1 shows the layout of the satellite transceiver chain.

Figure 1: Satellite Transceiver Block Layout