Youn H. Choung

NASA acts autotrack antenna feed system

This paper presents the spacecraft monopulse tracking feed system of the multibeam antenna (MBA) for the NASA Advanced Communication Technology Satellite (ACTS). The MBA has approximately 0.3O half-power beamwidth; the spacecraft alignment requirement is 0.025O. The feed system is designed to receive linearly polarized communication signals from 28.9 to 30.0 GHz and to provide the elevation and azimuth error tracking signals at 29.975 GHz within 0.01 O tracking accuracy. The feed system (Figure 1) utilizes a single multiflare conical horn and a multimode coupler (MMC). To provide a symmetric primary pattern for communication signals, a three-flaresection conical horn’ is utilized due to the need for simple configuration, light weight, and small size for the spacecraft. The MMC2 utilizes the lowest three circular waveguide modes, i.e., TE,,, TM,,,, and TE, to achieve the sum and two difference channels, respectively. The two difference channels are time multiplexed in the autotrack biphase modulator and then coupled to the sum channel. Theory, physical description, and experimental data of the feed system will be discussed.

Wideband double-slot cross-notch antenna

This paper presents an extremely wide frequency band antenna with polarization diversity. For versatile usage, the antenna needs to have two orthogonal ports to generate dual polarization. Depending on the polarization network, the polarization combination can either be vertical and horizontal or RHCP and LHCP. This antenna has excellent RF performance for a multioctave frequency bandwidth.

Wideband monopulse tracking feed

This paper presents a compact monopulse tracking feed using a single corrugated horn and a TM/sub 01/ mode tracking coupler for wideband operation. The demo feed system is such that the communication channel operates from 12 to 30 GHz and the tracking channel operates from 24 to 28 GHz. The feed was designed to have a 10 dB beamwidth of 30 /spl deg/ to achieve the maximum efficiency for a Cassegrain antenna. The coupler is designed by a longitudinal traveling wave mechanism and utilizes the circular TE/sub 11/ and TM/sub 01/ modes that provide the sum and the difference channels, respectively, to achieve monopulse tracking.

Dual-band offset gimballed reflector antenna

There are two ways to scan a reflector antenna using a gimbal. One is to gimbal the whole antenna assembly, called gimballed antenna assembly. The other is to gimbal the reflector only while the feed and support structure are stationary, called gimballed reflector. The pros and cons for the two approaches are listed. In summary, the gimballed reflector has more advantages than the gimballed antenna assembly such as a simple mechanical structure, light weight, and low manufacturing cost. However, the only disadvantage of the gimballed reflector is the scan loss associated with the feed displacement due to the reflector focal point change. The antenna consists of a front-fed offset gimballed reflector and a circularly polarized dual-frequency band feed. The gimballed reflector allows scanning the beam within any Earth coverage area. The antenna is capable of providing simultaneous EHF reception and SHF transmission for the MILSTAR payload.

MMIC compatible slotline antenna

EHF phased array antennas use MMIC amplifiers and phase shifters to alleviate size, power, and weight concerns. Incorporating these MMIC devices into an affordable phased array for practical applications is very challenging. As a first step, we have built and tested a MMIC compatible slotline antenna which can be used as a radiating element for a phased array. This paper presents the design of this slotline radiating element, which can be connected directly to the MMIC device, avoiding complex interconnection in the transition region between the radiating element and the MMIC component.