Abstract: Disclosed are a frame transmission method using a selective beamforming and a communication apparatus to perform the frame transmission method. The communication apparatus may determine a beamforming matrix based on classification information in which a plurality of subcarriers used for communication is classified into a plurality of frequency units, may map a long training field (LTF) sequence to the beamforming matrix, and transmit a beamforming training (BF-T) frame including the mapped LTF sequence to a plurality of stations, may receive, from the plurality of stations having receiving the BF-T frame, feedback information generated based on a reception strength of the BF-T frame, and may allocate frequency units to data frames to be transmitted to the plurality of stations based on the feedback information, and transmit the data frames using the allocated frequency units. The reception strength of the BF-T frame may be determined at each station for each frequency unit.

Abstract: A wireless communication method and apparatus in a wireless local area network (WLAN) system are disclosed. A wireless communication method according to one embodiment may include generating a high-efficiency Wi-Fi (HEW) frame including at least one of an HEW-SIG-A field and an HEW-SIG-B field which include channel information for communications according to an Orthogonal Frequency-Division Multiple Access (OFDMA) mode, and transmitting the generated HEW frame to a reception apparatus.

Abstract: Provided are a chromium catalyst precursor, an ethylene oligomerization catalyst including the same, and a method of preparing an ethylene oligomer using the same. More particularly, a chromium catalyst precursor which may oligomerize ethylene with high activity and high selectivity in spite of not using methylaluminoxane (MAO) or modified-methylaluminoxane (MMAO), an oligomerization catalyst including the same, and a method of preparing an ethylene oligomer using the same are provided.

Abstract: Provided are an integrated circuit (IC) package having balls designed to minimize contact resistance, a test apparatus for testing the IC package, and a method of manufacturing the IC package. The IC package is a ball grid array (BGA) package including solder balls, the solder balls having substantially flat bottoms. The balls of the BGA package are Pb-free balls, and are polished using a mechanical polishing method or a chemical polishing method to have the substantially flat bottoms. The test apparatus includes a plurality of channels, a test board having a wiring pattern connected to the channels, and an IC socket having a plurality of Pogo pins respectively connected to lands of the wiring pattern. The top ends of the Pogo pins of the IC socket are made substantially flat to increase the area that contacts the substantially flat bottom surfaces of the BGA package.

Abstract: Provided are example embodiments of a test supporting device including a radio frequency (RF) line adapted to transmit an RF signal from an RF terminal to test equipment, a direct current (DC) line connected to the RF line at a first end and adapted to connect to the test equipment at a second end, and a capacitor connected to the DC line at a first end and connected to ground at a second end. Example embodiments of the present invention may also provide a test method including measuring a radio frequency (RF) signal, and measuring a direct current (DC) signal passed through an open stub.

Abstract: Provided is a probe card including: a printed circuit board comprising a ground electrode; at least one dielectric disposed below the ground electrode; and a plurality of needles, each of which comprises: a first end portion contacting a wafer pad of a semiconductor device, a second end portion electrically connected to the printed circuit board, and the remaining portion excepting the first and second end portions surrounded by the at least one dielectric. A metal plate is disposed below the at least one dielectric; and a connecting pin electrically connects the metal plate to the ground electrode and fixes the at least one dielectric and the metal plate to the printed circuit board.

Abstract: Provided is a probe card including: a printed circuit board comprising a ground electrode; at least one dielectric disposed below the ground electrode; and a plurality of needles, each of which comprises: a first end portion contacting a wafer pad of a semiconductor device, a second end portion electrically connected to the printed circuit board, and the remaining portion excepting the first and second end portions surrounded by the at least one dielectric. A metal plate is disposed below the at least one dielectric; and a connecting pin electrically connects the metal plate to the ground electrode and fixes the at least one dielectric and the metal plate to the printed circuit board.