Antenna Modules for X-band AESA
Antenna module components, dimensions and performance parameters can be adjusted depending on the type of AESA radiating element and maximum output power requirements. The manufacturing process and main structural elements remain the same, preserving the design and technological continuity. The pictures below present two types of modules developed in S&PE PULSAR.
Antenna module (Fig. 1) comprises 32 dual-polarization transmit/receive modules (TRM), 4 microstrip 8-channel antenna arrays, 8 divider/adders by 8, beam pattern formation device, 2 secondary power supply sources, antenna control unit, microwave and low-frequency wiring.
Antenna modules have different configurations of T/R modules and different composition of receiving and transmitting channels, depending on radar system requirements. TRMs are the basis of signal processing spatial channel of antenna module and AESA. TRMs account for about 80 % of the cost of the antenna module. Transmit/receive modules have been developed for each type of antenna module (type 1 and 2). All TRMs are based on powerful GaN HEMTs manufactured by PULSAR. Power amplifier hybrid ICs based on these transistors are providing the required output power levels at pulse length τp = 10–60µs and duty cycle Q = 10. Receiving and transmitting channels comprise three types of GaN transistor dies with gate width Wg1 = 250µm, Wg2 = 1000µm, Wg3 = 5000µm. Specific output power Pout ≥ 5W/mm. Noise figure for GaN HEMT with Wg1 = 250µm at F = 10GHz equals Kn ≤ 1.9dB.
Depending on the system using TRM, there are additional requirements for the amount of channels per single module. Performance characteristics of designed modules are given in Table 1.
Type 1 transmit/receive module is a sealed single-channel dual-polarization module with coaxial input/output. TRM provides amplification and transmission of signal in one of the two polarization modes (H or V), as well as receiving and amplification of reflected signal in two polarization modes (HV, H or V). The module operates in simplex mode. The module has a function of independent control of receiving and transmitting channel phase response, as well as receiving channels frequency response. For that purpose, the module includes digital six-digit phase shifters, five-digit attenuators, and control board comprising power supply and control circuit. Monitoring function has been implemented during the module development, providing through monitoring of receiving and transmitting channels, power supply, control and modulation protection circuits, as well as controlling the temperature levels and providing an emergency shut-down of the TRM in case of overheat. Fig. 3 presents TRM block-diagram.
Type 2 TRM is a sealed dual-channel module with a transmitting and receiving signal polarization switching function “1 in — 4 out”. The module is designed in such a way that digital attenuators and phase shifters in transmitting channel and power preamplifier are components of TRM receiving channels. TRM block-diagram is given in Fig. 4.
Transmitting/receiving modules feature is linking input and output ports to the structure of transmitting part of antenna module, which requires additional thermal, structural and radioengineering design of TRM to implement the desired characteristics of antenna module. Figs 5 and 6 present the TRMs developed within the research.
Antenna module electrical parameters measurements have been carried out in an anechoic chamber. The anechoic chamber comprises an automated test board with two rotary supports, near-field scanner and equipment for measuring antenna module parameters with an aperture up to 0.5 meter in the far-field. Fig. 7 shows the type 1 antenna module on the rotary support of the anechoic chamber.
Electronic scanning is performed in elevation plane with adjustment increment of 1°. Scan sector is ±20 degrees. Measured results testify to a good match with simulations, which indicates the appropriate design and technological decisions made while developing the antenna module. Fig. 8. shows beam patterns of ¼ antenna modules (type 1) in elevation plane. Beam pattern of type 2 antenna module is shown in Fig. 9.
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