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Introduction
Published in Shiban Kishen Koul, G. S. Karthikeya, Millimetre Wave Antennas for 5G Mobile Terminals and Base Stations, 2020
Shiban Kishen Koul, G. S. Karthikeya
Since, the sub-6 GHz bands have high spectral congestion, future wireless standards could be migrated to the millimeter wave frequency range, which is easier said than done, as the design for sub-6 GHz bands is well-known for operating link budgets and receiver sensitivity. But the inherent problem with the millimeter wave frequencies is the high path loss compared to existing cellular communication standards. It must also be observed that the atmospheric absorption in the 60 GHz band is close to 20 dB/km, as is evident from Figure 1.1. An attenuation of 7 dB/km is observed as a result of heavy rainfall rates of 1 inch (25 mm) per hour for cellular propagation at 28 GHz, which translates to a mere 1.4 dB of attenuation over 200 m distance. Free space path loss and the penetration losses are relatively higher, which could be mitigated by high gain antennas. Penetration loss could be as high as 30–40 dB for common building materials such as bricks, concrete and glass window panes. This aspect would deteriorate the link budget severely, the feasibility of maintaining the link budget with decent power at the base station or access point for a given receiver sensitivity, is yet to be implemented.
Radio Wave Propagation
Published in Jerry C. Whitaker, The RF Transmission Systems Handbook, 2017
A typical problem in the design of a radio frequency communications system requires the calculation of the power available at the output terminals of the receive antenna. Although the gain or loss characteristics of the equipment at the receiver and transmitter sites can be ascertained from manufacturer’s data, the effective loss between the two antennas must be stated in a way that allows for the characterization of the transmission path between the antennas. The ratio of the power radiated by the transmit antenna to the power available at the receive antenna is known as the path loss and is usually expressed in decibels. The minimum loss on any given path occurs between two antennas when there are no intervening obstructions and no ground losses. In such a case when the receive and transmit antennas are isotropic, the path loss is known as free space path loss.
Fading
Published in Paulo Montezuma, Fabio Silva, Rui Dinis, Frequency-Domain Receiver Design for Doubly Selective Channels, 2017
Paulo Montezuma, Fabio Silva, Rui Dinis
The signal attenuation of an electromagnetic wave (represented by a reduction in its power density), between a transmitting and a receiving antenna as a function of the propagation distance, is called path-loss. As the relative distance between the transmitter and receiver increases, the power radiated by the transmitter dissipates as the radio waves propagate through the channel. This is commonly referred to as free-space path-loss and refers to a signal propagating between the transmitter and receiver with no attenuation or reflection. This is the simplest model for signal propagation and is based on the free-space propagation law. Let us consider the free-space propagation model. It considers the line of sight channel in which there are no objects between the receiver and the transmitter, and it attempts to predict the received signal strength assuming that power decays as a function of the distance between the transmitter and receiver.
Wideband circular polarized Fabry-Perot cavity antennas for V-band indoor point-to-point communications
Published in Electromagnetics, 2019
Saman Kabiri, Evangelos Kornaros, Franco De Flaviis
Due to higher free-space path loss at the V-band frequency spectrum, high-gain antennas are desirable to compensate this loss. Also, planar structures are amenable to be integrated into other modules of the transmitter or receiver ends. Planar Fabry-Perot Cavity (FPC) antennas are well-known for providing a highly-directive beam by exciting the structure from a single feeding point (Hosseini, Capolino, and De Flaviis 2015). Planar FPCs, in their general forms, consist of a Partially-Reflective-Surface (PRS) placed on top of a ground plane. Leaky waves (LW) are excited between these two surfaces. As shown in (Lovat, Burghignoli, and Jackson 2006), the radiation performance of FPC antennas is explained based on the excitation of the leaky waves inside the cavity. As discussed thoroughly in (Jackson et al. 2011), one of the main constraints of FPCs antennas is their low 3-dB gain-bandwidth (GBW), defined as a frequency range within which the broadside gain of the antenna stays within 3-dB below its peak value. As shown in (Jackson et al. 2011), the GBW is reversely proportional to the relative permittivity of the substrate forming the cavity. Therefore, for a given substrate, the bandwidth decreases as the gain increases correspondingly. The trade-off between the gain and bandwidth implies that larger bandwidth can be achieved by relaxing the directivity of the FPC, i.e. reducing the reflectivity of the PRS. An extra directivity can be achieved by employing a sparse array antenna as initially investigated in (Kabiri et al. 2014; Kabiri, Kornaros, and Flaviis 2015). Inter-element spacing, , in sparse arrays in contrast to dense arrays are larger than typical value of , where is the free-space wavelength at the operating frequency.