Figure 13(b) shows the improved circuit model and Fig. 14 shows input impedance of the pendulum array prototype, coil and the circuit model plotted across frequency. The peaking of the input impedance indicates a greater portion of the input power is coupled to the pendulum system while the power consumption caused by the Ohmic resonance of coil is relatively reduced. Note that not all the modes were predicted by the circuit model due to the fact the mutual coupling among the pendulum elements are not included in the model demonstrating the superiority and completeness of the full wave model. The estimated Q factor at the in-phase mode is around 62.2 as previously demonstrated using the circuit model. To our knowledge, this is the first time such a high Q factor has been achieved in a mechanical antenna system using magnetic dipoles at ULF, demonstrating the potential of magnetic pendulum arrays for efficient ULF transmission.
As the growth of mobile technology network increasing exponentially due to which radio frequency becomes more valuable natural resources. Shortage of bandwidth creates an enormous opportunities for researchers and engineers for exploration of underutilize millimeter wave spectrum in order to design and develop future technologies. It is a need of an hour to do extensive studies on the impact of millimeter wave technologies as both indoor and outdoor environments. This paper describes the various studies carried out earlier in the field of radio wave propagation at 60 GHz in different outdoor environments.
They use channel sounder which has variable rate PN sequence generator. For 38 GHZ they had 400 Mcps and for 60 GHz they had 750 Mcps. The millimeter wave up down convertor get the input of IF frequency of 5.4 GHz. These convertors contain mixer and LO frequency multipliers which give output of 37.625 and 59.4 GHz. The 38 GHz Tx and Rx used vertically polarized horn antennas with gain of 25 dB and half power beam width of 7. The 60 GHz Tx and Rx used vertically polarized antenna whose gain is 25 dB and contain beam width of 7.3.
The TX used in this was consisted of SMF100A microwave signal generator of 10 GHz frequency which was attached to frequency multiplier SMZ90 which multiplies by 6. Then it was connected to V-Band horn antenna of 24dBi gain and 11 beam width. The RX system consisted of same antenna system used in TX. It was then connected to low noise amplifier NIZ-3387. The signal was then sent to harmonic mixer FS-Z90. Then signal was down converted and sent to vector signal analyzer FSQ26.
For measuring the effect of rain of radio wave propagation especially at 60 GHz the studies are carried out by Walther et al [17] at two different sites namely UK and Singapore. They have obtained the data from the Rutherford Application Laboratory (RAL) located in southern part of England. Rain rate and drop size distribution was parameters used by them. Rain rate was observed from rain gauge and DSD was obtained from impact type drop size disdrometer, RD-69.
The studies done by Simon et al. [19] for calculating effects of vegetation on radio wave propagation at 60 GHz. The parameters used by them are cumulative density function and probability density function and compared them against different present models. The experimental setup was explained in [19].
The experiment was performed at various sites. The first site contains 3 foliated maple trees and one foliated flowering crab tree. The link distance was 63.9 m. Second site consists of several spruce and one pine tree in a row which resembles a wall. The link distance was 110 m. The third site consists of leafless maple tree and one leafless flowering crab tree. The link distance was 63.9 m. The result obtained from all the three experimental sites shows that the extreme value and lognormal model best fits the RF attenuation characteristics between trees. It was observed from experiment that propagation at 2 and 60 GHz was frequency and wind speed dependent. The attenuation observed through tree was larger when size of obstruction lies in the foliated path and wavelength are similar in size. The values of AFD and LCR were statistically modeled.
A simulation model was developed by Michael et al. [20] for studding effects of vegetation on radio wave propagation. In this model they have generated signal fading caused by swaying vegetation by using multiple mass spring model which represent tree and turbulent wind model. Different parameters used in this model are cumulative distribution function (CDF), level cross rate (LCR), auto correlation function (ACF) and average fade rate (AFR). Similarities between results obtained from this model and experiment results from [19] were observed.
Consider a typical indoor communication scenario and a MIMO system with N t transmit and N r receive antennas both of omni-directional pattern operating in the 60 GHz band. The radio wave propagation at 60 GHz suggests the existence of a strong line-of-sight (LOS) component as well as the multi-cluster multi-path components because of the high path loss and inability of diffusion [3, 4]. Such a near-optical propagation characteristic also suggests a 3-D ray-tracing technique in channel modeling (see Figure 1), which is detailed in [12]. In our analysis, the transceiver can be any device, defined in IEEE 802.15.3c [5] or 802.11ad [6], located in arbitrary positions within the room. For each location, possible rays in LOS path and up to the second-order reflections from walls, ceiling, and floor are traced for the links between the transmit and receive antennas. In particular, the impulse response for one link is given by
denotes the cluster constitution by rays therein, where α(i,k), τ(i,k), , , , are the intra-cluster parameters for k th ray in cluster i. Some inter-cluster parameters are usually location related, e.g., the severe path loss in cluster amplitude; some are random variables, e.g., reflection loss, which is typically modeled as a truncated log-normal random variable with mean and variance associated with the reflection order [12], if linear polarization is assumed for each antenna. Besides, most intra-cluster parameters are randomly generated. On the other hand, for the short wavelength, it is reasonable to assume that the size of antenna array is much smaller than the size of the communication area, which leads to a similar geographic information for all links. It naturally accounts for the strong and near-deterministic LOS component and the independent realizations from reflection paths in modeling the overall channel response.
Over the last couple of decades analog-to-digital and digital-to-analog technologies have advanced exponentially, resulting in tremendous design degrees of freedom and arbitrary waveform generation (AWG) capabilities that enable sophisticated design of emissions to better suit operational requirements. However, radar systems typically require high powered amplifiers (HPA) to contend with the two-way propagation. Thus, transmitter-amenable waveforms are effectively constrained to be both spectrally contained and constant amplitude, resulting in a non-convex NP-hard design problem.
Estimating the spatial angle of arrival for a received radar signal traditionally entails measurements across multiple antenna elements. Spatially diverse Multiple Input Multiple Output (MIMO) emission structures, such as the Frequency Diverse Array (FDA), provide waveform separability to achieve spatial estimation without the need for multiple receive antenna elements. A low complexity Multiple Input Single Output (MISO) radar system leveraging the FDA emission structure coupled with the Linear Frequency Modulated Continuous Wave (LFMCW) waveform is experimentally demonstrated that estimates range, Doppler and spatial angle information of the illuminated scene using a single receiver antenna element. In comparison to well-known spatially diverse emission structures (i.e., Doppler Division Multiple Access (DDMA) and Time Division Multiple Access (TDMA)), LFMCW-FDA is shown to retain the full range and Doppler unambiguous spaces at the cost of a reduced range resolution. To combat the degraded range performance, an adaptive algorithm is introduced with initial results showing the ability to improve separability of closely spaced scatterers in range and angle. With the persistent illumination achieved by the emission structure, demonstrated performance, and low complexity architecture, the LFMCW-FDA system is shown to have attractive features for use in a low-resolution search radar context.
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