NL195080C - Delay line frequency discriminator. - Google Patents

Description

«1 195080 * Delay line frequency discriminator

The invention relates to a delay line and a reference line, each serving to transmit a component of a radio frequency signal; decoupling means for forming these components; and a frequency adjuster.

Such a delay line frequency discriminator is known from US-A-4,387,347 and finds application in radar transmitters. Such a radar transmitter can form part of a target finder which is arranged on board a guided projectile, for example a ballistic-launched bomb guided in the final phase.

It is particularly desirable that such a radar transmitter has small dimensions and a low cost price, and thus the use of large-scale integration (LSI) of the electronics is desirable. Microwave source components suitable for LSI generally have a strong non-linear control voltage / output frequency characteristic. This leads to problems when the radar output signal must include a repeating frequency sweep (chirp), the frequency varying linear sawtooth generator being used to control a microwave source, because then the frequency of the output signal from the source 15 will not be linear in time . The source could be driven with a voltage waveform adapted to compensate for this non-linearity, but, in particular because the linearity of the source may depend on external parameters such as the antenna load, a complex and time-consuming adjustment of every channel are needed.

It is an object of the invention to determine the linearity of the known delay line frequency discriminator.

20 improve.

To this end, the invention provides a delay line frequency discriminator of the aforementioned type, characterized by means for splitting each component into a signal for two detectors each comparing the signals, the signal being a combination of the components for each of the two detectors; an equalizer that receives a signal from the detectors to keep the input power at a constant level; an absorption member for absorbing parasitic radiation; and a means adapted to use the reflections of the detectors to improve the size of the linear region of the dicriminer.

The invention will be elucidated with reference to the drawing with reference to the figures, in which: figure 1 shows a block diagram of an open loop transmitter; Figure 2 is a block diagram of a transmitter in a closed loop; Figure 3 is a cross-sectional view of a microstrip line; Figure 4 shows an adjustable frequency discriminator with an equalizer; Figure 5a is a graphical representation of the response of the diode 1 (D1); Fig. 5b is a graphical representation of the response of the diode 2 (D2); Figure 5c is a graphical representation of the (D1-D2) response; Figure 5d is a graphical representation of the slope of Figure 5c; Fig. 6a is a graphical representation of the power versus the normalized frequency response of the discriminator around the outputs to the diodes D1 and D2; Figure 6b is a graphical representation of the slope versus normalized frequency of Figure 5c; Figure 7 is a cross-sectional view of a microstrip covered with a layer of dielectric material; Figure 8 is a top view of a resonant aborption member in a microstrip circuit; and Figure 9 is a perspective view of the resonance absorber of Figure 8.

45

Future ballistic weapons will require "intelligent" radar systems, with small dimensions, a low cost price and, if possible, easy to manufacture. The advent of surface mount technology and large-scale integration of electronics has encouraged the development of small transmitting / receiving systems for the millimeter area with low cost.

50 The transmission sight / receiver for the millimeter area is a major challenge with regard to the low cost, the small dimensions and the simplicity of manufacture.

A particular problem exists when a vibration over a broad band is necessary with a linearity of the order of 1%. The source has a frequency / voltage characteristic that is far from linear (for example ± 20% of ideal) and depends on the antenna load and the like. This precludes the pre-shaping of the control voltage from the oscillator because the setting requirements are complex and increase the manufacturing time. Down-converting the source signal using a low-frequency discriminator in a closed loop configuration increases the complexity and volume of the 195080 2 transceiver. A direct measurement of the source frequency can be performed with a "simple" * delay line discriminator which, when used as a feedback element in a closed loop, will provide a linear vibration with a high linearity. The simple delay line discriminator offers a low cost price, small dimensions and can be easily manufactured.

When an open loop amplifier as shown in Figure 1 transmits an input signal 1 from a modulator 2 via an oscillator 3, the output signal 4 has a non-linear frequency / time characteristic. This is due to the non-linear voltage-frequency characteristic of the oscillator which is a basic property of microwave sources in general.

To obtain a linear frequency-time characteristic, a closed loop control can be used to compensate for the non-linearity of the oscillator. This is shown in Figure 2. The output signal 5 of the modulator is supplied to an oscillator 8 via a connection 6 and an amplifier 7. A discriminator 9 and another amplifier 10 serve to adjust the resulting input signal in a feedback loop 11 so that the output signal 12 of the oscillator has linear frequency time / characteristic. The discriminator in the feedback loop can be in the form of a microstrip on a thin substrate with a low dielectric constant. Figure 3 shows a microstrip delay line discriminator in which the microstrip line 13 has a nominal substrate thickness H of about 76 micrometers, a dielectric constant of about 2.1, a line width W of 0.13 millimeters and a line thickness T of 0.017 micrometers and a characteristic impedance of approximately 70 ohms. Figure 4 shows an embodiment of the discriminator according to the invention. This consists essentially of two branched line couplings 14 and 15, a reference line 16, a delay line 17 and a pair of mixing diodes D1 and D2, which are indicated by reference numbers 18 and 19 respectively. The delay line 17 and one of the mixing diodes, if these if a phase detector works, have the joint effect of a frequency discriminator.

A radio frequency (R.F.) input signal 20 is distributed approximately equally between the reference line 16 and the delay line 17 by means of the tapped line coupling 14. The fourth port or the isolated port 21 is terminated with an adapted R.F. load 22. In an ideal discriminator, no power would flow into this gate because it is properly terminated with the characteristic impedance for which that device was designed. However, due to imperfections in the manufacture of the circuit and due to reflections from the diodes 18 and 19, the modified R.F. load desired. The split of the power is a function of the impedances of the branches. These impedances are also set to maintain proper adjustment over the operating frequency range. In the discriminator design, both branched line couplings 14 and 15 are designed to provide half the power to each tap (i.e., a 3dB coupling). The power that the coupling 15 enters from the reference line 16 splits approximately equally between the diode gates 18 and 19. Similarly, the R.F. signal from the delay line path 17 equally distributed between the diode gates. The output signals 40 and 41 of the diodes D1 and D2, respectively, are a function of the phase difference between the delay line and the reference line paths. Figures 5a and 5b show the ideal diode output responses at a road difference of 3.25 λί, where λ, ≤ equal to the microstrip wavelength, between the delay line and the reference line.

Figure 5c shows the difference response and Figure 5d the slope of this characteristic.

A model was made of the microstrip discriminator using, for example, Super 40 Compact and the power arriving at diodes 18 and 19 versus the normalized frequency is shown in Figure 6a. Figure 6b shows the difference of the difference curve of Figure 5c, which has a linearity percentage of = 0.1% over a frequency deviation of + 0.002 f0, where f0 is the central frequency of the frequency range. The sum of the diodes 18 and 19 is a measure of the input power variation which must be removed in order to obtain a correct discriminator characteristic. When comparing 45 with a voltage reference, an error signal is derived that controls the shunt equalizing dead 23 and thus equalizes the sum signal.

The mixing diodes 18 and 19 and the equalizing diode 23 are adapted to the micro-strip line by the respective open short wave lines 24, 25 and 26. The output signals of the diodes 18 and 19 can be filtered through respective layer filters 42 and 43.

50 In an ideal system, all the power that arrives at diodes 18 and 19 would be absorbed and processed. However, due to adjustment problems and the like, a portion of the incoming signal is reflected back to the coupling 15 and then through the entire circuit and finally back to the diodes 18 and 19. This makes the received signal more complicated.

The reflected components can be added to or subtracted from the 55 main signals received by the diodes 18 and 19 to improve the size of the discriminator's linear region. To make this addition or subtraction possible, the reflected and hand signals must be in phase.

3 195080 * The equalizing diode acts as an attenuator to keep the output signal constant. The current setup can be replaced by a double diode.

The R.F. load can be replaced by a load diode, for example a PIN diode which can be set to control the reflected signals so that they can be in phase with the main signal and can therefore be used to increase the linear range.

The circuit patterns of the discriminator are recorded on the substrate using conventional photolithographic techniques for printed circuits and can therefore in principle be produced cheaply. The used mixing diodes are commercially available GaAs MOTT diodes. A possible substrate for the discriminator is a 0.5 oz rolled copper RT-Duriod 5890, a pure, non-reinforced PTFE laminate.

A dielectric frequency regulator can be placed in the delay line 17 of the discriminator, with which F0 can be varied or preset. Because the wavelength of the microstrip line (X11 is given by the expression: v _ k ° 15 l'Ve; where Ere = effective dielectric constant λο = wavelength in the free space, the effective dielectric constant can be increased by the microstrip line 13 to be coated with a dielectric cover layer 45. The analysis of a microstrip line covered with a layer of loss material layer, as shown in Figure 7, is known from Bahl et al. "Design of

Microstrip Antenna Covered with a Dielectric Layer ”IEEE Trans, or Antennas and Propagation, Vol AP-30 No. 2 P314-318.

Increasing the effective dielectric constant by covering the microstrip delay line with a dielectric layer increases the electrical length and thereby decreases the central operating frequency. With a dielectric frequency setting 28 as shown in Figure 1, made from for example TPX (ER = 2.1) with a 0.53 mm thickness covering 30% of the microstrip delay line 17, it is possible to reduce the frequency by = 4%. A microstrip line emits considerable radiation at any point where a change occurs in the electric field pattern which is the case in a bend or a discount, such as a change in line width. The parasitic radiation from the microstrip circuit can have a disturbing influence on the properties of the discriminator, that is to say its linearity.

A resonance absorber 29 made from, for example, carbonyl iron / epoxy resin can be placed over the microstrip substrate to minimize the effect of the parasitic radiation. Figures 8 and 9 show views of the resonance absorber 19 which is generally a semicircular channel following the chain pattern, as shown in the cross-sectional view along the lines x - x 35 in Figure 8.

Claim 40 Delay line frequency discriminator comprising a delay line and a reference line, each serving to transmit a component of a radio frequency signal; decoupling means for forming these components; and a frequency adjuster, characterized by means for splitting each component into a signal for two detectors each comparing the signals, the signal for each of the two detectors being a combination of the 45 components; an equalizer that receives a signal from the detectors to keep the input power at a constant level; an absorption member for absorbing parasitic radiation; and a means adapted to use the reflections of the detectors to improve the linear region of the discriminator. 1 55

Claims (2)

195079 4 »Conclusions * Method for repairing an oxide-based refractory body by spraying a powder mixture against a surface of the body at elevated temperature and in the presence of oxygen, the powder mixture comprising refractory oxide particles and fuel particles reacting exothermically with the oxygen to form a refractory oxide, the fuel particles being selected from magnesium, aluminum, silicon and mixtures consisting of two or more of magnesium, aluminum and silicon, the powder mixture further comprising only silicon carbide particles as active ingredient, characterized in that the silicon carbide particles are present in an amount of 1 to 10% by weight based on the powder mixture. A powder mixture for the repair of the oxide-based refractory bodies, which mixture comprises: - 80 to 95% by weight of refractory particles containing a refractory oxide; and - 5 to 20% by weight of fuel particles which react exothermically with the oxygen to form a refractory oxide, the fuel particles being selected from magnesium, aluminum, silicon and mixtures consisting of two or more of magnesium, aluminum and silicon wherein the refractory particles further contain only silicon carbide particles as active ingredient, characterized in that the silicon carbide particles are present in an amount of 1 to 10% by weight based on the powder mixture.