Date of Award
Master of Science (MS)
Dejan S. Filipovic
In radio frequency (RF), microwave, and millimeter wave (mmw) repeater applications, the receiver (RX) often needs to detect small power levels while simultaneously transmitting (TX) the same signal amplified significantly without distorting the incoming signal. In some applications, this can be done with time division or frequency division duplexing techniques; however, there are full duplex repeater applications that require simultaneous transmit and receive at the same time and same frequency. These full duplex systems often face the challenge of self-interference caused by the transmitter (TX to RX isolation).
This thesis focuses on enhancing the isolation between two antennas on a repeater system using different impedance surfaces. These surfaces designed to suppress the electromagnetic surface waves that propagate. For this thesis, broadband, mmw repeater systems mounted on cylinders are considered. Both numerical and analytical studies are conducted as well as fabrication and measurements are performed for cylindrical repeater applications.
From a literature survey, we present a general theory on the concept of surface and generalize these impedance surfaces into three types: corrugations, pin bed, and mushroom/patch structures. Uniform depth corrugations are first considered due to their simple geometry and rich history. Theoretical approaches demonstrate how these corrugations work as an impedance surface and discuss the 2:1 frequency bandwidth limitation that is fundamental to their geometry.
To overcome the bandwidth limitation, other analytical techniques are considered where the corrugations are tapered in depth such that they are engineered to choke the surface currents. This technique is shown to work consistently over wide bandwidths and is implemented onto both flat and cylinder ground planes to validate these studies and techniques.
Alternatively, reactive loading of the uniform depth corrugations is shown to lead to bandwidth improvement. This eventually directs the studies to the mushroom-type impedance surfaces. These types of surfaces can be easily and accurately fabricated using printed circuit boards which can be designed on conformal substrates making them an ideal candidate for cylinder platform applications. Two types of these mushroom structures are studied in depth in this thesis and both demonstrate high isolation improvement over wide bandwidths in numerical studies and measurement results.
Allen, Brad Frank, "Isolation Enhancement for Cylindrical Structure Millimeter-Wave Repeaters" (2018). Electrical, Computer & Energy Engineering Graduate Theses & Dissertations. 158.