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From Channel Modeling to System Performance Evaluation
Published in Athanasios G. Kanatas, Athanasios D. Panagopoulos, Radio Wave Propagation and Channel Modeling for Earth–Space Systems, 2017
Konstantinos P. Liolis, Pantelis-Daniel Arapoglou
The choice of circular polarization is related to the legacy coming from SISO mobile satellite systems to avoid the effect of Faraday rotation (depolarization). Nevertheless, as both polarizations are being transmitted, Faraday rotation can be removed at the receiver by operating in the polarization domain. Note that at the satellite antenna side, typically the antenna feed provides two linear polarization ports. The two circular polarizations can then be simply obtained using two different orthomode transducer topologies able to simultaneously generate the RHCP/LHCP inputs (ESA TAS-E, 2012). For a given overall radio frequency (RF) payload power, the transmission in two distinct polarizations within the same beam has the further advantage of reducing by 3 dB the power handling in the high-power part of the payload.
Satellite systems
Published in Geoff Lewis, Communications Technology Handbook, 2013
Terminals are divided into two basic sections (see Fig. 31.6). An outdoor section comprising low noise block convertor (LNC) and high power amplifier (HPA) are usually contained within a single casing and mounted at the antenna focal point. The HPA, which is a semiconductor device, commonly produces an RF power of some 2 to 3 W. This assembly also carries the orthomode transducer and waveguide filters. These are necessary to separate the transmit and receive signals. Both transmitter and receiver function on the dual conversion, double superhet principle. The local oscillator is normally a crystal controlled phase lock loop, with frequency synthesis to select the correct frequencies for up- and down-link operation. The typical 1st IFs are around 1 GHz for Ku band and 600 MHz for C band, while the 2nd IF is commonly either 70 or 140 MHz.
Satellite Antennas
Published in Jerry D. Gibson, The Communications Handbook, 2018
Yeongming Hwang, Youn Ho Choung
There are two techniques to achieve this required isolation. One way is to use two orthogonal polarizations. One channel carries a vertical polarization [or right-hand circular polarization (RHCP)], and the other channel carries a horizontal polarization [or left-hand circular polarization (LHCP)] with more than 30-dB isolation. This can be done using a polarizer (for the CP case) and an orthomode transducer placed right after the feed horn. Another method is to use two spot beams pointing at different locations with high (about 30 dB) spatial isolation. This can be achieved using two feeds (or feed clusters) of the reflector to generate low sidelobes. Low sidelobes can be achieved with minimum spillover energy by the use of a high taper feed on the reflector.
Compact high-gain composite horn antenna for space-borne beacon application
Published in International Journal of Electronics, 2019
Ramesh Chandra Gupta, Milind Bhagwan-rao Mahajan, Rajeev Jyoti
A specially profiled axial–radial corrugated horn, as shown in Figure 1, has been devised and implemented to get enhanced EoC gain and compact size. A very close agreement between the predicted and measured results for Ku-Tx/Tx beacon horn antenna has been achieved. This horn is obtained by a proper combination of stepped, axial corrugated and radial corrugated sections, which control amplitude and phase of higher order modes at the aperture of the horn. The superposition of the different modes in proper ratio provides the desired and enhanced RF performance. Combination of three-sections (i.e. stepped, axial and radial section) of the horn, provide extra flexibility of design optimization. Synthetic geometry and photograph of the fabricated hybrid beacon horn antenna at Ku-band are depicted in Figure 1. The synthesised geometry of the horn causes ease in its mechanical design and manufacturing. This horn maintains lightweight with its counterpart antenna. The radial corrugated section of the horn is combined profile of linear and spline, which could be extended to a multi-profiled section to attain optimisation flexibility and customised RF performance. This beacon horn is customised to make available higher EoC gain over India plus Lakshadweep and A&N islands. A smooth-walled circular to a rectangular waveguide (WR-75) continuous transition and stepped OMT (orthomode transducer) are used at the input of the beacon horn antenna. The accommodation of the Ku-Beacon antenna on spacecraft is discussed with help of its near field considering different nearby scatterers. Implementation of antenna tilt and its impact on RF Performance is also described.