METHOD AND ARRANGEMENT RELATING TO ANTENNAS

Abstract: The invention refers to an arrangement for receiving and mixing electromagnetic waves. The arrangement comprises an antenna element (24) and an amplifying transistor (10, 20). The arrangement includes means to apply a gate electrode (22) of a amplifying transistor, a locally generated oscillator signal (LO) and externally generated radio frequency (RF) from the antenna element. An output signal (IF) from the amplifying transistor is a function of said radio frequency (RF) and said locally generated oscillator signal (LO).

Description: METHOD AND ARRANGEMENT RELATING TO ANTENNAS Technical field The present invention refers to a method and an arrangement for receiving and mixing electromagnetic waves, which arrangement includes an antenna element and an amplifying transistor. Background of the invention Mixers integrated in the antennas in radar systems and specially image generating radar systems are known earlier. Usually, known Schottky or HEMT mixers, for example, work in so-called resistive mixing mode and have drawbacks because they require a relatively high power for local oscillation (LO), which makes them practically difficult to realize. The LO power can either be supplied electrically into the integrated circuit or through air to the antenna and to the receiving mixer. In an antenna the incoming information is received as a radio frequency (RF) signal, which can be divided into a known portion (carrier wave) and an information carrying portion. LO, which is a locally generated signal is sent to a non-linear component together with the RF signal, which results in addition of RF and LO. A voltage powered transistor converts the product RF x LO to a current I RJ . X I L0 , the phase and amplitude of which corresponds to the information carrying portion of the RF signal. This is comparable to a frequency translation in the frequency plane. Normally, one is interested of the product If^ - f L0 | [ABS(f j yr - f LO )], which is called the intermediate frequency and the main part of the signal amplifying is done in this frequency. In high frequency applications, it is very important that LO power is low because LO sources are very expensive. In systems, in which many LO sources are used, not only the price but also the thermal losses which limit the system performance are important facts. EP-A1 -762530 describes a broadband, high temperature superconductive mixer antenna, which allows a superconductive power line exhibiting a high-resistance loss in the high-frequency region. This can be used in the low-frequency region with low loss. The invention according to this document can only be used in very low temperatures (in best case liquid hydrogen temperature) which does not suit the use in normal applications. A Superconductive-Insulator-Superconductive junction (SIS) is used as the non-linear element. At low temperatures SIS parameters are poor. The objective of the invention and characteristics One object of the present invention is to reduce the LO power, for example to less than a tenth compared to conventional techniques, which results in production of more compact, cheaper and less power consuming system realizations. Another object of the invention is to minimize the LO power, which leaks out from the system. Yet, one object of the invention is to provide a sensor with reduced noise factor compared with earlier prior art, which increases the sensitivity of the sensor. Through the invention, at a certain noise level and LO power higher frequency can be used. Preferably, the invention employs a high-frequency FET (Field Effect Transistor) as a non-linear mixer, which allows normal temperature applications. According to the invention a good amplifying is obtained and LO need is reduced, for example at 10 dB amplifying the necessary LO effect may be 20 dB. These objects and advantages are achieved by means of the arrangement described in the beginning which includes means to apply the control electrode of the amplifying transistor a locally generated oscillator signal and externally generated radio frequency from the antenna element, so that the output signal from the amplifying transistor is a function of the radio frequency and the locally generated oscillation. The method according to the invention for a receiver of electromagnetic waves, which comprises an antenna element and an amplifier unit for mixing and amplifying the received signals is characterized by carrying out the mixing and amplifying functions at least in one and the same transistor. Description of the drawings In that following, the invention is described with reference to a number of embodiments illustrated in a non-limiting way in attached drawings, in which: Fig. 1 is a schematic, very simplified circuit diagram of one embodiment, according to the present invention . Fig. 2 is a schematic layout over one embodiment, according to the present invention, in so-called microstrip technique. Fig. 3 is a schematic circuit diagram for the layout shown in fig. 2. Fig. 4 is a schematic and slightly simplified matrix including the device shown in fig. 2. Detailed description of the embodiment Preferably, the invention may be a part of a radar receiver and especially a part of a micro or extremely high frequency sensor comprising a receiver integrated in an antenna, which is build by means of so-called active "gate-mixer", which is based on an active component (amplifying transistor) of FET (Field Effect Transistor) , HEMT (High Electron Mobility Transistor), BJT (Bipolar Junction Transistor), HBT (Hetrostructure Bipolar Transistor) or the like. The invention combines the mixing and amplifying functions in one and same transistor, which reduces the number of active components and thereby also the power consumption. Fig. 1 shows schematically the operation principle of the transistor 10 and its circuit diagram. The local oscillation (LO) and the radio frequency (RF) are applied to the gate electrode 11. The intermediate frequency IF, i.e., the difference between RF and LO is produced at the drain electrode 12 of the transistor. The transistor is Supplied with Direct Current (DC) at the drain electrode 12. Also, the gate 11 of the transistor is supplied with DC. By varying the gate voltage Vg s a maximal conversion gain is obtained. The source 13 is grounded. The embodiment shown in fig. 1 can be used in a receiver element, for example as a pixel in a two-dimensional array of the same receiver. The RF and LO signals are combined in the antenna element and then applied to the gate electrode of the amplifying transistor. The transistor can either be connected in "active mode" or in "ground gate mode", so that the transistor amplifies the frequency at the mixer operation point. Because both LO and RF signals are applied to the gate electrode, both LO and RF will be amplified in the transistor element, which means that the LO signal can have relatively low amplitude. This is a condition that allows realization of large arrays of receivers without extensive LO operation power. Figs. 2 and 3 show one detailed embodiment, where fig. 2 shows the layout of the embodiment in so-called micro-strip technique and fig. 3 is the circuit diagram. The mixer, i.e. the transistor 20, according to this embodiment is of so-called "gate mixer" type and comprises of the terminals source 21, gate 22 and drain 23. The antenna 24, in this case, is a so-called patch antenna, in which one of polarization 25 is used to couple LO and the other one 26 to couple RF (signal). LO and RF are connected to the gate electrode 22. The mixing process is obtained because the relationship between the gate voltage and the output signal (23) is non-linear. The gate electrode is fed with voltage N gs via a low-pass filter comprising R„ C, and L,. The drain electrode 23 is fed via a low-pass filter consisting of R 2 , C 2 , and L2. Moreover, a stub 27 is connected to drain which short-circuits between RF and LO so that the intermediate frequency IF can be outputted through the terminal 28. N gs and V^ are so adjusted that an optimal performance is achieved. In this example, it is assumed that LO and RF have different polarizations. Different polarizations can be produced by using a polarizer, which combines LO and RF and at output they become in different polarizations with very small losses. This means that the amplifying can be obtained for both RF and LO. Advantage with such an arrangement is that the antenna can be tailored for RF and LO frequencies, respectively, by varying the side length of the patch, i.e. the patch antenna may have rectangular geometry. If the frequencies are close to each other (within the resonance frequencies) it is also possible to supply the LO and RF in the same polarization. In that case only one connection to the antenna is needed instead of two, which is shown in figs. 2 or 3. By using a gate mixer, in which both the signal and LO are amplified, the requirements on LO are reduced. This is very important in high-frequency applications. Through the gate mixer low losses are obtained. Moreover, no losses between antenna and transistor are obtained. In the gate mixer it is very important to apply both the LO and signal with so little loss as possible, otherwise the performance is deteriorated, either through the sensitivity deterioration or increased LO requirements. In a conventional gate mixer, the LO is applied with directional coupler or ring filter, but these couplers have losses between 3 and 10 dB. Because of these losses, the decreasing potential of the LO power will be wasted. The embodiment shows one of many possible antenna configurations. The receiver element can also be designed in multilayer, strip-line, slot-line, co-planar waveguide technique or a combination of the same. The antenna element can be of patch, slot, horn type or a combination of these. The transistor can be coupled either in "grounded-gate mode" or "active mode". Experiments have shown that the signal-to-noise ratio through use of the invention reduces, for example with 5-8 dB and that the LO power becomes lower than 0,1 mW/pixel compared to 1-10 mW for the known sensors. By using patch antenna's 24 characteristic and polarization, LO 25 and RF 26 are applied in different polarizations and no interferences appear. The stub 27, which is an open circuit, is used to allow the mixer operate correct ly. R2 and R3 are used to supply the DC current of the device and to decouple. Moreover, these allow extraction without losses in IF at IF 0Ut 28 from the drain 23. Fig. 4 shows the layout of a 4 x 4 matrix including 16 elements according to fig. 2. The device is intended to function at approximately 10 GHZ, but 8 x 8 or larger matrices for operation areas from about 10 to 100 GHZ are also possible. The invention allows a very compact construction, which is well adapted for integrated image generating radar and radiometers, which can be used for instance in multistatisc radars, where the transmitter and receiver are separated in space. The image generating radar can be used for safer identification of radar echoes and as navigation aid in aircrafts or other vehicles at fog or smoke. The image generating radiometers can for instance be used to detect oil spillage or the like through aiφlane monitoring, detect oil spillage from ships or via aircraft or detect objects which otherwise are invisible for the radar, such as vehicles based on "stealth technique". An array of sensors according to the invention can for example be used to focus a lens or a parabolic antenna in a "staring" array configuration. While we have illustrated and described preferred embodiments of the invention, it is obvious that several variations and modifications within the scope of the attached claims may occur.

Claims: CLAIMS 1. An arrangement including an antenna element (24) and an amplifying transistor (10, 20) for receiving and mixing electromagnetic waves, characterized in, that the arrangement includes means to apply a locally generated oscillator signal (LO) and externally generated radio frequency (RF) from the antenna element to a gate electrode (22) of the amplifying transistor, and that an output signal (IF) from the amplifying transistor is a function of said radio frequency (RF) and said locally generated oscillator signal (LO). 2. An arrangement according to claim 1, characterized in, that the antenna element (24) and said transistor (10, 20), which comprises an active mixer, are integrated. 3. An arrangement according to claim 1 or 2, characterized in, that said radio frequency (RF) and said locally generated oscillator signal (LO) are applied to the antenna element from two mutually orthogonal directions. 4. An arrangement according to any of claims 1-3, characterized in, that the amplifying transistor is one of FET, HEMT, BJT and HBT. 5. An arrangement according to one of claims 1-4, characterized in, that said radio frequency (RF) and locally generated oscillator signal (LO) is applied to the antenna element with same mutual polarization. 6. An arrangement according to claim 1, characterized in, that the amplifying transistor is arranged in "active" or "grounded gate mode", preferably so that the transistor provides amplifying at the operation frequency of the mixer. 7. An arrangement according to any of claims 1-6, characterized in, that the transistor is supplied with direct current via drain and gate electrodes. 8. An arrangement according to claim 7, characterized in, that the direct current is supplied through a low-pass filter 9. An arrangement according to claim 7 or 8, characterized in, that a voltage applied to the gate electrode is actively adjustable so that maximum conversion amplifying is obtained. 10. An arrangement according to any of preceding claims, characterized in, that the arrangement is made in microstrip, multilayer, strip-line, slot-line, co-planar waveguide technique or a combination of said techniques. 11. An arrangement according to any of claims 1-9, characterized in, that the antenna element is of so-called patch, slot, horn type or a combination of these. 12. An arrangement according to any of preceding claims, characterized in, that the electromagnetic waves are microwaves or micrometer waves. 13. An antenna matrix including an arrangement according to any of claims 1-12. 14. A antenna matrix according to claim 13, characterized in, that the matrix is one or two-dimensional. 15. A antenna matrix according to claim 13 or 14, characterized in, that the matrix is arranged in focus of a lens or a paraboloidal aerial, so that each individual arrangement generates a pixel of an image. 16. A method at a receiver for electromagnetic waves, which receiver includes an antenna element and an amplifying unit for mixing and amplifying of received signals, characterized in, that the mixing and amplifying functions are executed at least in one and the same transistor. 17. A method according to claim 16, characterized in, that a local oscillation (LO) and a radio frequency (RF) from the antenna element is applied to the gate electrode of the transistor and that one intermediate frequency is outputted on a drain electrode of the transistor.

Inventors: ANGELOV ILTCHO, ZIRATH HERBERT, ANGELOV, ILTCHO, ZIRATH, HERBERT
Applicants: ANGELOV ILTCHO, ZIRATH HERBERT, ANGELOV, ILTCHO, ZIRATH, HERBERT
Application year: 1998
Main classification: H01Q1
IPC codes: H01Q1, H01Q9, H01Q21, H01Q23, H04B1